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Pszichológia
Authors:
László Séra
,
György Révész
,
Dóra Vajda
, and
Róbert Járai

. Chandna , A. , Pennefather , P. M. , Kovács , I. , Norcia , A. M. ( 2001 ): Contour integration deficits in anisometropic amblyopia . Investigative Ophthalmology and Visual Science , 42 ( 3 ), 875 – 878

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of neocortex. Neuron, 56 (2), 226–238. Field, D. J., Hayes, A., Hess, R. F. (1993): Contour integration by the human visual system: evidence for a local “association field”. Vision Res, 33 (2), 173

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The primary visual cortex (V1) of the mammalian brain is equipped with a specifically connected network of neurons that can potentially solve difficult image processing tasks. These neurons are selectively tuned for locations in visual space and also for line orientation. The coupling of location and orientation tuning results in the neural representation of the visual world in terms of local features. These local features, e.g., oriented line segments, will have to be linked together in order to parse the visual world into regions corresponding to object and ground. Although standard models of V1 do not address the issue of interacting neuronal populations, we suggest that the long-range connectivity pattern of V1 provides an architecture where spreading neural activity may lead to pertinent figure-ground segmentation. The model relies on the fact that in addition to the processing units, their connections are also selectively tuned for space and orientation. From the computational point of view, the model uses a minimalist approach that applies the fundamental concepts of Gestalt psychology – proximity, similarity and continuity – to the spreading of neuronal activation signals. This model is successful in predicting psychophysical performance of human observers, and provides an account of the computational power of V1.

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Abstract

Perceptual organization (PO) impairments have been repeatedly demonstrated in schizophrenia. The extent to which these impairments can be reduced or eliminated, however, has received less attention, and evidence on this issue has not been previously reviewed. The literature suggests that whether normal experience-dependent change in perceptual organization occurs in schizophrenia depends on factors such as: stimulus grouping strength, extent of practice, type of cues upon which top-down feedback can be generated, and patient characteristics (trait and state). Therefore, the purpose of this paper is to review and synthesize the available evidence on plasticity and other forms of change in PO in schizophrenia, and to relate it to current data and theories on plasticity, including perceptual learning (PL) in healthy people. This can clarify the computational and neural mechanisms involved in experience-dependent and state-related aspects of PO in schizophrenia, and also contribute to a greater understanding of the mechanisms involved in normal PL. A major finding that emerges from a review of the data is that the conditions under which PL of PO does not occur in schizophrenia closely parallel the conditions under which PO is reduced in a single test administration. That is, when stimulus-driven cues to grouping are strong, PL of PO occurs in patients; in contrast, when top-down feedback is required to organize novel or weakly grouped stimuli, PL of PO tends not to occur in patients. Moreover, even with strongly grouping stimuli, change tends to occur only via repetition; when processing of more abstract cues is required to generate top-down feedback, change tends not to occur. In addition, within-session PL in people with schizophrenia appears to be more impaired than learning over multiple days, supporting the separability of fast and slow plasticity mechanisms; however, more research with a larger class of stimuli is needed on this issue.

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Abstract

In our everyday interactions we encounter a plethora of novel experiences in different contexts that require prompt decisions for successful actions and social interactions. Despite the seeming ease with which we perform these interactions, extracting the key information from the highly complex input of the natural world and deciding how to interpret it is a computationally demanding task for the visual system. Accumulating evidence suggests that the brain solves this problem by combining sensory information and previous knowledge about the environment. Here, we review the neural mechanisms that mediate experience-based plasticity and shape perceptual decisions. We propose that learning plays an important role in the adaptive optimization of visual functions that translate sensory experiences to decisions by shaping neural representations across cortical circuits in the primate brain.

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. Gervan , P. & Kovacs , I. (in press,) 2010 ). Sleep dependent modulation of learning in contour integration . Journal of Vision . A. Karni D

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