The faculty of language: what's special about it?

FOXP2 and the role of cortico-basal ganglia circuits in speech and language evolution

PURPOSE OF THE REVIEW

A reduced dosage of the transcription factor FOXP2 leads to speech and language impairments probably owing to deficits in cortical and subcortical neural circuits. Based on evolutionary sequence analysis it has been proposed that the two amino acid substitutions that occurred on the human lineage have been positively selected. Here I review recent studies investigating the functional consequences of these two substitutions and discuss how these first endeavors to study human brain evolution can be interpreted in the context of speech and language evolution.

RECENT FINDINGS

Mice carrying the two substitutions in their endogenous Foxp2 gene show specific alterations in dopamine levels, striatal synaptic plasticity and neuronal morphology. Mice carrying only one functional Foxp2, show additional and partly opposite effects suggesting that FOXP2 has contributed to tuning cortico-basal ganglia circuits during human evolution. Evidence from human and songbird studies suggest that this could have been relevant during language acquisition or vocal learning, respectively.

SUMMARY

FOXP2 could have contributed to the evolution of human speech and language by adapting cortico-basal ganglia circuits. More generally the recent studies allow careful optimism that aspects of human brain evolution can be investigated in model systems such as the mouse.

The gradual emergence of phonological form in a new language

The division of linguistic structure into a meaningless (phonological) level and a meaningful level of morphemes and words is considered a basic design feature of human language. Although established sign languages, like spoken languages, have been shown to be characterized by this bifurcation, no information has been available about the way in which such structure arises. We report here on a newly emerging sign language, Al-Sayyid Bedouin Sign Language, which functions as a full language but in which a phonological level of structure has not yet emerged. Early indications of formal regularities provide clues to the way in which phonological structure may develop over time.

Unity and diversity in human language

Human language is both highly diverse-different languages have different ways of achieving the same functional goals-and easily learnable. Any language allows its users to express virtually any thought they can conceptualize. These traits render human language unique in the biological world. Understanding the biological basis of language is thus both extremely challenging and fundamentally interesting. I review the literature on linguistic diversity and language universals, suggesting that an adequate notion of 'formal universals' provides a promising way to understand the facts of language acquisition, offering order in the face of the diversity of human languages. Formal universals are cross-linguistic generalizations, often of an abstract or implicational nature. They derive from cognitive capacities to perceive and process particular types of structures and biological constraints upon integration of the multiple systems involved in language. Such formal universals can be understood on the model of a general solution to a set of differential equations; each language is one particular solution. An explicit formal conception of human language that embraces both considerable diversity and underlying biological unity is possible, and fully compatible with modern evolutionary theory.

Perceptual and conceptual priming of environmental sounds

It is still unknown whether sonic environments influence the processing of individual sounds in a similar way as discourse or sentence context influences the processing of individual words. One obstacle to answering this question has been the failure to dissociate perceptual (i.e., how similar are sonic environment and target sound?) and conceptual (i.e., how related are sonic environment and target?) priming effects. In this study, we dissociate these effects by creating prime-target pairs with a purely perceptual or both a perceptual and conceptual relationship. Perceptual prime-target pairs were derived from perceptual-conceptual pairs (i.e., meaningful environmental sounds) by shuffling the spectral composition of primes and targets so as to preserve their perceptual relationship while making them unrecognizable. Hearing both original and shuffled targets elicited a more positive N1/P2 complex in the ERP when targets were related to a preceding prime as compared with unrelated. Only related original targets reduced the N400 amplitude. Related shuffled targets tended to decrease the amplitude of a late temporo-parietal positivity. Taken together, these effects indicate that sonic environments influence first the perceptual and then the conceptual processing of individual sounds. Moreover, the influence on conceptual processing is comparable to the influence linguistic context has on the processing of individual words.

Bards, poets, and cliques: frequency-dependent selection and the evolution of language genes

The ability of humans to communicate via language is a complex, adapted phenotype, which undoubtedly has a recently evolved genetic component. However, the evolutionary dynamics of language-associated alleles are poorly understood. To improve our knowledge of such systems, a population-genetics model for language-associated genes is developed. (The model is general and applicable to social interactions other than communication.) When an allele arises that potentially improves the ability of individuals to communicate, it will experience positive frequency-dependent selection because its fitness will depend on how many other individuals communicate the same way. Consequently, new and rare alleles are selected against, posing a problem for the evolutionary origin of language. However, the model shows that if individuals form language-based cliques, then novel language-associated alleles can sweep through a population. Thus, the origin of language ability can be sufficiently explained by Darwinian processes operating on genetic diversity in a finite population of human ancestors.

