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Abstract:
Lateralized stimuli accelerate manual responses whenever
their location coincides to the hand that performs the response.
Recent EEG studies provided evidence that one main process
responsible for these effects is an activation of the hemisphere
that processes the stimulus location that reaches the motor cortex
and thereby facilitates manual responses. Time course and
topographies of asymmetric EEG components (event-related
lateralisations = ERLs) indicate that the origin of the effect is
not located in primary visual areas but in the posterior parietal
cortex. In a recent study, we investigated whether spatial
information without location information evokes similar effects. We
used dot-patterns (both isoluminant and non-isoluminant) that
coherently moved into one direction. EEG was recorded from 53
electrode sites. Subjects had to press a button either at the side
where the dots moved to (compatible) or opposite to it
(incompatible). Responses were faster in compatible than in
incompatible trials, independently from stimulus luminance. ERLs
reflecting fast encoding of direction were visible for
non-isoluminant stimuli only. Differing results on ERLs for the two
stimulus types might reflect differing processing in magno- and
parvocellular pathways. Magno-cells (sensitive to bright stimuli)
are processing faster than parvo-cells and project into the dorsal
stream, which is proposed to process visual information for action.
However, the appearance of compatibility effects independently from
stimulus luminance indicates that information that is initially
processed within the ventral path has efficiently access to the
dorsal stream.
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