Visual Perception Week 8 Notes
Visual Perception Week 8 Notes PSYC 3124
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This 22 page Class Notes was uploaded by Freddi Marsillo on Sunday March 6, 2016. The Class Notes belongs to PSYC 3124 at George Washington University taught by Dr. John Philbeck in Spring 2016. Since its upload, it has received 32 views. For similar materials see Visual Perception in Psychlogy at George Washington University.
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Date Created: 03/06/16
Visual Perception Notes Week 8 3/6/16 5:31 PM Paper: “Perceiving Distance: A Role of Effort and Intent” – Witt et al. A different definition of distance perception • Perception of spatial layout is a function of optical information, and a function of the perceiver’s potential to act on the environment • Perception of distance is a function of distal extent + the action that the perceiver tends to perform + effort associated with this action Rationale of the current experiment • Apparent egocentric distance increased when participants wore a heavy backpack (Proffitt et al., 2003) • Changing the relationship between walking effort and concurrent optic flow produced a visuomotor effect (Rieser et al., 1995) • A recalibration between walking energy and anticipated optic flow changes the anticipated effort required to walk a given extent • Increasing anticipated walking effort led to increases in estimated distance (Proffitt et al., 2003) Is this effect general or functionally specific? • In Riser et al. (1995) aftereffects were observed for blindwalking but not for throwing targets when blindfolded, or for turning in place when blindfolded • Prediction of current study: o Perceived distance should increase after walking on the treadmill (increase in effort) if participants were intending to walk but not if they were intending to throw Experiment 1 – Will anticipated effort for throwing influence distance perception? • Design: 24 participants were assigned to either the heavy ball or light ball condition • Participants threw wither ball to 4 targets ranging in distance from the participant (3-11m) • After throwing the ball 3 times, participants were asked to estimate distance to the target • Results: o Participants in the heavy ball condition perceived the targets as being farther away than did those who threw the lighter ball Experiment 2 – Throwing effort and perceived distance: perceptual matching • Design: participants were either assigned to the heavy ball or the light ball condition. They were also assigned to one of two conditions: “in” or “out.” • “In” condition: poles were initially placed directly behind the target and moved towards the double marks • “Out” poles were initially placed on the doubled marks and moved towards the target • 12 male and 12 female participants in each of the four trials • Procedure: o The double marks. “Out” poles were initially placed on the doubled marks and moved towards the target o For each distance, participants threw the ball three times to each target. After the third throw, two experimenters help up the two poles. o In the “in” condition, the poles were help up directly behind the target. In the “out” condition, the poles were help up at the doubled marks. o While holding the ball, participants gave instructions to the experimenters about whether to move towards or away from each other until they thought that the distance between the two poled matched the distance from the observer (them) from the target (egocentric distance). o Then, they were asked to make a final throw to the target. • Results: o Wanted to determine whether effort for throwing affected the visual distance-matching task o Ran a 2*2*2*4 ANOVA with repeated measures on the last factor. o The main effect for ball was significant. Participants who threw the heavy ball positioned the poles to be farther apart than participants who threw the light-ball. o The main effect for pole condition was also significant. Participants in the “in” condition positioned the poles to be closer than participants in the “out” condition. o The only interaction that was significant was the interaction between pole condition and distance. o Results show that effort for throwing influences apparent egocentric distance judgments Experiment 3 – throwing effort and perceived distance: blind walking • Design: assigned to either heavy ball or light ball condition. Five male and five female participants were in each condition and each blind walked to the 6 target distances (2 practice and 4 test trials) • Procedure: Practice targets were placed at 5 and 9 m and the test targets were placed 4, 6, 7, 10 m (practice and distance targets randomized) • Participants were instructed to throw to each target till they hit it (no more than 3 times). • They were then turned 180 degrees to face a new direction so they would respond to distance and NOT location of the target with blindfold on. • They then attempted to walk the perceived target distance. Distance participants walked was in meters • Results: A 2*2*4 ANOVA with repeated measures on the last factor was run in order to determine whether effort for throwing influenced blind walking • The effect of effort for throwing does not extend to blind walking • The only time that perception is influenced is by throwing and not by walking Experiment 4 – Effort for throwing and intention • Design: experiment 4 looked at how effort of throwing and intentions affected participants’ perceived distance. Participants were assigned to either the ‘intend-to-walk’ group or the “intend- to-throw” group. (All participants had experience throwing the ball prior) • Those