Abstract
Directing visual attention to spatial locations or to non-spatial stimulus features can strongly modulate responses of individual cortical sensory neurons. Effects of attention typically vary in magnitude, not only between visual cortical areas but also between individual neurons from the same area. Here, we investigate whether the size of attentional effects depends on the match between the tuning properties of the recorded neuron and the perceptual task at hand. We recorded extracellular responses from individual direction-selective neurons in the middle temporal area (MT) of rhesus monkeys trained to attend either to the color or the motion signal of a moving stimulus. We found that effects of spatial and feature-based attention in MT, which are typically observed in tasks allocating attention to motion, were very similar even when attention was directed to the color of the stimulus. We conclude that attentional modulation can occur in extrastriate cortex, even under conditions without a match between the tuning properties of the recorded neuron and the perceptual task at hand. Our data are consistent with theories of object-based attention describing a transfer of attention from relevant to irrelevant features, within the attended object and across the visual field. These results argue for a unified attentional system that modulates responses to a stimulus across cortical areas, even if a given area is specialized for processing task-irrelevant aspects of that stimulus.
Highlights
Visual attention is the mechanism that selectively modulates sensory processing according to behavioral relevance
We found that effects of spatial and feature-based attention in middle temporal area (MT), which are typically observed in tasks allocating attention to motion, were very similar even when attention was directed to the color of the stimulus
Our data are consistent with theories of object-based attention describing a transfer of attention from relevant to irrelevant features, within the attended object and across the visual field.These results argue for a unified attentional system that modulates responses to a stimulus across cortical areas, even if a given area is specialized for processing task-irrelevant aspects of that stimulus
Summary
Visual attention is the mechanism that selectively modulates sensory processing according to behavioral relevance. Numerous single-unit studies in awake behaving primates have documented neural correlates of spatial and feature-based attention in various areas of visual cortex (reviewed in Desimone and Duncan, 1995; Treue, 2001; Reynolds and Chelazzi, 2004; Maunsell and Treue, 2006). The neural correlate of spatial attention consists of an increase in firing rates if attention is directed to the stimulus inside the receptive field (RF) of the recorded neuron, as opposed to somewhere else. The neural correlate of feature-based attention consists of an increase in firing rates if the attended feature matches the preferences of the neuron under study, independent of the spatial focus of attention (note that the term ‘feature’ refers to a particular property within a given stimulus dimension, e.g., upwards motion is a feature within the stimulus dimension of motion, and blue is a feature within the stimulus dimension of color). Few single-unit studies have investigated neural correlates of object-based attention (Roelfsema et al, 1998; Fallah et al, 2007; Wannig et al, 2007)
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