Abstract
Fundamental to all human languages is an unlimited expressive capacity and creative flexibility that allow speakers to rapidly generate novel and complex utterances. In turn, listeners interpret language “on-line,” incrementally integrating multiple sources of information as words unfold over time. A challenge for theories of language processing has been to understand how speakers and listeners generate, gather, integrate, and maintain representations in service of language processing. We propose that many of the processes by which we use language place high demands on and receive contributions from the hippocampal declarative memory system. The hippocampal declarative memory system is long known to support relational binding and representational flexibility. Recent findings demonstrate that these same functions are engaged during the real-time processes that support behavior in-the-moment. Such findings point to the hippocampus as a potentially key contributor to cognitive functions that require on-line integration of multiple sources of information, such as on-line language processing. Evidence supporting this view comes from findings that individuals with hippocampal amnesia show deficits in the use of language flexibly and on-line. We conclude that the relational binding and representational flexibility afforded by the hippocampal declarative memory system positions the hippocampus as a key contributor to language use and processing.
Highlights
The role of hippocampus in the formation and subsequent retrieval of new enduring memory is well-established (Cohen and Squire, 1980; Squire, 1992; Cohen and Eichenbaum, 1993; Gabrieli, 1998)
In subsequent analyses aimed at characterizing discourse processes in amnesia, we found that, while the semantic content of the references were similar across amnesia and comparison participants the patients exhibited a general lack of flexibility in their referential expressions (Duff et al, 2008b)
In our study on reported speech, we found that there were no group differences in the amount of talk, in the conversational sessions of patients with hippocampal amnesia interacting with a clinician there were only half as many reported speech episodes (RSEs) (M = 30.3; SD = 16.9) as there were in sessions with healthy comparisons (M = 61.5; SD = 30.1), a difference that was statistically significant (Duff et al, 2007)
Summary
The cited studies used visual or visuospatial stimuli, the strong implication is that the hallmark flexibility and integration of hippocampus-dependent representations will be deployed and rapidly available when any materials are processed in an ongoing fashion, and that the performance of patients with hippocampal lesions and declarative memory deficits will consequentially suffer These provocative findings regarding the time course of hippocampal contributions to on-line processing have profound implications for theories of language processing and use. This work has revealed deficits across various aspects of linguistic and discourse functions suggesting that patients with hippocampal amnesia have difficulty establishing, recovering, maintaining and using declarative memory representations throughout a conversation when the demands on flexible and creative uses of language are high We recently extended this line of work to examine on-line language processing (Rubin et al, 2011) and have initial, tantalizing evidence for hippocampal mediation in real-time language processing. At the heart of our proposal is that these same features—on-line processing of rich representations from multiple domains—are key demands of the flexible use and on-line processing of language
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