Thresholds of recognition of different features of colored stimuli.
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Cerebral Cortex↗
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Results for “Form Perception”
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[The influence of similarity in the naming of Stroop items].
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Adolescent↗
[Visual information processing in humans].
Recent advances in parallel information processing of primates and humans have been reviewed. First, I review what is known about physiology and anatomy of the primate visual pathways. Several lines of evidence suggest that the primate visual system consists of the parvocellular (P) and the magnocellular (M) pathways. M-system originates from the A retinal ganglion cells that project to the visual cortex (V1) via the magnocellular layers of the lateral geniculate nucleus (LGN). This system plays an important role for motion and stereopsis. P-system derives from the B retinal ganglion cells that project to V1 via the parvocellular layers of the LGN. This system shows selectivity for color vision and form perception. Second, I focus on the information processing of the human visual pathways. Psychophysical evidence suggests that there are also P and M systems in humans. However, there have been few electrophysiological studies which intend to separate the responses specific to P and M systems in human visual evoked potentials (VEPs). Based on the physiological distinctions between P and M systems, the use of isoluminant color patterns and apparent motion display allows us to evaluate P and M systems, respectively.
Animals↗
Localization and lateralization of stereoscopic processing in the human brain.
Positron emission tomography was used to investigate the neural substrate of stereopsis. Changes in cerebral blood flow were measured in nine volunteers while they judged the orientation of a rectangular cyclopean shape in random dot stereograms. This experimental condition was compared with two control conditions, one having a two-dimensional shape but no cyclopean stimulus, the other having neither shape nor cyclopean stimulus. Blood flow increases were observed in areas 17 and 18 in the right hemisphere when comparing experimental with control conditions; blood flow decreases occurred in the right inferotemporal cortex. Results indicate that stereopsis begins in posterior visual areas in the right cerebral hemisphere. Under ambiguous stereoscopic conditions, participation of more anterior areas in the temporal lobe may be elicited.
Cerebrovascular Circulation↗
[Stereoscopic perception. Probable intervention of pulvinar neurons in the cat (author's transl)].
With the aid of a programme of automatic analysis it has been possible to determine the visual fields of each eye in the case of binocular cells in the pulvinar, lateral-posterior and supageniculate nuclei. The visual properties determined by stimulation of one eye were often similar to those of the other eye. By an objective method of determination of the centre of activity of the receptive fields it was possible to measure disparities between large fields of neurons of these structures. These disparities are compatible with the intervention of these associative nuclei of the postero-lateral thalamus in the mechanisms in stereoscopic vision.
Animals↗
Organizational determinants of subjective contour: the subjective Necker cube.
With specially arranged inducing elements on a white surface of uniform luminosity, a phenomenally complete Necker cube can be seen in any array where only the 'corners' of the cube are physically represented. The subjectively seen bars of the cube disappear when the inducing 'discs' are seen as 'holes' in an interposing surface, through which the corners of a partially occluded cube are viewed. Illusory brightness effects are also observed in connection with the different organizations of this ambiguous figure.
Cues↗
Checkerboards and color aftereffects.
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Afterimage↗
Center-surround antagonism based on disparity in primate area MT.
Most neurons in primate visual area MT have a large, modulatory region surrounding their classically defined receptive field, or center. The velocity tuning of this "surround" is generally antagonistic to the center, making it potentially useful for detecting image discontinuities on the basis of differential motion. Because classical MT receptive fields are also disparity-selective, one might expect to find disparity-based surround antagonism as well; this would provide additional information about image discontinuities. However, the effects of disparity in the MT surround have not been studied previously. We measured single-neuron responses to variable-disparity moving patterns in the MT surround while holding a central moving pattern at a fixed disparity. Of the 130 neurons tested, 84% exhibited a modulatory surround, and in 52% of these, responses were significantly affected by disparity in the surround. In most cases, disparity effects in the surround were antagonistic to the center; that is, neurons were generally suppressed when center and surround stimuli had the same disparity, with decreasing suppression as the center and surround stimuli became separated in depth. Also, the effects of disparity and direction were mainly additive; i.e., disparity effects were generally independent of direction, and vice versa. These results suggest that the MT center-surround apparatus provides information about image discontinuities, not only on the basis of velocity differences but on the basis of depth differences as well. This supports the hypothesis that MT surrounds have a role in image segmentation.
Analysis of Variance↗
Subconfigurations of the human form in the perception of biological motion displays.
We report four experiments examining processes that contribute to the perception of point-light displays of human locomotion. In three experiments, we employed a simultaneous masking paradigm to examine the visual system's use of configural information in global analyses of biological motion displays. In the fourth experiment, we obtained descriptions of our stimulus displays from naive observers. Performance in both the detection and identification studies suggests that the visual system responded equivalently to figures exhibiting any organization of limbs that is consistent with the human form. Moreover, the subconfigurations best detected were also most likely to be described independently as depicting a human figure. Thus our findings provide evidence that the visual system can exploit characteristic subconfigurations of the human form in the perception of human locomotion.
Adult↗
Distributions of alternation rates in various forms of bistable perception.
Studying the temporal dynamics of bistable perception can be useful for understanding neural mechanisms underlying the phenomenon. We take a closer look at those temporal dynamics, using data from four different ambiguous stimuli. We focus our analyses on two recurrent themes in bistable perception literature. First, we address the question whether percept durations follow a gamma distribution, as is commonly assumed. We conclude that this assumption is not justified by the gamma distribution's approximate resemblance to distributions of percept durations. We instead present two straightforward distributions of reciprocal percept durations (i.e., rates) that both easily surpass the classic gamma distribution in terms of resemblance to empirical data. Second, we compare the distributions arising from binocular rivalry with those from other forms of bistable perception. Parallels in temporal dynamics between those classes of stimuli are often mentioned as an indication of a similar neural basis, but have never been studied in detail. Our results demonstrate that the distributions arising from binocular rivalry and other forms of bistable perception are indeed similar up to a high level of detail.
