Contains reports on two research projects

Bliss, J. C.

Mason, Samuel J.

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XX. SENSORY AIDS RESEARCHProf. S. J. Mason C. M. Ferrar W. M. MacurdyJ. C. Bliss W. G. Kellner R. J. MassaD. A. Cahlander D. G. Kocher H. G. RobertsR. J. Dirkman D. E. TroxelA. RESEARCH OBJECTIVESThe long-range objective of the Sensory Aids Research group is to help people withsensory handicaps to communicate more effectively with their environment. Those whohave been deprived of vision are our primary concern.Since the group was formed, in the fall of 1959, work has begun in the areas ofreading aids, mobility aids, sensory adaptation, and special projects. We are inclose contact with Mr. John Dupress, Director of Technological Research for theAmerican Foundation for the Blind, who acts as consultant to the group. We also keepin close touch with groups at Harvard University, Tufts University, and M.I.T. (withLincoln Laboratory, in particular) that have directly or indirectly related interests inthis field.The group members - graduate students, for the most part - can all be clas-sified as communication engineers. In attempting to gain the necessary backgroundfor research work in sensory aids, we have come to appreciate that there is nosuch class of people as "the blind." Lack of sensory capability is a matter ofdegree; all of us are partially or totally blind under various conditions of emotionalstress, fatigue, viewing angle, light level, preconditioning, and so forth. More-over, blind people have the same endowment in intelligence, energy, motivation, andadaptability to other senses as the rest of the population. Thus, although the title,"sensory aids research for the blind," furnishes a convenient and motivating repre-sentation of the activities of this group, it is a grossly oversimplified descriptionof our work.We may expect that a given artificial sensory device or system will be (a) useful tosome handicapped people, (b) useless to others with the same handicap, (c) possiblyuseful or interesting to some unhandicapped people, and (d) useful as a tool for researchon sensory adaptation, if not as a practical sensory aid. In the immediate future, mostof the experimental work will fall in class (d).Both reading machines and mobility machines can be analyzed with respect to threeparts: (a) the sensor, pickup, or scanner, (b) the computer, filter, or data proces-sor, and (c) the display, or output transducer. A tremendous range of possibilitiesexists for each of these three parts. Work is in progress on a double-spot scannerfor letter identification in standard type fonts, and also on a curve-tracer for acquisi-tion, but not direct letter identification, of printed or handwritten material. Mobility-aid sensors of active (acoustic sonar) and passive (optical detection of ambientenvironmental light) types are being studied. For both reading and mobility machines,we anticipate doing much work on tactile and kinesthetic displays. A kinesthetic dis-play is any display that permits the subject to sense a spatial motion pattern (forexample, by moving his finger or writing upon his hand, or through sequentialtactile stimulation of points on his skin with a speed and spacing that produce asensation of motion).Current special projects include: a typewriter for simultaneous production of visibleEnglish text and punched-tape-coded Class 2 Braille; a two-channel FM miniaturizedtransmitter for telemetering the binaural reception at two microphones mounted nearthe ears of a sightless subject during mobility experiments; an electronic curve tracerfor printed characters; a range-selective optical detector; and a modified Braille tapereader.S. J. Mason181(XX. SENSORY AIDS RESEARCH)B. DISCRIMINATORY THRESHOLDS FOR THE SENSE OF TOUCHKnowledge of the capabilities of the human senses as communication channels and abetter understanding of sensory recognition and signal-detection characteristics areneeded for the development of output devices for sensory aids. In particular, in orderto transmit information to a human by means of the sense of touch, one needs to knowthe ability of the human to discriminate changes along the various dimensions in whichinformation can be coded. A basic waveform, which might be used in a sensory-aiddevice to convey