Complex spatial updating in simulated low vision

Critical to low vision navigation are the abilities to recover scale and update a three-dimensional representation of space. In order to investigate whether these abilities are present under low vision conditions, we employed the triangulation task of eyesclosed indirect walking to previously viewed targets on the ground. In experiment 1, we explored the feasibility of simulating low-vision more precisely using a novel material. In experiments 2 and 3, we investigated distance perception under normal vision and simulated low vision conditions. Visually directed walking measures, such as the direct and indirect walking tasks, can be used as a measure of absolute distance perception. The indirect walking task requires that the observer continually update the location of the target without any further visual feedback of his/her movement or the target's location. Normally sighted participants were tested monocularly in a degraded vision condition and a normal vision condition on both indirect and direct walking to previously viewed targets. Surprisingly, we found no difference in walked distances between the degraded and normal vision conditions. Our results provide evidence for intact spatial updating even under severely degraded vision conditions, indicating that participants can recover scale and update a three-dimensional representation of space under simulated low vision.

COMPLEX SPATIAL UPDATING IN SIMULATED LOW VISION by Margaret Romaine Tarampi A thesis submitted to the faculty of The University of Utah in partial fulfillment of the requirements for the degree of Master of Science Department of Psychology The University of Utah May 2010 Mastcr Scicncc Copyright © Margaret Romaine Tarampi 2010 All Rights Reserved THE U N I V E R S I T Y OF UTAH G R A D U A T E SCHOOL SUPERVISORY COMMITTEE APPROVAL of a thesis submitted by Margaret Romaine Tarampi This thesis has been read by each member of the following supervisory committee and by majority vote has been found to be satisfactory. Raymond Kesner T H E UNIVE R SITY U T A H GRADUAT E SCHOOL thcsis submined Romainc cach ofthc fo llowing -'a<hL~"~i':'~S~'"'"~h~~Cr~e'~m_RC,=g~'h~'------== ::===------ THE U N I V E R S I T Y OF UTAH G R A D U A T E SCHOOL FINAL READING APPROVAL To the Graduate Council of the University of Utah: I have read the thesis of Margaret Romaine Tarampi in i t s f i n a i f o r m and have found that (1) its format, citations, and bibliographic style are consistent and acceptable; (2) its illustrative materials including figures, tables, and charts are in place; and (3) the final manuscript is satisfactory to the supervisory committee and is ready for submission to The Graduate School. Date Sarah Creem-Regehr Chair: Supervisory Committee Approved for the Major Department A Chair/Dean ^J Approved for the Graduate Council Charles A. Wight Dean of The Graduate School T H E UNIVERSITY U TA H GRADUATE SCHOOL APPROVAL in its fin al form thaI I ) figures. satisfac tory commillee Dale +.~~--~--=:::::==-- Crccm-Rcgchr Commitlt'c '7= Cynthia Berg ABSTRACT Critical to low vision navigation are the abilities to recover scale and update a three-dimensional representation of space. order to investigate whether these abilities are present under low vision conditions, we employed the triangulation task of eyes-closed indirect walking to previously viewed targets on the ground. In experiment 1, we explored the feasibility of simulating low-vision more precisely using a novel material. In experiments 2 and 3, we investigated distance perception under normal vision and simulated low vision conditions. Visually directed walking measures, such as the direct and indirect walking tasks, can be used as a measure of absolute distance perception. The indirect walking task requires that the observer continually update the location of the target without any further visual feedback of his/her movement or the target's location. Normally sighted participants were tested monocularly in a degraded vision condition and a normal vision condition on both indirect and direct walking to previously viewed targets. Surprisingly, we found no difference in walked distances between the degraded and normal vision conditions. Our results provide evidence for intact spatial updating even under severely degraded vision conditions, indicating that participants can recover scale and update a three-dimensional representation of space under simulated low vision. In eyes­closed hislher and a normal vision condition on both indirect and direct walking to previously viewed targets. Surprisingly, we found no difference in walked distances between the degraded and normal vision conditions. Our results provide evidence for intact spatial updating even under severely degraded vision conditions, indicating that participants can recover scale and update a three-dimensional representation of space under simulated low vision. For my parents, who have always offered me unconditional love and support in my academic and personal pursuits TABLE OF CONTENTS ABSTRACT INTRODUCTION 1 Low Vision Navigation 2 4 Simulating Low Vision 7 OVERVIEW OF PROJECT 9 EXPERIMENT 1 11 Method 11 Participants 11 Materials Design and Procedure 12 Results Coding Analysis Results and Discussion 15 EXPERIMENT 2 18 Method 18 Participants 18 Materials 18 Design 20 Procedure 20 Results Coding 25 Results and Discussion 27 EXPERIMENT 3 32 Method 32 ABSTRACT ...................................................................................... iv ACKNOWLEDGMENTS ........................................................................ viii rNTRODUCTION ................................................................................. 1 .................................................................. Distance Perception .................... ...... ............................................ Simulating Low Vision .................................................................. 7 OVERVIEW OF PROJECT ........ ...... ... ................. .................................... 9 EXPERIMENT I .................................................................................. II Method .. .................................. ......... ......................................... 11 Participants ....................................................................... 11 Materials .......................................................................... 12 Design and Procedure ........................................................... 12 Results ...................................................................................... 15 Coding ............................................................................. 15 Analysis ......................... .. ... ... ......................................... 15 Results and Discussion ............ .... ....................... .............. .... 15 ......................................... ... .. ...... ..... ..... ........ .. . .... .. ... ...................................................................................... ........................ ........ ....................................... .......................................................................... ............................................................................. ......................................................................... ... ................................................................................... 25 ............................................................................. Analysis .......................................................................... 26 ......................................................... EXPERiMENT .. .. .......... ..... .. .... .. ... ... .. . ..... .. .. ........ ................. ........... ...................................................................................... Participants Procedure 33 DISCUSSION , vii Panicipants .... ............. .. ... ... .. .. ....................... ................... 32 Materials ....... ........................... .. ................................... ... 33 Design ............................................................................ 33 Procedure ...... .................................................................... 33 Results ....................................... .. ............................................. 33 Coding .. .. .. .. .. ..... ........ .. .. ............ .............................. ....... .33 Analysis ... ... ... .. ...... ............... ......... .. .. . .... . ....... .. ..... .. ....... 33 Results and Discussion ... .. .. ................. . .. ... ............ ............... 34 GENERAL DiSCUSSiON ............................................................. ....... .. 35 CONCLUSIONS AND FUTURE DIRECTIONS ........ .. ..................... .... .. ...... 40 REFERENCES ...................... .............. .......... .. .... ............... .. .. ............. . 