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Abstract:
We have used the oddball (OB) paradigm to determine with
event-related fMRI how the brain processes novelty in object
location, or identity, or both. A standard object was briefly
presented at a standard location every 1.65s with an oddball
appearing on average every 12s while subjects monitored for any
deviants (3 oddball types -- Identity OB: novel object at standard
location, Location OB: standard object at novel location, and
conjunction OB: novel object at novel location). Cross-correlation
analysis was performed between experimental and expected signal
intensity waveforms for each oddball types, and pixel-based
statistical analysis was applied on Talairach-referenced composites
to determine areas that were significantly activated (p <
.0005). The results from 20 subjects indicate that 1) Identity OBs
activated bilaterally the lateral occipital area posteriorly and
the fusiform/lingual gyrus along the collateral sulcus more
anteriorly. 2) Location OBs demonstrated predominantly
right-hemisphere activation in areas immediately dorsal to the
shape-related regions in the middle occipital and temporal gyri,
the posterior angular gyrus, and anteriorly in the lateral fissure.
3) Conjunction OBs engaged the same regions that were activated by
each of the single oddballs. We conclude that spatial and object
features engage adjacent but distinct regions of the visual system,
and that the conjunction of these features does not recruit any
areas beyond those associated with the single features.
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