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At least 739 records · Page 41Linked to original sources
PubMed1980

Visual aftereffects derived from inspection of orthogonally moving patterns.

Alternate inspection of patterns moving in orthogonal directions induces an aftereffect in which a stationary test pattern seems to move in a new direction. This direction is the resultant of the two directions of aftereffect that would have arisen from separately inspecting each of the moving patterns. The direction in which objects appear to move, like their color and depth, can thus depend on a synthesis of unperceived components.

Afterimage↗
PubMed1980

Specific reading disability: differences in contrast sensitivity as a function of spatial frequency.

Contrast thresholds for sine-wave gratings of spatial frequencies of 2, 4, 12, and 16 cycles per degree were determined for normal and disabled readers at a range of stimulus durations. Normal readers demonstrated monotonically decreasing sensitivity with increasing spatial frequency at exposure durations between 40 and 100 milliseconds. At exposure durations of 150 to 1000 milliseconds, they showed peak sensitivity at 4 cycles per degree. In comparison, disabled readers showed monotonically decreasing sensitivity with increasing spatial frequency at all stimulus durations. The difference in sensitivity pattern across spatial frequencies was greatest at stimulus durations approximately equal to fixation durations during reading.

Afterimage↗
PubMed1977

A phantom-motion aftereffect.

Motion aftereffects, typically found to result only from localized retinal stimulation, were obtained within regions of the visual field that had not been stimulated by moving contours. "Phantom" stripes are seen moving through a physically homogeneous (empty) region of the visual field when vertical stripes move above and below that region. Immediately afterward, stationary stripes in the previously empty region appear to move in the opposite direction. This phantom-motion aftereffect provides a novel instance of the way global structure affects processes that have been assumed to be influenced only by simpler local spatial and temporal variables.

Afterimage↗
PubMed1988

Visual after-effects associated with the use of high-resolution visual display units.

A long-lasting visual after-effect associated with the use of a high-resolution green visual display unit (VDU) is described in eight normal volunteers. Its duration to a standard VDU exposure is measured. It is related to the McCollough effect and is thought to be either a fatiguing of green colour-coded edge-detectors or an associative phenomenon. A reduction or loss of the usual foveal peak of the critical flicker frequency (CFF) to red is also described.

Adult↗
PubMed1974

'Flight of colours' in lesions of the visual system.

A bright pocket flashlight was directed into one eye for 10 seconds; the subject then closed the eyelids and reported the sequence of after-image colours observed. Lesions of the visual system which compromised bilateral central colour vision also reduced or abolished the `flight of colours'. This simple bedside test of each eye independently is of value in detecting mild defects of central vision.

Adolescent↗
PubMed2001

A disorder of colour perception associated with abnormal colour after-images: a defect of the primary visual cortex.

A 64 year old woman with posterior cortical atrophy secondary to probable Alzheimer's disease is described. Her presenting symptom was of seeing objects as abnormally coloured after prior exposure to a coloured stimulus. Formal testing disclosed that the patient experienced colour after-images of abnormal latency, duration, and amplitude.The demonstration of prolonged colour after-images in a patient with a cortical disease process provides strong evidence that the generation of colour after-images is mediated at least in part by the visual cortex. A mechanism for the generation of colour after-images is proposed in which abnormal prolongation of the images results from excessive rebound inhibition of previously excited wavelength selective neurons in V1. This may occur as a consequence of the relative sparing of inhibitory interneurons in V1 in the context of the degeneration of excitatory neurons that occurs in Alzheimer's disease.

Afterimage↗
PubMed1971

Perception.

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Afterimage↗
PubMed1975

Perception.

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Adaptation, Ocular↗
PubMed1985

Palinoptic phenomena as an error mechanism in resolving alexia without agraphia. A case report.

Palinoptic, visual perseverative, or prolonged positive after-image phenomena have most often been met in right-sided occipital pathology. Less frequent with left-sided lesions they can be associated with the alexia without agraphia syndrome (with or without color naming deficit or hemifield loss). This is illustrated by our case in which rapidly fading visual reduplicative sensations--rather than linguistic incompetence--were apparently responsible for most of his paralexic errors.

Afterimage↗