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Results for “Differential Threshold”

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At least 37 records · Page 2Linked to original sources
PubMed1978

Analysis of the detection of a moving line.

A model is proposed to explain the effects of line motion on visual sensitivity. The model incorporates recent evidence for parallel "pattern" and "flicker" systems. An element of either system consists of a spatial filter followed by a temporal filter; the characteristics of these filters were derived from previous psychophysical measurements. The model may be used to demonstrate why visual sensitivity to optimum triangular-wave motion is greater than for optimum square-wave motion, which, in turn, is greater than for on-off presentation. The predictions of the model are in reasonable agreement with threshold-amplitude data for triangular-wave and square-wave motion; the model is also consistent with threshold-frequency data for small-amplitude sinusoidal motion.

Differential Threshold↗
PubMed1979

Effect of information feedback on temporal discrimination in concurrent and post-feedback measures.

College students estimated time intervals (5, 6, 7, 8, and 9 sec.) where one group (N = 20) received information feedback in terms of actual interval durations and a second group (N = 18) received no information. Theshold measures were then taken for all subjects using the method of constant stimuli (comparison stimuli of 5, 6, 7, 8, and 9 sec. and a 7-sec. standard). In addition to increased accuracy and consistency of judgments, the feedback group showed a decreasing Weber fraction during the estimation phase, while the Weber fraction for the no-feedback group increased. The feedback group retained only a slight advantage in subsequent threshold measures; group differences in difference thresholds and derived nonparametric estimates of d' were nonsignificant.

Differential Threshold↗
PubMed1977

Response of rapidly and slowly adapting mechanoreceptors and vibratory sensitivity in human hairy skin.

Single unit activity was recorded percutaneously with microelectrodes from 38 rapidly adapting (RA) mechanoreceptors of the dorsal surface of the hand in 49 awake human subjects. Tuning characteristics were determined for 28 RA-fibers at various frequencies between 5 and 100 cps of sinusoidal mechanical stimulation. In separate experiments human thresholds of vibration perception were studied under comparable conditions. Several RA-mechanoreceptive fibers were broadly tuned, showing no clearly defined best frequency in the range between 5 and 20 cps. Other RA-fibers had a minimum of sensitivity between 20 and 40 cps. For either lower or higher frequencies, stronger stimuli were required to elicit one nerve impulse per stimulus cycle. These RA-receptors may be related to the perception of low frequency oscillation (flutter). They cannot account for human vibration sensitivity in the higher frequency range, since tuning of the receptors required considerably higher amplitudes than perception. Sixteen slowly adapting (SA) mechanoreceptors of Type I and II showed a frequency modulation in phase with low frequency mechanical oscillations of stimulus amplitudes far below human thresholds for perception of movement.

Action Potentials↗
PubMed1978

Movement discrimination capacities in the cat.

Cats were trained to discriminate moving from nonmoving targets or one direction of movement from another. Various stimulus changes, e.g., size, direction, and rate, were then introduced as a test for generalization of the dimension of movement. Thresholds for detection for minimal movement were also determined. The results showed that (a) for cats, discrimination of movement is more difficult than discriminations based on brightness; (b) the dimension of movement is completely generalized across stimulus configuration but incompletely generalized for direction of movement; (c) the mean movement detection threshold was found to be 3.3 degrees/sec; (d) the thresholds for minimal movement and direction of movement were essentially identical; and (e) stimulus-viewing strategies were found to play an important role in the threshold determinations. The results of the generalization tests are consistent with the physiological properties of neurons found to be sensitive to movement in the cat visual system. The movement threshold values were found to lend support to the view that resolution and slow movement thresholds are correlated.

Animals↗
PubMed1979

Comparison of contrast thresholds of large bars and checks measured by VECPs and psychophysically as a function of defocusing.

The effects of defocusing the image on the contrast threshold were studied both for checkerboard and bar patterns at various low spatial frequencies, and comparison was made between psychophysical results and visually evoked cortical potentials (VECPs) results. VECP threshold was defined as the contrast necessary for obtaining a criterion amplitude of 5 muV. When increasing the degree of defocusing, the lowest contrast threshold shifted towards larger checks or bars, the contrast threshold increased more abruptly for smaller sizes, and the VECP contrast thresholds increased more than the psychophysical ones, especially for smaller sizes. No significant difference was found in the contrast thresholds between the results with bar patterns and checkerboard patterns, except that for bars, the VECP threshold as defined was approx. 0.2 log units higher than those for checkerboard.

Differential Threshold↗
PubMed1979

The effects of stimulation of ear acupuncture points on the body's pain threshold.

Six ear acupuncture points, one non-acupuncture ear point, and the body locus Ho-Ku (LI-4) were electrically stimulated in order to compare the effects of stimulation on the body's pain threshold at selected loci on various points on the body by measurement with a radiation heat-type Pain Meter on 5 subjects. The ear points, with the exception of the non-acupuncture ear point, were found to be effective even in peripheral body regions in varying degrees. Ear stimulation did not increase the threshold as rapidly as Ho-Ku. In all cases where the pain threshold was raised, the effect persisted after electrical stimulation had stopped.

Acupuncture Therapy↗