,. CEU Article .-- The Acuity of Echolocation: Spatial ...people.csail.mit.edu/santani/PDFs/Teng_Whitney_2011_JVIB.pdfcommon, especially the Snellen chart (Snellen, 1863). More powerful

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Abstract Compared with the echolocation performance of an expert who is =----- --- - = =-=-~=====----- ~ - bull - --- - -------- -~ ----- - shy blind sighted novices rapidly learned size and position discrimination with

surprising precision We used a novel task to characterize the population distrishyr-==___ ~ middot~7~3~=~~~~-~~--=-middot r -~__

bution of echolocation skills in sighted persons and report the highest-known - --~~~~~~~= ------==~ human echolocation acuity in the expert who is blind=~-=~~-=~

Echolocation is a specialized application of spatial hearing that uses reflected aushyditory infonnation to localize objects and represent the external environment Alshythough it has been documented extenshysively in nonhuman species such as bats and dolphins (see for example Harley Putman amp Roitblat 2003 Simmons Moffat amp Masters 1992 Thomas Moss amp Vater 2004) its use by some persons who are blind as a navigation and objectshyidentification aid has received far less atshytention Echolocation helps these individ-

We thank Armilene Abucay Arina Fukushymoto Katherine Kruser David Horton Bryan Low and Elizabeth Louie for assistance in experimental preparation and data collection Additional thanks to David Horton for assisshytance in preparing the manuscript

0 EARN CEUs ONLINE

by answering questions on this article For more infonnation visit lt httpjviborgCEUsgt

uals to navigate their environments to engage in goal-directed action to recogshynize objects and to perceive textures

The basis for these functions lies in the spatial resolution provided by the practice of echolocation as conceived in Figure 1 Without sufficient spatial resolution it is difficult or impossible to recognize objects surfaces and scenes and to navigate the environment This principle is similar to that articulated for visual processing (Marr 1982) and auditory models (Slaney 1998)

Historically empirical research on hushyman echolocation focused on people who were blind (Ammons Worchel amp Dallenshybach 1953 Kellogg 1962 McCarty amp Worchel 1954 Rice amp Feinstein 1965 Supa Cotzin amp Dallenbach 1944) while the extent to which echolocation abilities are accessible to sighted persons remains a largely open question Quantitative studies of spatial echolocation skills in sighted inshydividuals are rare and have yielded equivshyocal results (Hausfeld Power Gorta amp Harris 1982 Kellogg 1962 Rice 1969)

20 Joumal of Vistlollmpainnellt amp Blindness January 2011 copy2011 AFB All Rights Reserved

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0 CEU Article

The Acuity of Echolocation Spatial Resolution in Sighted Persons Compared to the Performance of an Expert Who Is Blind Santani Teng and David Whitney

___ __ ___ _ _ __ __ _ _

A

0 CEU Article

B

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C Stimulus preparation Echololtation

M~ Go signal --liIII ~recllCk --liIII clicks a ~ostcltckr Judgment (f I~ Judgment

o ~~((~

Figure 2 Setup and trial sequence for Experiment 1 Front (A) and lateral (B) views of the echoshylocation stimulus setup Each trial began with an immediate response without clicking after which the participant began clicking and then made a second judgment (C)

13 inches) from a frame supporting two flat circular acrylic discs The largest disc with a diameter of 254 centimeters (about 10 inches)-the standard stimushylus-was randomly located on the top or bottom of the display One of the six comp31ison disks ranging from 51 centishymeters (2 inches) to 229 centimeters (about 9 inches) in diameter was located in the other position (method of constant stimuli) The auditory angle (measured from the ears) subtended by the difference between the diameters of the standard and comparishyson disk in each pairing condition (see Figshyure 2) was manipulated within the range of 44 degrees to 317 degrees

The participants judged whether the larger stimulus was on the top or bottom in what is known as a two-alternative forced choice task (2AFC) The task was pershyformed twice sequentially in each trial The first passive judgment (the no-click judgment) controlled for any possible amshybient auditory information (see Figure 3A) For the second click judgment the parshyticipants used active echolocation that is

they made clicking noises with their tongues against the roofs of their mouths (self-paced) The participants were given no feedback Each of four sessions contained 100 trials and lasted between one and two

hours We conducted additional sessions at 33

50 and 75 centimeters (about 12 inches 20 inches and 30 inches respectively) for a subset of four participants after the initial four-session training period The differshyences in the auditory angle in the 50- and 75-centimeter conditions ranged from 29 degrees to 221 degrees and 19 degrees to 150 degrees respectively The sessions were pseudorandornly interleaved