in the “intend-to-walk” group anticipated that after estimating the distance of a target, they were to walk to it • Those in the “intend-to-throw” group anticipated that after estimating the distance of a target, they were to blind throw a heavy ball to it • Procedure: o They completed 4 practice distances and 4 test distances. The practice targets were placed at 3, 5, 9, and 11 m, and the test targets were placed at 4, 6, 8, and 10 m. o For the 4 test targets, after estimating the distance of the target, half the participants were given the ball and asked to close their eyes and throw to the target. The other half of the participants was asked to put on a blindfold and to walk to the target. • Results: o The experiment found that participants in the “intend-to- throw” group consistently overshot the estimated distance o These results suggest that the effect of effort for throwing on conscious distance perception is functionally specific, and depends on the action the perceiver intends to make Experiment 5 – effort for walking and intention • Design: this experiment looked at the effort of walking and intentions affected participants’ perceived distance. Participants were once again assigned to either the “intend-to-walk” group or the “intend-to-throw” group • Those in the “intend-to-throw” group anticipated that after estimating the distance of a target, they were to throw a heavy ball to it those in the “intend-to-walk” group anticipated that after estimating the distance of a target, they were to walk to it. • However, in this experiment, experimenters manipulated anticipated walking effort using Proffitt (’s) et al (2003) methods during a pre-test round. Participants were placed on a treadmill received zero optic flow. • In Proffitt's own experiment, he found that this manipulation caused a recalibration between walking energy and resulting optic flow, and thereby increased effort for walking, which induced an increase in apparent egocentric distance. • Procedure: o Each participant completed a practice round, a pretest round and a test round. o In the pre-test round, participants estimated the distance of three targets 6, 8, and 10 m. o Next, participants completed their walk or throw task. In the pre-test round, participants in the “intend-to-walk” group walked on the treadmill without optic flow for their estimated distance. o In the test round, target was placed at 8 m away. Participants removed the blindfold, estimated the distance to the target, and then either blind walked or threw to the target. • Results: o Relative to the pretests, participants in the blind walk condition overestimated the target in the test condition while participants in the throw condition underestimated the target in the test condition. o These results suggest that perception is influenced by the effort associated with an intended action, and thus is functionally specific. • Conclusion: o Perceived distance is a function of: 1) actual distance as specified by optical variables, 2) what we are intending to do, and 3) the effort associated with this intended action Paper: “The Various Perceptions of Distance” – Woods et al. Overview • It has been suggested that objects appear farther away when more effort is required to act upon them (e.g. throwing a ball) • Authors of this study found nothing to suggest that this is true • However, effort in verbal reports was affected when participants were asked to take into account cognitive (nonvisual) factors • Authors believe that this is because participants were encouraged to take into account non-perceptual connotations of distance while not changing distance at all Methods Experiment 1: • 24 participants were alternately assigned to either backpack or no- backpack condition • Each participant made 24 distance estimates. They divided these estimates into two blocks of six practice trials, followed by two blocks of six test trials. Six stimulus distance were presented in random order in each block • The target was a 0.23 m tall cone • The experiment took place on a flat, grassy field (120 m / 100 m). Golf tees marking target locations for experimenters were not visible to participants • Participants held a 12-inch ruler as a scale reference throughout testing. Participants stood at a central location for the duration of the study; targets were presented in one of six possible directions (0°, 30°, 60°, 120°, 150°, 180°). • They then turned to view the target and verbally reported the distance (in feet and inches) from themselves to the targtet. Then converted these distances into meters • Predicted that participants wearing a weighted backpack would verbally report distances as being significantly greater than those not wearing a backpack Results Experiment 1: • Conducted a 2 (backpack) * 2 (sex) * 2 (test block) * 6 (distance) repeated-measures multivariate analysis of variance • Test block and distance were varied within subjects, while backpack and sex were manipulated between subjects. • Performed analysis on both the full 24-participant data set and also on the data set after removing the 2 outliers that were found. o No effect of backpack • Implications: o Averaging over target distance, our estimates of Proffitt et al.’s (2003) standard errors were 0.30 m in the no-backpack condition and 0.48 m in the backpack condition. Standard errors for no-backpack participants were slightly larger than those reported by Proffitt et al., but those of backpack participants were comparable o This suggests that our null results were not due to increased variability in our data relative to theirs. Methods Experiment 2: • The authors attempted to replicate a Witt et al