Correlating declarative/procedural memory with language variation

Antonio Benítez-Burraco, David Gil, Ljiljana Progovac, Candy Cahuana and Tatiana Tatarinova

When it comes to language, declarative memory is typically implicated in vocabulary learning and irregular phenomena across domains, most commonly associated with memorized, opaque, formulaic chunks of language (e.g. idioms and proverbs), while procedural memory is implicated in compositional, automated, rule-governed aspects of language (see e.g. Ullman, 2004, 2015 and references there; see also Heyselaar et al., 2017; Elyoseph et al., 2020, for impairments). We contend that this distinction is evocative of the esoteric/exoteric language types. Roughly speaking, esoteric languages are characterizable as exhibiting simpler (less layered) syntaxes, but larger, more complex phonologies and morphologies, with more irregularity, and with more formulaic/memorized language (e.g. Wray and Grace, 2007). In contrast, exoteric languages are characterizable as involving more complex and more layered syntaxes, with more specialized (obligatory) grammaticalized distinctions, such as specialized tense marking, specialized thematic role marking, subordination marking, etc.
While both memories are essential for language, partly overlapping/redundant in their functions (Ullman, 2015), and while both language types rely on both memories, our hypothesis is that predominantly esoteric languages rely more on declarative memory, while predominantly exoteric languages, in comparison, rely more on procedural memory. This is consistent with Ullman’s (2015, p. 142) claim that greater complexity of rules or patterns, including grammatical rules or constraints, may lead to a greater relative dependence on procedural memory (Ullman 2015, p. 142). This consideration directly engages the long-standing linguist’s puzzle in characterizing linguistic variation, where researchers often report trade-offs in complexity among different domains, the puzzle that has engendered various controversies, and that has become crucial for understanding the nature of language evolution in terms of gradually increasing complexity (see e.g. the contributions in Sampson, Gil and Trudgill, 2009). Ultimately, because cognitive biases can be linked to (epi)genetic modifications, we expect this differential reliance concerning both types of memories to be detectable in differences in the allele frequencies of specific genes. As reported in e.g. Ullman (2015), various genes have been found to play a role in declarative memory, e.g., BDNF and APOE (see also Henke, 2010; Squire and Wixted, 2011; Eichenbaum, 2012), whereas certain genes playing a role in procedural memory have been identified, too, including FOXP2, PPP1R1B and DRD2 (see e.g. Packard, 2008; Doyon et al., 2009; Ashby et al., 2010; Eichenbaum, 2012).
In addition to offering a fresh look at this long-standing puzzle, this hypothesis also has an advantage of being testable. To test it, we are seeking correlations between a variety of parameters that are associated with the esoteric/exoteric dimension, on the one hand, and, on the other hand, i) the procedural vs. declarative memory abilities of the speakers and ii) the frequency in the population of the candidate gene alleles for the genes reported to be implicated in declarative vs. procedural memory. The goal is to provide not only a precise and tangible characterization of the esoteric/exoteric divide, but also a tangible way to engage the neurobiological and the genetic foundation of language variation, necessary to shed light on language evolution.

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