Language Evolution and Computation Bibliography

Contemporary disputes about the origins and evolution of language are reviewed. The main issues involved are: how many mutations gave rise to the Language faculty, whether a new cognitive domain was thereby created, how powerful Language was from the beginning, whether the initial function of Language was private thought or public communication, and whether natural selection influenced its rise.

The neurobiology of language has to specify the cognitive architecture of complex language functions such as speaking and comprehending language, and, in addition, how these functions are mapped onto the underlying anatomical and physiological building blocks of the brain (the neural architecture). Here it is argued that the constraints provided by the classical anatomical measures (cytoarchitectonics and myeloarchitectonics) are in our current understanding only very loose constraints for detailed specifications of cognitive functions, including language learning and language processing. However, measures of the computational features of brain tissue might provide stronger constraints. For understanding cognitive specialization, for the time being we thus have to put our cards on measures of functional instead of structural neuroanatomy. The implication for an evolutionary stance on the neurobiology of language is that in a crossspecies comparative perspective one needs to identify the factors that gave rise to the properties of the canonical microcircuits in the neocortex, and to the large scale network organization that created the language-readiness of the human brain.

Although humans are unmatched in their capacity to produce speech and learn language, comparative approaches in diverse animalmodelsareabletoshedlightonthebiologicalunderpinnings of language-relevant traits. In the study of vocal learning, a trait crucial for spoken language, passerine birds have been the dominant models, driving invaluable progress in understanding the neurobiology and genetics of vocal learning despite being only distantly related to humans. To date, there is sparse evidence that our closest relatives, nonhuman primates have the capability to learn new vocalisations. However, a number of other mammals have shown the capacity for vocal learning, such as some cetaceans, pinnipeds, elephants, and bats, and we anticipate that with further study more species will gain membership to this (currently) select club. A broad, cross-species comparison of vocal learning, coupled with careful consideration of the components underlying this trait, is crucial to determine how human speech and spoken language is biologically encoded and how it evolved. We emphasise the need to draw on the pool of promising species that havethusfarbeenunderstudiedorneglected.This isbynomeansa call for fewer studies in songbirds, or an unfocused treasure-hunt, but rather an appeal for structured comparisons across a range of species, considering phylogenetic relationships, ecological and morphological constrains, developmental and social factors, and neurogenetic underpinnings. Herein, we promote a comparative approachhighlightingthe importanceofstudyingvocal learning ina broad range of model species, and describe a common framework for targeted cross-taxon studies to shed light on the biology and evolution of vocal learning.

The search for the anatomical basis of language has traditionally been a search for specializations. More recently such research has focused both on aspects of brain organization that are unique to humans and aspects shared with other primates. This work has mostly concentrated on the architecture of connections between brain areas. However, as specializations can take many guises, comparison of anatomical organization across species is often complicated. We demonstrate how viewing different types of specializations within a common framework allows one to better appreciate both shared and unique aspects of brain organization. We illustrate this point by discussing recent insights into the anatomy of the dorsal language pathway to the frontal cortex and areas for laryngeal control in the motor cortex.

Predicting the occurrence of future events from prior ones is vital for animal perception and cognition. Although how such sequence learning (a form of relational knowledge) relates to particular operations in language remains controversial, recent evidence shows that sequence learning is disrupted in frontal lobe damage associated with aphasia. Also, neural sequencing predictions at different temporal scales resemble those involved in language operations occurring at similar scales. Furthermore, comparative work in humans and monkeys highlights evolutionarily conserved frontal substrates and predictive oscillatory signatures in the temporal lobe processing learned sequences of speech signals. Altogether this evidence supports a relational knowledge hypothesis of language evolution, proposing that language processes in humans are functionally integrated with an ancestral neural system for predictive sequence learning.

The production of vocalizations by monkeys and apes is often described as highly constrained and fundamentally different from human speech. We review recent field studies of baboons and bonobos that suggest greater flexibility. Calls function to reduce the uncertainty inherent in social interactions. Vocal production, like individuals’ responses to calls, is subtly tuned to variation in the social context, including a caller’s assessment of how a listener is likely to respond. We suggest parallels between the decision to vocalize and laboratory, neurophysiological tests of social decisions. We also discuss implications for theories of language evolution.

While a long history of neuropsychological research places language function within a primarily left-lateralized frontotemporal system, recent neuroimaging work has extended this language network to include a number of regions traditionally thought of as 'domain-general'. These include dorsal frontal, parietal, and medial temporal lobe regions known to underpin cognitive functions such as attention and memory. In this paper, we argue that these domain-general systems are not required for language processing and are instead an artefact of the tasks typically used to study language. Recent work from our lab shows that when syntactic processing - arguably the only domain-specific language function - is measured in a task-free, naturalistic manner, only the left-lateralized frontotemporal syntax system and auditory network are activated. When syntax is measured within the context of a task, several other domain-general networks come online and are functionally connected to the frontotemporal system. While we have long argued that syntactic processing does not occur in isolation but is processed in parallel with semantics and pragmatics - functions of the wider language system - our recent work makes a strong case for the domain-specificity of the frontotemporal syntax system and its autonomy from domain-general networks.

Progress in linking between the disparate levels of cognitive description and neural implementation requires explicit, testable, computationally based hypotheses. One such hypothesis is the dendrophilia hypothesis, which suggests that human syntactic abilities rely on our supra-regular computational abilities, implemented via an auxiliary memory store (a ‘stack’) centred on Broca’s region via its connections with other cortical areas. Because linguistic phonology requires less powerful computational abilities than this, at the finitestate level, I suggest that there may be continuity between animal rule learning and human phonology, and that the circuits underlying this provided the precursors of our unusual syntactic abilities.

Human language shows combinatoriality in its phonology (both in speech and in sign language) and its grammar, while both types appear to be absent in the communication systems of our closest evolutionary relatives. In this article, we observe that productive combinatoriality is difficult to evolve, because it requires multiple components to be put in place simultaneously for it to function. To understand how it nevertheless evolved in human language, we focus on combinatoriality in phonology, for which most evidence is available. We discuss findings and theories from three domains: linguistics (descriptive, experimental and corpus linguistics), comparative biology (including some fossil indicators) and (computer) models. We tentatively conclude that many of the biological prerequisites for combinatorial phonology and compositional semantics are shared with other animals, but that a uniquely human pressure for large vocabularies and uniquely human processes of cultural evolution are key in understanding the origins of combinatoriality in language

Structured sequence processing tasks inform us about statistical learning abilities that are relevant to many areas of cognition, including language. Despite the ubiquity of these abilities across different tasks and cognitive domains, recent research in humans has demonstrated that these cognitive capacities do not represent a single, domain-general system, but are subject to modality-specific and stimulusspecific constraints. Sequence processing studies in nonhuman primates have provided initial insights into the evolution of these abilities. However, few studies have examined similarities and/or differences in sequence learning across sensory modalities. We review how behavioural and neuroimaging experiments assess sequence processing abilities across sensory modalities, and how these tasks could be implemented in nonhuman primates to better understand the evolution of these cognitive systems.