42 ACKNOWLEDGMENTS This work was supported NIH grant 1 R01 EY017835-01. by I ROI 0 I. INTRODUCTION As we navigate through the world, we utilize spatial features important to visual accessibility. Visual accessibility is the use of vision and other aspects of spatial cognition to travel efficiently and safety through an environment, to perceive the spatial layout of key features in the environment, and to keep track of one's location in the layout. It depends not only on object detection and classification but also on distance perception of environmental locations with respect to one's own self-movement. Normally sighted individuals are able to determine the location of objects in the environment almost effortlessly. These object locations in the environment guide our actions. Knowing where a fire hydrant is located allows us to walk around it. Knowing where a curb is located allows us to step over it. Knowing where an overhang is located allows us to duck our head. We are continuously using information about object locations in order to safely and efficiently navigate spaces. Egocentric distance perception is a measure relevant to navigation because, as we move through spaces, we have to make judgments about the location of objects relative to ourselves. Because perception is representational in nature, perceptual judgments, including methods that utilize behavioral measures, must be used to characterize perception indirectly. Methods that rely on visually guided action based measures include visually-directed pointing, direct walking (also called blind walking), and triangulation methods (triangulation by pointing, triangulation by walking, and indirect . locations in order to safely and efficiently navigate spaces. 2 walking). Visually directed walking measures, such as the direct walking task, are used as a measure of absolute distance perception. In a direct walking task, the observer walks without vision to a previously viewed target. Under full cue conditions, participants have been shown to be accurate on average in this task across normally-sighted participants (Loomis, Da Silva, Fujita, & Fukusima, 1992; Philbeck & Loomis, 1997; Rieser, Ashmead, Talor, & Youngquist, 1990; Thomson, 1983). Low-vision individuals navigate the world under visually degraded conditions where the visual information that they receive is impaired by the nature of their vision-based disability. Surprisingly, our previous findings have shown no differences in performance on a direct walking task between a full cue condition and a simulated low-vision condition (Tarampi, Creem- Regehr, & Thompson, 2008). It is possible, however, that the good performance with severely degraded vision in this task was a result of planning strategies which did not require updating of the three-dimensional layout of space or the ability to recover scale. The intention of this study was to test the hypothesis that observers form and update representations of spatial locations in a simulated low-vision distance estimation task. The first aim of the study was to compare an alternative method for simulating low-vision in order to determine if it is possible to separately degrade acuity and contrast. The second aim was to test more complex spatial updating abilities in simulated low-vision by utilizing an indirect walking task. Low Vision Navigation Low-vision can refer to a loss of acuity, contrast, or field that cannot be corrected with standard lenses, surgery, or medical treatments. It is complex, often involving a combination of deficits, and can manifest as an eye disease such as cataracts or macular (Loomis, Da Silva, Fujita, & Fukusima, 1992; Philbeck & Loomis, 1997; Rieser, Ashmead, Talor, & Youngquist, 1990; Thomson, 1983). Low-vision individuals navigate the world under visually degraded conditions where the visual information that they receive is impaired by the nature of their vision-based disability. Surprisingly, our previous findings have shown no differences in performance on a direct walking task between a full cue condition and a simulated low-vision condition (Tarampi, Creem­Regehr, & Thompson, 2008). It is possible, however, that the good performance with severely degraded vision in this task was a result of planning strategies which did not require updating of the three-dimensional layout of space or the ability to recover scale. low­vision low­vision degeneration. Adaptive and low-vision devices can be used to help these individuals perform daily tasks such as reading, writing, and cooking. However many low-vision individuals do not rely on external aids such as canes or dog guides to aid spatial orientation and navigation. Instead they depend on their remaining vision as well as their other senses in order to get around (Ludt & Goodrich, 2002). Therefore it is important to ascertain the perceptual capabilities of individuals with profound low-vision not only because of the applied implications for rehabilitation and the design of environmental spaces but also for the theoretical implications for the nature of perception and action. This problem statement alludes to both a perceptual issue of spatial perception in low-vision as well as a methodological issue of simulating low-vision in a useful way. Existing low-vision research on navigation has primarily focused on obstacle avoidance while walking (Kuyk, Elliott, Biehl, & Fuhr, 1996; Long, Reiser, & Hill, 1990; & to-collision. while walking task, the constant feedback from the observer's intact vision and other the position of the stimuli. Their response is perhaps more reliant on the initial visual 3 low­vision Marron Bailey, 1982; Pelli, 1987), which is a key aspect of mobility. This work does not directly address the ability to recover absolute distance and the overall scale of the space under low-vision conditions, since the constant feedback from eye-open walking allows obstacle avoidance strategies involving only relative distance and time-to­collision. The ability to recover scale is critical for components of navigation such as path planning and spatial updating of locations with movement. In an obstacle avoidance sensory inputs acts as an additional input to correct motor action, a characteristic of closed-loop spatial behavior. Open-loop walking, on the other hand, involves the participant performing actions without any further visual feedback about their position or 4 input. Another difference between open-loop and closed-loop behavior is that in open-loop walking, the distance walked is typically measured and interpreted as an indication of the perceived egocentric distance of target. Mobility in obstacle avoidance while walking studies is typically measured by recording the number of contacts with obstacles, the number of pauses or full stops, and the time to complete the task. Given these multiple dependent variables and the complexity of low-vision deficits, not surprisingly these low-vision navigation studies indicate mixed findings as to the impairments most detrimental to this particular mobility task. For example, Pelli (1987) found that mobility was not impaired with artificially restricted acuity, contrast, or field. In contrast, mobility studies with actual low-vision individuals have found that al., & in low illumination conditions, Kuyk, Elloitt, Biehl, and Fuhr (1996) found that Distance Perception In low-vision navigation, another essential ability is the accurate judgment of object locations in the environment (Ludt & Goodrich, 2002). Judgments of distance to target locations may be defined as egocentric versus exocentric and absolute versus relative. Egocentric and exocentric refer to the reference frame used. Egocentric distance is the distance measured from the observer to a target location in the environment. An egocentric frame of reference is body-centered and view dependent. Exocentric distance is the distance measured between a target location and an external object. An exocentric open­loop intact field of view and contrast sensitivity are more important for successful mobility than acuity under full cue conditions (Long, et aI., 1990; Marron Bailey, 1982). While individuals with field loss or field loss combined with degraded acuity were more impaired on a mobility task than those with just acuity loss. 5 frame of reference is environment-centered and view independent. Absolute and relative distances refer to different types of distance perception. Absolute distance is specified in some standard unit of measure. Relative distance can be useful for comparing two or more distances as it is defined as a comparison between visually determined distances. Relative distance information is not sufficient however for determining absolute distance without scaling information. Vision provides a rich set of sources of information for relative distance, but only a few of these visual cues directly indicate absolute size and distance. Beyond distances of a few meters from the viewer, the primary visual information for scale comes from familiar size and body scaled perspective information, though observer-induced motion parallax may also play a role. Low-vision, particularly when it involves severely degraded acuity and contrast, almost certainly impacts familiar size, though there has been little if any controlled study of this. Reductions in acuity and contrast affect perspective-based visual information by reducing high frequency detail used to infer vanishing points and lines and texture gradients. Depending on the nature of the environment under view and the degree of degradation, this would be predicted to impact of low-vision on motion parallax is less clear, though there is some evidence that it provides at best a weak indication of absolute distance (Beall, Loomis, Philbeck, & Fikes, 1995). Tasks that exploit visually directed walking to targets and spatial updating make use of the skills necessary for accurate absolute egocentric localization of objects in the environment. Measurements of perceived