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At least 163 records · Page 9Linked to original sources
PubMed1996

A general model for the perception of space and motion.

The perception of space and motion involves successive transformations of signals with respect to different reference systems. The visual input is coded in terms of retinal coordinates. The retinocentric values from each eye require to be unified, and to be combined with signals for eye position and movement. This egocentric reference provides a signal for the angular size, motion, or orientation of the stimulus with respect to the observer. The egocentric signals are transformed to a coordinate system that is three-dimensional-the geocentric frame of reference. Further transformations can occur at earlier levels owing to patterncentric interactions within the visual field. When the geocentric signal corresponds to the physical dimensions of space and motion, this is referred to as perceptual constancy.

Acceleration↗
PubMed2004

Visual perception in space and time--mapping the visual field of temporal resolution.

To characterize temporal aspects of information processing in the human visual field, we studied the topographical distribution of temporal and non-temporal performance parameters in 95 normally sighted subjects. Visual field maps of double-pulse resolution thresholds (DPR) (the minimum detectable temporal gap between two light stimuli) and simple visual reaction times (RT) (measuring the speed of reaction to a light stimulus) were compared to maps of luminance thresholds determined by standard perimetry. Thus, for the first time, the topography of a visual variable without temporal constraints (perimetry) could be compared to visual variables in the temporal domain, with (RT) and without (DPR) motor reaction. The goal of the study was to obtain and to describe the pattern of co-variation of performance indicators. In all three measures, performance was best in the central visual field and dropped significantly towards the periphery. Although the correlation between DPR and RT was significant, shared variance was low, and we observed large topographical differences between these two temporal-performance variables. In contrast, DPR and perimetric thresholds correlated more substantially, and visual field maps were similar. The Gestalt of DPR maps shares characteristics of basic visual processing (e.g., light sensitivity), but it also reflects top-down influences, i.e., from spatial attention. Although the correlation between DPR and RT suggests common characteristics between these two temporal variables, the topographic distributions reveal significant differences, indicating separate underlying processing mechanisms.

Adolescent↗
PubMed1990

Shape, size and relative space position perception in neglect patients.

Shape, size and relative position in space perception were tested in 17 right brain damaged (RBD) patients with neglect symptoms, 10 RBD patients without neglect and 11 controls. Simultaneous pair comparison task in free vision was used. Two arrangements of the visual display were used: side by side and top-bottom. Neglect patients' performance was comparable to RBD and controls in the shape and size test, but was below the other groups in the relative space position test. The selective failure of neglect patients in the position task did not depend on the spatial arrangement of the visual display, which may indicate a general perceptual deficit, rather than a deficit restricted to the neglect hemifield.

Aged↗
PubMedDate not supplied

Perception of horizontal head and trunk rotation in patients with loss of vestibular functions.

In patients with loss of vestibular functions, we studied psychophysically the self-motion perception for 'trunk in space' and 'head in space' during various combinations of horizontal head and trunk rotation in the dark. The results were compared to those of normal subjects. For their 'trunk in space' perception, the subjects relied on their internal image of space, derived from the vestibular receptors in the head, and referred their trunk to this as a reference by adding to it a nuchal trunk-to-head signal. The patients, by contrast, always considered the trunk as stationary. Obviously because they were devoid of any space cues, they abandoned or suppressed a neck contribution to their 'trunk in space' perception, which, in fact, would yield an erroneous perception in almost all conditions in the dark. Both the patients and the subjects based their 'head in space' perception on their internal representation of 'trunk in space' and added to this a nuchal head-to-trunk signal. However, the patients' head-to-trunk signal, unlike that of the subjects, was considerably larger than the actual head-to-trunk rotation at low stimulus frequency. We relate this finding to some unconscious modification of their neck muscle activity during passive head rotation. It appears that the patients' gain of the neck input per se is not increased, but rather that subsets of this input are modified according to the particular function they serve.

Adolescent↗
PubMed1980

Deficits in space-form perception in patients with sex chromosome mosaicism (45,X/46,XY).

Several studies have shown that selective deficits in space-form perception are found in patients with Turner's syndrome, associated with 45,X or a structural anomaly of an X chromosome. The authors sought to determine whether significant deviations from normal or from Turner's syndrome (relative to space perception) occur when a Y chromosome is present. The four patients studied, aged between 4 1/2 and 24 years, had a karyotype of 45,X/46,XY and a phenotype ranging from sexual ambiguity at birth to typical Turner's syndrome. Although all were in the normal intelligence range (IQ 80 or above), on testing they demonstrated below-average ability in tasks involving visualization of spatial forms, and their drawings were generally immature. The results suggest that patients with sex chromosome mosaicism X/XY may have similar deficits in space-form perception and orientation to those previously demonstrated in Turner's syndrome.

Adolescent↗
PubMed2003

Voluntary head movement and allocentric perception of space.

Although visual input is egocentric, at least some visual perceptions and representations are allocentric, that is, independent of the observer's vantage point or motion. Three experiments investigated the visual perception of three-dimensional object motion during voluntary and involuntary motion in human subjects. The results show that the motor command contributes to the objective perception of space: Observers are more likely to apply, consciously and unconsciously, spatial criteria relative to an allocentric frame of reference when they are executing voluntary head movements than while they are undergoing similar involuntary displacements (which lead to a more egocentric bias). Furthermore, details of the motor command are crucial to spatial vision, as allocentric bias decreases or disappears when self-motion and motor command do not match.

Awareness↗
PubMedDate not supplied

[Development of spatial orientation during pilot training].

The problem of spatial orientation of pilots flying high-altitude aircraft is in the focus of present-day aviation medicine because of a growing number of accidents in the air. One of the productive lines of research is to study spatial orientation in terms of active formation and maintenance of its imagery in a complex environment. However investigators usually emphasize the role of visual (instrumental) information in the image construction, almost ignoring the sensorimotor component of spatial orientation. The theoretical analysis of the process of spatial orientation has facilitated the development of the concept assuming that the pattern of space perception changes with growing professional experience. The concept is based on an active approach to the essence, emergence, formation and variation in the pattern of sensory perception of space in man's consciousness. This concept asserts that as pilot's professional expertise increases, the pattern of spatial orientation becomes geocentric because a new system of spatial perception evolves which is a result of the development of a new (instrumental) type of motor activity in space. This finds expression in the fact that perception of spatial position inflight occurs when man has to resolve a new motor task--movement along a complex trajectory in the three-dimensional space onboard a flying vehicle. The meaningful structure of this problem which is to be implemented through controlling movements of the pilot acts as a factor that forms this new system of perception. All this underlies the arrangement of meaningful collection of instrumental data and detection of noninstrumental signals in the comprehensive perception of changes in the spatial position of a flying vehicle.

Aerospace Medicine↗
PubMed1993

Egocentric reference and asymmetric perception of space.

Normal dextrals performed tactilo-kinesthetic bisection tasks in a median position, at three directions of gaze: 30 degrees to the left, 30 degrees to the right, 0 degree. Instead of pseudoneglect phenomenon, a deviation of the subjective middle to the side opposite to the direction of gaze and hand use was found, whichever hand was used. The results are interpreted in terms of displacement of the position of the egocentric reference and are discussed with respect to activation theory. It is argued that pseudoneglect is part of a more general asymmetric perception of space phenomenon which depends on the position of the egocentric reference.

Adult↗