Finally to compare the sighted particshyipants performance to that of an expert we enlisted an echolocator (EB to mainshytain his anonymity) who has been totally blind since infancy taught himself to echolocate during childhood and now teaches echolocation to individuals who are blind and sighted To avoid ceiling effects we tested EB exclusively at a distance of 75 centimeters where angular

copy2011 AFB All Rights Reserved ]oul17al of ViSUfil Impairment amp BliuJness Januruy 2011 23

t bull bull shy --~----~ - - - -~-

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0 CEU Article

Frequencyintenslty Physical stimulus propenles spectral ripples

Echolocation

Basic low-level spatial cues

Texture shape discrimination (surface representation)

Size distance position (spatial resolution)

ITDILO spectral cues

Figure 1 Proposed five-level invertedshypyramid representational framework for various levels of cues comprised by echolocation lTD = interaural time differences llD = mshyteraural level differences

Stoffregen and Pittenger (1995) suggested that some form of echolocation may serve as a routine albeit subliminal perceptual aid for sighted as well as blind individushyals but noted that the literature is sorely lacking in this regard especially for sighted persons

Tables 1 and 2 outline prior studies of echolocation in persons who are blind and those who are sighted although the list is not exhaustive Table 1 includes psychophysical echolocation experiments involving self-generated echo stimuli

Table 1

Table 2 includes studies in which sighted persons performed navigation detection or discrimination tasks of a passive or nonshyspatial nature We did not include studies of electronic or mechanical sonar-based navishygational aids The evidence indicates that few psychophysical experiments with sighted persons have been conducted espeshycially using self-generated echo stimuli (as would be expected in an ecological conshytext) With that constraint only two prior studies (Kellogg 1962 Rice 1969) invesshytigated the spatial resolution of sighted pershysons echolocation with conflicting results Kellogg s participants were unable to pershyform the task and Rice s participants pershyformed tasks at competent yet inferior levshyels compared to participants who were blind No study of which we are aware specifically tested echolocation experts who presumably represent the height of hushyman echolocation performance

For vision a variety of acuity tests are common especially the Snellen chart (Snellen 1863) More powerful measures of the spatial resolution of vision are also available (Kniestedt amp Stamper 2003) Because human echolocation is often disshycussed as an auditory perceptual aid in navigation and object perception it IS

Previous studies of echolocation by blind and sighted participants Spatial resolution estimated from active self-generated echoes

Study Blind participants Sighted participants

Kellogg (1962) 2 2 Welch (1964) 0 0 Rice et al (1965) 5 0 Rice amp Feinstein (1965) 4 0 Rice (1967) 5+4+6+4 0

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Rice (1969) 6+8 8 + 3 Ashmead Hill amp Talor (1989) 10 + 15 0

Note The number of participants separated by plus signs indicates participants in separate experiments within a study

copy2011 AFB All Rights Rese rved JOl rnai of Visuallmpaimlent amp Blindness January 201 1 21

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o CEU Article

Table 2 Previous studies of blind and sighted echolocation Navigation passive and nonspatial discrimination tasks


Cotzin amp Dallenbach (1950) 2 2 Worchel amp Berry (1952) 0 15 Ammons et al (1953) 0 20

Kohler (1964) 0 267 + 20 + 48 Bassett amp Eastmond (1964) 0 1 Clarke Pick amp Wilson (1975) 8 8 Juurmaa amp Suonio (1975) 10 5 Hausfeld et al (1982) 18 + 18 + 45 Strelow amp Brabyn (1982) 8 14 Boehm (1986) 5 11 Rosenblum Gordon amp Jarquin (2000) 0 20 + 26 Hughes (2001) 0 5 + 10 + 20 + 11 Doucet et al (2005) 12 20 Despres Candas amp Dufour (2005) 0 15 + 30 Dufour Despres amp Candas (2005) 12 20 Schenkman amp Nilsson (2010) 10 10

