Recurrent temporal networks and language acquisition—from corticostriatal neurophysiology to reservoir computing

Peter F Dominey

doi:10.3389/fpsyg.2013.00500

Abstract

One of the most paradoxical aspects of human language is that it is so unlike any other form of behavior in the animal world, yet at the same time, it has developed in a species that is not far removed from ancestral species that do not possess language. While aspects of non-human primate and avian interaction clearly constitute communication, this communication appears distinct from the rich, combinatorial and abstract quality of human language. So how does the human primate brain allow for language? In an effort to answer this question, a line of research has been developed that attempts to build a language processing capability based in part on the gross neuroanatomy of the corticostriatal system of the human brain. This paper situates this research program in its historical context, that begins with the primate oculomotor system and sensorimotor sequencing, and passes, via recent advances in reservoir computing to provide insight into the open questions, and possible approaches, for future research that attempts to model language processing. One novel and useful idea from this research is that the overlap of cortical projections onto common regions in the striatum allows for adaptive binding of cortical signals from distinct circuits, under the control of dopamine, which has a strong adaptive advantage. A second idea is that recurrent cortical networks with fixed connections can represent arbitrary sequential and temporal structure, which is the basis of the reservoir computing framework. Finally, bringing these notions together, a relatively simple mechanism can be built for learning the grammatical constructions, as the mappings from surface structure of sentences to their meaning. This research suggests that the components of language that link conceptual structure to grammatical structure may be much simpler that has been proposed in other research programs. It also suggests that part of the residual complexity is in the conceptual system itself.

Highlights

We begin with the neurophysiological basis of orienting behavior, which provides the framework that leads to language
In order to test the model in a language processing task, we identified a task that had been developed by Caplan et al (1985) in which aphasic subjects listened to sentences and had to indicate the corresponding meaning by pointing to images depicting the agent, object and recipient
We found strong correlational support for this hypothesis, observing that in agrammatic aphasic patients with left peri-sylivan (Broca’s region) lesions, there was a significant correlation between performance in the nine sentence-type Caplan task of syntactic comprehension, and a task of abstract sequence processing (Dominey et al, 2003)

Summary

INTRODUCTION

We begin with the neurophysiological basis of orienting behavior, which provides the framework that leads to language. In the 1980’s research in the oculomotor system of the cat and macaque monkey reached a certain height of completion, and the neural circuits that processed information from visual input to motor response were specified at a fairly high level of detail [reviewed in Dominey and Arbib (1992)]. This represented an important phase in cognitive neuroscience, because the same circuits that specified motor control and spatial attention in the oculomotor system were templates for parallel circuits that would provide part of the basis for higher cognitive function and language. At the same time that the functional neuroanatomy of the oculomotor loop had been quite well characterized and modeled www.frontiersin.org

Recurrent temporal networks and language

Findings

DISCUSSION