study, the results of which indicated that participants estimated higher distances for a ball thrown when the ball was heavier. It was hypothesized that this was because perceived distance was correlated with effort exerted in throwing the ball. • The experiment was performed indoors in a space that contained some irregularly spaced floor markings. Targets to throw the ball to were presented along 6 radii, which were divided across two starting locations. The experimenter would then roll the ball back to the participant for the next throw. • 24 participants partook. Each participant was assigned to a heavy- ball or light-ball condition and gave 12 estimations Results Experiment 2: • Subjects expended appropriate amount of effort in throwing the ball • No effect of ball weight on verbal distance estimates (contradicting Witt et al) • Differences in methodology could be the reason for this; this study was more varied than that of Witt et al (e.g. Witt et al study did not explicit report between and within subjects variability while this one did) o However, standard errors in both studies were comparable, suggesting that the differences in data were not due to difference in response variability • Since variability was not likely to account for the differences, Experiments 3 & 4 attempted to test the methodology Methods Experiment 3: • Purposes were to evaluate whether intention to act was the essential missing component in preventing replication in Experiment 2 and what effect the inclusion of such a component had on subject responses (essentially the difference between Experiments 2 and 3) • 24 Participants were assigned in alternating order to either a heavy-ball or light-ball condition (same design as in Experiment 2) • Procedure differed only in that after verbally estimating a particular target distance, participants lowered a blindfold and immediately attempted to throw to that target. o This was done to ensure that the participants’ ball-throwing intention was appropriately matched to the target distance, which they were asked to verbally estimate Results Experiment 3: • Despite the inclusion of an intention to act component, there was once again no effect of ball weight on verbal estimates. • Women tended to undershoot significantly more for 8-m and 10-m target distances. This occurred both under blind and sighted throwing, suggesting it was due primarily to motoric factors • Inclusion of an intention component significantly increased verbal estimates of distance Methods Experiment 4: • Despite inclusion of an intention to act component, studiers were still unable to replicate Witt et al.’s findings. o One possible reason, and the reason for Experiment 4, could be because of the testing environment. Witt et al.’s study was done in a grassy field, whereas these prior experiments have been done on an indoor surface with visible floor markings. Thus, Experiment 3 was replicated outdoors. • Design: Identical to Experiment 3. • Procedure: identical to Experiment 3 except it was outdoors Results Experiment 4: • Again, no effect of the effort manipulation on verbal estimates. • Participants who were tested indoors gave significantly larger verbal estimates of distance than participants who were tested outdoors. • However, there was again no effect of ball weight. • Men threw significantly farther than females. • Men threw farther in the outdoor environment than in the outdoor environment. No such effect was observed among women. • But most importantly, Witt et al. study was once again unable to be replicated, suggesting that the use of an indoor versus outdoor environment was not the critical factor. Method Experiment 5: • Laboratory and effort manipulation was the same as Experiment 3 and the procedure was generally similar except all three instructions were used • Participants were assigned to one of three instruction groups o Objective distance o Apparent distance o Nonvisual factors • Experimenters were aware that ball conditions and instruction groups, they were kept blind to the specific experimental hypotheses and trained to maintain a neutral and consistent affect with participants to avoid unintentional biasing of participants. Results Experiment 5: • We performed a 2 (ball weight) * 2 (sex) * 3 (instruction group) * 2 (test block) * 4 (distance) repeated-measures multivariate analysis of variance • Verbal estimates o A strong trend for an Instruction * Weight interaction • Neither the objective-distance nor apparent-distance instruction groups demonstrated any between subjects effects • The nonvisual-factors group demonstrated a between-subjects effect of ball weight • Heavy-ball participants gave significantly larger verbal distance estimates than light-ball participants • Distance and a Distance * Ball Weight interaction were the only significant within-subjects effects • Blind-throwing performance o Repeated-measures of multivariate analysis of variance involving the 4-m and 6-m blind-throwing trials showed no ball weight effect in any of the instruction groups o Perceived distance was not affected by the effort manipulation • Implications: o Nonvisual-factors instruction did yield significantly different verbal responses than did the other two instruction conditions and was the only condition associated with effort-related effects. Implications for Future Research Three main levels of significance • Empirical: At least some of Proffitt’s effort-related findings, though providing valuable insight into the factors that affect overt distance judgments, maybe more fragile than has been heretofore appreciated • Methodological: Highlights the vital importance of providing explicit