Teng Whitney 2011 JVIB

8/13/2019 Teng Whitney 2011 JVIB

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Abstract: Compared with the echolocation performance of a- --- .....-:.. . = : : : : : ' : ' = : : : ' : : . : : : : . = : . . ~ = = = = =' : ' ,-. .. ---.' - - . - - ..-' blind, sighted novices rapidly learned size and position disc

surprising precision. We used a novel task to characterize the p__ : : : . : . : . ~ 7 = ~ ~ - . : . ~ r __ bution of echolocation skills in sighted persons and report the

; ~ ~ ~ : ~ : ~ ~ = - - : - - - = = human echolocation acuity in the expert who is blind.- = ~ ~ - =Echolocation is a specialized applicationof spatial hearing that uses reflected auditory infonnation to localize objects andrepresent the external environment. Although it has been documented extensively in nonhuman species, such as batsand dolphins (see, for example, Harley,Putman, & Roitblat, 2003; Simmons,Moffat, & Masters, 1992; Thomas, Moss,& Vater, 2004), its use by some personswho are blind as a navigation and objectidentification aid has received far less attention. Echolocation helps these individ-

We thank Armilene Abucay, Arina Fukumoto, Katherine Kruser, David Horton, BryanLow, and Elizabeth Louie for assi stance inexperimental preparation and data collection.Additional thanks to David Horton for assistance in preparing the manuscript.

0' EARN CEUs ONLINEby answering questions on this article .For more infonnation ,visit: < http://jvib.org/CEUs> .

uals to navigate theirengage in goal-directednize objects , and to per

The basis for thesethe spatial resolutionpractice of echolocatiin Figure 1. Withoutresolution, it is difficultrecognize objects, surfand to navigate the eprinciple is similar tofor visual processing (auditory models (Slane

Historically, empiricalman echolocation focusewere blind (Ammons, Wbach, 1953; Kellogg, 1Worchel, 1954; Rice &Supa, Cotzin, & Dallenbthe extent to which echare accessible to sightedlargely open question. Qof spatial echolocation sdividuals are rare and hocal results (Hausfeld,Harris, 1982; Kellogg, 1

20 Joumal of Vstl ollmpainnellt & Blindn ss . January 2011 2011 AFB, All Righ ts Re served

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0' CEU ArticleThe Acuity of EcholocationResolution n Sighted PersoCompared to the Performanof an Expert Who Is BlindSantani Teng and David Whitney
http://jvib.org/CEUshttp://jvib.org/CEUs


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Frequency,intensltyPhysical stimulus propenles spectral ripples

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Texture, shape discrimination(surface representation)

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ITD.ILO. spectral cues

igure 1. Proposed five-level, invertedpyramid representational framework for variouslevels of cues comprised by echolocation.lTD = interaural time differences; ll..,D = mteraural level differences.Stoffregen and Pittenger (1995) suggestedthat some form of echolocation may serveas a routine, albeit subliminal, perceptualaid for sighted as well as blind individuals, but noted that the literature is sorelylacking in this regard, especially forsighted persons.

Tables 1 and 2 outline prior studies ofecholocation in persons who are blindand those who are sighted, although thelist is not exhaustive. Table 1 includespsychophysical echolocation experimentsinvolving self-generated echo stimuli;Table 1

spatial nature. We did not include studies ofelectronic or mechanical sonar-based navigational aids. The evidence indicates thatfew psychophysical experiments withsighted persons have been conducted, especially using self-generated echo stimuli (aswould be expected in an ecological context). With that constraint, only two priorstudies (Kellogg, 1962; Rice, 1969) investigated the spatial resolution of sighted persons' echolocation, with conflicting results:Kellogg' s participants were unable to perform the task, and Rice ' s participants performed tasks at competent, yet inferior, levels compared to participants who wereblind. No study of which we are awarespecifically tested echolocation experts,who presumably represent the height of human echolocation performance.

