| |
Abstract:
Simultanagnosia is characterized by the failure to "see" more
than one object at a time. We report data from a simultanagnosic
whose performance was influenced by semantic variables and
exhibited repetition blindness. JD is a 63 year-old man with
bilateral parietal infarcts who was referred because of difficulty
with vision. He exhibited optic ataxia, left visual extinction, and
simultanagnosia. Naming of single objects and words was relatively
preserved. He performed well on pre-attentive visual tasks but
poorly on attention requiring tasks. The effect of semantic
variables was assessed on a variety of tasks in which JD was asked
to name two visually presented words or pictures. He was told that
there were always two stimuli present. There were three conditions:
1. drawings/words were from different semantic categories; 2.
drawings/words were from the same semantic category; 3.
drawings/words were different versions of the same item (e.g., 2
different hammers; words differed in font). Collapsing across the
two tasks, he identified both stimuli on 46/152 (30%) trials in
condition 1, 68/152 (45%) trials in condition 2, and 5/117 (4%)
trials in condition 3. These data are inconsistent with accounts
which attribute simultanagnosia to deficits in low-level visual
perception or early visual selection but suggest that even
unreported stimuli may be processed to a semantic level. The
striking repetition blindness observed with unlimited presentation
is consistent with the hypothesis that JD suffers from a limitation
in binding semantic representations to visual stimuli.
|
