Lesions to the left lateral prefrontal cortex impair decision threshold adjustment for lexical selection

Abstract

Patients with lesions in the left prefrontal cortex (PFC) have been shown to be impaired in lexical selection, especially when interference between semantically related alternatives is increased. To more deeply investigate which computational mechanisms may be impaired following left PFC damage due to stroke, a psychometric modelling approach is employed in which we assess the cognitive parameters of the patients from an evidence accumulation (sequential information sampling) modelling of their response data. We also compare the results to healthy speakers. Analysis of the cognitive parameters indicates an impairment of the PFC patients to appropriately adjust their decision threshold, in order to handle the increased item difficulty that is introduced by semantic interference. Also, the modelling contributes to other topics in psycholinguistic theory, in which specific effects are observed on the cognitive parameters according to item familiarization, and the opposing effects of priming (lower threshold) and semantic interference (lower drift) which are found to depend on repetition. These results are developed for the blocked-cyclic picture naming paradigm, in which pictures are presented within semantically homogeneous (HOM) or heterogeneous (HET) blocks, and are repeated several times per block. Overall, the results are in agreement with a role of the left PFC in adjusting the decision threshold for lexical selection in language production.

Word selection deficits and multiword speech

“…It is also unclear the degree to which difficulties in producing words in situations of competition (in isolation or context) is a result of damage to a selection mechanism in the left PFC and/or damage or access to representations stored in the left temporal cortex (e.g., Noonan, Jefferies, Visser, & Ralph, 2013; Harvey & Schnur, 2015). Of the six patients with left PFC damage reported by Anders and colleagues (in press), three of the six had around 20% damage or more to the left temporal cortex. We should also consider the role of the left PFC in grammatical and phonological encoding required for multiword speech (e.g., Bookheimer, 2002; Hagoort, 2005).…”

“… Through computational modelling of language behaviour in both healthy and brain-damaged individuals, Anders, Riès, van Maanen and Alario (in press) propose that to facilitate word selection when alternatives compete for production, the left lateral prefrontal cortex (PFC) changes the threshold for word selection. Because selecting a word during multiword speech involves resolving competition from target-related competitors as well as words produced in the past and future, a word-selection deficit caused by damage to the left PFC may result in difficulties in producing multiword speech.…”

“…The ability to select a representation in the face of myriad competitors is a critical process not only in language production but across other domains including language comprehension (e.g., Novick, Trueswell, & Thompson-Schill, 2005), memory retrieval (e.g., Anderson, Bjork, & Bjork,1994), action planning (e.g., Watson & Buxbaum, 2015) and decision making (e.g., Miller & Cohen, 2001). Anders, Riès, van Maanen and Alario’s (in press) computational work provides a framework with which to understand how we select a word when semantically related words compete for production. This advance is particularly important in its proposals for how this process breaks down in those with language deficits as a result of brain damage.…”

“…The work from Anders and colleagues (in press) suggests that when selection occurs in situations of competition, the selection process changes in at least two ways. First, lexical representations more slowly accumulate activation in situations of competition (for reasons that continue to be explored, for example see Snyder and colleagues, 2010).…”

“…In a group study of blocked-cyclic naming in 12 individuals with aphasia following stroke (Schnur et al, 2006), the more errors produced in semantically homogeneous versus heterogeneous picture naming (the same measure of selection deficit as in Anders and colleagues, in press) the fewer words produced in sentences and the fewer overall words per minute produced during narrative speech (i.e., a retelling of the Cinderella fairy tale analyzed using the Quantitative Production Analysis; Rochon, Saffran, Berndt, & Schwartz, 2000). Speer and Wilshire (2014) found a similar set of results in a study of sentence production in five speakers with non-fluent aphasia (usually coincidental with left frontal damage) and four speakers with fluent aphasia (associated with damage to left posterior brain regions).…”