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appropriate to investigate quantitatively Experiment 1 Size discrimination detection thresholds and the limits of The goal of the first experiment was to spatial acuity that human echolocation measure echolocation and the learning affords its practitioners Such quantifishy of echolocation in sighted participants cations have been preliminarily deshy who performed a size-discrimination scribed in participants who are blind task Because similar tasks have been (Rice amp Feinstein 1965 Rice Feinshy used before (Hausfeld et aI 1982 stein amp Schusterman 1965) but little Kellogg 1962 Rice 1969) with mixed is known about similar characteristics results we used a size-discrimination in persons who are sighted (or newly paradigm to compare our results to blind) Thus the study presented here those of previous studies quantitati vely characterized the spatial precision with which sighted persons METHODS

can echolocate We also directly comshy We conducted the experiment in a soundshypared the spatial resolution of echoloshy proof echo-damped room Eight healthy cation in sighted novices with that of an neurologically normal volunteers particishyexpert echolocator who is blind Our pated Each gave informed consent under results show that some sighted individshy human subjects protocols approved by the uals can learn to echolocate with exshy Institutional Review Board at the Univershytraordinary precision approaching that sity of California Davis as did the expert of experts who become blind early in who is blind The participants were blindshytheir lives folded and seated 33 centimeters (about

22 loumal of VisUilllmpairment amp Blindness January 2011 copy20 11 AFB All Rights Reserved

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--- -- _----- -- - ---------=-==== Angular size difference (deg)----~shy- - - -~-- -------- - - --shy

Angular size difference (deg) Angular size difference (deg) _------------- shy--_-------__- ---shy Figure 3 Results of Experiment 1 Panel (A) Size-discrimination performance for 8 sighted

subjects over 4 sessions at a distance of 33 centimeters Error bars represent SEM Panel (B) Difference scores (click minus no-click) showing the perfonnance benefit of echolocation

_ increasing across sessions Panel (C) Comparison of two individual psychometric functions--- -- --~- -------------_ --_ _ - --_---------- shy1gt- - --- - 1 - -- - bullbull~----------------shy

~ and 75 discrimination thresholds calculated from single-session performances Horizontal error bars represent bootstrapped 95 confidence intervals

differences between stimuli subtended creasing sizes whether clicking facilitated from 19 degrees to 150 degrees discrimination and whether performance

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ANALYSIS three-way (4 X 2 X 6) repeated-measures Data from the sessions at 33 centimeters analysis of variance (ANOYA) with withinshywere analyzed in two ways First we tested subjects factors of session clicking (noshywhether discrimination improved with in- click versus click) and separation as well asC_ ~~~_~ 24 JounUlI of Visual lmpainnenr amp Blindness January 201 1 copy2011 AFB All RighlS Reserved~ ~--=~~==-=shy

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post-hoc tests (see the Results for Experishyment 1) Second where possible we fitted logistic psychometric curves to results from individual runs and group data using Wichshymann and Hills (200la) procedure with bootstrapped confidence intervals (Wichshymann amp Hill 200lb) (see Figure 3A for a single-session example) It was not possible to calculate thresholds for all the sessions because of the participants low perforshymance on early or difficult sessions

RESULTS EXPERIMENT 1 Figure 3A shows the no-click and click data for the sighted participants first four sessions at a distance of 33 centimeters The solid lines represent performance in the clicking condition the dashed lines represent the no-click baseline A threeshyway (4 X 2 X 6) repeated-measures ANOVA with within-subjects factors of session clicking and separation revealed significant main effects of clicking (F17 = 44737 p lt 001) and separation (F5 35 = 607 p lt 001) Although the main effect of session was not significant (F321 =140 p = 27) a significant sesshysion X clicking interaction (F3 21 = 475 p = 011) suggests that session effects were carried by only the click condition whereas the no-click baseline perforshymance remained stable Subsequent repeated-measures ANOVAs that were performed separately on the no-click and click conditions confirmed this finding showing a significant main efshyfect of session (F3 21 = 359 p = 031) for the click condition but not for the no-click condition (F3 21 = 248 p =

09) The no-click data collapsed over four sessions from all participants did not differ significantly from chance (PBonf gt 05 for all conditions)

Training effects were evident for the four sessions at 33 centimeters Initially the participants had great difficulty echoshylocating even large differences in the size of objects Subsequent sessions showed significant improvements with their pershyformance markedly better after a single session and approaching asymptote after three sessions as indicated by the signifshyicant effect of session Figure 3B emphashysizes the effects of session as difference scores between no-click and click perforshymance rather than raw percentages

