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PubMed2005

Interactions between orientation and contrast modulations suggest limited cross-cue linkage.

Recent studies of texture segmentation and second-order vision have proposed very similar models for the detection of orientation modulation and contrast modulation (OM and CM). From the similarity of the models it is tempting to assume that the two cues might be processed by a single generalised texture mechanism; however, recent results (Kingdom et al, 2003 Visual Neuroscience 2 65-76) have suggested that these cues are detected independently, or at least in a mechanism that is able to maintain an apparent independence between the cues. We tested new combinations of OM and CM and found that CM at 0.4 cycle deg(-1) facilitates the detection of OM at 0.2 cycle deg(-1) when the peaks of contrast align with the extremes of orientation. There is also some evidence of weak facilitation of CM by OM under the same conditions. Further, this facilitation can be predicted by filter--rectify--filter channels optimised for the detection of each cue, adding weight to the argument that texture cues are processed in a single generalised mechanism that nonetheless achieves cue independence or near-independence in many circumstances. We also found that the amount of suprathreshold masking produced by an orientation cue depends on the overall percept formed by that cue.

Computational Biology↗
PubMed1992

Handwriting and perceptual-motor skills in clumsy, dysgraphic, and 'normal' children.

Among various perceptual-motor tests, only visuomotor integration was significant in predicting accuracy of handwriting performance for the total sample of 59 children consisting of 19 clumsy children, 22 nonclumsy dysgraphic children, and 18 'normal' children. They were selected from a sample of 360 fourth-graders (10-yr.-olds). For groups of clumsy and 'normal' children, the prediction of handwriting performance is difficult. However, correlations among scores on 6 measures showed that handwriting was significantly related to visuomotor integration, visual form perception, and tracing in the total group and to visuomotor integration and visual form perception in the clumsy group. The weakest correlations occurred between tests measuring simple psychomotor functions and handwriting. Moreover, clumsy children were expected to do poorly on tests measuring aiming, tracing, and visuomotor integration, but not on tests measuring visual form perception and finger tapping. Dysgraphic children were expected to do poorly on visuomotor integration only.

Child↗
PubMed1986

Temporal neocortical injuries in rats impair attending but not complex visual processing.

The effects of variations of the distance between the relevant stimuli and the animals' response sites were observed upon the performances of a black-white discrimination habit for normal rats or subjects prepared with either bilateral injuries to the visual or temporal neocortex. In addition, the animals were given a strict test of visual form perception. Subjects with injuries to the visual cortex failed the test of visual form perception but performed like normals in discriminating a spatially discontiguous problem. In contrast, subjects with temporal injuries exhibited enormous performance deficits when trained on a spatially discontiguous problem but performed like normals on the test of form perception. The findings parallel the results of studies using primates and suggest that bitemporal injuries result in impairments of attending and not of complex visual processing.

Animals↗
PubMed1980

Depicted angle of forms and perception of line drawings.

Subjects were presented with projections of either rectangular or elliptic forms which appeared either on their own or upon the following figures: (a) a face of a portrayed cube, (b) a parallelogram identical with (a), and (c) a rectangle of equal width and area to (a). Four different angles of projection were used for both the forms and for the background figures. In the composite figures these angles were varied independently. The subjects were required to judge the width of the forms. The forms were judged to be wider when presented on backgrounds (a) and (b) than when presented on background (c) or alone, especially at greater angles of projection. This suggests that the implicit-shape constancy effect is independent of relational effects resulting from the frame surrounding the form.

Adult↗
PubMed1997

Visual motion perception after brain damage: II. Deficits in form-from-motion perception.

We investigated form-from-motion perception (FFM perception) in a sample of 39 patients with acquired brain damage. Pronounced FFM deficits were found in two patients (FM1 and FM2) with biparietal lesions. Both patients were able to identify the relevant figure, when it was not embedded in obstructive texture. Moreover, they could localize the figures in the FFM condition, although they could not reliably identify them. The two patients had normal motion coherence thresholds. Their performance in a static figure-ground task did not differ from that of other patients. These findings imply that the FFM deficits are not caused by impairment of basic visual motion or form perception but are the consequence of damage to a parietal brain structure involved in the combined analysis of visual motion and form information. The nature and functional role of this brain structure as well as the implications of our results for models of FFM perception are discussed.

Adult↗
PubMed1996

The relative efficacy of cues for two-dimensional shape perception.

