ABSTRACT
Aphasia has traditionally been viewed as a loss or impairment of language. However,
evidence is presented suggesting that language mechanisms are fundamentally preserved
and that aphasic language behaviors are instead due to impairments of cognitive processes
supporting their construction. These processes may be understood as a linguistically
specialized attentional system that is vulnerable to competition from other processing
domains. We present two models of attention that focus on competition for central
processing and discuss findings from dual-task studies of normal and aphasic performance.
First, competing language and nonlanguage tasks appear to share limited-capacity,
parallel processing resources. Second, aphasic individuals demonstrate slowed central
processing that could be due to a reduction in processing capacity or ability to allocate
that capacity. Third, the attention models discussed bear a coherent relationship
to current models of language processing. Clinical implications of a cognitive processing
account of aphasia are also considered.
KEYWORDS
Aphasia - attention - psychological refractory period
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1
Considerable variability has also been demonstrated to occur across language modalities
(gesturing, writing, talking, reading, and listening) and across levels of language.
However, psycholinguistic operations unique to each processing modality appears to
account for a substantial amount of the variability. This source of within-subject
variability is not discussed here.
2
Navon and Miller
[63 and Tombu and Jolicoeur
[64 independently developed models that are mathematically identical. Tombu and Jolicoeur
referred to it as a central capacity sharing model. In this article, we adopt Navon and Miller's terminology , single resource.
3
Although it is acknowledged that capacity limits and/or processing bottlenecks may
occur in the pre- and postcentral stages under some circumstances, such limits are
proposed to be independent of and qualitatively different from the central bottleneck.
[54 67
4
The predictions that RT1 will be affected by SOA and task 2 difficulty depend on a
number of assumptions, including the assumptions that the total available resource
capacity is limited and constant, or at least does not vary systematically with SOA
or task difficulty.
[63 64 Although these assumptions are arguable, they are helpful in making the models and
their predictions tractable, and detailed discussion of them is beyond the scope of
this article.
5
Although a manual high/low tone identification task may be subject to verbal encoding,
the degree of verbal processing for such a task should be minimal relative to that
required for a picture-naming task.
William.Hula@va.gov