Representative psychometric functions for one skilled sighted participant BL and the blind expert echolocator EB are shown in Figure 3C Their 75 threshshyolds (145 degrees and 80 degrees reshyspectively) indicate that both were profishycient in discriminating differences in sizes in single sessions The best perforshymances during individual sessions among the sighted participants discriminated difshyferences in the auditory angle as small as 53 degrees (although all the participants average performance was coarser than EBs single-session threshold)

Figure 4 shows pooled click data from the four observers who underwent addishytional sessions at larger distances for a comparison data from EB s single sizeshydiscrimination session is shown as well Each curve represents the averaging of three asymptotic sessions for each of four observers at the distance indicated Reshygardless of the distance performance varshyied along the same curve when plotted against the angular size difference indeshypendently of linear distance Psychometshyric curves fitted to group performance yielded thresholds of 169 degrees at 33 centimeters and 192 degrees at 50 centimeters (group performance at 75

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copy2011 AFB AU Rights Reserved JoLtl71al of Visuallmpairmenl amp Blindness January 2011 25

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Angular size difference (deg)

Figure 4 Distance effects on size discrimination Representative elTor bars indicate SEM

centimeters did not exceed 75) Monte localization To investigate whether novice Carlo simulation showed that the curves sighted echolocators could approach the were not significantly different (p = 27) spatial resolution of an expert who is blind This finding suggests that thresholds are we measured echolocation in an auditory constrained by the difference in the auditory version of a vernier acuity task like that angle subtended by the stimuli rather than used by vision scientists (McKee amp Wesshyby the absolute stimulus size or distance theimer 1978) A typical visual-vernier within the range that we tested Overall acuity task involves a pair of line segments the results demonstrate that sighted pershy arranged end to end slightly displaced orshysons can learn to use echolocation to thogonally to their orientation participants discriminate precisely the size of an obshy detenrune the direction of displacement on ject over a range of near-field distances each trial (McKee amp Westheimer 1978

Westheimer amp McKee 1977) Vernier acushyExperiment 2 Echolocation ity can reveal extremely fine discrimination vernier acuity thresholds smaller than the width of a sinshyThe first experiment revealed that untrained gle photoreceptor (Westheimer 1979 Wesshysighted participants can quickly learn to theimer amp McKee 1977)-the finest posshyecholocate However it remains unclear sible spatial resolution of perception what level of spatial precision they attain Several previous studies of echolocation and how this level compares to that of exshy presented single stimuli in detection or loshypert echolocators who are congenitally calization experiments or pairs of stimuli in blind In addition size discrimination while 2IFC (two-interval forced choice) discrimshya nominally spatial task may not tap or ination experiments Adapting vernier quantify the fine-grained limits of spatial stimuli to an echo-perception domain

26 JOLtnat of Viswtlmpail11e111 amp Blindness January 2011 copy20 11 AFB Al l Rights Reserved

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afforded us a new measure of spatial precishysion in echolocation uniquely allowing us to measure relative (rather than absolute or egocentric) spatial localization Spatial pershyception depends largely on relative localshyization and this vernier method provides a means to characterize the resolution of aushyditory spatial acuity

METHODS

We used a setup similar to Experiment 1 (see Figure SA) Eleven sighted particishypants who met the same criteria and informed-consent conditions as those in Expeliment 1 sat blindfolded facing the frame at a distance of 50 centimeters Two vertically separated disks of 203 centimeters each in diameter or about 8 inches) were presented with one of five horizontal center-to-center separations from 11 degrees to 132 degrees of audishytory angle (Figure SA) Using the method of constant stimuli 20 trials on average were collected for each of five vernier sepshyarations for a total of 100 trials per session (1-2 hours per session) The participants reported whether the top disk was located to the right or left of the bottom disk (2AFC task) Trials were conducted and analyzed in the same general manner as in Experishyment 1 Each observer participated in a minshyimum of five sessions to ensure asymptotic performance

Expert echolocator EB was available for two sessions of the vernier acuity task On the basis of a running average (bin width 10 trials) EB reached asymptotic performance in the second session The first session was conducted at 75 centishymeters and the second at 100 centimeters (about 39 inches) to avoid ceiling effects In the first session EB partici pated in 20 trials at each of four vernier separations

ranging from 075 degrees to 45 degrees

of auditory angle In the second session the four vernier separations ranged from 057 degrees to 34 degrees To achieve asymptotic performance as quickly as possible all the participants were given correct or incOlTect feedback after each trial (Herzog amp Fahle 1997)