For vision, a variety of acuity tests arecommon, especially the Snellen chart(Snellen, 1863). More powerful measuresof the spatial resolution of vision are alsoavailable (Kniestedt & Stamper, 2003).Because human echolocation is often discussed as an auditory perceptual aid innavigation and object perception, it IS

Previous studies of echolocation by blind and sighted participants: Spatial resolution estimatedfrom active self-generated echoes.Study Blind participants Sighted participantsKellogg (1962) 2 2Welch (1964) 0 0Rice et al (1965) 5 0Rice & Feinstein (1965) 4 0Rice (1967) 5 4 6 4 0

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2011 AFB, All Rights Reserved J l.rnai of Visu llmpaim le nt & Blindness January 201 1 21

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Angularsize difference(deg,) Angularsizedi._.. ,----- , ------.- ._------ _.._ --- Figure 3, Results of Experiment 1. Panel (A): Size-discrimination performa

subjectsover 4 sessionsat adistanceof 33 centimeters, Errorbars representDifference scores (click minus no-click) showing the perfonnance benefi_ increasing across sessions, Panel (C) :Comparisonof two individual psych- .-.- -. ~ ..--.---------._ ... , ..--_ .._ - --._--- ---- - 1-. -- .- - - - - - - - - - - and 75% discrimination thresholds calculated from single-session performerrorbarsrepresentbootstrapped95% confidence intervals,differences between stimuli subtended creasing sizes, whether clfrom 1.9degrees to 15,0degrees, discrimination, and whet

: . ~ ~ : . . : - - = = = - - improved with training,- : . . . : . . . ,- ~ ~ : : - -:-:; . ANALYSIS three-way (4 X 2 X 6) rData from the sessions at 33 centimeters analysisof variance(ANOwereanalyzed in twoways,First,wetested subjects factors of sessiowhether discrimination improved with in- clickversusclick)andsep: ~ ~ ~ : : ; : _ ~ : ;24 JounUlI o Visual lmpainnenr & Blindness January201 1 2011 AFB,All RighlS Reserved: . : : : . : : . : : : : : ~ ~ = = : -..-...... ..... . .. . . . - - - - ~ .. -.. .. ', .,.-... ...--- ,._ -----_.....--.: . I, . ... -. . .. .. ..

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individual runs and group data, using Wichmann and Hill's (200la) procedure, withbootstrapped confidence intervals (Wichmann & Hill, 200lb) (see Figure 3A for asingle-session example). It was not possibleto calculate thresholds for all the sessionsbecause of the participants' low performance on early or difficult sessions.RESULTS, EXPERIMENT 1Figure 3A shows the no-click and clickdata for the sighted participants' first foursessions at a distance of 33 centimeters.The solid lines represent performance inthe clicking condition; the dashed linesrepresent the no-click baseline. A threeway (4 X 2 X 6) repeated-measuresANOVA with within-subjects factors ofsession, clicking, and separation revealedsignificant main effects of clickingF1.7 = 44.737; p < .001) and separationF 5 = 6.07; p < .001). Although the

main effect of session was not significant321 =1.40; p = .27), a significant session X clicking interaction 3 21 = 4.75;p = .011) suggests that session effects

were carried by only the click condition,whereas the no-click baseline performance remained stable. Subsequentrepeated-measures ANOVAs that wereperformed separately on the no-clickand click conditions confirmed thisfinding, showing a significant main effect of session 3 21 = 3.59; p = .031)for the click condition but not for theno-click condition 3 21 = 2.48 , p =.09). The no-click data collapsed overfour sessions from all participants didnot differ significantly from chance(PB on f > .05 for all conditions).

locating even large differences in the sizeof objects. Subsequent sessions showedsignificant improvements, with their performance markedly better after a singlesession and approaching asymptote afterthree sessions, as indicated by the significant effect of session. Figure 3B emphasizes the effects of session as differencescores between no-click and click performance, rather than raw percentages.

Representative psychometric functionsfor one skilled sighted participant, BL,and the blind expert echolocator EB areshown in Figure 3C. Their 75 thresholds (14.5 degrees and 8.0 degrees, respectively) indicate that both were proficient in discriminating differences insizes in single sessions . The best performances during individual sessions amongthe sighted participants discriminated differences in the auditory angle as small as5.3 degrees (although all the participants'average performance was coarser thanEB's single-session threshold) .

Figure 4 shows pooled click data fromthe four observers who underwent additional sessions at larger distances; for acomparison, data from EB' s single sizediscrimination session is shown as well.Each curve represents the averaging ofthree asymptotic sessions for each of fourobservers at the distance indicated. Regardless of the distance, performance varied along the same curve when plottedagainst the angular size difference, independently of linear distance. Psychometric curves fitted to group performanceyielded thresholds of 16.9 degrees at33 centimeters and 19.2 degrees at 50centimeters (group performance at 75

