Gestures, Vocalizations, and Memory in Language Origins

Abstract

This article discusses the possible homologies between the human language networks and comparable auditory projection systems in the macaque brain, in an attempt to reconcile two existing views on language evolution: one that emphasizes hand control and gestures, and the other that emphasizes auditory–vocal mechanisms. The capacity for language is based on relatively well defined neural substrates whose rudiments have been traced in the non-human primate brain. At its core, this circuit constitutes an auditory–vocal sensorimotor circuit with two main components, a “ventral pathway” connecting anterior auditory regions with anterior ventrolateral prefrontal areas, and a “dorsal pathway” connecting auditory areas with parietal areas and with posterior ventrolateral prefrontal areas via the arcuate fasciculus and the superior longitudinal fasciculus. In humans, the dorsal circuit is especially important for phonological processing and phonological working memory, capacities that are critical for language acquisition and for complex syntax processing. In the macaque, the homolog of the dorsal circuit overlaps with an inferior parietal–premotor network for hand and gesture selection that is under voluntary control, while vocalizations are largely fixed and involuntary. The recruitment of the dorsal component for vocalization behavior in the human lineage, together with a direct cortical control of the subcortical vocalizing system, are proposed to represent a fundamental innovation in human evolution, generating an inflection point that permitted the explosion of vocal language and human communication. In this context, vocal communication and gesturing have a common history in primate communication.

Integration of faces and vocalizations in ventral prefrontal cortex: Implications for the evolution of audiovisual speech

“…These combined data are consistent with a role for VLPFC in a ventral auditory processing stream for auditory objects, including vocalizations. The localization of this auditory processing area to the ventral prefrontal region of Old World monkeys suggests a functional similarity between it and human language-processing regions in the ventral or inferior frontal lobe of the human brain (10,71,72).…”

Word learning is mediated by the left arcuate fasciculus

“…Axonal tracing studies in monkey have shown that the AF connects to more dorsal regions of the temporo-parietal cortex (11,14), whereas diffusion tensor imaging (DTI) studies in humans show a greater level of connectivity to auditory regions of the temporal lobe (10,12). On the basis of these anatomical differences between human and other species, it has been suggested that the evolutionary expansion of auditory-motor connections allowed humans to develop a system for auditory working memory critical for learning complex phonological sequences (1,15). There is, however, no experimental evidence so far that links the anatomy of the AF with word learning ability.…”

Keeping timbre in mind: Working memory for complex sounds that can't be verbalized.

“…Within Baddeley's classic model of workitig memory the auditory component is represented by the concept of the "phonological loop," consisting of a phonological store, which can hold acoustic or speech information for 1-2 seconds, and an articulatory control process, which can refresh and thereby maintain information held in the phonological store indefinitely via rehearsal (Baddeley, 1986(Baddeley, , 1992. Processes underlying the phonological loop likely rely on lateral prefrontal, temporoparietal, and posterior superior temporal brain areas connected by a nerve fiber tract, the arcuate fasciculus, and, as such, the phonological loop spans a sensorimotor interface that serves to maintain and shape both verbal and tonal information (Aboitiz, 2012;Hickok, Buchsbaum, Humphries, & Muftuler, 2003;Hickok & Poeppel, 2007;Koelsch et al, 2009;Loui, Alsop, & Schlaug, 2009). How well multiple abstract nonverbalizable sounds that are of a constant pitch might be supported by a phonological loop mechanism is not known.…”