Depressive tendencies in childhood and adolescence as defined by process-oriented experiments.
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Adolescent↗
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Results for “FIGURAL AFTEREFFECT”
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An associative interpretation of the indirect McCollough effect.
Following an induction procedure in which a coloured grid is alternated with a square of a complementary colour, subjects report colour after-effects on both the grid orientation present during induction and the orthogonal non-induced grid orientation. The after-effect reported on the induced grid orientation is called the McCollough effect (ME). The after-effect reported on the non-induced grid orientation is called the indirect ME. There is evidence that the ME represents an instance of Pavlovian conditioning. The present results support a conditioning interpretation of the indirect ME and are inconsistent with interpretations of the indirect ME that attribute the phenomenon to special orthogonal coding mechanisms within the visual system.
Adult↗
Visual functions of the elderly.
This review of the literature describes the limitations in visual functions that affect the elderly's ability to accomplish the tasks of daily living. Decline in accommodation for near vision begins as early as 10 years of age, while visual acuity begins to diminish at 18 years of age. These and other limitations are the result of normal age-related physiological changes in the mechanisms underlying visual function. In order to compensate for the visual limitations of the elderly, environmental modifications are recommended. The planners of institutional and other environments need to consider architectural features that allow optimal visual performance and, thereby, encourage safe mobility. Adaptations are suggested to assist the elderly in the accomplishment of daily living tasks.
Accommodation, Ocular↗
A gem from the past: Pleikart Stumpf's (1911) anticipation of the aperture problem, Reichardt detectors, and perceived motion loss at equiluminance.
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Figural Aftereffect↗
The interplay between stereopsis and structure from motion.
In a series of psychophysical experiments, an adaptation paradigm was employed to study the influence of stereopsis on perception of rotation in an ambiguous kinetic depth (KD) display. Without prior adaptation or stereopsis, a rotating globe undergoes spontaneous reversals in perceived direction of rotation, with successive durations of perceived rotation being random variables. Following 90 sec of viewing a stereoscopic globe undergoing unambiguous rotation, the KD globe appeared to rotate in a direction opposite that experienced during the stereoscopic adaptation period. This adaptation aftereffect was short-lived, and it occurred only when the adaptation and test figures stimulated the same retinal areas, and only when the adaptation and test figures rotated about the same axis. The aftereffect was just as strong when the test and adaptation figures had different shapes, as long as the adaptation figure contained multiple directions of motion imaged at different retinal disparities. Nonstereoscopic adaptation figures had no effect on the perceived direction of rotation of the ambiguous KD figure. These results imply that stereopsis and motion strongly interact in the specification of structure from motion, a result that complements earlier work on this problem.
Adaptation, Ocular↗
Effect of the angle of tilt of the inspection figure on the magnitude of a kinesthetic aftereffect.
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Afterimage↗
Eye direction aftereffect.
Three experiments using computer-generated human figures showed that after a prolonged observation of eyes looking to the left (or right), eyes looking directly toward the viewer appeared directed to the right (or left). Observation of an arrow pointing left or right did not induce this aftereffect on the perceived eye direction. Happy faces produced the aftereffect more effectively than surprised faces, even though the image features of the eyes were identical for both the happy and the surprised faces. These results suggest that the eye direction aftereffect may reflect the adaptation of relatively higher-level mechanisms analyzing the other's eye direction.
Adult↗
Visual persistence of figures defined by relative motion.
In order to measure visual persistence of figures that were solely defined by relative motion (motion-defined figures or motion figures), random-dot kinematograms were used to form stimulus figures in the two-frame, missing element task introduced by Di Lollo, V. (1977 Nature, 257, 241-243). Experiment 1 showed that motion-defined figures persisted for about 130 msec after the termination of the stimulus presentation (i.e. after the dots stopped moving). This was similar to but several tens of milliseconds longer than the visual persistence of figures which were defined by a luminance difference (luminance-defined figures or luminance figures) in the same random-dot pattern. Since motion detectors are not found in the retina or lateral geniculate in primates, our results strongly suggest that visual persistence is not only a retinal phenomenon but also a cortical one. Experiment 2 investigated the possible influence of motion aftereffects on the visual persistence of motion figures. The results showed that coherent movement of the dots over the whole display after the stimulus offset did not reduce the visual persistence of motion figures, suggesting that the source of this persistence is not a motion aftereffect. In Experiment 3, visual persistence for the motion-defined figures was shown to be longer than that for luminance-defined figures independently of the contrast of the stimulus figure as long as the stimuli could be seen clearly enough. This suggests that different mechanisms are involved in the visual persistence of motion-defined and luminance-defined figures.
Afterimage↗
Measurement of a visual motion aftereffect in the rhesus monkey.
A monkey was trained to discriminate between a shrinking and expanding test figure presented after steady fixation of the center of a rotating spiral. Differential shifts in the animal's perception of size constancy were found for clockwise and counter-clockwise rotation of the spiral. The magnitude of the aftereffect was within the range found in human subjects.
