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Semantics and Pragmatics of Monkey Communication  

Philippe Schlenker, Emmanuel Chemla, and Klaus Zuberbühler

Rich data gathered in experimental primatology in the last 40 years are beginning to benefit from analytical methods used in contemporary linguistics, especially in the area of semantics and pragmatics. These methods have started to clarify five questions: (i) What morphology and syntax, if any, do monkey calls have? (ii) What is the ‘lexical meaning’ of individual calls? (iii) How are the meanings of individual calls combined? (iv) How do calls or call sequences compete with each other when several are appropriate in a given situation? (v) How did the form and meaning of calls evolve? Four case studies from this emerging field of ‘primate linguistics’ provide initial answers, pertaining to Old World monkeys (putty-nosed monkeys, Campbell’s monkeys, and colobus monkeys) and New World monkeys (black-fronted Titi monkeys). The morphology mostly involves simple calls, but in at least one case (Campbell’s -oo) one finds a root–suffix structure, possibly with a compositional semantics. The syntax is in all clear cases simple and finite-state. With respect to meaning, nearly all cases of call concatenation can be analyzed as being semantically conjunctive. But a key question concerns the division of labor between semantics, pragmatics, and the environmental context (‘world’ knowledge and context change). An apparent case of dialectal variation in the semantics (Campbell’s krak) can arguably be analyzed away if one posits sufficiently powerful mechanisms of competition among calls, akin to scalar implicatures. An apparent case of noncompositionality (putty-nosed pyow–hack sequences) can be analyzed away if one further posits a pragmatic principle of ‘urgency’. Finally, rich Titi sequences in which two calls are re-arranged in complex ways so as to reflect information about both predator identity and location are argued not to involve a complex syntax/semantics interface, but rather a fine-grained interaction between simple call meanings and the environmental context. With respect to call evolution, the remarkable preservation of call form and function over millions of years should make it possible to lay the groundwork for an evolutionary monkey linguistics, illustrated with cercopithecine booms.

Article

The Social Brain Hypothesis and Human Evolution  

Robin I. M. Dunbar

Primate societies are unusually complex compared to those of other animals, and the need to manage such complexity is the main explanation for the fact that primates have unusually large brains. Primate sociality is based on bonded relationships that underpin coalitions, which in turn are designed to buffer individuals against the social stresses of living in large, stable groups. This is reflected in a correlation between social group size and neocortex size in primates (but not other species of animals), commonly known as the social brain hypothesis, although this relationship itself is the outcome of an underlying relationship between brain size and behavioral complexity. The relationship between brain size and group size is mediated, in humans at least, by mentalizing skills. Neuropsychologically, these are all associated with the size of units within the theory of mind network (linking prefrontal cortex and temporal lobe units). In addition, primate sociality involves a dual-process mechanism whereby the endorphin system provides a psychopharmacological platform off which the cognitive component is then built. This article considers the implications of these findings for the evolution of human cognition over the course of hominin evolution.

Article

Somatosensory System Organization in Mammals and Response to Spinal Injury  

Corinna Darian-Smith and Karen Fisher

Spinal cord injury (SCI) affects well over a million people in the United States alone, and its personal and societal costs are huge. This article provides a current overview of the organization of somatosensory and motor pathways, in the context of hand/paw function in nonhuman primate and rodent models of SCI. Despite decades of basic research and clinical trials, therapeutic options remain limited. This is largely due to the fact that (i) spinal cord structure and function is very complex and still poorly understood, (ii) there are many species differences which can make translation from the rodent to primate difficult, and (iii) we are still some way from determining the detailed multilevel pathway responses affecting recovery. There has also been little focus, until recently, on the sensory pathways involved in SCI and recovery, which are so critical to hand function and the recovery process. The potential for recovery in any individual depends on many factors, including the location and size of the injury, the extent of sparing of fiber tracts, and the post-injury inflammatory response. There is also a progression of change over the first weeks and months that must be taken into account when assessing recovery. There are currently no good biomarkers of recovery, and while axon terminal sprouting is frequently used in the experimental setting as an indicator of circuit remodeling and “recovery,” the correlation between sprouting and functional recovery deserves scrutiny.