egocentric distance, such as the direct walking task, are fundamental to not only understanding aspects of navigation but also to playa negatively affect both the accuracy and precision of distance judgments. The potential 6 understanding other complex behaviors, such as performance in athletics and dance, that involve distance perception. In previous studies (Tarampi, et al., 2008), we investigated absolute distance perception in normal vision and simulated low-vision conditions utilizing the visually directed walking task of direct walking to targets. In the direct walking paradigm, targets were two sizes of bright orange traffic cones, located on the ground-plane at egocentric distances of 2, 2.5, 3, and 3.5 meters. In some trials, no target was present in order to verify object detection and recognition in the low-vision condition. On each trial, subjects were asked if they could see the target. If they responded affirmatively, they walked blindfolded to the apparent target location. Even though in the low-vision condition the orange cones appeared as barely detectable orange blobs, group-averaged data exhibited near accuracy in walked distances. Walked distances in the normal acuity condition were also accurate, consistent with many other studies, with the between-subject variability somewhat less than for the reduced acuity condition. We replicated these findings in a different setting at target distances of 2, 3, 4, 5, and 6 meters. The underlying processes used by observers to accurately perform in the direct walking task under low-vision conditions remain debatable. If participants are using spatial updating to perform the task accurately, they are able to recover scale and update a three-dimensional representation of space as they locomote even under low-vision conditions. Although it is assumed that spatial updating is involved in the direct walking task, it could be argued that participants are using alterative processes that do not rely on a three-dimensional representation of space, yet lead to accurate performance. It could be argued that participants are using a simple pre-planning strategy when performing the aI., ground-plane at egocentric distances of2, 2.5, 3, and 3.5 meters. In some trials, no target was present in order to verify object detection and recognition in the low-vision of2, task such as counting steps or estimating distance in a standard unit of measurement like feet or meters. Because subjects show accuracy in making absolute distance judgments in the direct walking task, a triangulation task could be used to test more complex spatial updating. Performance is more variable using triangulation methods, but on average accuracy is seen with little systematic error under full-cue conditions (Fukusima, Loomis, & Da Silva, 1997; Loomis, Klatzky, Philbeck, & Golledge, 1998; Loomis & Philbeck, 2008; Thompson, et al., 2004). A triangulation task, such as indirect walking, requires that the observer is continually updating the location of stimuli without any further visual feedback of their movement or of the location of the stimuli. This task would also make it difficult for the observer to use pre-planning strategies. The indirect walking task would therefore address whether individuals under low-vision conditions are able to maintain an accurate three-dimensional representation of space. Simulating Low Vision Several issues arise from simulating low-vision. Previously, we simulated low-vision Hart, & & al., logMAR 0.1) on either side of a flat clear lens. The tested acuity of this setup ranged from 20/900 to 20/2000 using ETDRS Acuity testing. According to the World Health Organization's classification for low-vision and blindness, a visual acuity of 20/900 falls within the 7 aI., low­vision using Bangerter Occlusion Foils. These foils are typically used in prophylactic or therapeutic applications to treat conditions such as amblyopia. Bangerter foils are designed to degrade acuity but have also been shown to affect contrast (Odell, Leske, Hatt, Adams, Holmes, 2008; Perez, Archer, Artal, 2009). In the study mentioned earlier (Tarampi, et ai., 2008), we used one Bangerter Occlusion Foil with the stated acuity of approximately less than 10gMAR 0.1 (filter designated by manufacturer as < 201900 2012000 201900 8 profound low-vision range while a visual acuity of 20/2000 falls in the blindness range. Contrast sensitivity with this simulated low vision setup was too low to be measured using the Pelli-Robson Contrast Sensitivity Chart. Simulated low-vision that considerably reduces contrast can greatly affect visibility of targets at longer distances as was found with this setup for black and white targets separately at distances beyond 6m. In simulating low-vision conditions, a more precise simulation of acuity and contrast loss is needed. Deficits in acuity and contrast go hand-in-hand in actual low-vision, but experimentally it would be ideal to explore these deficits separately in order to identify each deficit's role in distance perception and spatial updating. This leads to the need of accurately quantifying the degree of degradation to acuity, contrast, and field by these simulators. Tools utilized by optometrists to determine acuity, contrast, and field can be used to measure the level of degradation relative to individual participants provided that testable values can be obtained. However, there is a limited understanding of the physics of how the simulations (in this case the foils) are degrading vision (Perez, et al., 2009). Further investigation is needed to determine how the Bangerter foils theatrical lighting diffusers or filters. Theatrical lighting diffusers do not reduce contrast as much as the Bangarter Foils and have a testable contrast sensitivity as measured by the Pelli-Robson Contrast Sensitivity Chart. Given that Bangerter Foils cause progressive al., could offer one possibility for decoupling contrast and acuity because they do not necessarily affect acuity and contrast equally. low­vision, aI., compare to actual low vision deficits. An alternative to the Bangerter Occlusion Foils is degradation to both acuity and contrast (Odell, et aI., 2008), theatrical lighting filters OVERVIEW OF PROJECT This project consisted of three experiments. In experiment 1, theatrical lighting filters were tested as an alternative method for simulating low-vision. Based on their physical properties, the theatrical lighting filters that had the best prospect of decoupling acuity and contrast were identified. The ETDRS Acuity Test and the Pelli-Robson Contrast Sensitivity Test were then used to measure individuals' acuity and contrast sensitivity values relative to different filters as compared to their normal tested acuity and contrast sensitivity. The dependant variables of interest were logMAR acuity and log contrast sensitivity. In experiments 2 and 3, participants performed a visually directed walking spatial updating task. The dependent variable of interest was the origin-to-endpoint distance. In experiment 2, participants took part in a degraded vision condition followed by a normal vision condition so that the participants remained naive to the experiment room until after the degraded vision condition was presented. Low-vision individuals often have to deal with novel environments. Presenting the degraded vision condition first ensured that cues related to familiarity of the space were not being utilized. However, there could be order effects seen with this experimental paradigm. In order to address this possibility, participants only took part in a normal vision condition in experiment 3. The normal vision condition in experiment 3 allowed for between-subject comparisons with both the degraded vision condition from experiment 2 (a comparison when each condition is 10gMAR naIve degraded vision condition from experiment 2 (a comparison when each condition is 10 presented first) and with the normal vision condition of experiment 2 (a comparison when the normal vision condition is presented first or following the degraded vision condition). If observers are not able to accurately spatially update their positions after viewing the target and environment under low-vision conditions, then they should show degraded performance on the indirect walking task compared to the normal vision viewing condition. If however, viewers do spatially update a three-dimensional representation of the space, they should show comparable performance in the two conditions. condit ions, EXPERIMENT 1 Experiment 1 examined alternative methods for simulating low-vision in normally sighted individuals. Theatrical lighting filters were identified as an option for possibly decoupling acuity and contrast as a low-vision simulator. Several theatrical lighting filters were tested to explore the feasibility of using these filters to simulate low-vision in a more precise way. Method Participants A total of 18 psychology students from the University of Utah participated as part of a course requirement or for extra credit. Eighteen (11 males and 7 females, mean age 25.4 years) participated in experiment 1 where eight were randomly assigned to test two of four filters (Lee 252, Lee 255, ROSCO 104, and ROSCO 101) along with their normal vision and ten (participants from experiment 2) were tested with the Cinegal 3047 filter used in the experiment 2 along with their normal vision. Each participant completed the task individually during the course of approximately a half an hour and received a half an hour's worth of credit towards a psychology course requirement. All participants had normal or corrected-to-normal vision. preCIse 12 Materials Experiment 1 was conducted in room 917 in the Social and Behavioral Science Building (BEH S) except for the individuals who participated in experiment 2 whose vision was tested in BEH 110. Each experimental session of experiment 1 consisted of vision tests and a debriefing. In the case of the participants from experiment 2, they performed the vision tests and debriefing after the experimental trials as outlined below. The ETDRS Acuity Test and the Pelli-Robson Contrast Sensitivity Test as well as the debriefing were administered in this room. Design and Procedure Participants were first asked for informed consent to participate in the study. They were also asked to fill out a short optional survey on their ethnic and racial information to fulfill grant requirements. 