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Abstract:
Temporal structure plays a major role in human understanding
of everyday events. It has been shown that, when asked, observers
are able to segment ongoing activity into temporal parts that are
reliable, meaningful, and correlated with ecologically relevant
features of the action. Here we present evidence that a network of
brain regions is tuned to the perceptual part structure of ongoing
activity. Participant watched movies of everyday activities (e.g.,
making a bed) while local brain activity was recorded with
functional MRI (fMRI). Following these passive viewing scans,
participants watched the same movies and were asked to tap a button
to mark the boundaries between natural and meaningful units.
Boundaries were identified at both a coarse and fine temporal grain
(during separate scans), and these boundaries were used to define
"trials" in an event-related fMRI analysis. A network of brain
regions showed reliable transient changes in activity, during the
passive viewing runs, at the location of event segment boundaries.
The most prominent regions of activity were a bilateral
parieto-occipital region (including human MT complex) and a right
superior frontal region (human frontal eye field). Areas that were
active during passive viewing were also active during the active
segmentation runs. In most regions, activity was greater for
coarse-unit boundaries than large-unit boundaries. These results
strongly indicate that a network of cortical regions tracks
observers' temporal segmentation of ongoing activity. Moreover,
this appears to be an naturally concomitant component of ongoing
perception, not tied to a particular task.
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