The visual system uses a variety of cues for form perception, including motion, color, binocular disparity, texture, and luminance. Physiological evidence suggests that these cues are processed by different neural mechanisms. Do the cues processed by some mechanisms convey any advantage for form perception when compared to cues processed by another? In response to this question we assessed the relative efficiency of several cues in conveying two-dimensional form from background noise. For the sake of comparison, every cue type used the same experimental design and stimulus set. Our results confirm that movement is one of the most efficient cues for shape perception. Also, a simple transient cue (an instantaneous flashing on or off) is equally useful. In comparison, local dot density (a type of texture cue) was the least efficient. The efficiencies of most other cues, such as color, stereopsis, and relative movement in noise, were conspicuously similar.

Adult↗
PubMed1993

Neural dynamics of motion perception: direction fields, apertures, and resonant grouping.

A neural network model of global motion segmentation by visual cortex is described. Called the motion boundary contour system (BCS), the model clarifies how ambiguous local movements on a complex moving shape are actively reorganized into a coherent global motion signal. Unlike many previous researchers, we analyze how a coherent motion signal is imparted to all regions of a moving figure, not only to regions at which unambiguous motion signals exist. The model hereby suggests a solution to the global aperture problem. The motion BCS describes how preprocessing of motion signals by a motion oriented contrast (MOC) filter is joined to long-range cooperative grouping mechanisms in a motion cooperative-competitive (MOCC) loop to control phenomena such as motion capture. The motion BCS is computed in parallel with the static BCS of Grossberg and Mingolla (1985a, 1985b, 1987). Homologous properties of the motion BCS and the static BCS, specialized to process motion directions and static orientations, respectively, support a unified explanation of many data about static form perception and motion form perception that have heretofore been unexplained or treated separately. Predictions about microscopic computational differences of the parallel cortical streams V1-->MT and V1-->V2-->MT are made--notably, the magnocellular thick stripe and parvocellular interstripe streams. It is shown how the motion BCS can compute motion directions that may be synthesized from multiple orientations with opposite directions of contrast. Interactions of model simple cells, complex cells, hyper-complex cells, and bipole cells are described, with special emphasis given to new functional roles in direction disambiguation for endstopping at multiple processing stages and to the dynamic interplay of spatially short-range and long-range interactions.

Animals↗
PubMed2006

Mechanism of neurophysiological treatment of amblyopia using functional magnetic resonance imaging.

PURPOSE: To research the mechanism of neurophysiological treatment of amblyopia by observing the visual cortex activation under rotating grating stimulus with functional magnetic resonance imaging (MRI), and identify the components of the activation. METHODS: Nine healthy volunteers were examined using gradient-recalled echo and echo-planar imaging (GRE-EPI) pulse sequence performed at the 1.5 Tesla MRI scanner. In the block designing, rotating grating, stationary grating and luminance were plotted as task states, stationary grating, luminance and darkness as control states, respectively. The tasks of stimuli included 6 steps. Imaging processing and statistical analysis were carried out off-line using statistical parametric mapping (SPM99) software in single-subject. RESULTS: Some individual areas of visual cortex were activated by various stimuli information supplied by rotating grating. The strong activation in the middle of occipital lobe related to the stimuli of luminance, bilateral activation of Brodmann's 19th area related to visual motion perception, and the mild activation in the middle of occipital lobe related to form perception. CONCLUSION: The plotting of control state is important in bock design. The effective visual information of rotating grating includes components of luminance, visual motion perception and form perception. Functional MRI has potential as a tool for studying the physiological mechanism of visual cortex.

Adult↗
PubMed1987

Psychophysical evidence for separate channels for the perception of form, color, movement, and depth.

Physiological and anatomical findings in the primate visual system, as well as clinical evidence in humans, suggest that different components of visual information processing are segregated into largely independent parallel pathways. Such a segregation leads to certain predictions about human vision. In this paper we describe psychophysical experiments on the interactions of color, form, depth, and movement in human perception, and we attempt to correlate these aspects of visual perception with the different subdivisions of the visual system.

Color Perception↗
PubMed1995

Regeneration of specific nerve cells in lesioned visual cortex of the human brain: an indirect evidence after constant stimulation with different spots of light.