instructions concerning what response attitude should be adopted and being sure that participants understand the difference among different connotations of distance. Also, emphasizes the importance of ensuring that experimenters interact with participants neutrally and consistently • Theoretical: Anticipated effort cannot be the sole factor, some factor must exert a powerful influence on perceived distance as a result of the multiple connotations of distance. • Effort likely does influence perceived distance under some circumstances, but that ball throwing and backpack encumbrance do not strongly elicit these effects. Proffitt et al: Perceiving Geographical Slant Introduction: Purposes of paper: • Provide normative description of overestimation in geographical slant • Motor index of geographical slant shows little evidence of the overestimations manifested in visual awareness • Our conscious perceptions of geographical slant are highly exaggerated • Perception of steepness is affected by physical fatigue • Geographical slant perception relates the actual physical slant of inclines to our behavioral potential • Hills look steeper from top than bottom • Locomote skillfully in context of gross overestimations of slant because of separate visual pathways Geographical Slant • Geographical slant is the inclination of surfaces relative to the environmentally specific horizontal • 3 different ways surface slant can be defined: o Relative slant: specifies the orientation of one surface with respect to the reference frame provided by another o Optical: specified in relation to the line of sight from the point of observation to the surface in question o Geographical slant: independent of viewpoint; its magnitude is specified in relation to the horizontal • Pitch is defined as the surface’s rotation away from horizontal around the x-axis slant is equivalent to the pitch angle that the surface makes with respect to the ground o Slant is equivalent to the pitch angle Perceiving Geographical Slant • Most studies done investigating optical slant • Studies found similar errors in estimating pitch • Errors believed to be due to problems in perceptual process • Optical slant perception studies focus on how selected information affects pitch perception vs. everyday geographical slant perception • Studies conducted by Kinsella-Shaw, Shaw, and Turvey (1992) o People are good at visually judging pitch • A common finding in all of these studies has been that surfaces appear to lie closer to the parallel plane than the perspective projection indicates – thus, subjects have systematically underestimated the pitch in relation to the picture plane • Underestimation from the picture plane is equivalent to overestimation from the ground plane • Generally, it has been thought that these underestimations are due to a tendency of judgments to conform to the pitch of the projection surface or reduction screen • The source of error seems to lie in perceptual processes as opposed to the availability of reliable information • Similar to those found for the perception of geographical slant: Perceived pitch is invariably overestimated in relation to the horizontal ground plane (underestimated relative to the vertical picture plane) • Although people overestimate geographical slant, they are not especially accident prone when walking up and down hills – people are able to accurately judge the maximum inclination that they can walk up, and people are also good at matching the pitch of a distal surface with that of a haptically (haptic = by touch) perceived surface Overview of Experiments Five experiments conducted • 1 – geographical pitch judgments from people at bottom of hills using three different types of measuring perception • 2nd– replication of the first, except hill viewed from the top rd th • 3 and 4 – replicated first and second but virtually • 5th– assess perception before and after fatigue Experiment 1 – Real hills viewed from the base Methods: • Recruited 150 males and 150 females • Nine hills on the University of Virginia o Needed to be near foot traffic o Top of the hill had to be over the horizon o Even surface o Inclinations 2°, 4°, 5°, 6°, 10°, 21°, 31°, 33° • Each participant viewed one hill, 30 people saw each hill, except for the 5° hill, which had 60 subjects Apparatus: • Three tests: o Verbal – said how big they perceived the pitch to be in degrees o Visual – used a disk with an adjustable angle to represent the cross-section of the inclination of the hill; subjects adjusted the disk to what they thought best represented the pitch of the hill while holding it approximately perpendicular to their line of sight o Haptic Procedure: • Part 1 o Viewed hills from the front while standing at the base o Instructed to look directly ahead and not to look at the sides o Judge angle of inclination of the hill with respect to the horizontal using the three tests in randomized order • Part 2 o Test subjects for internal consistency o Asked to adjust either the tilt board or disk to a set of verbally given angles Results: • Subjects’ verbal and visual perceptions reflect large overestimations of the actual inclines; haptic perceptions were more accurate • Haptic reports were not significantly different from the actual inclines of the hills • Visual and verbal reports were overestimations of the actual pitch angle of the hill • Gender difference in hill judgment: females had greater overestimation of inclination than males • In given angle tests: haptic measurements underestimated, and visual measurements more accurate • Overall, subjects displayed an internal consistency for the verbal, visual, and haptic measures, in