Article

What is a Sequence? The Neural Mechanisms of Perceptual, Motor, and Task Sequences Across Species and Their Interaction with Addiction  

Theresa M. Desrochers and Theresa H. McKim

Sequences permeate daily life. They can be defined as a discrete series of items or states that occur in a specific order with a beginning and end. The brain supports the perception and execution of sequences. Perceptual sequences involve tracking regularities in incoming stimuli, such as the series of sounds that make up a word in language. Executed sequences range from the series of muscle activations used by a frog to catch a fly to a chess master mapping her next moves. How the brain controls sequences must therefore scale to multiple levels of control. Investigating how the brain functions to accomplish this task spans from the study of individual cells in the brain to human cognition. Understanding the neural systems that underlie sequential control is necessary to approach the mechanistic underpinnings of complex conditions such as addiction, which may be rooted in difficult-to-extinguish sequential behaviors. Current research focuses on studies in both animal and human models and spans the levels of complexity of sequential control and the brain systems that support it.

Article

Auditory Processing in the Aging Brain  

Gregg Recanzone

Age-related hearing loss affects over half of the elderly population, yet it remains poorly understood. Natural aging can cause the input to the brain from the cochlea to be progressively compromised in most individuals, but in many cases the cochlea has relatively normal sensitivity and yet people have an increasingly difficult time processing complex auditory stimuli. The two main deficits are in sound localization and temporal processing, which lead to poor speech perception. Animal models have shown that there are multiple changes in the brainstem, midbrain, and thalamic auditory areas as a function of age, giving rise to an alteration in the excitatory/inhibitory balance of these neurons. This alteration is manifest in the cerebral cortex as higher spontaneous and driven firing rates, as well as broader spatial and temporal tuning. These alterations in cortical responses could underlie the hearing and speech processing deficits that are common in the aged population.

Article

Motion Processing in Primates  

Tyler S. Manning and Kenneth H. Britten

The ability to see motion is critical to survival in a dynamic world. Decades of physiological research have established that motion perception is a distinct sub-modality of vision supported by a network of specialized structures in the nervous system. These structures are arranged hierarchically according to the spatial scale of the calculations they perform, with more local operations preceding those that are more global. The different operations serve distinct purposes, from the interception of small moving objects to the calculation of self-motion from image motion spanning the entire visual field. Each cortical area in the hierarchy has an independent representation of visual motion. These representations, together with computational accounts of their roles, provide clues to the functions of each area. Comparisons between neural activity in these areas and psychophysical performance can identify which representations are sufficient to support motion perception. Experimental manipulation of this activity can also define which areas are necessary for motion-dependent behaviors like self-motion guidance.

Article

Visual Attention  

Sabine Kastner and Timothy J. Buschman

Natural scenes are cluttered and contain many objects that cannot all be processed simultaneously. Due to this limited processing capacity, neural mechanisms are needed to selectively enhance the information that is most relevant to one’s current behavior and to filter unwanted information. We refer to these mechanisms as “selective attention.” Attention has been studied extensively at the behavioral level in a variety of paradigms, most notably, Treisman’s visual search and Posner’s paradigm. These paradigms have also provided the basis for studies directed at understanding the neural mechanisms underlying attentional selection, both in the form of neuroimaging studies in humans and intracranial electrophysiology in non-human primates. The selection of behaviorally relevant information is mediated by a large-scale network that includes regions in all major lobes as well as subcortical structures. Attending to a visual stimulus modulates processing across the visual processing hierarchy with stronger effects in higher-order areas. Current research is aimed at characterizing the functions of the different network nodes as well as the dynamics of their functional connectivity.

