Cognitive deficits  

While aphasia has traditionally been described in terms of language deficits,
there is increasing evidence that many people with aphasia commonly experience
co-occurring non-linguistic  cognitive deficits  in areas such as attention, memory, executive functions
and learning.  [13]  [14]  [15]  By some accounts, cognitive deficits, such as
attention and working memory constitute the underlying cause of language
impairment in people with aphasia.  [16]  Others suggest that cognitive
deficits often co-occur but are comparable to cognitive deficits in stroke
patients without aphasia and reflect general brain dysfunction following
injury.  [17]  Whilst it has been shown that cognitive neural networks support
language reorganisation after stroke,  [18]  The degree to which deficits in
attention and other cognitive domains underlie language deficits in aphasia is
still unclear.  [19]

In particular, people with aphasia often demonstrate short-term and working
memory deficits.  [15]  These deficits can occur in both the verbal domain
[20]  [21]  as well as the visuospatial domain.  [22]  Furthermore, these
deficits are often associated with performance on language specific tasks such
as naming, lexical processing, and sentence comprehension, and discourse
production.  [23]  [15]  [24]  [25]  Other studies have found that most, but
not all people with aphasia demonstrate performance deficits on tasks of
attention, and their performance on these tasks correlate with language
performance and cognitive ability in other domains.  [15]  Even patients with
mild aphasia, who score near the ceiling on tests of language often
demonstrate slower response times and interference effects in non-verbal
attention abilities.  [26]

In addition to deficits in short-term memory, working memory, and attention,
people with aphasia can also demonstrate deficits in executive function.  [27]
For instance, people with aphasia may demonstrate deficits in initiation,
planning, self-monitoring, and cognitive flexibility.  [28]  Other studies
have found that people with aphasia demonstrate reduced speed and efficiency
during completion executive function assessments.  [29]

Regardless of their role in the underlying nature of aphasia, cognitive
deficits have a clear role in the study and rehabilitation of aphasia. For
instance, the severity of cognitive deficits in people with aphasia has been
associated with lower quality of life, even more so than the severity of
language deficits.  [30]  Furthermore, cognitive deficits may influence the
learning process of rehabilitation  [31]  [32]  and language treatment
outcomes in aphasia.  [33]  [34]  Non-linguistic cognitive deficits have also
been the target of interventions directed at improving language ability,
though outcomes are not definitive.  [35]  While some studies have
demonstrated language improvement secondary to cognitively-focused treatment,
[36]  others have found little evidence that the treatment of cognitive
deficits in people with aphasia has an influence on language outcomes.  [37]

One important caveat in the measurement and treatment of cognitive deficits in
people with aphasia is the degree to which assessments of cognition rely on
language abilities for successful performance.  [38]  Most studies have
attempted to circumvent this challenge by utilizing non-verbal cognitive
assessments to evaluate cognitive ability in people with aphasia. However, the
degree to which these tasks are truly "non-verbal" and not mediated by
language is unclear.  [19]  For instance, Wall et al.  [23]  found that
language and non-linguistic performance was related, except when non-
linguistic performance was measured by "real life" cognitive tasks.