Attention↗
Fundamental properties of intensity, form, and motion perception in the visual nervous systems of Calliphora phaenicia and Musca domestica.
Several classes of interneurons in the optic lobes and brain of the insects, Musca domestica and Calliphora phaenicia, have been studied in detail. Visual stimuli have been categorized on the basis of the properties of intensity, form, and motion. Response characteristics of the classes of neural units are described with respect to these three classes of visual stimuli. While those units that detect motion in select directions have a tonic response, form detection units have a phasic response only. Through correlation of the responses of these classes with visual stimuli, it is shown that these units integrate the responses of other units which have very small visual fields. The small-field units are presumed to integrate the output of a small group of adjacent retinula cells and to respond differentially to intensity, form, and motion. It is shown that the response of both form and motion detection units is independent of the direction of pattern intensity gradation. As a consequence of this independence, it is further shown that failure to detect motion properly must start at a spatial wavelength four times the effective sampling station spacing rather than twice as has been predicted previously.
Animals↗
The relationship between form and space perception, constructional abilities, and clumsiness in children.
The Sensory Integration and Praxis Tests (SIPT) (Ayres, 1989) were administered to 21 children with learning disabilities and 18 children without learning disabilities, aged 5 to 8 years. The children with learning disabilities were divided into two groups, clumsy and nonclumsy, on the basis of their scores on the Test of Motor Impairment (Stott, Moyes, & Henderson, 1984). It was hypothesized that the learning-disabled children in the clumsy group would score significantly lower than the learning-disabled children in the nonclumsy group on the six SIPT subtests that measure form and space perception and visual construction and that the nonclumsy learning-disabled children, in turn, would score significantly lower than the non-learning-disabled children. It was further hypothesized that there would be a significant correlation between the degree of clumsiness and the degree of visual-perceptual and constructional deficits. An analysis of the data indicated that both groups of learning-disabled children scored lower than the non-learning-disabled children on four of the six SIPT subtests. The clumsy and nonclumsy children with learning disabilities, however, differed from each other on only two subtests. The degree of clumsiness correlated significantly with three of the six subtests. The results are discussed in terms of variations in perceptual and motor skills related to subtypes of learning disabilities.
Child↗
THREE THEORETICAL VIEWS OF SLANT PERCEPTION.
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Form Perception↗
Visual areas involved in the perception of human movement from dynamic form analysis.
The perception of biological motion combines the analysis of form and motion. However, patient observations by Vaina et al. and psychophysical experiments by Beintema and Lappe showed that humans could perceive human movements (a walker) without local image motion information. Here, we examine the specificity of brain regions responsive to a biological motion stimulus without local image motion, using functional magnetic resonance imaging. We used the stimulus from Beintema and Lappe and compared the brain activity with a point-light display that does contain local motion information and was often used in previous studies. Recent imaging studies have identified areas sensitive to biological motion in both the motion-processing and the form-processing pathways of the visual system. We find a similar neuronal network engaged in biological motion perception, but more strongly manifested in form-processing than in motion-processing areas, namely, fusiform-/occipital face area and extrastriate body area.
Adult↗
Effects of form familiarity on perception of words, pseudowords, and nonwords in the two cerebral hemispheres.
Previous investigations of hemispheric processes of word perception provide a mixed picture of the sensitivity of each hemisphere to the familiarity of the visual form of lateralized displays. We investigated this issue by presenting words, pseudowords, and nonwords briefly to either the left (LH) or right (RH) hemisphere in lowercase, uppercase, and a matched, unfamiliar mixed-case form, and used an eye tracker to ensure central fixation and the Reicher-Wheeler task to suppress influences of stimulus asymmetry. Familiarity of form exerted a substantial effect on perception. In particular, perception of LH and RH displays of words, pseudowords, and nonwords was least accurate for mixed case, intermediate for upper case, and most accurate for lowercase. However, form had no effect on the LH advantage observed for words, pseudowords, and nonwords, indicating that form affected processing in both hemispheres to a similar extent. Moreover, LH and RH displays both showed that mixed case disrupted performance most for words, and more for pseudowords than for nonwords, indicating the sensitivity to form shown by each hemisphere reflected more than a general perceptual process. Implications for the role of form familiarity in hemispheric processing of words are discussed.
Adolescent↗
Perception of the form of stimulus increment as a method in assessment of the psychophysical relationship.
Among numerous procedures for determination of the psychophysical relation, one approach has seldom been applied. Essential in this method is to present a set of stimuli whose intensity increases in fixed time following different forms. The objective stimulus increment, which the subjects perceive as linear growth directly, represents the inverse psychophysical relation. In this paper the method was tested in the fields of click frequency and sound pressure. This procedure was named "Perception of the Form of Stimulus Increment in Time". In comparison to other psychophysical approaches, this one has several advantages. The principal ones are the following: (1) In assessing the psychophysical relation it is not necessary to try to measure the perceptual magnitude; and (2) the psychophysical relation is directly determined by its dynamic pattern. In this paper modifications to the method are reported which facilitate the subject's task and avoid some differences in subjects' individual approaches to the task. The modified procedure leads to results satisfactory independent of the influence of the factors irrelevant to the psychophysical relationship.
Acoustic Stimulation↗
REVERSAL AND NONREVERSAL SHIFT LEARNING IN NORMAL CHILDREN AND RETARDATES OF COMPARABLE MENTAL AGE.
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Child↗