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Biomedical subjects

L Matin

Publications and source records attributed to L Matin.

36 records · Page 2Linked to original sources
PubMed1990

The influence of saccade length on the saccadic suppression of displacement detection.

The decrease in sensitivity to spatial displacement which accompanies a voluntary horizontal saccadic eye movement was measured as a function of the length of the saccade. Threshold for detecting the displacement increased linearly from about 0.3 degrees to 1.2 degrees as saccade length increased from 4 degrees to 12 degrees. The variability (standard deviation) of the discrimination increased linearly with saccade length as well, and hence also linearly with the displacement threshold. These results, along with our previous finding that the increase is not a consequence of the saccadically generated spatiotemporal smearing of the retinal image (Li & Matin, 1990), support the proposal that displacement detection is based on a constant internal signal/noise ratio whose denominator is a measure of the variability of the extraretinal signal regarding eye position, and that the reduction in sensitivity is a result of a transient increase of this variability in the temporal neighborhood of a saccade.

Attention↗
PubMed1989

Visually perceived eye level and perceived elevation of objects: linearly additive influences from visual field pitch and from gravity.

Observing a pitched visual field (i.e. tilted around a horizontal axis in the observer's frontal plane) results in large changes in the elevation visually perceived to correspond to eye level (VPEL) and in the perceived elevation and size of stationary objects viewed against the field. With topforward pitch (top toward observer) VPEL lies above true eye level and objects appear smaller and lower; with topbackward pitch VPEL lies below true eye level and objects appear larger and higher. Oscillation of the pitched field induces synchronous perceived oscillation of elevation of a stationary target viewed against the field. Typical VPEL settings deviated from true eye level by 20 degrees with the field pitched at 40 degrees, although some individuals mislocalized by as much as 40 degrees. VPEL varied linearly with visual field pitch with individual slopes for the relation between VPEL and visual field pitch ranging from +0.42 to +0.78 (avg = +0.56). The linear correlation (r) between VPEL in darkness and against an erect visual field was +0.91. The two relations--VPEL vs visual field pitch, VPEL in darkness vs VPEL in the erect illuminated visual field (slope approximately equal to 0.5)--are both accurately predicted by the linear model: VPEL = kvV + kbB; in which V is the influence of visual field structure and B is the influence of the body-referenced mechanism which combines information regarding the orientation of the head relative to gravity, the position of the eye in the orbit, and the vertical location of the image on the retina; kv and kb are the relative weights of V and B with kv + kb = 1. In an illuminated field kv = kb approximately equal to 0.5; in the dark kv = 0, kb = 1.

Gravitation↗
PubMed1982

Oculoparalytic illusion: visual-field dependent spatial mislocalizations by humans partially paralyzed with curare.

In darkness, observers partially paralyzed with curare make large (greater thn 20 degrees) gaze- and dosage-dependent errors in visually localizing eye-level-horizontal and median planes, in matching the location of a sound to a light, and in pointing at a light. In illuminated, structured visual localization and pointing are accurate but errors in auditory-to-visual matches remain. Defects in extraretinal eye position information are responsible for all errors. The influence of extraretinal eye position information on visual localization is suppressed by a structured visual field but is crucial both in darkness and for intersensory localization if visual capture is prevented.

Auditory Perception↗
PubMed1972

Metacontrast and saccadic suppression.

A vertical slit of light illuminated during horizontal saccadic eye movements appeared as a horizontally extended smear when stimulation was terminated before the saccade ended. However, on trials for which duration of illumination of the slit was extended into the period after the saccade, the smear appeared shorter and dimmer, and a clear image of the slit was seen. With further increases in duration, no smears were seen at the highest luminance of the slit employed, although smears were more than 2 log units above threshold when flashes were brief. This saccadic suppression is discussed in terms of metacontrast, with the accumulated luminance in the period after the saccade primarily responsible for masking the effects of the stimulation received during the movement of the eye.

Eye Movements↗
PubMedDate not supplied

Multimodal basis for egocentric spatial localization and orientation.

The perceptual and sensorimotor mechanisms that guide our abilities at localizing and orienting in space integrate sensory information from vision and from a "body-referenced mechanism" that itself makes use of extraretinal signals regarding eye position relative to the head and head orientation relative to the body and to gravity. The experiments and theoretical treatment center on two perceptual dimensions: the visual perception of elevation and of orientation within the frontoparallel plane. Several experiments measuring localization in the horizontal plane are also treated. The experiments involve measurements of the physical elevation of visually perceived eye level (VPEL, a norm for perceived elevation), measurements of the physical orientation within the frontoparallel plane corresponding to visually perceived vertical (VPV), and measurements of the direction within a horizontal plane perceived as straight ahead (VPSA). VPEL and VPV are each significantly and systematically influenced by both the pitch and the roll of visual fields, and it is these influences that provide the basis for experimentally isolating the contributions of vision from those of the body-referenced mechanism. The VPEL discrimination is nearly invariant with variation in head and eye orientation. The possibility that influences from vision and from the body-referenced mechanism combine linearly is well supported. The visual influences on VPEL and VPV are controlled by the action of individual lines, and the same pitched-from-vertical lines (from pitched planes) or oblique lines within erect planes influence both discriminations. The Great Circle Model (GCM) accounts for the influences of individual lines, and contains rules for the influence of combinations of lines on both VPEL and VPV. GCM is interpreted by a 3-dimensional vector treatment in "egocentric orientation space."

Eye↗
PubMedDate not supplied

Combined influences of gravitoinertial force level and visual field pitch on visually perceived eye level.

Psychophysical measurements of the level at which observers set a small visual target so as to appear at eye level (VPEL) were made on 13 subjects in 1.0 g and 1.5 g environments in the Graybiel Laboratory rotating room while they viewed a pitched visual field or while in total darkness. The gravitoinertial force was parallel to the z-axis of the head and body during the measurements. The visual field consisted of two 58 degrees high, luminous, pitched-from-vertical, bilaterally symmetric, parallel lines, viewed in otherwise total darkness. The lines were horizontally separated by 53 degrees and presented at each of 7 angles of pitch ranging from 30 degrees with the top of the visual field turned away from the subject (top backward) to 30 degrees with the top turned toward the subject (top forward). At 1.5 g, VPEL changed linearly with the pitch of the 2-line stimulus and was depressed with top backward pitch and elevated with top forward pitch as had been reported previously at 1.0 g (1,2); however, the slopes of the VPEL-vs-pitch functions at 1.0 g and 1.5 g were indistinguishable. As reported previously also (3,4), the VPEL in darkness was considerably lower at 1.5 g than at 1.0 g; however, although the y-intercept of the VPEL-vs-pitch function in the presence of the 2-line visual field (visual field erect) was also lower at 1.5 g than at 1.0 g as it was in darkness, the G-related difference was significantly attenuated by the presence of the visual field. The quantitative characteristics of the results are consistent with a model in which VPEL is treated as a consequence of an algebraic weighted average or a vector sum of visual and nonvisual influences although the two combining rules lead to fits that are equally good.

Adult↗