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Abstract:
Abstract: Form-from-motion perception would likely require
combined processing in the ventral and dorsal visual stream.
Magnetencephalography (MEG) was used to investigate the processing
sequence and the influence of spatial attention on the processing
of such stimuli. Eight young healthy subjects were presented two
squares formed by randomly moving dots left and right of a fixation
cross. In the form-from-motion condition dots in these squares
moved in a coherent manner that defined shapes. In the
form-from-luminance condition, gray shapes appeared on the randomly
moving dot background. Subjects were instructed to attend to one
location and to discriminate the shapes. Evoked magnetic fields
were elicited only when the location of the stimuli was attended,
demonstrating a strong suppression of processing of the unattended
stimuli. This provides evidence for the idea of attentional control
over the processing of form-from-motion and form-from-luminance,
supporting early selection theories of attention. Source analyses
indicated activity in left V5 region, bilateral lateral occipital
(LO) and inferior temporal cortex as underlying the processing of
form-from-motion. These areas were activated by the
form-from-motion stimuli mostly in a serial manner. Behavioral
measures and evoked field timing analyses both indicated that
motion is processed first, presumably to extract the shape
information, which is then processed in the inferior temporal
cortex mainly in the right hemisphere. These results support a
model of serial processing of the visual streams, with a
interstream connection between V5 and V4. Activity in bilateral LO
and inferior temporal cortex appeared to be cue invariant.
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