Attention-modulated activity in visual cortex-More than a simple 'spotlight'

We assessed modulation of retinotopic visual cortex representing peripheral regions of the visual field while subjects engaged in a central attention task. The onset of an attention capturing central letter stream attenuated activity in representations of the peripheral locations. When these locations were empty, the observed reduction was the same whether subjects passively viewed or actively attended the letter stream. For locations containing distracting letters, however, an additional attenuation was observed during the active task. In a second experiment we found that representations of target incompatible peripheral letters were suppressed relative to a control task, whereas at the same time representations of compatible peripheral letters were relatively enhanced. The fMRI results are complemented by behavioral data demonstrating prolonged responses to probes presented at suppressed locations. In sum, our study suggests that activity modulation across the visual field representation not only reflects an attentional spotlight effect but is additionally shaped by the nature of sensory input at unattended locations as well as its relation to task demands.