Biomedical subjects
Publications and source records attributed to E C Lechelt.
The present study reports partial support for right-hemispheric specialization for spatial-haptic discrimination when using unfamiliar shapes that were intuitively nonverbal, with 40 subjects.
Thresholds for tactile discrimination of stimulus orientation discrepancy from standard or referent vertical, horizontal, and diagonal orientations were determined for sighted, visually impaired, and blind subject groups. The stimuli were presented to the ventral distal portion of the tip of the subject's left index finger via an Optacon. Although the subject groups did not differ in overall discrimination accuracy, for each group the deviations from vertical and horizontal standard orientations were discriminated reliably more accurately than the deviations from standard diagonals, ie the oblique effect was obtained. The bases for this tactual spatial anisotrophic effect appear to reflect both sensory--neurological and experiential factors.
A case is made for the use of tactile-vibratory stimulation in devising sensory-substitution systems for sensorily impaired humans.
Forward and backward masking functions were obtained for the detection of a 2-msec. tactile "test" pulse using two different masking patterns (5- or 10-pulse sequences) under conditions of both local and remote masking. Twelve ISIs (interval between "test" pulse and onset of the masking sequence) ranging from 10 to 76 msec. were used. A two-interval forced-choice (2-IFC) procedure was used in which observers were presented with two successive trains of tactile pulses, one having the "test" pulse at varying intervals prior (backward masking) to or after (forward masking) the masking sequence and one train having only a masking sequence. Observers were asked to report in which train of pulses they detected the "test" pulse. With local masking, i.e., when "test" pulse and masking sequence were presented to the same locus, there was substantially more forward than backward masking, and the 10-pulse sequence resulted in consistently greater amounts of masking than the 5-pulse mask. When the "test" pulse and masking sequence were delivered to different loci, i.e., the remote masking, the results were much less systematic. The data suggest that both peripheral and central factors contribute to the obtained masking functions and that both integration and interruption are producing the masking interference.
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Visual and haptic judgments of stimulus orientation were examined intramodally and crossmodally by having subjects reproduced standard stimulus orientations simultaneously with their inspection or after a delay. For all conditions, an oblique effect was obtained, i.e. vertical and horizontal orientations were reproduced reliably more accurately than oblique orientations. Although intramodal differences were large, with haptic errors being greater than visual errors, cross-model differences were small. Furthermore, while for intramodal conditions simultaneous visual reproductions were reliably more accurate than delayed reproductions but haptic reproductions were more accurate when delayed, cross-modal errors were reliable greater with simultaneous reproductions, regardless of whether the standard orientation was visual or haptic. The modality differences reflect basic differences in stimulus information processing and the stability of the oblique effect across the experimental conditions suggests that perceptual spatial anisotropic effects are strongly influenced by experiential factors.
Tactile discrimination of stimulus aperiodicity was investigated in a two-alternative forced-choice task by having subjects report which of two successively presented trains of mechanical pulses, one with complete pulse periodicity and one in which a single pulse was temporally displaced from its regular placement, was temporally irregular or aperiodic. Trains contained three, four, or five pulses and were presented at interpulse intervals of 60, 75, 85, 100, 125, and 150 ms. Aperiodic trains had one pulse, other than the first or last pulse, temporally advanced or receded by 40% of the interstimulus interval. Results showed that: (i) although the percentage of correct reports of aperiodicity decreased as presentation rate increased (smaller interpulse intervals), the amount of decrease was a function of the number of pulses in a train; (ii) the discrimination of aperiodicity was dependent upon the specific location of the irregularity within the stimulus temporal pattern; and (iii) all patterns with complete temporal reversals of their successive interpulse intervals yielded nearly equivalently accurate reports of aperiodicity. These data suggest that central, attentional factors are involved in the discrimination of stimulus aperiodicity.
Temporal imbalances between the successive stimulation of pairs of loci on each forearm altered judgments of the equality of the spatial extents between sets of loci. The spatial judgments became increasingly inaccurate as the temporal imbalance was increased, i.e., the Tau effect. Changes in stimulus intensity also influenced the dependency of spatial judgments on temporal factors. The data suggest that concomitant variations of spatial, temporal, and intensitive components of a vibrotactile stimulus "package" can produce systematic perceptual effects of potential significance in the design of vibrotactile sensory substitution systems.
Visual spatial numerosity perception was investigated as a function of spatial orientation and surround conditions. 3 to 13 dots arranged linearly in horizontal, vertical, or oblique orientations were presented for 200 msec. in either a square or circular stimulus field. For patterns with small numbers of dots (3 to 7), surround and orientation conditions did not substantially alter perceived number except vertical arrangements were judged as having reliably more dots than identical horizontal arrangements. For large dot-number patterns (8 to 13), surround significantly altered perceived number and left oblique linear arrangements were judged to have reliably more dots than equivalent arrangements in all other orientations.
Temporal numerosity discrimination was investigated for visual, auditory and tactile senses. Trains of two to nine signals (flashes, clicks, taps) were presented at rates of from 3 per sec. to 8 per se. The subjects were instructed specifically to report only the number of signals counted. Significant modality differences were obtained. Auditory counts were almost perfectly accurate inder all conditions. Visual judgement of number, which were consistently the least accurate, were underestimated. The error increased appreciably as the rate increased from 3 per sec. to 6 per sec. but decreased with rates of 7 per sec. and 8 per sec. Tactile reports also underestimated the actual number of signals, the underestimation increasing linearly as a function of rate.
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