Negation, questions, and structure building in a homesign system

Deaf children whose hearing losses are so severe that they cannot acquire spoken language, and whose hearing parents have not exposed them to sign language, use gestures called homesigns to communicate. Homesigns have been shown to contain many of the properties of natural languages. Here we ask whether homesign has structure building devices for negation and questions. We identify two meanings (negation, question) that correspond semantically to propositional functions, that is, to functions that apply to a sentence (whose semantic value is a proposition, ϕ) and yield another proposition that is more complex (¬ϕ for negation; ?ϕ for question). Combining ϕ with ¬ or ? thus involves sentence modification. We propose that these negative and question functions are structure building operators, and we support this claim with data from an American homesigner. We show that: (a) each meaning is marked by a particular form in the child's gesture system (side-to-side headshake for negation, manual flip for question); (b) the two markers occupy systematic, and different, positions at the periphery of the gesture sentences (headshake at the beginning, flip at the end); and (c) the flip is extended from questions to other uses associated with the wh-form (exclamatives, referential expressions of location) and thus functions like a category in natural languages. If what we see in homesign is a language creation process (Goldin-Meadow, 2003), and if negation and question formation involve sentential modification, then our analysis implies that homesign has at least this minimal sentential syntax. Our findings thus contribute to ongoing debates about properties that are fundamental to language and language learning.

Twitter evolution: converging mechanisms in birdsong and human speech

Vocal imitation in human infants and in some orders of birds relies on auditory-guided motor learning during a sensitive period of development. It proceeds from 'babbling' (in humans) and 'subsong' (in birds) through distinct phases towards the full-fledged communication system. Language development and birdsong learning have parallels at the behavioural, neural and genetic levels. Different orders of birds have evolved networks of brain regions for song learning and production that have a surprisingly similar gross anatomy, with analogies to human cortical regions and basal ganglia. Comparisons between different songbird species and humans point towards both general and species-specific principles of vocal learning and have identified common neural and molecular substrates, including the forkhead box P2 (FOXP2) gene.

Recursion in aphasia

This study investigates how aphasic impairment impinges on syntactic and/or semantic recursivity of human language. A series of tests has been conducted with the participation of five Hungarian speaking aphasic subjects and 10 control subjects. Photographs representing simple situations were presented to subjects and questions were asked about them. The responses are supposed to involve formal structural recursion, but they contain semantic-pragmatic operations instead, with 'theory of mind' type embeddings. Aphasic individuals tend to exploit the parallel between 'theory of mind' embeddings and syntactic-structural embeddings in order to avoid formal structural recursion. Formal structural recursion may be more impaired in Broca's aphasia and semantic recursivity may remain selectively unimpaired in this type of aphasia.

The application of rules in morphology, syntax and number processing: a case of selective deficit of procedural or executive mechanisms?

Declarative memory is a long-term store for facts, concepts and words. Procedural memory subserves the learning and control of sensorimotor and cognitive skills, including the mental grammar. In this study, we report a single-case study of a mild aphasic patient who showed procedural deficits in the presence of preserved declarative memory abilities. We administered several experiments to explore rule application in morphology, syntax and number processing. Results partly support the differentiation between declarative and procedural memory. Moreover, the patient's performance varied according to the domain in which rules were to be applied, which underlines the need for more fine-grained distinctions in cognition between procedural rules.

The redundancy of recursion and infinity for natural language

An influential line of thought claims that natural language and arithmetic processing require recursion, a putative hallmark of human cognitive processing (Chomsky in Evolution of human language: biolinguistic perspectives. Cambridge University Press, Cambridge, pp 45-61, 2010; Fitch et al. in Cognition 97(2):179-210, 2005; Hauser et al. in Science 298(5598):1569-1579, 2002). First, we question the need for recursion in human cognitive processing by arguing that a generally simpler and less resource demanding process--iteration--is sufficient to account for human natural language and arithmetic performance. We argue that the only motivation for recursion, the infinity in natural language and arithmetic competence, is equally approachable by iteration and recursion. Second, we submit that the infinity in natural language and arithmetic competence reduces to imagining infinite embedding or concatenation, which is completely independent from the ability to implement infinite processing, and thus, independent from both recursion and iteration. Furthermore, we claim that a property of natural language is physically uncountable finity and not discrete infinity.