RESULTS EXPERIMENT 2 A two-way repeated-measures ANOVA (clicking X separation) on the data for all the sighted participants yielded a signifishy

cant effect of clicking (Fuo = 69 p = 025) Although the effect of separation collapsed across clicking conditions did not reach significance (F4 4o = 198 P =

116) the condition X separation interacshy

tion was significant (F4 4o = 274 P =

042) Thus clicking was significantly helpful to the participants because the noshyclick groups performance never exshyceeded chance levels and the effect of stimulus separation is clearly carried by the click condition A repeated-measures ANOVA on only the click condition reshyvealed a significant effect of stimulus sepshy

aration F440 = 276 P = 041 To conshyfirm that the effect was not driven by outlying values we performed a nonparashymetric chi-square analysis on the particishypants performance at each individual stimulus separation A fixed-sequence inshycremental application of the Bonferroni correction for multiple comparisons (Westfall amp Krishen 2001) indicated that group performance was significantly above chance levels for the two greatest separations 66 degrees and 132 degrees (K = 736 p = 014 K = 446 p =

014 respectively see Figure SD) The representati ve plots in Figure 5B

show psychometric functions fitted to

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Proportion correct (by separation amp session)

Figure 5 Stimulus setup and results of Experiment 2 Panel (A) Vernier experiment setup Panel (B) Psychometric functions showing vernier acuity for sighted participant BL and expert echoloshycator EB Pane) (C) Group plot of Vernier discrimination performance Panel (D) Histogram of performances across all sessions by sighted pruticipants at each stimulus separation Indiv Ss = individual subjects or participants

individuals data However the initial group analysis belies the widely varying performance among the participants and

sessions (Figure SC) reftecting a large increase in the difficulty of the tasks

from Experiment 1 For example the highest group mean performance at the widest separation (132 degrees) was 63S but the performance of the indishy

vidual participants at that separation

_-- __--____- ----- 28 loumal of Visual lmpainnent amp Blil1dl1ess January 2011 copy2011 AFB All Rights Reserved

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ranged from 456 to 950 that is some participants were highly proficient at the task others were less so and some failed completely Two sighted partIcIpants BL and KK performed best in the range of the auditory angles that we sampled performing at higher than 75 correct and allowing us to compute thresholds from psychometric functions as in Experiment 1 Thresholds pooled over all the sessions were 41 deshygrees for BL and 67 degrees for KK These are the finest discriminations among the sighted participants although not necessarshyily at an expert level by comparison EB s 75 threshold during his second session was 158 degrees

Although a full comparison between sighted and blind echolocators would reshyquire a larger sample than that used in the present study our results suggest that not all sighted participants can be equally trained Nevertheless the results convincshyingly demonstrate sufficiency-some sighted participants can achieve echoloshycating precision approaching that of an experienced echolocator who is blind

Discussion In two experiments we tested the spatial resolution of the echolocation abilities of sighted participants and one expert echoshylocator who is blind constraining the echo-producing vocalizations to selfshygenerated clicks In Experiment 1 the sighted participants could be readily trained in coarse echolocation ability even without explicit feedback about their performance feedback did not signifishycantly alter their performance Furthershymore size-discrimination thresholds were roughly constant with increasing disshytance so the difference in the size of the

angle rather than distance may be the key metric of size discrimination using echolocation (Rice et aI 1965) Experishyment 2 used a novel and challenging vershynier acuity task to measure the spatial resolution of echolocation precisely An important finding which differed from those of all previous studies was that with sufficient training some sighted pershysons learn to echolocate with a level of proficiency that approaches that of expert echolocators who are congenitally blind

The second experiment introduced a new measure of echolocation acuity-the vernier stimulus This stimulus provides a means of operationally defining the acuity of echolocation akin to the spatial acuity of vision and potentially a basis for obshyjective measurement and comparison across individuals and individual differshyences It could be especially valuable if active echolocation becomes more prevshyalent as a navigational aid for individuals who are blind (Ashmead 2008) The subshystantially finer resolution measured for EB and BL relative to their sizeshydiscrimination performance also suggests that although auditory vernier discriminashytion may be a more difficult task it also could measure fine spatial resolution in echolocation

