Merge-Generability as the Key Concept of Human Language: Evidence From Neuroscience

Abstract

Ever since the inception of generative linguistics, various dependency patterns have been widely discussed in the literature, particularly as they pertain to the hierarchy based on “weak generation” – the so-called Chomsky Hierarchy. However, humans can make any possible dependency patterns by using artificial means on a sequence of symbols (e.g., computer programing). The differences between sentences in human language and general symbol sequences have been routinely observed, but the question as to why such differences exist has barely been raised. Here, we address this problem and propose a theoretical explanation in terms of a new concept of “Merge-generability,” that is, whether the structural basis for a given dependency is provided by the fundamental operation Merge. In our functional magnetic resonance imaging (fMRI) study, we tested the judgments of noun phrase (NP)-predicate (Pred) pairings in sentences of Japanese, an SOV language that allows natural, unbounded nesting configurations. We further introduced two pseudo-adverbs, which artificially force dependencies that do not conform to structures generated by Merge, i.e., non-Merge-generable; these adverbs enable us to manipulate Merge-generability (Natural or Artificial). By employing this novel paradigm, we obtained the following results. Firstly, the behavioral data clearly showed that an NP-Pred matching task became more demanding under the Artificial conditions than under the Natural conditions, reflecting cognitive loads that could be covaried with the increased number of words. Secondly, localized activation in the left frontal cortex, as well as in the left middle temporal gyrus and angular gyrus, was observed for the [Natural – Artificial] contrast, indicating specialization of these left regions in syntactic processing. Any activation due to task difficulty was completely excluded from activations in these regions, because the Natural conditions were always easier than the Artificial ones. And finally, the [Artificial – Natural] contrast resulted in the dorsal portion of the left frontal cortex, together with wide-spread regions required for general cognitive demands. These results indicate that Merge-generable sentences are processed in these specific regions in contrast to non-Merge-generable sentences, demonstrating that Merge is indeed a fundamental operation, which comes into play especially under the Natural conditions.

Enhanced activations in syntax-related regions for multilinguals while acquiring a new language

“…Even though we used a limited set of words and tested syntactic features like subject-verb agreement, the number of their combinations became infinite, thus requiring the acquisition of syntactic knowledge as opposed to explicit rule and pattern learning in general. This syntactic knowledge is crucially underlain by Mergegenerability 34 , the key concept of human language, which is in marked contrast with artificial rules in general.…”

“…Activations in this region actually predicted "the Degree of Merger," i.e., the maximum depth of merged subtrees (called Mergers), in a sentence; the more binary syntactic nodes (or branches) the sentence had, the more active the region became 31,32 . It has been reported that there were differential activations when participants were exposed to natural versus artificial rules of sentences 33,34 . We showed localized activation in the left language areas including the L. IFG under the Natural condition, while under the Artificial condition, activation was observed in the bilateral LPMC, together with wide-spread regions 34 .…”

“…It has been reported that there were differential activations when participants were exposed to natural versus artificial rules of sentences 33,34 . We showed localized activation in the left language areas including the L. IFG under the Natural condition, while under the Artificial condition, activation was observed in the bilateral LPMC, together with wide-spread regions 34 . In the present study of natural languages, we examined how the deep properties of sentence constructions (e.g., coordination and subordination) were generalized for the bilinguals and multilinguals.…”

Music-experience-related and musical-error-dependent activations in the brain

“…2017 ; Tanaka et al. 2017 , 2019 ). For the MRI data acquisition, the participant was in a supine position, and his or her head was immobilized inside the radiofrequency coil.…”

Constructions in Minimalism: A Functional Perspective on Cyclicity

“…While a lot of generative work has been published on how to best formulate the basic combinatorial operation Merge (see Fukui, 2011;Tanaka et al, 2019 for recent empirical work), there is less research on the question of where the elements to be merged actually come from (or, more accurately, the existing research on Merge and its domains has other ways to frame the question; see section "The Numeration and Derivation Layering"). Because clauses and complex phrases contain words, the simplest suggestion would be that the domain of Merge is the Lexicon.…”