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Biomedical subjects

M Hollins

Publications and source records attributed to M Hollins.

8 recordsLinked to original sources
PubMed1991

Vibrotactile adaptation on the face.

Threshold amplitude for vibration is elevated if testing is preceded by extended exposure to a vibratory adapting stimulus of appropriate amplitude and frequency. This phenomenon, previously studied almost exclusively on the hand, is here shown for the first time to occur on the face as well. Adaptation is then used analytically to determine that the two-branched threshold-versus-frequency function obtained on the face by Verrillo and Ecker (1977) represents the activity of two distinct mechanisms. Action spectra of vibrotactile adaptation reveal the presence of both mechanisms even in subjects whose unadapted threshold function (like that reported by Barlow, 1987) shows no sign of duplexity. Finally, the data suggest that on the face (unlike the hand), cross-channel adaptation may occur at high adapting amplitudes.

Adult↗
PubMed1990

Time course and action spectrum of vibrotactile adaptation.

In a series of experiments designed to explore the processes underlying adaptation of the sense of flutter-vibration, vibrotactile threshold was measured on the pad of the index finger, using Békésy tracking. Unadapted thresholds were first measured, for a number of frequencies (4-90 Hz) and contactor sizes (1-8 mm diameter). As expected, these measurements indicated the presence of (1) a Pacinian system possessing spatial summation and increasing in sensitivity, as frequency was raised, at the rate of 12 dB/octave; and (2) a non-Pacinian system showing little spatial summation, and with a frequency characteristic matching that of the NP I mechanism of Bolanowski et al. (1988). These baseline data of Experiment 1 guided the selection of stimulus parameters for subsequent experiments, in which threshold for a test stimulus was measured before, during, and after periods of vibrotactile adaptation. In Experiment 2, test stimuli of 10 Hz and 50 Hz were combined factorially with 30-dB SL adapting stimuli of the same two frequencies. When the test stimulus was 10 Hz, the two adapting frequencies were equally effective in raising threshold; however, when the 50-Hz test stimulus was used, the 50-Hz adapting stimulus raised threshold by a greater amount than did the 10-Hz adapter. These results confirm on the finger the independence of adaptation in Pacinian and non-Pacinian channels, a result previously established on the thenar by other workers. For all four frequency combinations, threshold rose exponentially with a time constant of 1.5-2 min. In Experiment 3, an action spectrum was determined, showing the adapting amplitude needed at each of a series of frequencies to raise the threshold of a 10-Hz stimulus by 10 dB; this spectrum was essentially flat from 30 to 90 Hz. The results, taken in conjunction with what is known about rapidly adapting cutaneous mechanoreceptors, imply that the effectiveness of an adapting stimulus is not determined solely by the amount of activity it generates in first-order afferents.

Adult↗
PubMed1988

Perception of the length of voluntary movements.

Two experiments were performed to study the ability of blindfolded subjects to estimate distance on the basis of proprioceptive cues. In the first experiment, subjects judged the length of metal rods that they were allowed to explore freely. With this access to positional as well as other cues, subjects' estimates were a nearly linear function of actual length. These data closely paralleled control measurements obtained under conditions of visual, rather than haptic, inspection. In the second experiment, each subject slid his or her index finger laterally along a straight path delimited by the apparatus, and then gave a magnitude estimate of the distance through which the finger had moved. Velocity of movement was manipulated by asking subjects, on each trial, to move at one of five speeds ranging from "very slow" to "very fast"; these instructions elicited velocities spanning a 100-to-1 range. Magnitude estimates of distance in this second experiment increased as a function of actual distance, but decreased as a function of velocity. This latter phenomenon resembles the dependence of perceived distance on velocity that has been shown by other investigators to occur when a stimulus object is drawn across the skin. The data of the present study are consistent with the hypothesis that the perceived length of an active movement depends on a combination of movement and position signals from primary and secondary sensory fibers in muscle spindles.

Adult↗
PubMed1978

Factors influencing cutaneous directional sensitivity.

The influence of stimulus velocity and traverse length on the ability of human subjects to indicate in which of two opposite directions a brush moved along the skin was determined using a forced choice procedure. Stimulus velocities ranged from 0.75 to 250 cm/sec, and traverse lengths ranged from 0.5 to 6 cm; measurements were made on both the thenar eminence and the preaxial upper arm. Performance was expressed in terms of "critical traverse length" i.e., that traverse length at which, for a given velocity, the subject would correctly identify the direction of brush motion on 75% of the trials. The data indicate that the capacity to identify direction of tactile stimulus motion increases with traverse length and is optimal for velocities between 3 and 25 cm/sec. The overall level of performance was better on the thenar than on the upper arm.

Adult↗
PubMed1978

Representation of moving stimuli by somatosensory neurons.

The findings obtained in neurophysiological and psychophysical investigations using tactile stimuli that move at constant velocity across the skin are reviewed. For certain neurons in the postcentral gyrus of the cerebral cortex (S-I) of macaque monkeys, direction of stimulus motion is a "trigger feature"" i.e., moving tactile stimuli evoke vigorous discharge activity in these neurons only if the stimuli are moved in a particular direction across the receptive field. This directional selectivity is maximal when stimulus velocity is between 5 and 50 cm/sec, and falls off rapidly at lower or higher velocities. The capacity for human subjects to correctly identify the direction of stimulus motion on the skin exhibits a similar dependence on stimulus velocity. The similar effects of velocity on neural and psychophysical measures of directional sensitivity support the idea that direction of stimulus motion on the skin can only be recognized if the moving stimulus optimally activates the group of S-I neurons for which that directions of simulus motion is the trigger feature.

Action Potentials↗
PubMed1976

Does accommodative micropsia exist?

Subjects matched the size of a test target seen under various conditions of accommodation and convergence to the size of a reference target seen under constant conditions. Convergence, as expected, had a substantial effect on perceived size, while accommodation by itself had little or none.

Accommodation, Ocular↗