Art - DeYoe (P)

Helmholtz1 and William James2 each noted the potential dissociation between the point of gaze fixation and the focus of attention within the field of view. More recently, this phenomenon has been compared to a ‘spotlight’ that evokes attentional enhancement of visual information within a circumscribed region of visual space or within the confines of a target object3–5. Information inside the spotlight is processed more quickly or more efficiently, whereas outside the spotlight, information is processed “less, or differently, or not at all”6–8. However, the physiological basis of this spatially restricted attentional effect has remained obscure. Both neuroimaging and single-neuron studies have shown that visual attention can modulate responses in a number of visual areas9–17. It still remains controversial whether true attentional modulation occurs at the earliest stages of cortical processing such as primary visual cortex18. Although attention-related shifts of cortical activation have been observed previously19–21, there has not been a convincing demonstration that such shifts have a precise spatial metric concordant with a subject’s ability to accurately move the focus of attention. Here, we report experiments in which we used fMRI with human subjects to demonstrate focal enhancement of cortical activity that moves in precise register with covert shifts in the focus of attention. We show that these shifts are metrically accurate within the cortical representations of the visual field found in occipitotemporal visual cortex. (An animation of the cortical progression of attentional enhancement can be viewed at http://www.mcw.edu/cellbio/visionlab.)