| Summary: | Introduction
The local-global dimension (Navon, 1977) has been studied extensively in healthy controls and preference for globally processed stimuli has been validated in both the visual and auditory modalities. Critically, the local-global dimension has an inherent interference resolution component, a type of cognitive control, and left-prefrontal-cortex-damaged (LPFC) individuals have exhibited inability to override habitual response behaviors in item recognition tasks that involve representational interference (Hamilton & Martin, 2005; Novick, Trueswell, & Thompson-Schill, 2005). However, very little is known about how the local-global attentional dimension affects LPFC-damaged individuals with aphasia in language and non-language domains that involve cognitive control mechanisms.
Methods
Eight patients with damage in the left PFC and twenty age- and education-matched language-unimpaired adults have participated in the study. Non-verbal tasks included an online Global-Local Identification task (designed after Navon, 1977) asking from participants to identify global geometrical shapes, which were made up of smaller (local) geometrical configurations while inhibiting local ones, and vice versa. In congruent trials, local and global shapes coincided whereas in incongruent trials they did not. Apart from the local and global condition, the task included a mixed local-global condition, in which participants were asked to identify global and local shapes interchangeably. Participants’ updating functions were independently measured by an online 2-back digit task where individuals were presented with digit sequences and were asked to respond by pressing a pre-specified key once a digit matched the digit occurring two digits earlier. The study also involved four online language tasks: (a) a task testing the interpretation of pronouns (Peristeri & Tsimpli, 2013) in globally ambiguous sentential contexts, (b) a task testing the interpretation of homophones in sentences requiring global processing, (c) a task testing the participants’ sensitivity to local, grammatical gender conflicts of single words in a picture-word interference task, and, (d) a task testing participants’ sensitivity to local orthographic violations in the stems and suffixes of single words in a semantic judgment task.
Results
In the Global-Local Identification task, LPFC-damaged patients with non-fluent aphasia performed more poorly in both accuracy (42% correct) and RTs on the local incongruent trials—where identification of the local shape presupposed inhibition of the global configuration—than any other global incongruent or congruent category. Controls were slower (but accurate) in local incongruent trials. On the other hand, PFC-damaged patients (along with controls) performed at ceiling level in the 2-back digit task, thus, indicating no deficit in their updating abilities. With respect to the language tasks, the patients performed more poorly in RTs in the tasks tapping on the integration of local cues relative to the tasks where conflict resolution was critically dependent on the parser’s sensitivity to global context.
Discussion
Overall, the local-global dimension seems to critically influence the performance of LPFC-damaged individuals with non-fluent aphasia in both language and non-language domains. A possible interpretation is that participants were able to override conflict more easily in tasks tapping on global than local processing. Broader implications for distinct types of inhibitory processes depending on the level of processing will be discussed.
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