COMPARISON TO PREVIOUS STUDIES

Previous studies did not definitively meashysure the acuity or spatial resolution of echolocation in sighted individuals (see Table 1) As we discussed earlier Rice (1969) and Kellogg (1962) were closest but published conflicting results Kohler (1964) recruited many sighted particishypants for his investigations of auditory orienting but tested passive detection of obstacles not spatial discrimination

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Experiments with blindfolded sighted subjects tested the discrimination of shapes with no explicit spatial component and no measure of acuity (Hausfeld et aI 1982) Arias and Ramos (1997) and Arias Curet Moyano Joekes and Blanch (1993) tested repetition pitch a proposed echolocation cue (Bassett amp Eastmond 1964) in sighted persons but did not explicitly test spatial resolution or the perception of self-generated echoes

The considerable variability in pelforshymance in the present study may help exshyplain the varying results in prior work The distribution of echolocation ability in typishycally hearing sighted persons ranges from complete inability to near-expert thresholds (Experiment 2) and varies with specific echolocation tasks (Experiment 1 versus Experiment 2) The small number of subshyjects in previous studies could have proshyduced inconsistent patterns of results that reflect this distribution Future investigashytions of the underlying cues used in echoshylocation for example should leverage the individual differences present in echolocashytion ability

TRAINING ECHOLOCATION

Tables 1 and 2 show that most previous studies of echolocation focused on the pershyformance of persons who were blind with training potential an implied motivation of the research We showed that some naive sighted persons with relatively limited trainshying can approximate the spatial resolution of an expert with several decades worth of experience all the sighted participants in our study achieved at least a coarse ability to echolocate (Experiment 1) Not all parshyticipants reached this level of precision (Exshyperiment 2) however it is not clear that all persons who are blind can echolocate

equally either without a substantially larger population of randomly sampled persons who are blind than has been tested previshyously (rarely more than six per study) The minimum thresholds achieved by some of the sighted participants in our study over relatively few sessions in Experiment 1 apshyproached those reported previously for parshyticipants who were blind (Kellogg 1962 Rice et aI 1965) although EBs perforshymance exceeded them That is EB had spatial-acuity and size-discrimination thresholds that rivaled or exceeded the spatial resolution of all previous estimates in the literature that used self-generated cues as well as previous estimates of auditory spatial resolution involving passhysive listening to noise stimuli (Blauert amp Allen 1997)

Thus echolocation per se is not a rare ability practiced by a few skilled individshyuals the crucial spatial resolution composhynent of the skill although not immedishyately accessible to most untrained persons can be readily learned Objective measures of echolocation acuity like our vernier technique are critical to evaluatshying training programs of the type offered by EB our results therefore hold promise for such programs that are geared to inshydividuals who are newly blind

Conclusions We have characterized the spatial resoshylution of novice and expert human echoshylocation using size discrimination and novel relative spatial localization tasks We showed that perceptual learning of echolocation can be rapid without feedback and that some sighted individuals can be trained in echolocation to a level of precision that approaches that of expert echolocators who are congenitally blind

30 l oumal of Visual Impairment amp Blindness January 2011 copy20ll AFB All Rights R~erved

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The developmental time course of echoloshycation skills and their neural correlates in individuals who are blind and sighted and the characterization of the most important echolocation cues remain fertile avenues for future research Pragmatically research and training programs in both orientation and mobiHty and echolocation should consider including adults who have recently become blind

References Ammons C H Worchel P amp Dallenbach

K M (1953) Facial vision The percepshytion of obstacles out of doors by blindfolded and blindfolded-deafened subjects American Journal of Psychology 66519-553

Arias C Curet C A Moyano H F Joekes S amp Blanch N (1993) Echoloshycation A study of auditory functioning in blind and sighted subjects Journal of Vishysual Impairment amp Blindness 87 73-77

Arias C amp Ramos O A (1997) Psyshychoacoustic tests for the study of human echolocation ability Applied Acoustics 51 399-419

Ashmead D H (2008) Visual experience and the concept of compensatory spatial healing abilities In 1 J Rieser D H Ashshymead F F Ebner amp A L Com (Eds) Blindness and brain plasticity in navigashytion and object perception (pp 367-380) New York Lawrence Erlbaum

Ashmead D H Hill E W amp Talor C R (1989) Obstacle perception by congenishytally blind children Perception and Psyshychophysics 46 425-433