Animals↗
Attention-dependent brief adaptation to contour orientation: a high-level aftereffect for convexity?
In contrast to the abundant literature investigating how orientation coding depends on edges defined by various image features, relatively little is known about how coding of orientation might also depend on the two distinct functional roles that oriented edges commonly play. Oriented lines can delineate outline contours of a figure or they can form texture. The results of five experiments using orientation aftereffects measured with brief tests (27 ms, backward masked; adapt-to-test interval=201 ms) provided evidence that brief stimuli (<135 ms) selectively adapt coding of contour-line orientation rather than coding of line-texture orientation. Furthermore, parametric results revealed that the rapidly adapting aftereffects for contour orientation are characterized by (1) broad orientation tuning (peaking at +/-30 degrees to +/-50 degrees from test orientation), (2) indifference as to how the contours are defined (e.g. bright lines, high-pass-filtered lines, faint lines generated by the spatial inhomogeneity of visual sensitivity), (3) rapid saturation at low contrast energy, (4) strong modulation by selective attention, and (5) relative size tolerance. These characteristics appear to parallel those of cells in the high end of the visual form processing pathway (such as inferotemporal cortex). It is thus suggested that the rapidly adapting contour orientation aftereffects reported here may be mediated by high-level neural units that encode global configurations of orientation (e.g. convexity and concavity).
Adaptation, Physiological↗
Evidence for color-contingent organizational aftereffects.
An effort was made to produce negative organizational aftereffects in response to a perceptually ambiguous stimulus that can be seen as a cube in either of two orientations. 6 subjects were adapted to alternative disambiguated versions of the ambiguous cube, shown either in green or magenta light. When tested with the ambiguous figure shown in either green or magenta light, 5 subjects showed negative aftereffects while one subject showed a positive aftereffect. The aftereffects showed an average change in preferred organization of 25%. The results are interpreted in terms of both cognitive and hard-wired processes.
Adult↗
Interocular transfer of visual aftereffects.
A number of the well-known visual after-effects of adaptation exhibit interocular transfer, so that presentation of an adaptation figure to one eye produces a temporary change in the performance of the nonadapted eye. This outcome is usually attributed to the involvement of binocular visual neurons that respond to stimulation of either eye. The fact that interocular transfer is incomplete (i.e., the transferred aftereffect is smaller in magnitude than that induced and measured in the same eye) is routinely cited as evidence for the involvement of monocular neurons. This article critically examines these two interpretations, which are developed in terms of a neural model of interocular transfer. No evidence, logical or empirical, was obtained for rejecting the model. Our analysis further shows that the model must assume some type of pooling process that operates over all tested neurons, both adapted and unadapted. Finally, general implications of the interocular transfer model are discussed, the aim being to delimit the conclusions that may be drawn from interocular transfer experiments.
Adaptation, Ocular↗
The hierarchical nature of perceiving direction of motion in depth from optic flow.
Monocular adaptation to flow fields of optic expansion and contraction juxtaposed on either side of fixation influenced subsequently perceived rotation direction of a figure rotating in depth (kinetic depth effect) about its vertical axis with a normally ambiguous direction. This influence was shown to be asymmetric since adapting to optic expansion produced significantly more aftereffects of translation in depth than did adapting to perceived rotation in depth when viewing a neutral test stimulus. The results are evidence for a hierarchical processing model for the perception of motion in depth from optic flow. Serendipitously, we discovered a new aftereffect from viewing kinetic depth rotation with direction specified by proximity-luminance covariation (PLC). The results and other research are discussed in terms of neural network models with synergistic interactions between levels.
Adaptation, Physiological↗
[Interhemispheric asymmetry in rats differentiating figures by size].
Motor alimentary conditioned reflex was elaborated in Wistar line rats to presentation of various pairs of figures, those of larger area serving as positive signals. In tests on animals with intact brain and with unilateral hemispheric cortical inactivation, new pairs of figures were used besides basic stimuli. The level of analysis in testing experiment was lower than normal: by 5.6% at intact brain, by 16.4%--at right hemisphere inactivation, by 36.4%--at left hemisphere inactivation. Elimination of the left hemisphere produced prolongation of the conditioned reaction time, signs of frustration and aftereffect. In conditions of right hemisphere inactivation the level of discrimination of figures depended on their specific properties and the side of presentation. Conclusion is made on dominating role of the left hemisphere in analysis of abstract and concrete characteristics of visual stimuli, in control of temporal, spatial and emotional characteristics of reactions in situations when considerable abstraction and distinguishing of generalizing invariant sign "more-less" is necessary for elaboration of the conditioned reflex.
Animals↗
From elements to perception: local and global processing in visual neurons.
