Deregulated Semantic Cognition Follows Prefrontal and Temporo-parietal Damage: Evidence from the Impact of Task Constraint on Nonverbal Object Use

Abstract

Semantic cognition, which encompasses all conceptually based behavior, is dependent on the successful interaction of two key components: conceptual representations and regulatory control. Qualitatively distinct disorders of semantic knowledge follow damage to the different parts of this system. Previous studies have shown that patients with multimodal semantic impairment following CVA--a condition referred to as semantic aphasia (SA)--perform poorly on a range of conceptual tasks due to a failure of executive control following prefrontal and/or temporo-parietal infarction [Jefferies, E., & Lambon Ralph, M. A. Semantic impairment in stroke aphasia versus semantic dementia: A case-series comparison. Brain, 129, 2132-2147, 2006]. Although a deficit of core semantic control would be expected to impair all modalities in parallel, most research exploring this condition has focused on tasks in the verbal domain. In a novel exploration of semantic control in the nonverbal domain, therefore, we assessed eight patients with SA on two experiments that examined object use knowledge under different levels of task constraint. Patients exhibited three key characteristics of semantic deregulation: (a) difficulty using conceptual knowledge flexibly to support the noncanonical uses of everyday objects; (b) poor inhibition of semantically related distractor items; and (c) improved object use with the provision of more tightly constraining task conditions following verbal and pictorial cues. Our findings are consistent with the notion that a neural network incorporating the left inferior prefrontal and temporo-parietal areas (damaged in SA) underpins regulation of semantic activation across both verbal and nonverbal modalities.

What we talk about when we talk about access deficits

“…By contrast, storage deficit (SD) patients show virtually no effect of cueing [8][9][10]. A similar cueing effect has also been shown for miming object use: performance was better when participants were presented with a picture of the object and its name than when presented with only its name [11].…”

“…Summary of key access deficit phenomena, tasks in which they have been shown, and patients (or patient groups) that have shown the effect. phenomenon task patients sensitivity to cueing picture naming 10/10 SA patients [8] a ; 4/4 SA patients [9] a ; 6/6 SA patients [10] a object use 8/8 SA patients [11] a sensitivity to presentation rate spoken word-to-picture matching AA [12]; HEC [13]; VER [14]; YOT [15]; AZ [17,18]; UM-103 [19]; HA, DZ [20];…”

Semantic diversity: A measure of semantic ambiguity based on variability in the contextual usage of words

“…This task required participants to access the appropriate aspect of a word's meaning to match it to its synonym, meaning that words with highly variable meanings would likely be at a disadvantage. In earlier work, we established that patients with semantic aphasia have difficulty selecting which aspects of their semantic knowledge are relevant in a particular task or context ("semantic control"; Jefferies & Lambon Ralph, 2006;Noonan et al, 2010;Corbett, Jefferies, & Lambon Ralph, 2011). Thus, we predicted that patients with semantic aphasia would have difficulty comprehending highly ambiguous words because these words maximize selection demands.…”

Going beyond Inferior Prefrontal Involvement in Semantic Control: Evidence for the Additional Contribution of Dorsal Angular Gyrus and Posterior Middle Temporal Cortex

“…(1) Semantic control is underpinned by a distributed system, which includes posterior middle temporal and dAG regions, in addition to pFC: The nature and the degree of semantic impairment in SA patients have been shown to be largely consistent across pFC and temporoparietal lesion subgroups: Performance is poor on demanding tests of associative semantic knowledge, on assessments with semantically ambiguous materials, on nearest neighbor judgment tasks, which increase the degree of semantic distance between probes and targets and when naming pictures in the context of phonemic miscues, while less intrinsically demanding tests of identity matching (i.e., word-picture matching) are performed relatively well (Corbett, Jefferies, Ehsan, et al, 2009;Corbett et al 2011;Noonan et al, 2010;Jefferies & Lambon Ralph, 2006). This suggests that sites within temporoparietal cortex may form part of a large-scale distributed network underpinning semantic control; however, these studies lack spatial precision since SA cases typically have extensive lesions.…”