17.6

A QUANT工TATIVE COMP且R工SON METHOD OF BLIND MOBIL工TY A工DS

S.Tachi,＊Suppose that a device which directs or guides
a blind individual has somehow acquired information
about the direction of, and width of the path along
which it should lead the blind individual [1]. The
problem is the choice of sensory display of thepa廿1 and its safe margins appropriate for presen­tation to the remaining exterio-receptive senses ofthe blind individual.
工n this paper a method is proposed to quanti­tatively compare the display schemes communicating
the course the blind travelers should follow according to the inforn国tion the blind mobility aids
have acquired, and an optimal auditory display
scheme is sought.
官1e computer system emulates several display
devices which use amplitude modulation to indicate
the error of a subject ’s location from the indicat­
ed course. 官1e TRACK system measures the locationof a hllll則subject in real-time (2], and the error
is presented to the subJect through one of the回目ulated devices ．
四1e indicated course, human tra­jectory, and the error are recorded in the computerdisk memory (Fig. 1). 岱1e performance of the humanin each task is evaluated by calculating a transfer
function of the human with each device and thenusing this transfer function as the criterion forcomparison (Fig. 2).
Three attributes of the display were compared;l)whether the display is continuous or discrete;2)whether the subject is instructed to move toward
the sound or go away from it; and3)whether the presentaion is monaural or binaural(Fig. 3).
Figure 2 shows an example of the amplitude andthe phase of th邑transfer function of the subject
TS with the emulated device of MTC-type (Monaural­
TOward the sound-Continuous）. 明1e same kind oftransfer functions were estimated for all twelve,emulated devices used by two subjects.
A method is proposed to determine the optimal
display scheme quantitatively: .The sum of theeffective gain and the reciprocal of the effective
ti.rite delay is calculated based on the estimatedopen-loop transfer function of the subject witheach of the display devices. The normalized dis­
tance between the alternative display schemes was
statisticaliy calculated and used as the measure
to determine the superiority of one alternative
display scheme to another quantitatively.
For the compensatory auditory display schemes
experimented in this paper the Monaural-type (loudness cue only) and the Binaural 工I-type (loud­ness cue plus position cue) are superior to theBinaural 工・type (position cue only) •由e Monaural-Toward-Discrete-type was found tobe the best for one subject while the Binaural 工工－·TOward-Discrete-type was the best for another. 四1e
difference between subjects was also noticeable.
官1e superiority of one alternative display scheme
to another, however, was allll(コst independent of thesubject difference.
工t has been found to be feasible to design thedisplay scheme of blind mobilty aids using the pro­cedure reported, and the optimal choice can be made35thAC田嶋畠＊＊

R.W.Mann,

MARRIOTT HOTELand＊＊

D.Rowellbefore committing a particular design to lengthly
ctevelopment process.
More.over it will be possible to find out thebest display scheme for a particular subject, i.e.,the custom-made mobility aid for the blind, byusing the method reported.
l)S.Tachi et al.:Electrocutaneous Communication in
Seeing-Eye Robot(MELDOG), Proc.4th 工EEE/E阻S,1982
2)R.W.Mann et al.:Precise,rapid,automat ic 3-D po­
sition and orientation tracking of multiple mov’ing bodies, Biomechanics V工工工， HKC, ILL., 1982.

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This wo:i::k was supported by the .Japanese
Government and the National Eye 工nstitute of theU.S. Government.
Mechanical Engineering Laboratory, M工TI
JAP且N
Tsukuba Science City ， ιIbaraki 305*"' Massachusetts Institute of Technology U.S.A.
*PHILADELPHIA, PA’

22-24 SEPTEMBER 1 8299