Attentive tracking of moving targets: Psychophysical and neuroimaging evidence for an attentional motion process

Attention may serve a tracking function which is central to many visual tasks, particularly when there are multiple targets which cannot all be followed with eye movements. Common examples include negotiating a busy crosswalk or attending to team-mates and opponents in sports. Attentive tracking serves to pursue targets of interest, producing an attention-based motion signal even for stimuli which may not drive low-level motion systems. A series of experiments examined the functional characteristics and underlying neurophysiology of this process.; The first experiments used psychophysical techniques to characterize the properties of the motion signals from attentive tracking. They demonstrated motion aftereffects (MAEs) of attentive tracking: prolonged attentive tracking subsequently makes an ambiguously flickering grating appear to move in the opposite direction. These MAEs were observed even though none were seen with static tests, suggesting the effects did not result from adaptation in low-level motion systems. MAEs of attentive tracking were independent of the adapting contrast and the retinal location of the test pattern, further suggesting that they occurred at relatively late stages of motion processing.; The second experiments used functional magnetic resonance imaging (fMRI) to examine the neurophysiological basis of attentive tracking. Subjects viewed a number of moving items and used attention to keep track of a subset of them. Attentive tracking, compared to passive viewing of the same display, lead to moderately enhanced activation in motion areas and robust activation in superior parietal cortex. The degree of activation was proportional to the number of items tracked in most areas, except the frontal eye fields which may play more of an oculomotor role. Comparisons with data from other stimuli and tasks suggested that the superior parietal lobe plays a key role in attentive tracking, attentional shifting, and eye movements.; These results provide evidence for an attentive tracking process which acts at multiple levels of visual processing and is not limited to effects on early motion systems. Results are considered in terms of a cognitive process in which attention and motion are closely coupled to keep track of individuated objects as they move through visual space.