2011 AFB , AU Ri ghts Re served JoLtl al of Visuallmpairmenl & Blindness January 2011 25

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Angular size difference (deg .)Figure 4. Distance effects on size discrimination. Representative elTor bars icentimeters did not exceed 75%). Monte localization. To investigateCarlo simulation showed that the curves sighted echolocators coulwere not significantly different p = .27). spatial resolution of an expThis finding suggests that thresholds are we measured echolocatioconstrained by the difference in the auditory version of a vernier acuitangle subtended by the stimuli, rather than used by vision scientists (by the absolute stimulus size or distance theimer, 1978). A typicwithin the range that we tested. Overall, acuity task involves a pairthe results demonstrate that sighted per arranged end to end, slighsons can learn to use echolocation to thogonally to their orientatdiscriminate precisely the size of an ob detenrune the direction ofject over a range of near-field distances. each trial (McKee & We

Westheimer & McKee, 19Experiment 2: Echolocation ity can reveal extremely fivernier acuity thresholds, smaller than thThe first experiment revealed that untrained gle photoreceptor (Westheisighted participants can quickly learn to theimer & McKee, 1977echolocate. However, it remains unclear sible spatial resolution ofwhat level of spatial precision they attain Several previous studiesand how this level compares to that of ex presented single stimuli inpert echolocators who are congenitally calization experiments or pblind. In addition, size discrimination, while 2IFC (two-interval forceda nominally spatial task, may not tap or ination experiments. Aquantify the fine-grained limits of spatial stimuli to an echo-per

26 JOLt/n t of Vis wtlmpail11e111 & Blindness. January 2011 2011 AFB , Al l Rights Reserved

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2 011 AFB , All Rights Reserved Journal o Visuallmpairment & Blindness, January 2011 27

egocentric) spatial localization. Spatial perception depends largely on relative localization, and this vernier method provides ameans to characterize the resolution of auditory spatial acuity.METHODSWe used a setup similar to Experiment 1(see Figure SA . Eleven sighted participants, who met the same criteria andinformed-consent conditions as those inExpeliment 1 sat blindfolded facing theframe at a distance of 50 centimeters.Two vertically separated disks of 20.3centimeters each in diameter or about 8inches) were presented with one of fivehorizontal center-to-center separationsfrom 1.1 degrees to 13.2 degrees of auditory angle (Figure SA . Using the methodof constant stimuli, 20 trials on averagewere collected for each of five vernier separations, for a total of 100 trials per session(1-2 hours per session). The participantsreported whether the top disk was located tothe right or left of the bottom disk (2AFCtask). Trials were conducted and analyzedin the same general manner as in Experiment 1. Each observer participated in a minimum of five sessions to ensure asymptoticperformance.

Expert echolocator EB was availablefor two sessions of the vernier acuity task.On the basis of a running average (binwidth, 10 trials), EB reached asymptoticperformance in the second session. Thefirst session was conducted at 75 centimeters and the second at 100 centimeters(about 39 inches) to avoid ceiling effects.In the first session, EB participated in 20trials at each of four vernier separations

0.57 degrees to 3.4 degrees. To achieveasymptotic performance as quickly aspossible, all the participants were givencorrect or incOlTect feedback after eachtrial (Herzog & Fahle, 1997).RESULTS, EXPERIMENT 2A two-way repeated-measures ANOVA(clicking X separation) on the data for allthe sighted participants yielded a significant effect of clicking (Fuo = 6.9; p =.025). Although the effect of separationcollapsed across clicking conditions didnot reach significance (F4 .4o = 1,98; P =.116), the condition X separation interaction was signific.ant (F4 .4o = 2.74; P =.042). Thus, clicking was significantlyhelpful to the participants because the noclick group s performance never exceeded chance levels, and the effect ofstimulus separation is clearly carried bythe click condition. A repeated-measuresANOVA on only the click condition revealed a significant effect of stimulus separation, F4.40 = 2.76, P = .041. To confirm that the effect was not driven byoutlying values, we performed a nonparametric chi-square analysis on the participants performance at each individualstimulus separation. A fixed-sequence, incremental application of the Bonferronicorrection for multiple comparisons(Westfall & Krishen, 2001) indicated thatgroup performance was significantlyabove chance levels for the two greatestseparations, 6.6 degrees and 13.2 degreesK = 7.36, p = .014; K = 4.46, p =.014, respectively; see Figure SD).

