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Abstract:
Efforts to identify the developmental timecourses of the
ventral and dorsal visual streams, using various methodologies,
have led to conflicting results. In this experiment, we observed
developmental changes in electrophysiological responses to stimuli
designed to differentially activate the ventral and dorsal streams.
Right-handed individuals, ages 6 to 24, participated in a visual
event-related potential (ERP) study of motion and color perception.
Brain potentials were recorded from 29 scalp electrodes. Color task
stimuli were isoluminant blue and green high spatial frequency
gratings. ERPs were recorded when the blue bars of one stimulus
changed to red. Motion task stimuli were grayscale low spatial
frequency gratings. ERPs were recorded when the bars of one
stimulus moved rightward. Adults' ERPs were largest in response to
stimuli presented in the central and lower visual fields. Color
shifts elicited an early positivity, and motion elicited greater
negativity around 150ms. Motion responses were distributed more
dorsally and anteriorly than color responses. Young participants
produced larger ERPs with longer latencies. More pronounced
developmental changes were observed in responses to motion and to
upper visual field stimuli. We will discuss the implications of
these results for the hypothesis that the dorsal visual stream is
more modifiable with early experience than the ventral stream. This
hypothesis has been supported with data from various special
populations.
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