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Abstract:
The nature of chromatic input to motion processing has long
been an issue of debate. In particular, controversy exists
regarding whether chromatic motion processing relies on lower-level
processes or higher-level, attentionally-based processes. To
investigate directly the degree to which chromatic motion
processing is influenced by attentional mechanisms, we employed an
"opposed motion" stimulus (after Cavanagh & Anstis, 1991) to
obtain an estimate of the strength of chromatic input to motion-
the equivalent luminance contrast ("EqLC"). EqLCs were obtained
separately in two conditions: 1) single task- subjects reported
perceived direction of the opposed motion stimulus, and 2) dual
task- subjects were instructed to first perform an attentionally
demanding "vowel counting" task in the center of gaze before
reporting the direction of the opposed motion stimulus. Thus,
subjects' attention to the opposed motion stimulus was greatly
diminished in condition #2. Subjects were tested at both 2 and 8
Hz. EqLCs were significantly greater than 0% under all conditions,
indicating that chromatic cues provide significant input to motion
processing even in the near absence of attention. However, EqLCs
were significantly lower in the dual task, as compared to the
single task, condition (with the greatest effects at 2 Hz),
demonstrating a substantial influence of attention on chromatic
input to motion. Thus, both lower-level and higher-level
attentional mechanisms appear to contribute to chromatic motion
processing.
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