The defective parts of the visual field of two brain-injured patients were stimulated with different spots of light. There is evidence for at least five independent visual functions which can be restored due to constant stimulation of the blind part of the visual field: (1) The constant stimulation of the blind part of the visual field with spots of white light leads to an increase of the visual field for the perception of white light only. (2) The constant stimulation with spots of light of different wavelengths leads to an increase of the visual field for different color perception. To enlarge the visual field for the perception of the color red, a light stimulus with the wavelength of 656 nanometers (nm) was used; for the visual field for the perception of the color green 525 nm; for yellow 578 nm; and for blue 450 nm. (3) The constant stimulation of the blind visual field with black and white light bars of different orientations and constellations leads to an increase of the foveal acuity and an improvement of form perception in the periphery of the visual field. The results suggest that the recovery of visual functions, different color perception and form perception, may depend upon neuronal regeneration in the human visual cortex; regeneration occurs with adequate and constant stimulation of its specific neurons.

Adolescent↗
PubMedDate not supplied

[The characteristics of the forms of perceptive and cognitive activities in adolescent chimpanzees].

The study of cognitive activity in four 4-6-year-old chimpanzees was carried out during visual their discriminating and summarizing of signals (pictures of natural objects and volume figures). It was established that apes were able to compare the signals according to their size. Chimpanzees were successful in transferring their experience from one image type to another. The data obtained proof that apes were able to summarize, operate with abstract ideas and think logically.

Aging↗
PubMed2006

Delayed response to animate implied motion in human motion processing areas.

Viewing static photographs of objects in motion evokes higher fMRI activation in the human medial temporal complex (MT+) than looking at similar photographs without this implied motion. As MT+ is traditionally thought to be involved in motion perception (and not in form perception), this finding suggests feedback from object-recognition areas onto MT+. To investigate this hypothesis, we recorded extracranial potentials evoked by the sight of photographs of biological agents with and without implied motion. The difference in potential between responses to pictures with and without implied motion was maximal between 260 and 400 msec after stimulus onset. Source analysis of this difference revealed one bilateral, symmetrical dipole pair in the occipital lobe. This area also showed a response to real motion, but approximately 100 msec earlier than the implied motion response. The longer latency of the implied motion response in comparison to the real motion response is consistent with a feedback projection onto MT+ following object recognition in higher-level temporal areas.

Adult↗
PubMed1992

Projective invariance and the kinetic depth effect.

Seven experiments test the assumption that, in the kinetic depth effect, observers have reliable and direct access to the equivalence of shapes in projective geometry. The assumption is implicit in 'inverse optics' approaches to visual form perception. Observers adjusted a comparison shape to match a standard shape; both standard and comparison were portrayed as in continuous rotation in space, using a graphics computer. The shapes were either plane quadrilaterals or solid prisms. The angular difference of the planes of the shapes was varied, as was the dot density of a texture in those planes. Departure from projective equivalence was measured in six studies by measuring the planar analogue of cross ratio, and in a seventh by measuring the cross ratio for points in space. Projective equivalence was not found to be perceived uniformly, except in one experiment that did not involve rotation in depth. Otherwise changes in orientation of up to 180 degrees about a single coordinate axis had no significant effect on matches in shape, while changes in orientation about more than one coordinate axis produced significant effects. The addition of texture and a change in rotation speed did not correct departures from projective equivalence.

Adult↗
PubMed1995

The McCollough effect reveals orientation discrimination in a case of cortical blindness.

BACKGROUND: The McCollough effect is a colour after-effect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns--such as a red-and-black vertical grating and a green-and-black horizontal grating--are viewed alternatively for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. RESULTS: Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90 degrees differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. CONCLUSIONS: These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.

Adult↗
PubMed1989

Ordinal structure in the visual perception and cognition of smoothly curved surfaces.

In theoretical analyses of visual form perception, it is often assumed that the 3-dimensional structures of smoothly curved surfaces are perceptually represented as point-by-point mappings of metric depth and/or orientation relative to the observer. This article describes an alternative theory in which it is argued that our visual knowledge of smoothly curved surfaces can also be defined in terms of local, nonmetric order relations. A fundamental prediction of this analysis is that relative depth judgments between any two surface regions should be dramatically influenced by monotonicity of depth change (or lack of it) along the intervening portions of the surface through which they are separated. This prediction is confirmed in a series of experiments using surfaces depicted with either shading or texture. Additional experiments are reported, moreover, that demonstrate that smooth occlusion contours are a primary source of information about the ordinal structure of a surface and that the depth extrema in between contours can be optically specified by differences in luminance at the points of occlusion.

Cognition↗