Behavioral Signatures of Memory Resources for Language: Looking beyond the Lexicon/Grammar Divide

Abstract

Although there is a broad consensus that both the procedural and declarative memory systems play a crucial role in language learning, use, and knowledge, the mapping between linguistic types and memory structures remains underspecified: by default, a dual-route mapping of language systems to memory systems is assumed, with declarative memory handling idiosyncratic lexical knowledge and procedural memory handling rule-governed knowledge of grammar. We experimentally contrast the processing of morphology (case and aspect), syntax (subordination), and lexical semantics (collocations) in a healthy L1 population of Polish, a language rich in form distinctions. We study the processing of these four types under two conditions: a single task condition in which the grammaticality of stimuli was judged and a concurrent task condition in which grammaticality judgments were combined with a digit span task. Dividing attention impedes access to declarative memory while leaving procedural memory unaffected and hence constitutes a test that dissociates which types of linguistic information each long-term memory construct subserves. Our findings confirm the existence of a distinction between lexicon and grammar as a generative, dual-route model would predict, but the distinction is graded, as usage-based models assume: the hypothesized grammar-lexicon opposition appears as a continuum on which grammatical phenomena can be placed as being more or less "ruly" or "idiosyncratic." However, usage-based models, too, need adjusting as not all types of linguistic knowledge are proceduralized to the same extent. This move away from a simple dichotomy fundamentally changes how we think about memory for language, and hence how we design and interpret behavioral and neuroimaging studies that probe into the nature of language cognition.

Keywords: Declarative; Divided attention; Dual task paradigm; Grammar; Language; Lexicon; Memory; Procedural.

Fig. 1

Response latencies for the four stimulus Types across ST and CT conditions (left panel); response latencies for the four types of implicit learners across both Conditions (middle panel); response latencies for the three types of explicit learners across Conditions (right panel). Whiskers represent the 95% lower and upper confidence interval limits.

Fig. 2

Plot of observed versus predicted frequencies for matched and mismatched responses across two experimental conditions (left and right panels) and four language types. The bars represent the observed frequencies (green for Mismatch, orange for Match) and the black horizontal lines represent the predicted frequencies.

Fig. 3

Variability (i.e., moving SDs) for the four stimulus Types across Single task and Concurrent task conditions. Whiskers represent the 95% lower and upper confidence interval limits.