Construction grammar

Construction grammar, or constructionist approaches more generally, emphasize the function of particular constructions as well as their formal properties. Constructions vary in their degree of generality, from words to idioms to more abstract patterns such as argument structure constructions, topicalization, and passive. There is also no division drawn between semantics and pragmatics, as all conventional aspects of constructions are encoded within the constructions themselves; thus constructions can include information about information structure, register, or genre. The majority of constructionist approaches are also usage based, in that they recognize that we retain a great deal of item-specific information. An important desideratum of constructionist approaches is that they interface naturally with what we know about language acquisition, language change, and language typology. In order to capture generalizations within a given language, constructions are related via an inheritance hierarchy, with more abstract, productive constructions being directly related to their more idiomatic instantiations. The functions of particular constructions as well as domain general cognitive and social cognition are appealed in order to capture cross-linguistically valid typological generalizations. Copyright © 2010 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.

Charles Darwin and the evolution of human grammatical systems

Charles Darwin's evolutionary theories of animal communication were deeply embedded in a centuries-old model of association psychology, whose prodromes have most often been traced to the writings of Aristotle. His notions of frequency of occurrence of pairings have been passed down through the centuries and were a major ontological feature in the formation of associative connectivity. He focused on the associations of cause and effect, contiguity of sequential occurrence, and similarity among items. Cause and effect were often reduced to another type of contiguity relation, so that Aristotle is most often evoked as the originator of the associative bondings through similarity and contiguity, contiguity being the most powerful and frequent means of association. Contiguity eventually became the overriding mechanism for serial ordering of mental events in both perception and action. The notions of concatenation throughout the association psychology took the form of "trains" of events, both sensory and motor, in such a way that serial ordering came to be viewed as an item-by-item string of locally contiguous events. Modern developments in the mathematics of serial ordering have advanced in sophistication since the early and middle twentieth century, and new computational methods have allowed us to reevaluate the serial concatenative theories of Darwin and the associationists. These new models of serial order permit a closer comparative scrutiny between human and nonhuman. The present study considers Darwin's insistence on a "degree" continuity between human and nonhuman animal serial ordering. We will consider a study of starling birdsongs and whether the serial ordering of those songs provides evidence that they have a syntax that at best differs only in degree and not in kind with the computations of human grammatical structures. We will argue that they, in fact, show no such thing.

13 Networks II: Teamwork

This chapter shows that for many tasks the use of signals is crucial in establishing the coordination needed for effective teamwork. Teamwork may in some circumstances be achieved by a simple exchange of signals between equals. In other situations a good team may need a leader.

3 Information

This chapter shows that information is carried by signals. It flows through signaling networks that not only transmit it, but also filter, combine, and process it in various ways. We can investigate the flow of information using a framework of generalized signaling games. The dynamics of evolution and learning in these games illuminate the creation and flow of information.

7 Learning

This chapter argues that investigation of reinforcement learning is a complement to the study of belief learning, rather than being a ‘dangerous antagonist’. It begins at the low end of the scale, to see how far simple reinforcement learning can get us, and then move up. Exactly how does degree of reinforcement affect the strengthening of the bond between stimulus and response? Different answers are possible, and these yield alternative theories of the law of effect.

11 Networks I: Logic and Information Processing

This chapter discusses the combination of simple signals to form complex signals. When multiple senders convey different information to a receiver (or to multiple receivers) the receiver is confronted with a problem of information processing. How does one take all these inputs and fix on what to output — what to do? Logical inference is only part of this bigger problem of information processing. It is a problem routinely solved every second by our nervous system as floods of sensory information are filtered, integrated, and used to control conscious and unconscious actions.

12 Complex Signals and Compositionality

This chapter focuses on an earlier point in the evolution of signaling. It considers how one might come to have — in the most primitive way — a complex signal composed of simple signals. This is done with the smallest departure possible from signaling models that have been previously examined in this book.

5 Evolution in Lewis Signaling Games

Signaling systems had been shown to be the only evolutionarily stable strategies in n-state, n-signal, and n-act signaling games. They were the only attractors in the replicator dynamics. In simple cases, it was clear why almost every possible starting point was carried to a signaling system. This chapter considers how far these positive results generalize.

2 Signals in Nature

This chapter surveys some of the signaling systems in nature. Darwin sees some kind of natural salience operating at the origin of language. At that point signals are not conventional, but rather the signal is somehow naturally suited to convey its content. Signaling is then gradually modified by evolution.

