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The visual cortex has the capacity for experience-dependent change, or cortical plasticity, that is retained throughout life. Plasticity is invoked for encoding information during perceptual learning, by internally representing the regularities of the visual environment, which is useful for facilitating intermediate-level vision—contour integration and surface segmentation. The same mechanisms have...
The functional architecture of adult cerebral cortex retains a capacity for experience-dependent change. This is seen following focal binocular lesions, which induce rapid changes in receptive field size and position. To follow the dynamics of the circuitry underlying these changes, we imaged the intrinsic long-range horizontal connections within the lesion projection zone (LPZ) in adult macaque primary...
In complex visual scenes, linking related contour elements is important for object recognition. This process, thought to be stimulus driven and hard wired, has substrates in primary visual cortex (V1). Here, however, we find contour integration in V1 to depend strongly on perceptual learning and top-down influences that are specific to contour detection. In naive monkeys, the information about contours...
All cortical and thalamic levels of sensory processing are subject to powerful top-down influences, the shaping of lower-level processes by more complex information. New findings on the diversity of top-down interactions show that cortical areas function as adaptive processors, being subject to attention, expectation, and perceptual task. Brain states are determined by the interactions between multiple...
Contour integration is an important intermediate stage of object recognition, in which line segments belonging to an object boundary are perceptually linked and segmented from complex backgrounds. Contextual influences observed in primary visual cortex (V1) suggest the involvement of V1 in contour integration. Here, we provide direct evidence that, in monkeys performing a contour detection task, there...
While recent studies of synaptic stability in adult cerebral cortex have focused on dendrites, how much axons change is unknown. We have used advances in axon labeling by viruses and in vivo two-photon microscopy to investigate axon branching and bouton dynamics in primary visual cortex (V1) of adult Macaque monkeys. A nonreplicative adeno-associated virus bearing the gene for enhanced green fluorescent...
Learning in shape identification led to global changes in activation across the entire visual pathway, as revealed with whole-brain fMRI. Following extensive training in a shape identification task, brain activity associated with trained shapes relative to the untrained shapes showed: (1) an increased level of activity in retinotopic cortex (RC), (2) a decrease in activation of the lateral occipital...
Two components of cortical circuits could mediate contour integration in primary visual cortex (V1): intrinsic horizontal connections and feedback from higher cortical areas. To distinguish between these, we combined functional mapping with a new technique for labeling axons, a recombinant adenovirus bearing the gene for green fluorescent protein (GFP), to determine the extent, density, and orientation...
Perceptual learning is a lifelong process. We begin by encoding information about the basic structure of the natural world and continue to assimilate information about specific patterns with which we become familiar. The specificity of the learning suggests that all areas of the cerebral cortex are plastic and can represent various aspects of learned information. The neural substrate of perceptual...
The response properties of cells in the primary visual cortex (V1) were measured while the animals directed their attention either to the position of the neuron’s receptive field (RF), to a position away from the RF (focal attention), or to four locations in the visual field (distributed attention). Over the population, varying attentional state had no significant effect on the response to an isolated...
Brightness discrimination thresholds and facilitation by lateral interaction were measured in five human observers and two monkeys. The subjects judged the brightness of one of four peripherally seen lines against a reference. This experiment was performed both when the observer was cued to the position of the test line (focused attention) and when there was no cue (distributed attention). Discrimination...
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