72° each participant testing two filters for a total of four acuity and contrast sensitivity measurements per filter. The filters that were tested were Lee 252: 1/8 White Diffusion, Lee 255: Hollywood Frost, ROSCO 104: Tough Silk, ROSCO 101: Light Frost, and Cinegal 3047: Light Velvet Frost. Following consent, participants were outfitted with a pair of welding goggles where the left eye was completely blacked out and the flat lens over the right eye was replaced with a single theatrical lighting filter precisely cut and placed within the welding goggle frame. The goggles allowed for only monocular viewing through the right eye aperture and had a tested field of view from the circular aperture of n° in the horizontal and 68° in the vertical. Dominant eye was not used because of the nature of the simulator. There five theatrical lighting filters were tested across 10 participants with Diffusion, Cinegal3047: Prior to the arrival of participants, the ETDRS Acuity Chart was hung blank side facing out so that the line equivalent to logMAR 0.0 (or the Snellen equivalent of 20/20) was 45" off the floor. Participants were asked to stand facing away from the chart at a distance of 1 meter from the front surface of the chart. The chart was evenly lit so that the surface was approximately 85 cd/m2 (not to exceed 120 cd/m2) as specified in the ETDRS instruction manual. There was no glare on the surface of the chart and at no point were any shadows cast on the chart. The ETDRS chart was then turned around so that it was right side facing out and participants were asked to turn around to face the chart. Starting with the first line and then continuing to the subsequent lines, participants were asked to recite out loud the letters on the chart from left-to-right until they got three or more letters wrong in a single line. There were five letters per line. Participants were encouraged to guess the letters if he or she had not yet met the criteria for discontinuing the test. Participants' scores on the ETDRS were determined by starting with a value of 1.10, then subtracting the value of the number of lines attempted multiplied by 0.10, then adding the value of the number of letters missed multiplied by 0.02, and then adding an adjustment for distance (add 0.0 for a viewing distance of 4 meters, add 0.3 for a viewing distance of 2 meters, or add 0.6 for a viewing distance of 1 meter). The resulting value was their logMAR acuity. Participants' logMAR acuity could be roughly converted into the more common Snellen visual acuity scale by multiplying 20 times 10 raised to the logMAR value. For example, if logMAR acuity is 0.9, Snellen acuity would be 20 x 10A0.9 or roughly 20/160. Participants were then asked to face away from the chart and were given another set of goggles with a different theatrical lighting filter in the right aperture. They then repeated the above process with the new set of goggles. Finally, 13 10gMAR distance of 1 meter from the front surface of the chart. The chart was evenly lit so that the surface was approximately 85 cd/m2 (not to exceed 120 cd/m2) as specified in the ETDRS instruction manual. There was no glare on the surface of the chart and at no point were any shadows cast on the chart. The ETDRS chart was then turned around so that it was right side facing out and participants were asked to tum around to face the chart. Starting with the first line and then continuing to the subsequent lines, participants were asked to recite out loud the letters on the chart from left-to-right until they got three or more letters wrong in a single line. There were five letters per line. Participants were encouraged to guess the letters ifhe or she had not yet met the criteria for discontinuing oflines 0.1 0, adding the value of the number of letters missed multiplied by 0.02, and then adding an adjustment for distance (add 0.0 for a viewing distance of 4 meters, add 0.3 for a viewing distance of 2 meters, or add 0.6 for a viewing distance of 1 meter). The resulting value was their 10gMAR acuity. Participants' 10gMAR acuity could be roughly converted into the more common Snellen visual acuity scale by multiplying 20 times 10 raised to the 10gMAR value. For example, iflogMAR acuity is 0.9, Snellen acuity would be 20 x 101\0.9 or roughly 20/160. Participants were then asked to face away from the chart and were given another set of goggles with a different theatrical lighting filter in the right aperture. They then repeated the above process with the new set of goggles. Finally, 14 participants were given a third set of goggles with a clear flat lens in the right aperture and were asked to stand 4 meters away from the chart. The process was repeated again from this distance to determine participants' normal acuity. The Pelli-Robson Contrast Sensitivity Chart was hung so that the center of the chart was 45" from the ground. Participants were fitted with the first pair of goggles and asked to stand 1 meter from front surface of the chart. The chart was evenly lit so that the surface was approximately 85 cd/m2 (not to exceed 120 cd/m2) as specified in the Pelli- Robson Contrast Sensitivity Chart instruction manual. There was no glare on the surface of the chart and at no point were any shadows cast on the chart. There were two triplets per line. Starting with the first line and then continuing to the subsequent lines, participants were asked to recite out loud the letters on the chart from left-to-right until participants got two or more letters wrong in a single triplet. Participants were encouraged to guess the letters if they had not yet met the criteria for discontinuing the test. Participants' scores on the Pelli-Robson Contrast Sensitivity Test were determined by the log value of the last triplet in which two or three letters were correctly read. The process as described above was repeated with the second and third set of goggles. Following the measurement of participants' normal log contrast sensitivity, the experimenter debriefed participants as to the nature of the experiment and answered any questions regarding the protocol. cdlm2 Pelli­Robson 15 Results Coding The raw data from experiment 1 consisted of four logMAR acuity readings and four log contrast sensitivity readings for each tested theatrical lighting filter of five filters. LogMAR acuity readings were averaged across subjects for one reading. Log contrast sensitivity was also averaged across subjects for one reading. Analysis In experiment 1, the logMAR acuity readings and the log contrast sensitivity readings were evaluated on the following ranges according to World Health Organization Classification of Vision Loss (WHO) and the National Research Council's Committee on Disability Determination for Individuals with Visual Impairments (NRC). A logMAR acuity between 1.4 and 1.7 represents the profound low-vision range in the WHO classification. A log contrast sensitivity below 1.5 represents a visual impairment and a contrast sensitivity below 1.0 constitutes a visual disability. A theatrical lighting filter with an acuity reading in the profound low-vision range and a contrast sensitivity greater than 1.0 represents a decoupling of acuity and contrast where acuity is more degraded than contrast. A theatrical lighting filter with an acuity reading better than the profound low-vision range and a contrast sensitivity less than 1.0 but greater than 0.0 represents a decoupling of acuity and contrast where contrast is more degraded than acuity. Results and Discussion From the filters that were tested, no filters degraded acuity more than contrast according to the a priori criteria described above. However, the range of tested log 10gMAR theatrica11ighting 10gMAR than 1.0 represents a decoupling of acuity and contrast where acuity is more degraded than contrast. A theatrical lighting filter with an acuity reading better than the profound low-vision range and a contrast sensitivity less than 1.0 but greater than 0.0 represents a decoupling of acuity and contrast where contrast is more degraded than acuity. oftested 16 Filter logMAR Acuity Log Contrast Sensitivity Decouple? Lee 252 0.02 1.24 No Lee 255 0.22 0.79 Yes ROSCO 104 0.12 0.94 Yes ROSCO 101 1.70 0.53 No Cinegal 3047 1.53 0.36 No contrast sensitivities for the ROSCO 101 (near log 0 to log 1.05) and the Cinegal 3047 (near log 0 to log 0.75) were close to meeting the minimum criteria for contrast sensitivity while meeting the criteria for logMAR acuity (average tested acuity of logMAR 1.70 with SD = .033 