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Results for “FORM PERCEPTION”

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PubMed1992

Haptic dominance in form perception: vision versus proprioception.

An experiment placed vision and touch in conflict by the use of a mirror placed perpendicular to a letter display. The mirror induced a discrepancy in direction and form. Subjects touched the embossed tangible letters p, q, b, d, W, and M, while looking at them in a mirror, and were asked to identify the letters. The upright mirror produced a vertical inversion of the letters, and visual inversion of the direction of finger movement. Thus, subjects touched the letter p, but saw themselves touching the letter b in the mirror. There were large individual differences in reliance on the senses. The majority of the subjects depended on touch, and only one showed visual dominance. Others showed a compromise between the senses. The results were consistent with an attentional explanation of intersensory dominance.

Adult↗
PubMed1991

The role of the superior colliculus in facilitating visual attention and form perception.

When interhemispheric transfer in cats is studied from an intact hemisphere to a hemisphere with a suprasylvian cortical lesion, excellent transfer of grating discriminations, but no transfer of forms, is present. Stimuli with global, repetitive features covering a large visual field (gratings), which can be discriminated by preattentive vision, are transferred; perception of stimuli with local features (forms), which require serial exploration using focal vision, is defective in the hemisphere with cortical lesion and transfer is lacking. Influence of the midbrain in facilitating focal vision is shown by the restoration of form discriminations after section of the superior collicular commissure. It is hypothesized that the perceptual defect after lesion in the suprasylvian cortex is due to poor spatial attention and its restoration after midbrain lesion is due to improved function of those collicular cells that mediate orienting of attention.

Animals↗
PubMed1984

Force of symmetry in form perception.

Many objects, natural and manufactured, have at least one axis of symmetry; thus, the detection of symmetry could facilitate the detection and representation of objects. Literature is reviewed that supports the notion that humans have effective and efficient symmetry-detection ability. The question addressed in the present research is whether symmetry detection leads to biases in representations of visual forms. Two types of experimental tasks were used: a similarity-judgment task and a matching-figures task in which reaction time to find identical figures in a display was measured. Stimuli varied in degree of measured symmetry. The results of the experiments reported here indicate that nearly symmetric standard forms are judged to be more similar to, and are more confusable with, even more symmetric forms than they are with less symmetric forms. The pull toward a more symmetric form does not occur for standard forms of lower symmetry. These findings can be accounted for by a two-stage process. First, the perceiver quickly determines the presence of overall symmetry. Then, if the form is perceived as having overall symmetry, the form is assumed, sometimes incorrectly, to have symmetry at the local level as well.

Discrimination Learning↗
PubMed1977

Form perception in stumptail macaques following posterior parietal and lateral frontal lesions.

Monkeys with bilateral posterior parietal and lateral frontal ablations were compared with normal animals on a series of four tests for their ability to relate elements of a visual pattern on the basis of the Gestalt principle of proximity. The operated animals showed no clear impairment on these tests of perceptual grouping. The three groups of monkeys were then trained to discriminate two faces and tested for generalisation to different views of the same faces. The pariental-operated monkeys showed less generalisation than the other animals to lateral mirror-images of the training stimuli, but more generalisation to inverted mirror-images. It is concluded that any deficit in "gestalt" perception following such lesions must be at a relatively high level.

Animals↗
PubMed1988

The role of the right hemisphere in form perception and visual gnosis organization.

Peculiarities of series of picture interpretations and Rorschach test results in patients with unilateral benign hemispheric tumours are discussed. It is concluded that visual perception in the right hemisphere has hierarchic structure, i.e., each successive area from the occipital lobe towards the frontal having a more complicated function. Visual engrams are distributed over the right hemisphere in a manner similar to the way the visual information is recorded in holographic systems. In any impairment of the right hemisphere a tendency towards whole but unclear vision arises. The preservation of lower levels of visual perception provides for clear vision only of small parts of the image. Thus, confabulatory phenomena arises, which are specific for right hemispheric lesions.

Adult↗
PubMedDate not supplied

[Relationship between indicators of equilibrium function and spatial-form perception in children with posture disorders].

The balance function and spatial-figurative thinking (SFT) of children aged 7 to 9 with and without disturbances of bearing were studied. A negative correlation was revealed between balance function and SFT in children with disordered bearing. The results of this study should be taken into account when carrying out hygienic measures for the prevention of bearing disorders in children.

