Neurobiological Mechanisms for Semantic Feature Extraction and Conceptual Flexibility

Abstract

Signs and symbols relate to concepts and can be used to speak about objects, actions, and their features. Theories of semantic grounding address the question how the latter two, concepts and real-world entities, come into play and interlink in symbol learning. Here, a neurobiological model is used to spell out concrete mechanisms of symbol grounding, which implicate the "association" of information about sign and referents and, at the same time, the extraction of semantic features and the formation of abstract representations best described as conjoined and disjoined feature sets that may or may not have a real-life equivalent. The mechanistic semantic circuits carrying these feature sets are not static conceptual entries, but exhibit rich activation dynamics related to memory, prediction, and contextual modulation. Four key issues in specifying these activation dynamics will be highlighted: (a) the inner structure of semantic circuits, (b) mechanisms of semantic priming, (c) task specificity in semantic activation, and (d) context-dependent semantic circuit activation in the processing of referential, existential, and universal statements. These linguistic-semantic examples show that specific mechanisms are required to account for context-dependent semantic function or conceptual "flexibility." Static context-independent concepts as such are insufficient to account for these different semantic functions. Whereas abstract amodal models of concepts did so far not spell out concrete mechanisms for context-dependent semantic function, neuronal assembly mechanisms offer a workable perspective.

Brain Activation During Conceptual Processing of Action and Sound Verbs

“…The first task was a lexical decision task in which participants were presented with action-and sound-related verbs in order to obtain brain activations specific for each feature category. In line with recent theoretical proposals of task-related conceptual flexibility (Hoenig et al, 2008;Pulvermüller, 2018;Sato, Mengarelli, Riggio, Gallese, & Buccino, 2008), implicit tasks such as the lexical decision task, for which retrieval of conceptual information is not directly relevant for task performance, might induce less activation within the modality-specific sensorimotor cortex than tasks requiring explicit semantic retrieval (Binder, Desai, Graves, & Conant, 2009;Kemmerer, 2015). Correspondingly, a direct comparison of explicit versus implicit task revealed a weaker activation of the motor system by action-related verbs during an implicit task (Popp et al, in press;Sato et al, 2008).…”

“…For example, conceptual processing of the word to throw activates sensory and motor brain areas that would also be activated during the execution of a throwing action. Grounded cognition theories vary depending on their explanations of the precise relationship between the sensorimotor systems and the conceptual system (for a review, see Meteyard, Cuadrado, Bahrami, & Vigliocco, 2012): While strong grounded cognition accounts assume an identical neural substrate between conceptual and sensorimotor processing including primary and secondary modality-specific cortex (Gallese & Lakoff, 2005;Pulvermüller, 2001), weaker variants of grounded cognition theories assume a hierarchy of neural circuits involving various levels of modality-specific (primary, secondary, or modality-specific association cortex), adjacent higherlevel multimodal cortices, as well as heteromodal semantic hub regions to be involved in the processing of conceptual information (Garagnani & Pulvermüller, 2016;Kiefer, Sim, Herrnberger, Grothe, & Hoenig, 2008;Pulvermüller, 2018;Simmons & Barsalou, 2003). These latter weaker grounded cognition accounts do not claim an identical neural substrate and a functional equivalence of conceptual and sensorimotor processing and can be thus considered as hybrid theories.…”

“…Although sensorimotor activations during explicit tasks may be stronger, they are also more likely to be confounded by attention to specific conceptual stimulus features (Pulvermüller, 2018) or by additional elaborative semantic processes like explicit semantic retrieval (Binder et al, 2009) or imagery (Chatterjee, 2010). Using an implicit lexical decision task, we were able to investigate the neural correlates of conceptual processing of different feature categories without possible influences of imagery or semantic elaboration processes (Chatterjee, 2010;Machery, 2007).…”

“…Based on the proposals of weaker grounded cognition theories, we assumed that conceptual processing of action-and sound-related verbs activates the same or adjacent sensory and motor areas that are also activated during real sensorimotor experiences. As indicated above, weaker variants of modality-specific theories assume a hierarchy of neural circuits involving various levels of modality-specific (primary, secondary, or modality-specific association cortex) as well as adjacent higher-level multimodal cortices to be involved in the processing of conceptual information (Garagnani & Pulvermüller, 2016;Kiefer et al, 2008;Pulvermüller, 2018;Simmons & Barsalou, 2003). These higherlevel sensorimotor or multimodal areas might not be strongly activated by all types of sensory stimuli in a given modality or by simple motor actions as typically realized in functional localizer tasks, thereby limiting the extent of the potential functional anatomical overlap (for a discussion, see Kiefer et al, 2008).…”

A cross-linguistic comparison of Spanish and English semantic norms: Looking at core features

“…Finally, it is crucial to acknowledge that the present results may only apply to concrete concepts. As shown by some studies, abstract concepts might lack of conceptual core (Pulvermüller, 2018) and exhibit remarkable processing differences (Bolognesi & Sten, 2018) compared to concrete concepts.…”