Abstract
Perceiving solid objects involves extracting information about their 3D structure, often using a combination of motion and binocular cues. Little is known about how visual attention affects these processes. fMRI-studies suggest that objects can be selected as a unit of spatial attention [1] and that attending to features within objects can change responses across the visual field [2]. Do spatial and feature attention modulate cortical responses to stereoscopic structure-from-motion (SFM) stimuli? To direct spatial attention, a cue appeared before each trial, directing attention left or right. Two rotating SFM-cylinders appeared, one left and one right of the central fixation point. Subjects performed a behavioural task on the cued cylinder. The cortical response to spatial attention should give differences in fMRI-responses between the attended vs unattended cylinder in visual areas (V1–V7, LO1,LO2, hMT+), while feature attention should be revealed by different response to similar or dissimilar directions of rotations of the two cylinders. We found that spatial attention strongly increased responses in both dorsal and ventral visual areas in a retinotopic manner. Higher areas in the intra-parietal-sulcus and the frontal-eye-fields were also modulated. However, neither behavioural nor fMRI-responses reflected the featural similarity between the two cylinders. One mechanism for this could be the reallocation of spatial attention.
The cortical responses to SFM-cylinder are modulated by spatial attention, but not by feature attention based on similarity. Preliminary data suggest that behavioural relevance of the feature of interest may be required to modulate the responses at the level of component features.
O'CravenK. M.DowningP. E.KanwisherN. (1999). fMRI evidence for objects as the units of attentional selection. Nature, 401(6753), 584–587.
SaenzM.BuracasG. T.BoyntonG. M. (2002). Global effects of feature-based attention in human visual cortex. Nat Neurosci., 5(7), 631–632.
Supported by the James S McDonnell Foundation and the Wellcome Trust.