that they represented an angle in the same way regardless of whether it was made in the context of an observed hill or of a spoken number Experiment 2 – Real hills viewed from the top Hypothesis • The perception of geographical slant relates distal inclines to our behavior potential Method and Procedure • Same as the first experiment except that the subjects were now looking down Results: • Same as Experiment 1 as the verbal and visual judgments reflected large overestimations of the inclines and the haptic reports were far more accurate • Gender differences: females showed a greater overestimation than males for the inclination of hills/greatest difference in verbal judgment • Verbally given angles: visual responses close to accurate and haptic responses were underestimated • Subjects were consistent in their visual and their haptic judgments, meaning that the judgments that they made in response to the verbally given angles were nearly equivalent to the judgments that they made for the hills, given their verbal reports on the inclination of the hills. Comparison of Experiments 1 and 2 Significant gender differences • Females’ overestimation in all three test types Viewpoint effects: • Effect was significant in visual and haptic measures, but not for verbal measures Interaction between hill pitch and viewpoint implies that the subjects respond differently to different hills depending on the uphill or downhill view • On smaller inclinations, subjects perceived the inclination to be either the same from top and bottom view or steeper from the base • For the three steepest hills, subjects tend to perceive the pitch as greater when they judged it from the top rather than from the base • The issue could be in adjusting the tilt board when judging haptic measurements from the top point of view because the movement is easier judging down than up • The issue could be viewpoint’s influence of haptic adjustments due to unknown factors Experiment 3 – Hills viewed from the base in virtual reality Purpose: • Obtain normative geographical perception data over a wider range of hills than can be naturally observed outside Methods: • Participants: 20 University of Virginia students (9 female, 11 male) • Stimuli: 12 simulated hills ranging from 5 to 60 degrees displayed in full color with a checkerboard road running up the middle of each. A “post” was located 10 meters from the base of each hill. The subjects’ viewpoint was at the base of each of these hills. Apparatus: • 2 VGX computers that projected images into the head mounted devices (HMD) creating the virtual reality (VR) and a tilt board that corresponded in reality with the 10 meter post seen in VR Design: asked participants to gauge according to two measures • Each subject saw all of the hills in a random order and, similar to Experiment 1, were told to verbally state to what degree they perceived the hill pitch/slant to be within the 5 to 60 degree range (verbal measure) • Additionally, each participant was asked to tilt the tilt board in front of them (they couldn’t see the board due to the VR headset they were wearing), to the degree of pitch they perceived the displayed hill to be (haptic measure) Results: • Overall, participants tended to overestimate the hill’s pitch when using a verbal measure and slightly underestimated the hill’s pitch when using the haptic measure, though the haptic measure tended to be more accurate for each participant • The verbal and haptic measures differed slightly, with the haptic measure being closer to the actual degree of the hill’s pitch displayed • However, the lines are almost parallel which speaks to the internal consistency between the verbal and haptic measures of each participant Experiment 4 – Hills viewed from the top in virtual reality Purpose: • The primary purpose of this experiment was to determine whether viewpoint would interact with pitch judgments as it had across Experiments 1 and 2 • Obtain pitch angle judgments from the tops of hills for inclinations not readily available in the real world • Assess the correspondence between the judgments for real hills and those presented in VR The primary question that the researchers were attempting to answer in this experiment was: Would the steepest hills look steeper from the top than from the bottom? They wanted to know if the change in perspective would affect the participants’ perception of hill pitch/slant. Methods: • Design: Experiment 4’s design was identical to Experiment 3’s, except that the perspective of the participant was now placed atop the hill as if they were standing on top of it • Apparatus, participants, and procedure: all were identical to Experiment 3 Results: • Similar to Experiment 3, Proffitt et al. observed that the verbal judgments made by the participants tended to be more inaccurate than the haptic judgments • The verbal judgement far overestimates the haptic judgment (that’s the judgment derived from the physical tilting of the tilting of the tiltboard to the perceived pitch of the hill displayed in their headsets). This trend holds mostly constant from Experiment 3 even when the participants’ perspective was shifted to the top of the hill. Comparison of Experiment 3 and Experiment 4 • Noticeable effect on both measures (verbal and haptic) likely due to the change in perspective of the participant • The change in perspective more drastically affected the verbal reports of hill pitch • Real hills – verbal judgments of hills were the same from the top and base perspectives for less steep hills • Real hills – steeper hills tended to be judged as even steeper when viewed from the top than from the base perspective • For haptic