Saturday, February 16, 2008

Visual Attention

Kanwisher, N. & Wojciulik, E. (November 2000). Visual Attention: Insights from Brain Imaging. Nature Reviews: Neuroscience, Volume 1, 91-98.

This review discusses four major questions related to attention's role in visual processing. First, where in the visual pathway does attention act? Second, what is able to be selected by attention? Third, how does attention affect neural responses? And fourth, where do attentional signals comes from?

Where in the visual pathway does attention act? It has been known for some time that substantial effects of attention can be found in the extrastriate cortex. However, it was not until recently that attentional modulation was discovered in earlier stages of the visual processing pathway (e.g. primary visual cortex). This may be more common when the processing load is considered high.

What gets selected by attention? Under different conditions, attention can select spatial locations, feature dimensions, whole visual objects, or even a combination thereof. However, these may not always be deployed with perfect control.

How does attention affect neural responses? Evidence exists which supports attention influence as being characterized as multiplicative (gain modulations) and/or additive (baseline shifts). And some postulate that increasing baseline activity in a neural population may bring these cells into a dynamic range where the same stimulus input will produce larger responses.

What is the source of attentional signals? Researchers have implicated the fronto-parietal network in providing top-down biasing signals to visual regions, and speculate that this system supports a very heterogeneous set of attention tasks.

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