The prevalent view of binocular rivalry holds that it is a competition between the two eyes mediated by reciprocal inhibition among monocular neurons. This view is largely due to the nature of conventional rivalry-inducing stimuli, which are pairs of dissimilar images with coherent patterns within each eye's image. Is it the eye of origin or the coherency of patterns that determines perceptual alternations between coherent percepts in binocular rivalry? We break the coherency of conventional stimuli and replace them by complementary patchworks of intermingled rivalrous images. Can the brain unscramble the pieces of the patchwork arriving from different eyes to obtain coherent percepts? We find that pattern coherency in itself can drive perceptual alternations, and the patchworks are reassembled into coherent forms by most observers. This result is in agreement with recent neurophysiological and psychophysical evidence demonstrating that there is more to binocular rivalry than mere eye competition.
A closed curve is much more than an incomplete one: Effect of closure in figure- Contributed by Bela Julesz, May 18, 1993 ABSTRACT Detection of fragmented closed contours gainst a cluttered background occurs much beyond the local coherence distance (maximal separation between seents) of nondosed contour. This Impli that the extent of interaction between locafly connet detectors I boosted accrding to the global stimulus structure. We further show that detectio of a target probe Is facilitated when the probe is positioned indde a dosed circle. To explain the srikig contour segetion ability found here, and performance enhancement inside cloed boundaries, we propose the existence of a synergetic process in early vision.
Visual development is thought to be completed at an early age. We suggest that the maturation of the visual brain is not homogeneous: functions with greater need for early availability, such as visuomotor control, mature earlier, and the development of other visual functions may extend well into childhood. We found significant improvement in children between 5 and 14 years in visual spatial integration by using a contour-detection task. The data show that long-range spatial interactions-subserving the integration of orientational information across the visual field-span a shorter spatial range in children than in adults. Performance in the task improves in a cue-specific manner with practice, which indicates the participation of fairly low-level perceptual mechanisms. We interpret our findings in terms of a protracted development of ventral visual-stream function in humans. Human visual development has been considered to be relatively fast and to give way to cognitive development after the basic visual functions are established in infancy, e.g., a very early preference for moving stimuli (1); the ability to process complex motion information at 4 months (2); color (3) and depth (4) discrimination also at around 4 months; and rapidly increasing acuity during the first year (5). However, human anatomical data indicate that, although the gross anatomical structure is constructed before birth, the maturation of neuronal circuits of the visual cortex may extend well into childhood (6, 7). More recent studies even raise the possibility of a significant increase in the number of cortical cells between birth and 6 years of age (8), implying a strikingly extended structural maturation of the human cortex, including the early visual areas (9). In light of these results, the question arises as to whether the maturation of human vision really comes to an end by the first or second year of life.Although behavioral studies of human visual development beyond the second year of age are rare, there is indication that children may encounter problems in tasks involving integration of information across the visual field for object representation: visual segmentation and form identification based on contrasts in texture (10, 11), motion (12), or color (13) and recognition of incomplete objects (14). Here, we directly test the development of visual spatial integration in a contour-detection task. We find that children (aged 5-14 years) perform poorly in the task compared with adults. Our control results clearly show that perceptual immaturity lies behind the poor performance. The results also suggest that there is immaturity at the level of long-range spatial interactions that might span a shorter spatial range in children than in adults. Experiment 1: Human Development of Spatial IntegrationTo segment the visual image and to form object boundaries in the course of perceptual organization, local orientational information extracted by selectively tuned neurons has to be integrated across the visual field. The efficiency of the integra...
Two relevant dimensions are revealed within which developmental patterns of perceptual organization might be investigated. Within the local-integrative dimension, employing a contour integration task, we found indications that spatial integration develops slowly. We also found reduced contextual modulation of a local target in children employing the Ebbinghaus illusion. Within the action-perception dimension, we hypothesize a relatively slow development of the perceptual system (mediated by the ventral visual stream), as compared to the development of the action system (mediated by the dorsal visual stream). Taken together, the data indicate that long-range neuronal connectivity supporting perceptual organization in the posterior pole of the brain, and in the ventral visual pathway is not fully developed in young children.
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