The representati ve plots in Figure 5Bshow psychometric functions fitted to

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1.1 0 22' 4.4' 6,6"Proportion correct (by separation & session)Figure 5. Stimulus setup and results of Experiment 2. Panel (A): Vernier exper(B): Psychometric functions showing vernier acuity for sighted participant BLcator EB. Pane) (C): Group plot of Vernier discrimination performance. Panof performances across all sessions by sighted pruticipants at each stimulus sepaindividual subjects or participants.

individuals' data. However, the initialgroup analysis belies the widely varyingperformance among the participants andsessions (Figure SC), reft.ecting a largeincrease in the difficulty of the tasks

from Experiment 1. Fhighest group mean perwidest separation (13.63.S , but the performvidual participants at

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some failed completely. Two sightedpartIcIpants, BL and KK, performedbest in the range of the auditory anglesthat we sampled, performing at higherthan 75 correct and allowing us tocompute thresholds from psychometricfunctions as in Experiment 1. Thresholdspooled over all the sessions were 4.1 degrees for BL and 6.7 degrees for KK. Theseare the finest discriminations among thesighted participants, although not necessarily at an expert level; by comparison, EB' s75 threshold during his second sessionwas 1.58 degrees.

Although a full comparison betweensighted and blind echolocators would require a larger sample than that used in thepresent study, our results suggest that notall sighted participants can be equallytrained. Nevertheless, the results convincingly demonstrate sufficiency somesighted participants can achieve echolocating precision approaching that of anexperienced echolocator who is blind.DiscussionIn two experiments, we tested the spatialresolution of the echolocation abilities ofsighted participants and one expert echolocator who is blind, constraining theecho-producing vocalizations to selfgenerated clicks. In Experiment 1, thesighted participants could be readilytrained in coarse echolocation ability,even without explicit feedback about theirperformance; feedback did not significantly alter their performance. Furthermore, size-discrimination thresholds wereroughly constant with increasing distance, so the difference in the size of the

ment 2 used a novel and challenging vernier acuity task to measure the spatialresolution of echolocation precisely. Animportant finding , which differed fromthose of all previous studies, was thatwith sufficient training some sighted persons learn to echolocate with a level ofproficiency that approaches that of expertecholocators who are congenitally blind.

The second experiment introduced anew measure of echolocation acuity thevernier stimulus. This stimulus provides ameans of operationally defining the acuityof echolocation akin to the spatial acuityof vision and potentially a basis for objective measurement and comparisonacross individuals and individual differences. It could be especially valuable ifactive echolocation becomes more prevalent as a navigational aid for individualswho are blind (Ashmead, 2008). The substantially finer resolution measured forEB and BL relative to their sizediscrimination performance also suggeststhat although auditory vernier discrimination may be a more difficult task, it alsocould measure fine spatial resolution inecholocation.COMPARISON TO PREVIOUS STUDIESPrevious studies did not definitively measure the acuity or spatial resolution ofecholocation in sighted individuals (seeTable 1). As we discussed earlier, Rice(1969) and Kellogg (1962) were closestbut published conflicting results. Kohler(1964) recruited many sighted participants for his investigations of auditoryorienting but tested passive detectionof obstacles, not spatial discrimination.

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0 CEU ArticleExperiments with blindfolded sightedsubjects tested the discrimination ofshapes with no explicit spatial componentand no measure of acuity (Hausfeld et aI.,1982). Arias and Ramos (1997) andArias, Curet, Moyano, Joekes, andBlanch (1993) tested repetition pitch, aproposed echolocation cue (Bassett &Eastmond, 1964), in sighted persons butdid not explicitly test spatial resolution orthe perception of self-generated echoes.

The considerable variability in pelformance in the present study may help explain the varying results in prior work. Thedistribution of echolocation ability in typically hearing, sighted persons ranges fromcomplete inability to near-expert thresholds(Experiment 2 and varies with specificecholocation tasks (Experiment 1 versusExperiment 2). The small number of subjects in previous studies could have produced inconsistent patterns of results thatreflect this distribution. Future investigations of the underlying cues used in echolocation, for example, should leverage theindividual differences present in echolocation ability.TRAINING ECHOLOCATIONTables 1 and 2 show that most previousstudies of echolocation focused on the performance of persons who were blind, withtraining potential an implied motivation ofthe research. We showed that some naivesighted persons with relatively limited training can approximate the spatial resolutionof an expert with several decades' worth ofexperience; all the sighted participants inour study achieved at least a coarse abilityto echolocate (Experiment 1 . Not all participants reached this level of precision (Experiment 2); however, it is not clear that allpersons who are blind can echolocate

equally either without a subpopulation of randomly sawho are blind than has beeously (rarely more than sixminimum thresholds achievthe sighted participants inrelatively few sessions in Eproached those reported preticipants who were blind (Rice et aI., 1965), althougmance exceeded them. Tspatial-acuity and size-thresholds that rivaled orspatial resolution of all prein the literature that usedcues, as well as previouauditory spatial resolutionsive listening to noise stiAllen, 1997).

