We recorded from over 50 direction-selective cells in the superior temporal sulcus of a macaque monkey performing a reaction-time task to investigate the role of attention in the processing of motion signals. The monkey was trained to attend a moving spot (the target) in the presence of one or more other moving spots (distractors) while maintaining fixation on a stationary fixation cross. In the first experiment one spot moved through the receptive field (RF) in the preferred direction while another spot moved outside the RF. Even though retinal stimulation was identical in both trial types a large majority of the cells (~85%) responded more strongly when the animal was instructed to attend to the stimulus within the RF, compared to trials on which he was attending the stimulus outside the RF (median increase 30%). In the second experiment both spots moved through the RF, but in opposite directions (preferred and anti-preferred direction of the neuron). Almost all cells (~90%) responded more strongly when the monkey was instructed to attend to the stimulus moving in the preferred direction, compared to trials in which he was attending the spot moving in the anti-preferred direction (median increase 150%). This result cannot be accounted for by shrinking receptive fields since it held true even when the two dots passed by each other very closely.
Our results demonstrate that while moving attention away from the receptive field will reduce a neuron╣s response to its preferred stimulus a much stronger effect can be observed when attention is switched between two stimuli that both fall within the receptive field. In that case the response of the neuron is strongly biased by the direction of motion of the attended stimulus even when the unattended stimulus is a more potent sensory stimulus. These findings are amongst the strongest extraretinal modulations of neural signals found in visual cortex to date and suggest an important role for attention in selectively enhancing neural signals related to stimuli of interest.