and average tested acuity of logMAR 1.53 with SD = 0.16, respectively). The Lee 255 (average tested acuity of logMAR 0.22 with SD = 0.15 and average tested contrast sensitivity of log 0.79 with SD = 0.14) and the ROSCO 104 (average tested acuity of logMAR 0.12 with SD = 0.11 and average tested contrast sensitivity of log 0.94 with SD = 0.08) did meet the criteria for degrading contrast more than acuity (see Table 1). The Lee 252 did not degrade acuity nor contrast enough to meet either criterion. These findings indicate that it possible to explore experimentally the role of a contrast deficit on spatial perception and cognition as we were able to identify low-vision simulators that degrade contrast more than acuity. We were not able to identify Table 1 Mean logMAR Acuity and Mean Log Contrast Sensitivity of Theatrical Lighting Filters l.05) Cinegal3047 10gMAR 10gMAR 1.70 with SD .033 and average tested acuity oflogMAR 1.53 with SD 0.16.' respectively). The Lee 255 (average tested acuity of log MAR 0.22 with SD = 0.15 and average tested contrast sensitivity oflog 0.79 with SD = 0.14) and the ROSCO 104 (average tested acuity of 10gMAR 0.12 with SD = 0.11 and average tested contrast sensitivity of log 0.94 with SD = 0.08) did meet the criteria for degrading contrast more than acuity (see Table 1). The Lee 252 did not degrade acuity nor contrast enough to meet either criterion. I 10gMAR 10gMAR 0.l2 l.70 Cinegal3047 17 simulators that degrade acuity more than contrast; however, these findings are promising that such a simulator exists and could be identified in the future as new theatrical lighting filters are made available. We used the Cinegal 3047 filters for experiment 2 because they were the only filters with an average tested acuity in the profound low vision range according to the WHO classification of vision loss. Ihe Iheatricallighting Cinega1 filte rs thcy thc loss, EXPERIMENT 2 Experiment 2 investigated egocentric distance perception under normal and degraded vision conditions to examine whether a perceptual representation could be recovered that supported more complex navigation than was originally demonstrated in Tarampi, et al. (2008). To explore the effects of simulated low-vision on a more complex distance-dependent spatial updating task, we employed the triangulation task of eyes-closed indirect walking and compared indirect walking performance to direct walking performance. Method Participants A total of 10 psychology students from the University of Utah participated as part of a course requirement or for extra credit. Ten (6 males and 4 females, mean age 21.8 years) participated in experiment 2 comparing degraded and normal viewing conditions. Each participant completed the task individually during the course of approximately one and a half hours and received one and a half hour's worth of credit towards a psychology course requirement. All participants had normal or corrected-to-normal vision. Materials Each participant wore noise-canceling headphones connected to a receiver unit and an mp3 player that played pink noise static to mask environmental noise. The eyes­closed performance. 19 experimenter administered instructions through a wireless microphone. For the degraded vision condition, participants wore blur goggles: welding goggles with a theatrical lighting gel (ROSCO Cinegel #3047: Light Velvet Frost), resulting in a tested acuity between 20/381 and 20/1261, and a tested contrast sensitivity between near 0 and 0.75 (see Figure 1). For the normal vision condition, participants wore clear goggles: welding goggles with clear flat plastic lens. Both sets of goggles allowed for only monocular viewing through the right eye aperture and had a tested field of view from the circular aperture of 72° in the horizontal and 68° in the vertical. The left eye was blacked out. In both conditions, participants wore a hood made of blackout cloth used during the actual experiment as a blindfold and that also served to block overhead and surrounding light cues. The targets were two sizes of black matte boxes (0.51 meters H x 0.32 meters W x 0.32 meters D; 0.56 meters H x 0.36 meters W x 0.36 meters D). The experiment room had 7.7 meters x 10.5 meters of walkable space and was approximately evenly lit. Experiment 2 was conducted in BEH S room 110 and in the adjacent hallways. Each experimental session consisted of training, a degraded vision condition, a normal vision condition, vision tests, and a debriefing. Training occurred in the hallway and included blind walking while being guided by the experimenter, blind walking on their own, direct walking task practice, indirect walking task practice, and practice raising/lowering the hood. The degraded vision condition and the normal vision condition occurred in BEH S room 110. A 5-minute break between conditions took place in the hallway. The ETDRS Acuity Test and the Pelli-Robson Contrast Sensitivity Test as well as a debriefing were administered in BEH S room 110. walk able raisingllowering Figure 1: Degraded vision goggles: welding goggles with the left eye occluded and a theatrical lighting gel in the right eye to impair vision Design Experiment 2 used a 2 (condition) x 2 (task) x 3 (distance) factorial design in which viewing condition (degraded or normal), task (direct or indirect walking), and distance were within-subjects variables. Participants were first asked for informed consent to participate in the study. They were also asked to fill out a short survey on their ethnic and racial information. Following consent, participants were outfitted with welding goggles that have a built-in blindfold as well as a set of noise-canceling headphones connected to a receiver unit and an mp3 player that played pink noise. The experimenter administered instructions through a wireless microphone that was picked up by participants' receiver unit. The noise-canceling set-up masked environmental noise. 20 I: letl nonnal), subj ects Procedure infonned infonnation. noise+Ca/1ccling noisc. panicipants' noisc-scI-cnvironmental 21 As part of training session, participants first got experience walking without vision while being guided by the experimenter through the hallway. During the experiment, the experimenter guided participants to and from different locations. Then participants had the opportunity to gain experience walking on their own while blindfolded as the experimenter assured their safety by walking next to them. The purpose of this training was so that participants began to feel comfortable walking on their own without vision. Following these initial experiences, the experimenter then demonstrated the direct walking task, which was one of the tasks that participants did in the experiment. The experimenter explained that participants would be led to a starting location blindfolded and then asked to raise the blindfold. Participants would view a target and its location in the environment, close their eyes, and then walk to the center of where they believed the object is located. It was stressed to participants that they should walk so that they were standing in the middle of where they believed the target was located and that it is important that they keep track of locations in the environment as they walked. The target was moved by the second experimenter so participants would not collide with it. The primary experimenter then demonstrated the direct walking task for participants. At that point, participants could ask any questions they had regarding the task and then they practiced the direct walking task in the hallway twice. Participants received no feedback regarding their performance. The experimenter then demonstrated the indirect walking task, which was other task that participants did in the experiment. As with the previous task, the experimenter explained that participants would be led to a starting location blindfolded and then asked to raise the blindfold. They viewed a target and a designated location in the environment as well as their location in the environment, closed their eyes, and then walked in a direction away from the target but toward the designated location. When prompted by the experimenter, participants paused and turned towards the perceived target, and then walked the rest of the way to the target location. Participants were encouraged again to walk to the center of where they believed the object was located. It was stressed that participants should walk so that they were standing in the middle of where they believe the target was located and that it was important that they keep track of locations in the environment as they walked. The target was moved by the second experimenter so participants would not collide with it. The experimenter then demonstrated the indirect walking task for participants. At that point, participants asked any questions they had regarding the task and then they practiced the indirect walking task in the hallway twice. Again participants did not receive any feedback regarding their performance. Upon completion of the training, participants removed the welding goggles that they wore during training. Participants then were shown how to raise and lower a hood that served as a blindfold during the experiment. The hood was made of blackout cloth and was lowered before walking to block the view of the target, environment and surrounding light cues. Participants were instructed to lift the hood but not take it completely off. Participants then were given written instructions for the experiment they are about to participate in and were given the opportunity to ask any questions they might have regarding the experiment protocol. They were then outfitted with a new pair of monocular degraded vision goggles for the experiment and told to wear the hood over the goggles. Participants were then led into the experiment room while blindfolded. 