Thus, echolocation perability practiced by a fewuals; the crucial spatial resnent of the skill , althougately accessible to mpersons, can be readily learmeasures of echolocationvernier technique, are critiing training programs of tby EB; our results thereforfor such programs that ardividuals who are newly bConclusionsWe have characterized thlution of novice and experlocation using size discrnovel, relative spatial locWe showed that perceptuecholocation can be rapid wand that some sighted inditrained in echolocationprecision that approachesecholocators who are con

30 l oumal of Visu l Impairment & Blindness Janu ary 2011 20ll AFB , All Rights R ~ e r v

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the characterization of the most importantecholocationcuesremainfertileavenuesforfutureresearch.Pragmatically,researchandtraining programs in both orientation andmobiHty and echolocation shouldconsiderincludingadultswhohaverecentlybecomeblind.

ReferencesAmmons, C H., Worchel, P. , & Dallenbach,K. M. (1953)."Facial vision": The perceptionof obstaclesoutof doorsbyblindfoldedandblindfolded-deafenedsubjects.AmericanJournal of Psychology, 66,519-553.

Arias, C, Curet, C A., Moyano, H. F,Joekes, S., & Blanch,N. (1993). Echolocation: A study of auditory functioning inblind and sighted subjects. Journal of Vi-sual Impairment &Blindness, 87, 73-77.Arias, C, & Ramos, O. A. (1997). Psychoacoustic tests for the study of humanecholocationability.Applied Acoustics, 51,399-419.

Ashmead, D. H. (2008) . Visual experienceand the concept of compensatory spatialhealingabilities. In 1. J.Rieser,D.H .Ashmead, F F. Ebner, & A. L. Com (Eds.),Blindness and brain plasticity in navigation and object perception (pp. 367-380).New York: LawrenceErlbaum.Ashmead, D. H ., Hill, E. W., & Talor,C R.(1989). Obstacle perception by congenitally blind children. Perception and Psychophysics, 46,425-433.

Bassett, . G., & Eastmond, E. 1. (1964).Echolocation:Measurementof pitchversusdistance for sounds reflected from a flatsurface. Journal of the Acoustical Societyof America, 36,911-916.

Blauert, J ., & Allen, J. S. (1997). Spatialhearing: The psychophysics of humansound localization (rev. ed.). Cambridge,MA: MIT Press.

Boehm,R. (1986). Theuseof echolocationas amobility aid for blind persons. Journal of

(1975). Obstacle detection with and without theaidof adirectionalnoisegenerator.American Foundation for the Blind Research Bulletin, 29, 67-85.

Cotzin,M.,& Dallenbach,K.M.(1950). "Facialvision":The roleof pitchandloudnessin theperceptionof obstaclesby theblind.American Journal of Psychology, 63,485515.

Despres,0.,Candas,V ., & Dufour,A. (2005) .Auditory compensation in myopic humans:Involvementof binaural, monaural, orechocues?Brain Research, 104, 56 65.

Doucet,M.E. ,Guillemot,J.P.,Lassonde,M. ,Gagne, J. P., Leclerc, C, & Lepore, F(2005). Blind subjects process auditoryspectralcuesmoreefficiently than sightedindividuals.Experimental Brain Research,160, 194-202.

Dufour, A., Despres, 0., & Candas, V.(2005). Enhanced sensitivity to echocuesin blind subjects. Experimental Brain Research, 165,515-519.

Harley, H. E., Putman, E. A., & Roitblat,H .L. (2003) .Bottlenosedolphinsperceiveobject features through echolocation. Nature. 424(6949), 667-669.

Hausfeld,S.,Power, R. P.,Gorta ,A., & Harris, P. (1982). Echo perception of shapeandtexturebysightedsubjects.Perceptualand Motor Skills. 55, 623-632.

Herzog,M.H ., &Fahle,M. (1997).Theroleoffeedbackin learningavernierdiscriminationtask. Vision Research 37,2133-2141.

Hughes,B. (2001). Activeartificialecholocation and thenonvisualperceptionof aperture passability. Human Movement Science 20 4-5) , 371-400.

Juurmaa, 1., & Suonio, K. (1975). Therole ofauditionandmotion in thespatialorientationof theblind and the sighted.ScandinavianJournal of Psychology. 16,209-216.Kellogg, W. N. (1962). Sonar system of theblind. Science, 137, 399-404.

Kniestedt,C, & Stamper,R. L. (2003). Visualacuityand its measurement. OphthalmologyClinics of North America, 16, 155-170.

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