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Abstract:
Abstract: Baylis, Driver & Rafal (1993) examined the
performance of stroke patients with visual extinction on an object
identification task. The subjects were presented colored letters,
either unilaterally or bilaterally, and were asked to report and
locate either the color or the shape of the letter. The experiment
was divided into blocks of trials, and within each block only one
of the two dimensions was relevant (either the color or the shape).
With bilateral presentations patients often missed the stimulus in
the contralesional visual field. This extinction was greater when
the two letters presented were the same in the relevant dimension.
However, similarity in the irrelevant dimension did not affect
response accuracy. The authors concluded that certain object
dimensions could be processed by the visual system even though
subjects were not aware of them, but only when that dimension was
relevant to the task. We were interested in the extent of
processing by patients when the relevant task dimension was not
known until after the visual display was presented. Therefore, in
the present study, we not only included trials in which the
relevant dimension was known before stimulus presentation, but also
trials in which the relevant dimension was known only after
stimulus presentation. The results are discussed with respect to
the original Baylis, Driver & Rafal (1993) study and the
general extinction literature.
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