Abstract
Attending a certain region in space enhances activity in visual areas retinotopically mapped to this region; stimuli presented in this region are preferentially processed. The zoom lens model of visual attention proposes that the attended region can be adjusted in size and predicts a tradeoff between its size and processing efficiency because of limited processing capacities. By means of event-related functional magnetic resonance imaging, we analyzed neural activity in multiple visual areas as a function of the size of an attended visual field region, which was defined by a spatial cue stimulus. After cueing, a target object, defined by a specific feature conjunction, had to be identified among objects within the cued region. Neural activity preceding the objects in multiple retinotopic visual areas correlated with the size of the attended region, as did subjects' performance. While the extent of activated retinotopic visual cortex increased with the size of the attended region, the level of neural activity in a given subregion decreased. These findings are consistent with the physiological predictions of the zoom lens model. Size-related modulations of neural activity were pronounced in early visual areas. We relate this finding to the small receptive field of these areas, whereby only neuronal units with receptive fields covering the attended region received a top-down bias. This preactivation of neuronal units may then have gated selective processing of the features of the object that appeared at the attended location, thus enabling feature integration and object identification.
Highlights
Typical visual scenes contain a variety of different objects, which because of the limited processing capacity of the visual system cannot be all processed simultaneously
By means of event-related functional magnetic resonance imaging, we analyzed neural activity in multiple visual areas as a function of the size of an attended visual field region, which was defined by a spatial cue stimulus
A neural basis of the attention spotlight has been found in recent functional magnetic resonance imaging studies, in which subjects were asked to attend a region in the visual field periphery while maintaining central fixation (Tootell et al, 1998; Brefczynski and DeYoe, 1999; Martinez et al, 1999; Somers et al, 1999)
Summary
While the extent of activated retinotopic visual cortex increased with the size of the attended region, the level of neural activity in a given subregion decreased. These findings are consistent with the physiological predictions of the zoom lens model. Size-related modulations of neural activity were pronounced in early visual areas We relate this finding to the small receptive field of these areas, whereby only neuronal units with receptive fields covering the attended region received a top-down bias.
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