judgments, participants gauged hills as steeper when viewing from the top perspective as opposed to the base • Because of the increased distance of the verbal measure from the actual measure of the hill, it is thought that the change in perspective more drastically affected the verbal reports of hill pitch • As with the findings for the real hills, verbal judgments for the less steep hills were the same from the top and base, or steeper from the base Experiment 5 – Effect of fatigue on perceiving geographical slant Overview – tested the idea that hills look steeper when fatigued Methods • Subjects: 60 intro to psych students from University of Virginia – 30 male, 30 female Stimuli: 5° and 31° hills Procedure • The subjects were told that they would be required to go on a run of their choice and would be answering questions both at the beginning and at the end of their runs. • They would be given the starting and finishing points for their runs, which were the 5° hill and the 31° hill, respectively, for half of the students • The other half started at 31° and finished at 5° • Instructed to go on run of their choice as long as they go from start to finish, and end very fatigued • Distracter questions were asked as well as questions about inclination at first hill and second hill Results • 5° Hill o Verbal and visual estimates of inclination greater after run o Haptic judgments had no significant change prior to and following run • 31° Hill o Similar results • Experiment 1 o Similar results prior to run Discussion/Conclusion Take-away points • Geographical pitch grossly overestimated in visual and verbal measures o Important function is to inform planning/modulation of gait so as to expend energy at a desired rate • Haptic measures of pitch show little evidence of slant overestimation – people are able to walk up hills without stumbling. Due to: o Actions are mediated by visual awareness following a transformation that compensates for overestimations o Presence of separate visual pathways • Hills perceived as steeper when viewed from top and/or when fatigued Durgin et al Paper Introduction • Response to Proffitt et al. • Geographical slant • Two-systems theory • Separate accurate motor representation of hills Palm Board Method • Used in the two-systems theory approach • Durgin: adjusting geographic slant of palm boards is NOT visually guided • Palm boards depend on wrist flexion (creating bias) • Two-systems theory approach – invalid Durgin’s Hypothesis • Testing hypothesis that palm board accuracy is related to the need for motion action to be accurately guided Experiment 1: Palm Board Bias • Not within reachable distance • 30 degree incline • Palm board condition usually set 10 degrees lower than free hand condition • Verbal responses recorded • Supported idea that palm board is biased Experiment 2: Replication with an outdoor hill • Same procedure as Experiment 1 • Freehand condition less accurate than in Experiment 1, but still more accurate than palm board condition Experiment 3: Palm board low slant estimates • Palm board greatly underestimated the slope of the stimuli presented • Freehand condition – much more accurate • Condition done with the stimuli within a reachable distance Experiment 4: Proprioception of wrist flexion is similarly biased • Proprioception: being aware of the position of your body parts • Participants: 25 undergrads and they got candy bars • Materials: markers on back of hands; 2 m black and white grid to decrease distortions o Visual stimulus: smooth white line against black circle • Procedure: align their hands (unseen) with stimulus using appropriate joint. Stimulus will disappear, new one appears • Results: o Wrist flexion is biased compared to elbow flexion o Suggests that the accuracy attributed to palm boards (for outdoor hills) is accidental rather than theoretically significant Experiment 5: Effects of arm posture on palm board estimates from memory • Participants: 36 (18 m, 18 f) o The participants’ posture was manipulated o 12 were tested with classic posture o The remaining 24 were tested with palm board just above their navel (12 sitting and 12 standing; sex was balanced in all conditions) o Materials: 3 campus paths (gave them verbal description, satellite photo of path, and a campus map) • Procedure: o Randomized order of 3 hill presentation o Participants turned around and closed their eyes. Fixed palm board to match their memory • Results: o Small changes in palm board heights produce large changes in palm board estimates Discussion • Bhalla and Proffitt (1999) reported that athletes set their palm boards higher • Durgin does not really agree, saying that fatigue MIGHT be an influence on perception • We don’t usually look at our hands when moving, especiailly if it’s a wrist movement • Our free-hand measures, used shoulder, elbow, and wrist joints to control the hand • Showed good calibration in regards to reachable surfaces when the hand was moving naturally and freely without any artificial constraint • Palm boards are biased and insensitive measures • Instead of the two-systems theory, the experiments and research suggest that there exists only one exaggerated representation of geographical inclination • Hajnal et al. found pedal overestimation of haptic surfaces, and they tested this on blind participants as well (not likely due to visual exaggeration) • There are benefits in expanding the scale of geo slant for precise motor action Take-away point: Durgin argues that the process of perceiving geographical slant perception is not separated within the brain 3/6/16 5:31 PM 3/6/16 5:31 PM
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