Bassett G amp Eastmond E 1 (1964) Echolocation Measurement of pitch versus distance for sounds reflected from a flat surface Journal of the Acoustical Society of America 36911-916

Blauert J amp Allen J S (1997) Spatial hearing The psychophysics of human sound localization (rev ed) Cambridge MA MIT Press

Boehm R (1986) The use of echolocation as a mobility aid for blind persons Journal of

Visual Impairment amp Blindness 80 953shy954

Clarke N V Pick G F amp Wilson J P (1975) Obstacle detection with and withshyout the aid of a directional noise generator American Foundation for the Blind Reshysearch Bulletin 29 67-85

Cotzin M amp Dallenbach K M (1950) Fashycial vision The role of pitch and loudness in the perception of obstacles by the blind American Journal of Psychology 63485shy515

Despres 0 Candas V amp Dufour A (2005) Auditory compensation in myopic humans Involvement of binaural monaural or echo cues Brain Research 104 56-65

Doucet M E Guillemot J P Lassonde M Gagne J P Leclerc C amp Lepore F (2005) Blind subjects process auditory spectral cues more efficiently than sighted individuals Experimental Brain Research 160 194-202

Dufour A Despres 0 amp Candas V (2005) Enhanced sensitivity to echo cues in blind subjects Experimental Brain Reshysearch 165515-519

Harley H E Putman E A amp Roitblat H L (2003) Bottlenose dolphins perceive object features through echolocation Nashyture 424(6949) 667-669

Hausfeld S Power R P Gorta A amp Harshyris P (1982) Echo perception of shape and texture by sighted subjects Perceptual and Motor Skills 55 623-632

Herzog M H amp Fahle M (1997) The role of feedback in learning a vernier discrimination task Vision Research 372133-2141

Hughes B (2001) Active artificial echolocashytion and the nonvisual perception of apershyture passability Human Movement Scishyence 20(4-5) 371-400

Juurmaa 1 amp Suonio K (1975) The role of audition and motion in the spatial orientation of the blind and the sighted Scandinavian Journal of Psychology 16 209-216

Kellogg W N (1962) Sonar system of the blind Science 137 399-404

Kniestedt C amp Stamper R L (2003) Visual acuity and its measurement Ophthalmology Clinics ofNorth America 16 155-170

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Kohler I (1964) Orientation by aural cues American Foundation for the Blind Reshysearch Bulletin 4 14-53

Marr D (1982) Vision A computational inshyvestigation into the human representation and processing of visual information San Francisco W H Freeman

McCarty B amp Worchel P (1954) Rate of motion and object perception in the blind New Outlook for the Blind 48(11) 316shy322

McKee S P amp Westheimer G (1978) Imshyprovement in vernier acuity with practice Perception and Psychophysics 24 258shy262

Rice C E (1967) Human echo perception Science 155(763)656-664

Rice C E (1969) Perceptual enhancement in the early blind Psychological Record 19(1) 1-14

Rice C E amp Feinstein S H (1965) Sonar system of the blind Size discrimination Science 148 1107-1108

Rice C E Feinstein S H amp Schusterman R J (1965) Echo-detection ability of the blind Size and distance factors Joumal of Experimental Psychology 70 246-255

Rosenblum L D Gordon M S amp Jarquin L (2000) Echolocating distance by movshying and stationary listeners Ecological Psychology 12 181-206

Schenkman B N amp Nilsson M E (2010) Human echolocation Blind and sighted persons ability to detect sounds recorded in the presence of a reflecting object Pershyception 39 483-50l

Simmons 1 A Moffat A 1 amp Masters W M (1992) Sonar gain control and echo detection thresholds in the echolocating bat Eptesicus fuscus Journal of the Acoustical Society of America 91 1150-1163

Slaney M (1998) A critique of pure audishytion In D F Rosenthal amp N G Okuno (Eds) Computational auditory scene analshyysis (pp 27-41) Mahwah NJ Lawrence Erlbaum

Snellen H M D (1863) Art XXIV-Testshytypes for the determination of the acuteness of vision American Joumal of the Medical

Stoffregen T A amp Pittenger J B (1995) Human echolation as a basic fOim of pershyception and action Ecological Psychology 7 181-216

Strelow E R amp Brabyn 1 A (1982) Loshycomotion of the blind controlled by natural sound cues Perception 11 635-640

Supa M Cotzin M amp Dallenbach K M (1944) Facial vision The perception of obstacles by the blind American Journal of Psychology 57(2) 133-183