10 Inventing New Signals

This chapter presents a simple, tractable model for the invention of new signals. It can be easily studied by simulation, and connections with well-studied processes from population genetics suggest that analytic results are not completely out of reach.

6 Deception

This chapter shows that in all kinds of signaling systems in nature there is information transmission which is sufficient to maintain signaling, but there is also misinformation and even deception. Misinformation is straightforward. If receipt of a signal moves probabilities of states it contains information about the state. If it moves the probability of a state in the wrong direction — either by diminishing the probability of the state in which it is sent, or raising the probability of a state other than the one in which it is sent — then it is misleading information, or misinformation. If misinformation is sent systematically and benefits the sender at the expense of the receiver, then it is deception.

8 Learning in Lewis Signaling Games

This chapter argues that we can and do learn to signal. We are not the only species able to do this, although others may not do it so well. The real question is what is required to be able to learn to signal. Or, better, what kind of learning is capable of spontaneously generating signaling? If the learning somehow has the signaling system preprogramed in, then learning to signal is not very interesting. If the learning mechanism is general purpose and low level, learning to signal is quite interesting.

14 Learning to Network

This chapter introduces a low-rationality probe and adjust dynamics to approximate higher rationality learning in the basic Bala–Goyal models. Both best response dynamics and probe and adjust learned networks that reinforcement learning did not. In general, probe and adjust learns a network structure if best response with inertia does.

9 Generalizing Signaling Games: Synonyms, Bottlenecks, Category Formation

This chapter presents a model of signaling with invention of new signals. It maintains the assumption that in all contingencies sender and receiver get the same payoff. But even where sender and receiver continue to have pure common interest, relaxing the strict assumptions on payoffs imposed so far may lead to new phenomena.

1 Signals

Whatever one thinks of human signals, it must be acknowledged that information is transmitted by signaling systems at all levels of biological organization. Monkeys, birds, bees, and even bacteria have signaling systems. Multicellular organisms are only possible because internal signals coordinate the actions of their constituents. This chapter addresses two main questions: How can interacting individuals spontaneously learn to signal? How can species spontaneously evolve signalling systems? It discusses how we can bring contemporary theoretical tools to bear on these questions.

4 Evolution

Darwin was right about the broad outlines of the theory of evolution. Traits are inherited by some unknown mechanism. There is some process that produces natural variation in these traits. The traits may affect the ability of the organism to reproduce, and thus the average number of individuals bearing the traits in the next generation. Therefore, those traits that enhance reproductive success increase in frequency in the population, and those that lead to reproductive success below the average decrease in frequency. This chapter discusses the three essential factors in Darwin's account: (i) natural variation, (ii) differential reproduction, and (iii) inheritance.

Introduction

This introductory chapter begins with a discussion of signalling. It then argues that the relation of signalling theory to philosophy is epistemology, because it deals with selection, transmission, and processing of information. It is philosophy of (proto)-language. It addresses cooperation and collective action — issues that usually reside in social and political philosophy.

Wernicke's area homologue in chimpanzees (Pan troglodytes) and its relation to the appearance of modern human language

Human language is distinctive compared with the communication systems of other species. Yet, several questions concerning its emergence and evolution remain unresolved. As a means of evaluating the neuroanatomical changes relevant to language that accompanied divergence from the last common ancestor of chimpanzees, bonobos and humans, we defined the cytoarchitectonic boundaries of area Tpt, a component of Wernicke's area, in 12 common chimpanzee brains and used design-based stereologic methods to estimate regional volumes, total neuron number and neuron density. In addition, we created a probabilistic map of the location of area Tpt in a template chimpanzee brain coordinate space. Our results show that chimpanzees display significant population-level leftward asymmetry of area Tpt in terms of neuron number, with volume asymmetry approaching significance. Furthermore, asymmetry in the number of neurons in area Tpt was positively correlated with asymmetry of neuron numbers in Brodmann's area 45, a component of Broca's frontal language region. Our findings support the conclusion that leftward asymmetry of Wernicke's area originated prior to the appearance of modern human language and before our divergence from the last common ancestor. Moreover, this study provides the first evidence of covariance between asymmetry of anterior and posterior cortical regions that in humans are important to language and other higher order cognitive functions.

Word learning and lexical development across the lifespan

Word learning is one of the core components of language acquisition. In this article, we provide an overview of the theme issue on word learning, describing some of the ways in which research in the area has progressed and diverged. In recent years, word learning has become central in a wider range of research areas, and is important to research on adult, as well as child and infant language. We introduce 10 papers that cover the recent developments from a wide range of perspectives, focusing on developmental research, the influence of reading skills, neuroimaging and the relationship between word learning and general models of memory.

