A deficit of intermediate vision: Experimental observations and theoretical implications

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Abstract
The nervous system constructs visual representations hierarchically. Elementary features are extracted from the visual scene and grouped to form candidate objects, which may then be selected for attentional scrutiny. We wished to learn if intermediate vision (pre-attentive and effortiess grouping processes) can be damaged selectively and, if so, what the consequences of such damage might be. We present a patient with slgnificant visual disabilities following a traumatic brain injury. Her early vision was preserved. However, she had a deficit of intermediate vision as evidenced by an inability to: (i) link visual attributes into perceptual wholes effortlessly, (ii) search for visual targets pre-attentively and (iii) accurately perceive illusory contours. By contrast, she could deploy attention both panoramically and selectively. She also recognized real objects and described pictures. We conclude that intermediate vision can be damaged selectively. Attention can be deployed on a visual scene which has not been pre-attentively parsed. Grouping processes are not needed to recognize objects. Our findings suggest that the hierarchical organization of visual processing is more Interactive than implied by serlal feed-forward models.

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