22 23 The experimenter then guided participants to the starting location. The first trial served as an example to reiterate and clarify the experiment instructions. For the first trial only, participants viewed the target as the experimenter explained the instructions in the experiment setting. The experimenter pointed out the designated location in the experiment room. The designated location was a light-emitting diode (LED) presented at about eye-level on the right side wall. A LED is an electronic light source that is more efficient, durable, and long lasting compared to incandescent bulbs. Because of their small size, a LED creates a homogeneous light point with a wide viewing angle. Participants were asked to acknowledge the position of the designated location by turning to face it. They then were asked to turn back to face the target and note its location in the environment. The experimenter then instructed participants to lower the hood and to perform the indirect walking task. Participants' performance was not recorded for this first trial. They were guided back to the starting location while still blindfolded and reminded that they could have been asked to perform the direct walking task. Participants then did two additional practice trails without feedback - one each of the direct walking task and the indirect walking task. Following the practice trials, participants took part in 14 additional experiment trials. Each trial consisted of one of two black box targets located at a distance of 1.5, 3.1, or 6 meters for a total of two trials at each distance for each task. One dummy trial was also included at each of the distances of 4 and 5 meters in order to make the target trial distances less predictable. The task (direct or indirect walking), target size, and target distances were randomized across trails. For all of the trials, participants were allowed to view the target and its location in the environment for only 5 seconds. The experimenter then instructed 1.5,3.1, 24 participants to lower the hood. Once the hood was lowered they were told what task to perform. In the case of the direct walking task, participants walked without vision until they reached the target location. The final positions of the participants were marked with a sticker on the ground centered between their feet. The second experimenter recorded the x- and y-coordinates of the final position. In the case of the indirect walking task, participants first walked in an oblique direction without vision toward the previously seen LED. When prompted, participants paused and turned towards the perceived target, and then walked the rest of the way to the target without vision. The turning point was also marked with a sticker on the ground centered between the participants' feet in addition to the final stopping position. The second experimenter then recorded the x- and y-coordinates of both the turning location and the final position. Participants received no feedback regarding their performance at any time during the experiment. At the end of each trial they remained blindfolded as they were guided back to the starting location and as the next target was placed for the following trial. Upon completion of the trials in the degraded vision condition, participants were led out to the hallway blindfolded. They removed the hood and goggles, and were given degraded vision goggles. After the break, participants were given a different pair of monocular normal vision goggles and told to wear the hood over the goggles. Participants were then led into the experiment room while blindfolded. Participants then performed one practice trial of the indirect walking task followed by 14 trials as described above. Each trial consisted of one of two black box targets located at a distance of 1.5, 3.1, or 6 meters for a total of two trials at each feel. y­coordinates a 5-minute break to counteract any adaptation that may have occurred while wearing the 25 distance for each task. One dummy trial was also included at each of the distances of 4 and 5 meters. Upon completion of the trials in the normal vision condition, participants were lead out to the hallway blindfolded. They were told to remove the goggles and other equipment. They then were brought back into the experiment room where they completed the posttests. The posttests were conducted as described in experiment 1 except that participants' logMAR acuity and log contrast sensitivity were tested monocularly with the degraded vision goggles used in the experiment followed by testing monocularly with the normal vision goggles used in the experiment. Following the measurement of the participants' normal log contrast sensitivity, the experimenter debriefed participants as to the nature of the experiment and answered any questions regarding the protocol. Results Coding The raw data from experiment 2 consists of the x- and y-coordinates of the final stopping position and the turning point measured in meters relative to a coordinate grid system in the experiment room. The performance of each participant in the degraded vision condition trials generated a total of 6 x-y coordinates for the final stopping positions for the direct walking task and six sets of turning points and final stopping positions for the indirect walking task. Normal vision condition trials also generated six total x-y coordinates for the final stopping position in the direct walking task and six sets of x-y coordinates for the turning point and final stopping position in the indirect walking task. The x-y coordinates for the final stopping position were used to calculate the distance in meters from the starting location, or origin, and the final stopping position, or 10gMAR endpoint, resulting in an origin-to-endpoint distance (OE). The OE was averaged within subject for both the direct and indirect walking tasks in degraded vision and normal vision conditions. This resulted in three direct walking average distances in the degraded vision condition (for target distances of 1.5, 3.1, and 6 meters), three direct walking average distances in the normal vision condition, three indirect walking average distances in the degraded vision condition, and three indirect walking average distances in the normal vision condition. Analysis There are different analyses that can be used to evaluate direct walking and other triangulation methods - the mean y-coordinate of endpoint, the mean OE, and the mean y-intercept extrapolated from the heading direction following the turn. We used the OE analysis to compare direct and indirect walking performance. The OE is the distance between the x- and y-coordinates of the origin and the x- and y-coordinates of the endpoint. The OE analysis accounts for veering in both direct and indirect walking performance. For example, in the indirect walking task, if observers veer toward the right in the first leg then it would be predicted that observers would stop short of the y-intercept in the second leg. This presumes that observers believe that they did not veer and were therefore closer to the y-intercept than reality. The OE distance would conceivably be equal to the y-coordinate of the endpoint if observers were exact and did not veer. The mean y-coordinate of the endpoint could be used to compare direct and indirect walking performance. In the case of direct walking, using the y-coordinate of the endpoint would assume no veering when walking. Using the mean y-coordinate of the 26 y­intercept conceivably be equal to the y-coordinate of the endpoint if observers were exact and did not veer. endpoint to analyze indirect walking performance makes less sense since veering may occur in both the first leg as well as the second leg. Information is lost about the perceived and updating location if the y-coordinate is only analyzed and the x-coordinate of the endpoint is disregarded. Additional analyses could be preformed to compare these results to previous experiments that utilized triangulated walking (Fukusima, et al., 1997; Thompson, et al., 2004). In these previous studies, the observer did not walk all the way to the perceived target location. Instead the observer walked in a direction away from the target and when cued, turned and walked part way to the target or pointed towards the target. The perceived target location was purported to be the intersection of the trajectory of the observer or the pointing direction following the turn with the axis of the initial observation. This y-intercept is said to be the perceived and spatial updated target location in triangulation methods. A similar analysis could be done with our data using the slope-intercept form of the straight-line equation, ory mx b, where b is the y-intercept and m is the slope [m = (y2 -yi)/(x2 - xj)]. This assumes no veering in either the first or second leg. It also assumes that the observer walked in a straight-line after the turn. This analysis is not appropriate for analyzing indirect walking performance because of the aforementioned assumptions and because it disregards the actual endpoint of the observer. In triangulation by pointing and triangulation by walking, the observer points toward or walks a couple of steps toward the perceived and updated target location. These tasks leave little room for veering or meandering. Results and Discussion Overall walking accuracy was essentially the same in the degraded and normal viewing conditions and did not vary as a function of the direct versus indirect walking 27 aI., aI., or y = + y­intercept m [m = Y2 - Y J)/(X2 x J)]. 