Cognitive systems struggling for word order

We argue that the grammatical diversity observed among the world's languages emerges from the struggle between individual cognitive systems trying to impose their preferred structure on human language. We investigate the cognitive bases of the two most common word orders in the world's languages: SOV (Subject-Object-Verb) and SVO. Evidence from language change, grammaticalization, stability of order, and theoretical arguments, indicates a syntactic preference for SVO. The reason for the prominence of SOV languages is not as clear. In two gesture-production experiments and one gesture comprehension experiment, we show that SOV emerges as the preferred constituent configuration in participants whose native languages (Italian and Turkish) have different word orders. We propose that improvised communication does not rely on the computational system of grammar. The results of a fourth experiment, where participants comprehended strings of prosodically flat words in their native language, shows that the computational system of grammar prefers the orthogonal Verb-Object orders.

The myth of language universals: language diversity and its importance for cognitive science

Talk of linguistic universals has given cognitive scientists the impression that languages are all built to a common pattern. In fact, there are vanishingly few universals of language in the direct sense that all languages exhibit them. Instead, diversity can be found at almost every level of linguistic organization. This fundamentally changes the object of enquiry from a cognitive science perspective. This target article summarizes decades of cross-linguistic work by typologists and descriptive linguists, showing just how few and unprofound the universal characteristics of language are, once we honestly confront the diversity offered to us by the world's 6,000 to 8,000 languages. After surveying the various uses of "universal," we illustrate the ways languages vary radically in sound, meaning, and syntactic organization, and then we examine in more detail the core grammatical machinery of recursion, constituency, and grammatical relations. Although there are significant recurrent patterns in organization, these are better explained as stable engineering solutions satisfying multiple design constraints, reflecting both cultural-historical factors and the constraints of human cognition. Linguistic diversity then becomes the crucial datum for cognitive science: we are the only species with a communication system that is fundamentally variable at all levels. Recognizing the true extent of structural diversity in human language opens up exciting new research directions for cognitive scientists, offering thousands of different natural experiments given by different languages, with new opportunities for dialogue with biological paradigms concerned with change and diversity, and confronting us with the extraordinary plasticity of the highest human skills.

Neuroplasticity associated with tactile language communication in a deaf-blind subject

A long-standing debate in cognitive neuroscience pertains to the innate nature of language development and the underlying factors that determine this faculty. We explored the neural correlates associated with language processing in a unique individual who is early blind, congenitally deaf, and possesses a high level of language function. Using functional magnetic resonance imaging (fMRI), we compared the neural networks associated with the tactile reading of words presented in Braille, Print on Palm (POP), and a haptic form of American Sign Language (haptic ASL or hASL). With all three modes of tactile communication, indentifying words was associated with robust activation within occipital cortical regions as well as posterior superior temporal and inferior frontal language areas (lateralized within the left hemisphere). In a normally sighted and hearing interpreter, identifying words through hASL was associated with left-lateralized activation of inferior frontal language areas however robust occipital cortex activation was not observed. Diffusion tensor imaging -based tractography revealed differences consistent with enhanced occipital-temporal connectivity in the deaf-blind subject. Our results demonstrate that in the case of early onset of both visual and auditory deprivation, tactile-based communication is associated with an extensive cortical network implicating occipital as well as posterior superior temporal and frontal associated language areas. The cortical areas activated in this deaf-blind subject are consistent with characteristic cortical regions previously implicated with language. Finally, the resilience of language function within the context of early and combined visual and auditory deprivation may be related to enhanced connectivity between relevant cortical areas.

Social neuroscience

Social species, by definition, create emergent organizations beyond the individual that range in humans from dyads, families, and groups to cities, civilizations, and cultures. These emergent structures evolved hand-in-hand with neural, hormonal, and genetic mechanisms to support them because the consequent social behaviors helped these organisms survive, reproduce, and care for offspring sufficiently long that they too survived to reproduce. Social neuroscience is concerned with investigating these emergent structures and the underlying neural, hormonal, and genetic mechanisms that make them possible. As such, it represents an interdisciplinary approach devoted to understanding how biological systems implement social processes and behavior, and to using biological concepts and methods to inform and refine theories of social processes and behavior. Copyright © 2009 John Wiley & Sons, Ltd. For further resources related to this article, please visit the WIREs website.