Seeing Things Differently

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Science  28 Sep 2001:
Vol. 293, Issue 5539, pp. 2351-2353
DOI: 10.1126/science.293.5539.2351e

The visual system is traditionally regarded as being organized in a strongly hierarchical way. Early processing stages, such as area V1 (the primary visual cortex), perform their highly specialized task and then send this information to higher-order centers for analysis. Several findings have questioned this view. For instance, V1 neuronal responses are enhanced by attention when a monkey mentally traces a curve on a screen, but receptive fields on distracter curves are not enhanced. Interestingly, this attentional modulation, thought to come from higher order centers, occurs very late: several hundred milliseconds after the stimulus appears.

Now, Roelfsema and Spekreijse have varied the difficulty of separating the target and distracter curves, so that the monkey frequently makes errors distinguishing them. Responses of V1 neurons were enhanced if they fell on the curve that the monkey actually attended to even if it was not the correct choice (not the one that they were supposed to be attending to). These results strengthen the argument that V1 responses do not represent sensory input alone but can be modulated by top-down feedback, which can be a matter of interpretation. — PRS

Neuron31, 853 (2001).

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