Child↗
PubMed1990

Form perception and visual acuity in a chimpanzee.

A 6.5-year-old female chimpanzee learned to distinguish perfectly every letter of the alphabet in a matching-to-sample task with 26 letters as choice alternatives. Confusion of letters during the initial training was used to scale them in a multidimensional similarity space and to associate them in hierarchical clusters. The results resembled those obtained from similarity judgements by humans. Using letters of various sizes, a visual acuity test revealed that the chimpanzee's acuity was about 1.5, comparable to that in normal humans. The chimpanzee also readily learned to use letters as names of individual humans and chimpanzees. A species-typical feature was identified in the perceptual processes associated with complex forms, such as those involved in individual recognition.

Algorithms↗
PubMed1989

The effect of movement velocity on form perception: geometric illusions in dynamic displays.

We investigated the effects of movement velocity on the perception of simple geometric trajectories. We show that when an ellipse is traced by the continuous displacement of a spot against an empty background, the subjective aspect ratio (R = vertical axis/horizontal axis) of the figure depends on the law of motion of the spot. If the tangential velocity of the spot is constant, very large and subject-specific biases emerge in the perception of the aspect ratio. If the tangential velocity of the spot is made equal to that of an elliptic motion with aspect ratio R less than 1, and resulting from the vectorial composition of two harmonic functions (Lissajous motion) there is a general trend to perceive the ellipse as being flatter than in reality. The effect, however, is not symmetric: when the velocity follows a Lissajous modulation with R greater than 1, highly significant biases are still present in most subjects, but no common trend emerges from the experimental population. The results are discussed in the context of recent findings on the relationship between form and kinematics in spontaneous human movements.

Acceleration↗
PubMedDate not supplied

Psychophysical measures of illusory form perception: further evidence for local mechanisms.

Detection thresholds for a small light spot were measured at various distances from configurations (Kanizsa squares and other) consisting of white inducing elements on a dark background. Threshold distributions as a function of target position, number, size and spacing of contrast inducing elements were established. The data show that thresholds are elevated when the target is located close to one or more inducing element(s). Furthermore, threshold elevations diminish with increasing distance of the target from the configurations, increasing spacing and decreasing size of their inducing elements. When the target is flashed upon an illusory contour, no threshold elevation is observed in any of the conditions tested. Within incomplete illusory figures (only half of the square visible), the threshold gradients show the same tendencies. The present observations add further empirical support to the idea that illusory figures are built up by way of local mechanisms at early stages of processing.

Form Perception↗
PubMed1975

Visual form perception in deficient and normal readers as a function of age and orthographic-linguistic familiarity.

The present investigation directly assessed the hypothesis that poor readers sustain no basic disorder in visual-spatial functioning. In order to extend pervious results to younger children, the performance of poor and normal readers from both the second and sixth grades was compared. Adopting the format of an earlier investigation, a visual recall task was employed as the dependent variable, and it was predicted that poor readers would perform as well as normals with stimuli taken from Hebrew, an unfamiliar orthography. Accordingly, non-Hebrew poor and normal readers were compared with normal readers learning Hebrew on the production of varying length Hebrew words. As anticipated, children in the non Hebrew reader groups performed comparably on this task, but the performance of these subjects was inferior to that of children in the Hebrew groups. The data support the contention that visual perceptual disorder is an unlikely source of reading disability.

Age Factors↗
PubMed1991

Spatial organization of nonlinear interactions in form perception.

We examined the perception of structure in a family of visual textures whose second-order correlation structure is flat. These textures were generated by two-dimensional recursion rules, in a manner which extends the construction of Julesz, Gilbert and Victor (1978; Biological Cybernetics, 31, 137-140). Textures generated by some recursion rules elicited a visually salient percept of structure, while textures generated by other recursion rules did not. Textures whose statistical structure was visually salient produced evoked responses which differed from the response evoked by completely random textures. The size of this VEP difference correlated well with psychophysical measures. Since the textures were constructed to have identical global spatial frequency spectra, models for the extraction of visual structure must be essentially nonlinear. Models based on symmetry, information content, or simple spatial extent (but not pattern) of correlation fail to explain the observed results. Models based on the cooperative interaction of pairs of nonlinear subunits provide a reasonable qualitative account of the findings. The critical model features are (i) the presence of multiple nonlinear subunits, and (ii) a second nonlinearity, such as a threshold, at the stage of combination of subunit signals.

Adult↗