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At least 379 records · Page 21Linked to original sources
PubMed1979

Apparent movements induced by stroboscopic illumination of stabilized images.

Stroboscopic illumination of stabilized images causes habituation effects and illusory phenomena which, at low stimulation frequencies, show up as brighter patches. When a line is used as a stimulus, these patches are observed as brighter spots in the line surrounded by dimmer patches in the background. These locally brighter parts function as sources from which brightness spreads in the direction of the line at light-on and as sinks to which the brightness retracts again after light-off. This spread and retraction of the brightness induces the perception of movements. Higher stimulation frequencies or a diminished stimulus-background contrast enables the brightness to spread also in the direction perpendicular to the line contour, i.e., into the background. Again a perception of movement is induced, local displacements of a part of the field are observed as a result of the brightness spread. Tiny pinpoints of light, the smallest foveal perceptive elements, visible in lines narrower than 10 min arc (Gerrits, 1978), are also observed when these lines are illuminated with stroboscopic light. These tiny elements do not spread their brightnesses and so also no movement is induced. The results are discussed in relation to the properties of the perceptive elements and the cells activating them (habituation, barriers, filling-in).

Afterimage↗
PubMed1986

Effects of haloperidol and nomifensine on the visual aftereffects of tilt and movement.

An antipsychotic and two antidepressant drugs were studied for their effects on the visual aftereffects of tilt and movement in normal volunteers. Compared with placebo, haloperidol reduced the aftereffects. The antidepressant nomifensine enhanced the tilt but not the movement aftereffect, while maprotiline (another antidepressant) had no significant effect on either aftereffect. Control experiments showed that these changes were unlikely to have resulted from drug induced alterations in scanning eye movements during adaptation. The results are discussed with reference to possible dopaminergic influences on the visual system, and to some of the symptoms of schizophrenia.

Adult↗
PubMed1978

Properties of length-selective and non-length-selective adaptation mechanisms in human vision.

The contrast threshold elevation effect has been measured for one dimensional (grating) and for two dimensional (spot) stimulus patterns. It has been shown previously (Burton and Ruddock, 1978) that such stimuli elicit, respectively, non-length-selective and length-selective adaptation effects. It is established that, unlike the frequency shift effect, the contrast threshold elevation effect is sensitive to the width of the light but not to that of the dark elements of the stimulus patterns. Adaptation to spot patterns elicits a significant threshold elevation for detection of both spot and grating test stimuli, but only under monoptic viewing conditions. The experimental findings are summarized in a block-diagram and it is shown that adaptation to grating patterns is successfully described by the spatial frequency response data given by Maudarbocus and Ruddock (1973).

Adaptation, Physiological↗
PubMed1980

A quantitative model of the functional architecture of human striate cortex with application to visual illusion and cortical texture analysis.

Anatomical and physiological data from lower primates, and psychophysical data from humans, is used to construct a quantitative model of the local and global map structure (functional architecture) of human striate cortex. A series of successful estimates deriving from this model are reviewed, including a prediction for the width of human ocular dominance columns, which has recently been verified. A variety of perceptual phenomena are then discussed, from the point of view of cortical, rather than retinal, topography. It is suggested that the striate cortex may be viewed as a "cyclopean retina" whose non-linear map structure, summarized in terms of a concatenated complex logarithmic pattern, suggests insights into the nature of the Mackay complimentary image, the Frazer spiral, fortification illusions, and the relationship of the second order statistics of a visual stimulus to pre-attentive (textural) segmentation. Finally, the nature of neuronal representation is considered in the context of recent models of perceptual and cognitive function. It is suggested that anatomical re-mapping at successive stages of the CNS may provide a conceptual alternative to conventional single cell and connectionist models, and offers a viable approach towards a "field" theory of vision.

Afterimage↗
PubMed1978

Span of apprehension in hyperactive boys.

The spans of apprehension of hyperactive and normal boys were compared with a forced-choice letter-recognition task developed by Estes (1965). This task provides an estimate of the span which is relatively insensitive to either memory or motivational influences. The span size was the same for both groups when visual "noise" was absent. In the presence of noise, span size for the hyperactive boys decrease. Moreover, as the number of noise letters increased, the reduction in span size observed for the hyperactive boys increased. It is argued that this increasing reduction in span size represents a true deficit in attention.

Afterimage↗
PubMed1978

Positive after-image, PAI: early erasure by saccadic eye movement or Jendrassik manoeuvre.

Positive after-images (PAIs) evoked by low intensity stroboscopic flash are erased by voluntary large amplitude saccadic eye movements. The duration of the PAI is shortened by a Jendrassik manoeuvre. The results suggest that muscle spindle afferent impulses conducted centrally are involved in the erasure phenomenon. The duration of the PAI is modifiable by drugs. The social implications of PAI are considered briefly.

Adolescent↗
PubMed2005

Localization and motion perception during smooth pursuit eye movements.

We investigated the relationship between compensation for the effects of smooth pursuit eye movements in localization and motion perception. Participants had to indicate the perceived motion direction, the starting point and the end point of a vertically moving stimulus dot presented during horizontal smooth pursuit. The presentation duration of the stimulus was varied. From the indicated starting and end points, the motion direction was predicted and compared with the actual indicated directions. Both the directions predicted from localization and the indicated directions deviated from the physical directions, but the errors in the predicted directions were larger than those in the indicated directions. The results of a control experiment, in which the same tasks were performed during fixation, suggest that this difference reflects different transformations from a retinocentric to a head-centric frame of reference. This difference appears to be mainly due to an asymmetry in the effect of retinal image motion direction on localization during smooth pursuit.

Adolescent↗
PubMed2005

Effect of image orientation on the eye direction aftereffect.

After observing a face with the eyes looking to the left or right (adaptation stimulus), the perception of the eye direction of the subsequent face (test stimulus) is biased in the opposite direction of the adapted eye direction; this is called the eye direction aftereffect (EDAE). In the present study, the adaptation stimuli were rotated 90 degrees (clockwise or counterclockwise) or 180 degrees relative to the viewer. The EDAE was measured using upright test stimuli. For the 90 degrees rotation, prior observation of the 'leftward' and 'rightward' eye directions biased the perceived eye directions of the upright test stimuli to the right and left, respectively. These results suggest that the adaptation was induced utilizing an object-based (or face-based) reference frame. For the 180 degrees rotation, however, the results suggest that the adaptation was induced in a viewer-centered reference frame. The involvement of an object-based reference frame suggests that the EDAE reflected the adaptation of a relatively higher-level mechanism at least when the rotation angle from the upright position did not exceed 90 degrees .

Adult↗