Verb argument structure effects in aphasia are different at single-word versus sentence level
Many aphasia assessments and therapies select and/or sequence verbs based on
linguistic complexity of their verb argument structure (VAS). However, further empirical testing is
needed to fully understand whether and how VAS parameters affect the cognitive difficulty of verb
processing in different tasks and contexts.
The study investigated whether more linguistically complex VAS universally implies
more cognitively difficult verb processing, as predicted by the Argument Structure Complexity
Hypothesis (Thompson, 2003). We hypothesized that this would only be the case at sentence level,
whereas in single-word tasks more linguistically complex VAS would facilitate lexical access via
lexico-semantic associations with potential arguments, contrary to the Argument Structure
The effects of three VAS parameters (number of arguments,
number of valency frames, canonicity of thematic role marking) were tested in two tasks (single-
word naming and cued sentence production) in two aphasia types (fluent and non-fluent, 20
participants per group). We analyzed how VAS parameters affected accuracy and latency in naming
and canonicity and well-formedness in sentence production.
As hypothesized, VAS effects were different at the sentence versus
single-word level. In sentence production, one VAS parameter (the number of arguments) showed
the expected negative effect of greater linguistic complexity on sentence canonicity. No other
comparisons were significant, likely due to ceiling effects. In contrast, in single-word naming, VAS
effects were mixed. The number of valency frames showed the predicted facilitatory effect of
linguistic complexity. The number of arguments showed a non-significant statistical trend in the
same direction. For canonicity of thematic role marking, greater complexity had a negative effect on naming, possibly because it does not affect the number of lexico-semantic associates of the verb. All
findings pertained to both non-fluent and fluent aphasia.
When accounting for VAS parameters in selection or sequencing of verbs for
assessment or therapy, the cognitive difficulty of verb processing should be estimated for a
particular task. In sentence-level grammatical processing, most cognitively difficult verbs are those
with more linguistically complex VAS. In contrast, in single verb retrieval, verbs with more
linguistically complex VAS may be cognitively simpler if their richer lexico-semantic associations
with potential arguments provide extra routes of lexical access.