Article

Technological Origins: Primate Perspectives and Early Hominin Tool Use in Africa  

Susana Carvalho and Megan Beardmore-Herd

The origin of technology is believed to have marked a major adaptive shift in human evolution. Understanding the evolutionary process(es) underlying the first human adaptation to tool use, and the subsequent process(es) that led Homo sapiens to become the only extant primate fully dependent on technology, is one of the most stimulating topics of research of present-day archaeology. New fields of research have been founded (e.g. primate archaeology, Pliocene archaeology) during the quest to find out how old technology is, where it originated, and who were the first tool users. Historically, the vast majority of the information on this topic comes from the study of lithic (stone) tools, tools whose manufacture was generally believed to be a uniquely human characteristic until well into the 1960s. The production of lithic technology was linked first to the origin of the earliest hominins (the taxonomic group comprising modern humans, extinct human species, and all immediate human ancestors), being thought to have co-evolved with traits such as bipedalism or hunting/scavenging, and later to the evolution of the genus Homo and accompanying increases in brain size. As a result of breakthroughs in the field of primatology, and greater interdisciplinary work between archaeologists and primatologists, a paradigm shift in beliefs surrounding the uniqueness of human technology is underway. Following discoveries from the second half of the 20th century and the early 21st century, habitual tool use, tool manufacture, and the production of flakes are now known to occur in extant non-human species, firmly decoupling brain size expansion, bipedalism, and the origins of technology. Knapped stone tools and cut-marked bones have been discovered dating to ca. half a million years before the earliest evidence of Homo, giving rise to the possibility that earlier, previously unconsidered hominins, or even other extinct non-human primates, could have been responsible for the inception of tool use and manufacture. Following these advances, it is reasonable to hypothesize that the origins of technology may lie much further back in time than the earliest discovered modified stone tools—perhaps as far back as the late Miocene with the last common ancestor of Homo and Pan. Moreover, discoveries of lithic technology in more distantly related species, where convergent evolution is the most parsimonious explanation, strongly suggest the existence of multiple evolutionary pathways for technological emergence. While there is still much to unearth, the extension of the antiquity of modified stone tools, combined with the increased focus on interdisciplinary studies between archaeologists, primatologists, and paleoanthropologists, has gone a long way in overturning outdated beliefs by demonstrating that the development of technology is unlikely to have been a simple, linear process resulting from a single event or factor in the evolutionary history of humans.

Article

Pragmatics and Language Evolution  

Marieke Woensdregt and Kenny Smith

Pragmatics is the branch of linguistics that deals with language use in context. It looks at the meaning linguistic utterances can have beyond their literal meaning (implicature), and also at presupposition and turn taking in conversation. Thus, pragmatics lies on the interface between language and social cognition. From the point of view of both speaker and listener, doing pragmatics requires reasoning about the minds of others. For instance, a speaker has to think about what knowledge they share with the listener to choose what information to explicitly encode in their utterance and what to leave implicit. A listener has to make inferences about what the speaker meant based on the context, their knowledge about the speaker, and their knowledge of general conventions in language use. This ability to reason about the minds of others (usually referred to as “mindreading” or “theory of mind”) is a cognitive capacity that is uniquely developed in humans compared to other animals. What we know about how pragmatics (and the underlying ability to make inferences about the minds of others) has evolved. Biological evolution and cultural evolution are the two main processes that can lead to the development of a complex behavior over generations, and we can explore to what extent they account for what we know about pragmatics. In biological evolution, changes happen as a result of natural selection on genetically transmitted traits. In cultural evolution on the other hand, selection happens on skills that are transmitted through social learning. Many hypotheses have been put forward about the role that natural selection may have played in the evolution of social and communicative skills in humans (for example, as a result of changes in food sources, foraging strategy, or group size). The role of social learning and cumulative culture, however, has been often overlooked. This omission is particularly striking in the case of pragmatics, as language itself is a prime example of a culturally transmitted skill, and there is solid evidence that the pragmatic capacities that are so central to language use may themselves be partially shaped by social learning. In light of empirical findings from comparative, developmental, and experimental research, we can consider the potential contributions of both biological and cultural evolutionary mechanisms to the evolution of pragmatics. The dynamics of types of evolutionary processes can also be explored using experiments and computational models.

Article

Central Auditory Processing  

Josef P. Rauschecker

When one talks about hearing, some may first imagine the auricle (or external ear), which is the only visible part of the auditory system in humans and other mammals. Its shape and size vary among people, but it does not tell us much about a person’s abilities to hear (except perhaps their ability to localize sounds in space, where the shape of the auricle plays a certain role). Most of what is used for hearing is inside the head, particularly in the brain. The inner ear transforms mechanical vibrations into electrical signals; then the auditory nerve sends these signals into the brainstem, where intricate preprocessing occurs. Although auditory brainstem mechanisms are an important part of central auditory processing, it is the processing taking place in the cerebral cortex (with the thalamus as the mediator), which enables auditory perception and cognition. Human speech and the appreciation of music can hardly be imagined without a complex cortical network of specialized regions, each contributing different aspects of auditory cognitive abilities. During the evolution of these abilities in higher vertebrates, especially birds and mammals, the cortex played a crucial role, so a great deal of what is referred to as central auditory processing happens there. Whether it is the recognition of one’s mother’s voice, listening to Pavarotti singing or Yo-Yo Ma playing the cello, hearing or reading Shakespeare’s sonnets, it will evoke electrical vibrations in the auditory cortex, but it does not end there. Large parts of frontal and parietal cortex receive auditory signals originating in auditory cortex, forming processing streams for auditory object recognition and auditory-motor control, before being channeled into other parts of the brain for comprehension and enjoyment.