28 task (see Figures 2-3). For each participant, target distance, and task, we calculated the average turn point (when applicable) and endpoint by averaging the x- and y-coordinates separately. The distance between the origin and the endpoint was calculated in order to compare performance between the direct and indirect walking tasks. In experiment 2, a 2 (condition) x 2 (task) x 3 (distance) ANOVA was performed on the mean OE with condition, task, and distance as within-subjects variables. There was only a significant effect of distance (F2,i8 = 285.230,/? < 0.0001; n p 2 = 0.969), showing that distance walked increased with increasing absolute distance. Notably, there was no difference in OE between the degraded and normal viewing conditions (p = 0.216) and no interaction of viewing condition and task (p = 0.267). Although constant error was not affected by the viewing condition manipulation, we did find a difference in precision. Variable error, as a measure of precision, was calculated as the standard deviation of the mean distances walked at each distance for each participant in each task and condition. The same ANOVA as described above was performed on variable error for experiment 2, showing a significant effect of viewing condition (Fi,9 = p < 0.05; r)p 2 = 0.428) with greater variability in the degraded (mean = 0.302) than the normal (mean = 0.212). As consistent with other blind walking there (F2,is = 7.037,/? 0.01; np2 = 0.439). the visual conditions and tasks, we conducted a repeated measures multivariate analysis of variance (MANOVA) analyzing the two coordinates as a linear combination. Condition, task, and distance were within-subjects variables for Experiment 2. The tum F2,18 = 285.230, p 11/ = = = ANOV A (Fl,9 = 6.744, 11/ = studies, therc was also significant increase in variable error with increasing distance F2,18 = 7.037,p < 11/ = 0.439), To test whether the x- and y-coordinates may have been affected differently by 29 - Figure 2: Mean distances from the origin to the endpoint averaged across observers for direct walking task in the degraded and normal conditions (experiment 2) and the normal condition (experiment 3). Error bars represent -/+ 1 SEM. Average Across Subjects · Direct Walking 7 . I . ' .' --E 6 - - •. ' ..' ..' • • • 5 , .' • 0 bY-- •c ,,-."" /' - '" • I ."" / ' is 4 r ..... < -c "•, / r • - +-. Degraded 0 I '".;2 I _ Normal ~ " 3 ~' ;1( C c l ···Q··· NormaI2 U/ .0, -" 2 I .!•! ' ..' 0 ..- 1 . .' . .' .' ... .' 0 .. 0 1 2 3 4 5 6 7 Target Distance (m) nannal nonnal condi tion I 30 Figure 3: Mean distances from the origin to the endpoint averaged across observers for indirect walking task in the degraded and normal conditions (experiment 2) and the normal condition (experiment 3). Error bars represent -/+ 1 SEM. JO Average Across Subjects - Indirect Walking "'0·" NormaJ2 1 6 7 TargetOlstance 1m) ElTor I 31 MANOVA revealed a main effect of task (F2 ,8 = 5.252, p < 0.05; n p 2 = 0.568) and distance ( F 4 3 6 ~ 84.616, p < 0.0001; n p 2 0.983) and no significant interactions with condition. The effect of task is further qualified by the univariate analysis, which revealed a significant effect of the x-coordinate for task (Fi;9 = 11.247,/? < 0.008; np = 0.555) but not the y-coordinate. This reflects the tendency for participants to overshoot the x-coordinate in the indirect walking task (Mean = -3.08805 and -0.8674, for indirect and direct, respectively). There was also a main effect of the y-coordinate for distance F2,i8 = 270.193, p < 0.0001; n p 2 = 0.968), consistent with the finding that the location of the y-coordinate increased with target distance. For both walking tasks, walked distances did not differ between normal and degraded vision conditions indicating that observers can recover scale and update a three-dimensional representation of space as they locomote even under low-vision conditions. Walked distances did indicate that performance in the normal vision condition when second block of trials. oftask F2,8 11/ (F4,36 = 84.6l6,11/ = oftask F 1,9 = 11.247,p 11/ = = (F2,18 = P 11p2 = distance, three­dimensional following the degraded vision condition was less accurate than expected. To test whether this was an order effect, we conducted a second experiment involving only the normal condition in order to compare performance when judgments are made in the first versus EXPERIMENT 3 experiment 2, the normal condition was always performed after the degraded condition so as to prevent the participants from having full-cue experience with the room before making their low-vision judgments. As a consequence, it is possible that judgments in the normal condition would be influenced by the prior block of trials of degraded-vision trials. Thus, we conducted a second experiment involving only the normal condition, to serve as a comparison of judgments made in the first versus second block of trials. Other than having only one block of normal viewing trials, all other protocols in experiment 3 were identical to the protocol of experiment 2. The normal condition in experiment 3 allowed for a between-subject comparison with the normal condition of experiment 2 to test for order effects. Method Participants Ten psychology students from the University of Utah participated as part of a course requirement or for extra credit. Ten (6 males and 4 females, mean age 21.5 years) participated in experiment 3, a normal viewing condition which served as a control for possible order effects, as described below. Each participant completed the task individually during the course of approximately 1 hour and received 1 hour's worth of credit towards a psychology course requirement. All participants had normal or corrected-to-normal vision. In 33 Materials Experiment 3 was conducted in BEH S room 110 and in the adjacent hallways. Each experimental session of experiment 3 consisted of training, a normal vision condition, vision tests, and a debriefing. The materials were exactly the same as those outlined for experiment 2 except the participants wore only the clear goggles. Design Experiment 3 used a 2 (task) x 3 (distance) x 2 (order) design, with order as a between-subjects variable and task and distance as within-subjects variables. Procedure Other than having only one block of normal viewing trials, all other protocols in experiment 3 were identical to the protocol of experiment 2. Results Coding The raw data from experiment 3 were similar to the data from experiment 2 but only included data points from a normal vision condition. Analysis We used an OE analysis to compare direct and indirect walking performance in experiment 3 to direct and indirect walking performance in the normal condition of experiment 2. 34 Results and Discussion While distance estimates were slightly underestimated in both conditions in experiment experiment showed that this was not a result of factors associated with performing two blocks of trials, as there was no difference in performance as a function of order (see Figures 2-3). In experiment 3, a 2 (order) x 2 (task) x 3 (distance) ANOVA was performed on the mean OE with order (normal condition presented first or second) as a between-subjects variable and task and distance as within-subjects variables. The only significant effect was of distance F 2 , 3 6 = 367.988, p < 0.0001; n p = 0.953). There was no effect of order (p = 0.770). l4 c)(periment 2, 3 thal lhis arorder nonnal ( F2J6 = P TJp 2 = 0.953), GENERAL DISCUSSION Despite degrading vision to a range in profound low-vision, observers still performed the visually guided action based measures of direct and indirect walking to previously viewed targets as accurately as in the normal vision condition. The most plausible explanation for good performance observed under low-vision conditions in experiment 2 is that the participants were still able to use eye-height scaled angle of declination information - the angle from the observer's eye height to a target located on the ground plane (Ooi, Wu, & He, 2001; Sedgwick, 1986). Observers may be able to recover absolute distance by using eye height to scale relative distance information from perspective-based pictorial cues. It is still unclear how this level of precision was obtained from extremely blurry views of the target and whether or not visual information was used as the reference for the horizontal. As seen in Figure 4, even under the low-vision conditions there was visual information for the boundary between the floor and wall. It will be important to determine whether information such as this is critical to making accurate distance judgments. Questions of this sort have broader implications for making architectural spaces visually accessible. For example, a traditional practice in architectural interiors is to clearly delineate the floor and wall planes, deviating from this practice may cause problems for low-vision individuals who rely on this assumption to make judgments about locations in the environment. If observers are relying on angle of & It low­vision