discrete information, is a position pulse. Some experiments have beenperformed to determine the abilities of the human to discriminate between positionpulses of different amplitudes.A geared-down servomotor was used for the application of a position pulse to asubject's finger. The parameters of the position pulse were varied to determine dis-crimination thresholds for pulse height and pulse width, distinguishability of changesin pulse height and pulse width, and the effect of motion in different directions. Thethresholds were measured by a frequency method, according to which 5 stimuli distrib-uted over the range from the rarely noticeable difference to the almost always notice-able difference were presented repeatedly to the subject in random order. In each trial,the subject was presented with a standard stimulus and then with a comparison stimulus.The subject's response indicated whether the comparison stimulus was greater or lessthan the standard. The number of reports for each stimulus gives a map of the transi-tion zone (1).From these data, several quantities can be calculated. The mean of the errors forTable XX-1. Experimental results.Experiment 1 2 3 4 5 6 7 8Number 9 0Subject 1 2 3 4 4 4 4 4 4 4St 27.6 27.6 22.5 22.5 27.7 27.7 27.7 29 29 29Pulseion 68.8 68.8 110 110 90 50 200 95 95 95DurationPosition 1 1 1 1 1 1 1 2 3 1PSE 26.6 28.4 22.3 22.8 26.0 26.9 27.3 28.6 27.2 28.4CE -1.0 0.75 -0.16 0.31 -1.65 -0.82 -0.40 -0.41 -1.84 -0.567DL 2. 27 1. 79 1. 99 1. 80 1.46 1.62 1.64 2.36 1. 23 1.34eber's 0.0824 0. 0648 0.0887 0.080 0.0528 0. 0587 0.0591 0.0814 0.0424 0. 0462RatioNote: All times are in msec and all distances in mils.182(XX. SENSORY AIDS RESEARCH)the various stimuli is equal to the point of subjective equality (PSE). The PSE minusthe standard stimulus, St, gives the constant error (CE). The probable error is equalto the difference that is noticed 50 per cent of the time - the difference limen (DL).Weber's ratio was computed by dividing the DL by the standard stimulus.A summary of the results of the experiments is shown in Table XX-1. In experi-ments 1, 2, 3, and 4, the pulse-height DL was measured for four different subjects.Roughly, we found that a difference of less than 0. 002 inch out of a total movement of0. 025 inch, in which the duration of the pulse was approximately 100 msec and the risetime was approximately 15 msec, could be detected. Subject 4 showed some improve-ment throughout the tests because he had more practice than the others.In experiments 5, 6, and 7, the pulse-height DL was measured for three values ofpulse width. The purpose of these experiments was to determine whether or not theduration of the pulse has an appreciable influence on the DL for pulse height. Whilethe DL obtained with the 90-msec pulse was the smallest, the differences were onlyslight.In experiments 8, 9, and 10, the pulse-height DL was measured for three differentfinger positions. A sidewise motion with the knuckle bent (position 2) gave a larger DLthan either an up-and-down motion with the knuckle bent (position 3) or an up-and-downmotion with the finger extended (position 1).A single experiment was conducted to determine Weber's ratio for pulse-durationdiscrimination. This experiment gave a DL of 28. 7 msec out of 160 msec, or Weber'sratio of 0. 18. Apparently, motion can be detected more accurately than time in thisrange of the parameters.Finally, a single experiment was conducted with subject 4 to determine how well achange in pulse height can be distinguished from a change in pulse duration. Five pulsedurations (55, 75, 95, 115, and 135 msec) and five pulse heights (24, 27, 29, 31.3,and 35. 7 x 10 - 3 inch) were used. The subject was given a standard pulse, and then acomparison pulse. He was asked to report whether the comparison pulse was greater orless in height, and longer or shorter in time. Only one of these four answers was per-mitted. From the results of this experiment it appears that the subject can accuratelydetect a change in the area of the pulse, but he cannot discriminate between the changesin pulse height and the changes in pulse duration.J. C. BlissReferences1. R. S. Woodworth and H. Schlosberg, Experimental Psychology (Henry Holt andCompany, Inc., New York, 1954).183

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