Thomas J A Moss C F amp Vater M (2004) Echolocation in bats and dolphins Chicago University of Chicago Press

Welch 1 (1964) A psychoacoustic study of factors affecting human echolocation American Foundation for the Blind Reshysearch Bulletin 4 1-3

Westfall P H amp Krishen A (2001) Optishymally weighted fixed sequence and gateshykeeper multiple testing procedures Jourshynal of Statistical Planning and Inference 9925-40

Westheimer G amp McKee S P (1977) Inshytegration regions for visual hyperacuity Vision Research 17(1) 89-93

West~eimer G (1979) The spatial sense of the eye Proctor lecture Investigative Ophshythalmology amp Visual Science 18(9) 893shy912

Wichmann F A amp Hill N 1 (2001a) The psychometric function I Fitting sampling and goodness-of-fit Perception ana Psyshychophysics 63 1293-l313

Wichmann F A amp Hill N 1 (2001b) The psychometric function II Bootstrap-based confidence intervals and sampling Percepshytion and Psychophysics 63 1314-l329

Worchel P amp Berry J H (1952) The pershyception of obstacles by the deaf Joumal of Experimental Psychology 43(3) 187-194

Santani Teng MA graduate student researcher Whitney Laboratory for Perception and Action University of Califomia Berkeley 3210 Tolman Hall Berkeley CA 94720 e-mail ltsteng berkeleyedugt David Whitney PhD associate professor Whitney Laboratory for Perception and Action University of Califomia Berkeley e-mail lt whitneyberkeleyedugt Address all correshy

~= ~=-==~--- Sciences 44(92) spondence to Mr Teng -- shy -_ -- ---_ - ------------- ~

sect~~~~~~~~~~~~~~~~~~=~~~=---=--= 32 Journal of Visual fmpairment amp Blindness January 2011 copy2011 AFB All Rights Reserved

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C Stimulus preparation Echololtation

M~ Go signal --liIII ~recllCk --liIII clicks a ~ostcltckr Judgment (f I~ Judgment

o ~~((~

Figure 2 Setup and trial sequence for Experiment 1 Front (A) and lateral (B) views of the echoshylocation stimulus setup Each trial began with an immediate response without clicking after which the participant began clicking and then made a second judgment (C)

13 inches) from a frame supporting two flat circular acrylic discs The largest disc with a diameter of 254 centimeters (about 10 inches)-the standard stimushylus-was randomly located on the top or bottom of the display One of the six comp31ison disks ranging from 51 centishymeters (2 inches) to 229 centimeters (about 9 inches) in diameter was located in the other position (method of constant stimuli) The auditory angle (measured from the ears) subtended by the difference between the diameters of the standard and comparishyson disk in each pairing condition (see Figshyure 2) was manipulated within the range of 44 degrees to 317 degrees

The participants judged whether the larger stimulus was on the top or bottom in what is known as a two-alternative forced choice task (2AFC) The task was pershyformed twice sequentially in each trial The first passive judgment (the no-click judgment) controlled for any possible amshybient auditory information (see Figure 3A) For the second click judgment the parshyticipants used active echolocation that is

they made clicking noises with their tongues against the roofs of their mouths (self-paced) The participants were given no feedback Each of four sessions contained 100 trials and lasted between one and two

hours We conducted additional sessions at 33

50 and 75 centimeters (about 12 inches 20 inches and 30 inches respectively) for a subset of four participants after the initial four-session training period The differshyences in the auditory angle in the 50- and 75-centimeter conditions ranged from 29 degrees to 221 degrees and 19 degrees to 150 degrees respectively The sessions were pseudorandornly interleaved

Finally to compare the sighted particshyipants performance to that of an expert we enlisted an echolocator (EB to mainshytain his anonymity) who has been totally blind since infancy taught himself to echolocate during childhood and now teaches echolocation to individuals who are blind and sighted To avoid ceiling effects we tested EB exclusively at a distance of 75 centimeters where angular

copy2011 AFB All Rights Reserved ]oul17al of ViSUfil Impairment amp BliuJness Januruy 2011 23

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Documents

,. CEU Article .-- The Acuity of Echolocation: Spatial ...people.csail.mit.edu/santani/PDFs/Teng_Whitney_2011_JVIB.pdfcommon, especially the Snellen chart (Snellen, 1863). More powerful