conditions there was visual information for the boundary between the floor and wall. It will be important to determine whether information such as this is critical to making accurate distance judgments. Questions of this sort have broader implications for making architectural spaces visually accessible. For example, a traditional practice in architectural interiors is to clearly delineate the floor and wall planes, deviating from this practice may cause problems for low-vision individuals who rely on this assumption to make judgments about locations in the environment. If observers are relying on angle of 36 Figure 4: Simulation of the participant's view in normal (left) and degraded (right) conditions declination, manipulations of context such as the perceived horizon may elucidate this relationship. In addition to the main finding of comparable performance in spatial updating across the viewing conditions, there were several interesting additional outcomes of the distance estimation tasks. Although observers in our experiments performed with the same proficiency as comparable studies utilizing these tasks (He, Wu, Ooi, Yarbrough, & Wu, 2004; Loomis, et al., 1998; Philbeck, Loomis, & Beall, 1997), these outcomes necessitate further investigation. In experiment 2, performance on the direct and indirect walking in the normal vision condition less accurate than expected, showing underestimation at further distances. These findings were replicated in experiment 3, thus ruling out order effects. It is possible that this underestimation is due to the nonnal intcresting Loomis. perfonnance d irect tasks vis ion was thaI 37 unpredictability of the task during the viewing period as observers did not know whether they would perform the indirect or direct walking task until after their eyes were closed. Unpredictability was included in the task to be consistent with the experiment protocol in previous research (Philbeck, et a l , 1997) and so that participants would be further discouraged to rely on pre-planning strategies. There may be differences in the representation of visual information when the task is unknown or there may also be cognitive interference from the other task. Previous studies with multiple-task methodologies have shown underestimation of distance consistent with our present results (Loomis, et al., 1998; Philbeck, et al., 1997) but a clear understanding of the causes will require further examination. A second effect seen in both viewing conditions was the significant overshoot to the left in the x-coordinate for the indirect walking task. One speculative explanation for this bias could be right-eye monocular viewing. We chose to test monocularly with the right eye instead of monocularly with the observer's dominant eye because the degraded vision filter could not be precisely replicated in both eyes. It is also possible that there is a direction bias in the indirect walking task depending on the heading direction of the first leg. This bias is evident but not discussed in previous studies (He, Wu, Ooi, & al., walked initially in a direction to their right, a procedure chosen because of the configuration of the room. Future investigation could explore the influence of monocular viewing and initial heading direction on directional walking biases. In these spatial perception tasks, we relied on simulated low-vision in order to compare performance with normally-sighted individuals. Whether simulated low-vision aI., aI., aI., Yarbrough, Wu, 2004; Philbeck, et aI., 1997). Observers in our experiment always 38 can generalize to actual low-vision populations has not been well studied. A key question is whether individuals with prior visual experience (in the case of normally sighted individuals under simulated low-vision conditions) and individuals with no prior visual experience (in the case of early-onset actual low-vision individuals) are comparable in their spatial competence. Previous research indicates that spatial competence is not reliant on prior visual experience (Loomis, et al., 1993; Rieser, Hill, Talor, Bradfield, & Rosen, 1992). Rieser, et al. (1992) tested individuals with early-onset acuity loss, late-onset acuity loss, early-onset field and acuity loss, late-onset field and acuity loss, and totally blind as well as normal controls. Not surprisingly, the late-onset field loss group, the early-onset acuity group, and the late-onset acuity group were better than totally blind group. However the early-onset field loss group performed worse than totally blind. Loomis, Klatzky, Golledge, Cicinelli, Pellegrino and Fry (1993) investigated performance in simple and complex locomotion tasks as well as spatial updating tasks (real and imagined transformations of a spatial array) in normally sighted, congenitally blind, and adventitiously blind individuals. Loomis, et al. (1993) found no differences in the simple and complex locomotion tasks across participants. They concluded that prior visual experience does not strongly influence spatial competence. It is important to note that one study that did compare performance of actual low-vision individuals with simulated low-vision individuals and did not find a correlation in performance (Apfelbaum, Pelah, & Peli, 2007). Apfelbaum et al. (2007) observed participants with retinitis pigmentosa and normally sighted individuals with simulated tunnel vision in a heading assessment task. The difference in performance between the actual and simulated tunnel vision participants could be attributed to the complexity of aI., aI. aI. low­vision 39 the disease. Retinitis pigmentosa involves a number of visual deficits such as night blindness, reduced contrast sensitivity, and a progressive constriction from the periphery in the size of the visual field. In this study, the simulated tunnel vision observers only had a restricted FOV. Further research is needed to compare actual and simulated low-vision to determine if simulating low-vision is an accurate and comparable method for exploring spatial perception and cognition under low-vision conditions. Low-vision is a complex disease that may be difficult to simulate accurately for all cases. Diagnoses of low-vision involve a combination of visual deficits including acuity, although the viewing goggles did induce a restricted peripheral field of view (72° al., al., low­vision oflow-visual field, acuity and contrast. This study examined severely reduced contrast and in the horizontal and 68° in the vertical) as well but not to a level that is symptomatic of a low-vision deficit (less than 40° FOV in the horizontal). Existing low-vision navigation research indicates that field of view may be the most detrimental to actual low-vision navigation (Kuyk, et aI., 1996; Long, et aI., 1990; Marron & Bailey, 1982) given the types of mobility assessment tasks that involve eyes-open walking. The effects of a greater restricted field of view combined with reduced acuity and contrast on absolute distance judgments is unknown. Although generalizing data from simulated low-vision studies to a specific low-vision disease or deficit may be difficult, our results provide initial insight into the surprisingly good scaling of space under conditions in which targets are barely able to be seen. CONCLUSIONS AND FUTURE DIRECTIONS Our results provide evidence that participants can recover scale and update a perceptual representation of space under simulated low-vision at least out to distances of several meters. These abilities are important for path planning and spatial updating both of which are necessary in low-vision navigation. Further investigation is necessary to generalize these results to the updating of multiple target locations. Our finding of increased variability in responses may be attributed to increased uncertainty in one's self-position during updating, given the reduced visual context available during initial viewing of the environment. Precision in updating could be facilitated with the presence of multiple objects, as shown in a full-cue study suggesting that additional objects are treated as landmarks which can reduce response variability (Philbeck & O'Leary, 2005). Philbeck and O'Leary (2005) maintain that participants' positional uncertainty, or the uncertainty of one's self location as one moves through space without visual feedback, tends to increase as participants get further from their last known location because of increasing errors in self-motion signals (i.e., vestibular cues, proprioception, etc.). The presence of landmarks could increase precision by decreasing positional uncertainty. Additional objects could also serve as context and could be used as a relative distance cue. It may also be that although observers under low-vision conditions can update their self-position with respect to one object, they may not be able to update multiple locations at the same time, or they may use different memory strategies under full-cue versus self­position of multiple objects, as shown in a full-cue study suggesting that additional objects are & selflocation tends to increase as participants get further from their last known location because of increasing errors in self-motion signals (i.e., vestibular cues, proprioception, etc.). The presence of landmarks could increase precision by decreasing positional uncertainty. Additional objects could also serve as context and could be used as a relative distance cue. 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