Gestalt psychologists in the early part of the century challenged psychophysical notions that perceptual phenomena can be understood from a punctate (atomistic) analysis of the elements present in the stimulus. Their ideas slowed later attempts to explain vision in terms of single-cell recordings from individual neurons. A rapprochement between Gestalt phenomenology and neurophysiology seemed unlikely when the first ECVP was held in Marburg, Germany, in 1978. Since that time, response properties of neurons have been discovered that invite an interpretation of visual phenomena (including illusions) in terms of neuronal processing by long-range interactions, as first proposed by Mach and Hering in the last century. This article traces a personal journey into the early days of neurophysiological vision research to illustrate the progress that has taken place from the first attempts to correlate single-cell responses with visual perceptions. Whereas initially the receptive-field properties of individual classes of cells--e.g., contrast, wavelength, orientation, motion, disparity, and spatial-frequency detectors--were used to account for relatively simple visual phenomena, nowadays complex perceptions are interpreted in terms of long-range interactions, involving many neurons. This change in paradigm from local to global processing was made possible by recent findings, in the cortex, on horizontal interactions and backward propagation (feedback loops) in addition to classical feedforward processing. These mechanisms are exemplified by studies of the tilt effect and tilt aftereffect, direction-specific motion adaptation, illusory contours, filling-in and fading, figure--ground segregation by orientation and motion contrast, and pop-out in dynamic visual-noise patterns. Major questions for future research and a discussion of their epistemological implications conclude the article.
Contrast Sensitivity↗
Border-ownership-dependent tilt aftereffect.
Single-cell recordings from macaque visual cortex have shown orientation-selective neurons in area in V2 code for border ownership [J. Neurosci. 20, 6594 (2000)]: Each piece of contrast border is represented by two pools of neurons whose relative firing rate indicates the side of border ownership. Here we show that the human visual cortex uses a similar coding scheme by demonstrating a border-ownership-contingent tilt aftereffect. The aftereffect was specific for the adapted location, indicating that the adapted neurons have small receptive fields. We conclude that figure-ground organization is represented by border-ownership-selective neurons at early stages in the human visual cortex.
Adaptation, Ocular↗
[The systematics of mental disorders related to the sequelae of the accident at the Chernobyl Atomic Electric Power Station].
A dynamic survey was undertaken of mental status of those subjects exposed to ionizing radiation after Chernobyl NPP breakdown (n = 476). The examinees exhibited delayed course (up to 8 years) of psychopathologic disorders with the onset consequent upon working in the alienation zone or evacuation. On instituting some measures to form the pathological mental changes in the subjects described a process or psychopathologic development was noted to occur in 74 (15.5%) and 402 (84.5%) respectively. The psychopathologic disorders detected were arranged in the following classes: psycho-organic, neurotic, chiefly posttraumatic stressor, and psychosomatic ones, the relevant figures being as follows: 14.5% (n = 68), 12.05% (n = 58) and 58.0% (n = 176). A scheme of mental disorders related to the Chernobyl NPP breakdown aftereffects was suggested, which is likely to be amended in the course of further study. A specialized Ukrainian Psychoneurologic Rehabilitation Centre is envisaged, designed to give help to the Ch NPP accident survivors.
Adult↗
J.E. Purkynĕ's contributions to the physiology of the visual, the vestibular and the oculomotor systems.
J.E. Purkynĕ (1787-1869) was one of the leading physiologists in the first half of the 19th century, became the founder of the "exact subjectivism", and remained during his entire life a very careful observer in psychophysical experiments. He made moreover many important discoveries in anatomy, neuroanatomy, embryology and pharmacology. Despite his outstanding contributions to science, he remained in his general philosophy and feelings deeply attached to the Romantic spirit of the age. After Purkynĕ returned to Prague in 1849 he played an important role in his nation's search for a national identity and became a leading figure in the cultural and social life of Prague. Purkynĕ's contributions to the physiology of vision, the oculomotor and the vestibular systems are reviewed. In vision Purkynĕ discovered the Purkynĕ-tree, flicker patterns seen in diffuse light, moving light nebula in the Eigengrau, spatially patterned structures in pressure phosphenes, the antagonistic properties of Galvanic phosphenes with respect to current polarity, periodic afterimages, the Troxler effect for colour perception with the peripheral retina and the principle of the ophthalmoscope. The Purkynĕ-shift in chromatic sensitivity when the adaptation level shifts from scotopic to photopic vision was rediscovered by Purkynĕ. Purkynĕ was the first to describe the "Purkynĕ images" of the anterior and posterior surfaces of the cornea and the lens and the changes in the third Purkynĕ image when the eye accommodates. He described optokinetic nystagmus and optokinetic after-nystagmus and explained movement aftereffects as a habituation of the gaze motor system. Important contributions were made by Purkynĕ to the physiology of the vestibular system, but he did not propose the existence of peripheral receptors for this system. He believed that direct mechanical effects on certain parts of the brain (especially the cerebellum) are responsible for the mechanisms of vertigo. Purkynĕ's five categories of vertigo are still valid today (vertigo of motion, Galvanic vertigo, vertigo caused by general brain ischemia, height vertigo and vertigo caused by alcohol and other narcotics). Purkynĕ's contribution to sensory physiology can be considered as one of the essential foundations on which modern sensory physiology and psychophysics are built.
Adaptation, Ocular↗