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Abstract:
A rapidly activated mechanism for detecting discontinuities
in a homogenous context is of vital importance to organisms. Recent
studies suggest such a mechanism in the human visual system.
Specifically, ERPs to infrequent deviant stimuli among identical
standards revealed a negativity at 100 ms post-stimulus over
occipital scalp. This work addressed further properties of the
deviance-dependent negativity (DDN). Typical conditions consisted
of a rapid (400 ms ISI) trial sequence including two physically
different gratings presented on 80 and 20 % of the trials,
respectively. Thirty-channel ERPs to the gratings revealed that (1)
DDN is elicted equally by low (0.6 c/d) deviant spatial frequencies
among high (2.4) standards, as it is by high deviants among low
standards, and (2) it is also elicited equally by color deviance
(red deviants among blue standards or v.v). Third, DDN is preceded
in time by spatial-frequency-dependent potentials which are hardly
sensitive to stimulus probability. Fourth, dipole modeling suggests
that whereas the shorter-latency stimulus-specific potentials are
generated form the utmost back of the head, DDN generators are
slightly but significantly more anterior. Fifth, DDN does not
depend on the presence of intervening standards, i.e, it responds
to temporal, rather than to sequential probability (reflecting
'haven't seen you for a long time', rather than 'you're
different').
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