PubMed · 879266
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B Wick. 1977. Modified strobe flash for home pleoptics.. https://doi.org/10.1097/00006324-197703000-00012
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Sustained fixation of a bright coloured stimulus will, on extinction of the stimulus and continued steady fixation, induce an afterimage whose colour is complementary to that of the initial stimulus; an effect thought to be caused by fatigue of cones and/or of cone-opponent processes to different colours. However, to date, very little is known about the specific pathway that causes the coloured afterimage. Using isoluminant coloured stimuli recent studies have shown that pupil constriction is induced by onset and offset of the stimulus, the latter being attributed specifically to the subsequent emergence of the coloured afterimage. The aim of the study was to investigate how the offset pupillary constriction is generated in terms of input signals from discrete functional elements of the magno- and/or parvo-cellular pathways, which are known principally to convey, respectively, luminance and colour signals. Changes in pupil size were monitored continuously by digital analysis of an infra-red image of the pupil while observers viewed isoluminant green pulsed, ramped or luminance masked stimuli presented on a computer monitor. It was found that the amplitude of the offset pupillary constriction decreases when a pulsed stimulus is replaced by a temporally ramped stimulus and is eliminated by a luminance mask. These findings indicate for the first time that pupillary constriction associated with a coloured afterimage is mediated by the magno-cellular pathway.
Contextual elements can fundamentally change the perception of an embedded target. A recently discovered masking effect, shine-through, allows one to investigate the precise dynamics of contextual modulation of the human visual system. In this shine-through effect, a vernier precedes a grating comprising more than seven elements for display times as short as 10 ms. The vernier appears as a "shine-through" element superimposed on the grating. However, if additional single lines are presented above and below the grating, visibility of the shine-through element dramatically diminishes. Recent publications focused mainly on the spatial aspects of this contextual modulation. Here, we investigate its temporal characteristics. We show that contextual suppression can occur for context durations of 5-10 ms, even if contextual elements appear 100 ms before target onset. This contextual suppression is not due to the presentation of the contextual elements themselves since without the grating contextual elements exert only weak masking power. Only the combination of contextual elements and grating causes the contextual suppression.
One of our approaches to teaching a course in anatomy and physiology is to stress the fundamental, systems-level concepts. One successful strategy we use is to continually highlight the relationships among anatomy, physiology, and behavior. In this article, we describe a set of classroom demonstrations that stress these links while fostering critical thinking. These demonstrations, on the topic of sensory system structure and function, rely on two perceptual consequences of neural adaptation in the visual system: afterimages and aftereffects. Viewing specific visual stimuli under binocular or monocular conditions with interocular transfer permits several concepts to be observed and discussed, including neural adaptation, anatomical and functional segregation of visual system pathways, and the relationship among visual system structure, function, and perception. This article discusses how to produce and present the required visual stimuli, suggests a set of questions to stimulate critical thinking, and presents student evaluation of this activity.