Effects of attention on the processing of motion in macaque middle temporal and medial superior temporal visual cortical areas

The visual system is continually inundated with information received by the eyes. Only a fraction of this information appears to reach visual awarenes s. This process of selection is one of the functions ascribed to visual att ention. Although many studies have investigated the role of attention in sh aping neuronal representations in cortical areas, few have focused on atten tional modulation of neuronal signals related to visual motion. We recorded from 89 direction-selective neurons in middle temporal (MT) and medial sup erior temporal (MST) visual cortical areas of two macaque monkeys using ide ntical sensory stimulation under various attentional conditions. Neural res ponses in both areas were greatly influenced by attention. When attention w as directed to a stimulus inside the receptive field of a neuron, responses in MT and MST were enhanced an average of 20 and 40% compared with a condi tion in which attention was directed outside the receptive field. Even stro nger average enhancements (70% in MT and 100% in MST) were observed when at tention was switched from a stimulus moving in the nonpreferred direction i nside the receptive field to another stimulus in the receptive field that w as moving in the preferred direction. These findings show that attention mo dulates motion processing from stages early in the dorsal visual pathway by selectively enhancing the representation of attended stimuli and simultane ously reducing the influence of unattended stimuli.