Speech and language are considered uniquely human abilities: animals have communication systems, but they do not match human linguistic skills in terms of recursive structure and combinatorial power. Yet, in evolution, spoken language must have emerged from neural mechanisms at least partially available in animals. In this paper, we will demonstrate how our understanding of speech perception, one important facet of language, has profited from findings and theory in nonhuman primate studies. Chief among these are physiological and anatomical studies showing that primate auditory cortex, across species, shows patterns of hierarchical structure, topographic mapping and streams of functional processing. We will identify roles for different cortical areas in the perceptual processing of speech and review functional imaging work in humans that bears on our understanding of how the brain decodes and monitors speech. A new model connects structures in the temporal, frontal and parietal lobes linking speech perception and production.Our understanding of speech processing has both benefited and suffered from developments in neuroscience. The basic brain areas important for speech perception and production were established in the nineteenth century, and although our conception of their exact anatomy and function has changed substantially, some of the findings of Broca 1 and Wernicke 2 still stand (Supplementary Discussion 1 and Supplementary Fig. 1 online). What has lagged behind is a good model of how the brain decodes spoken language and how speech perception and speech production are linked. For example, the frameworks for cortical processes and pathways have taken longer to form in audition than in vision, and animal models of language have severe limitations 3 . The evolution of speech and language are likely to have depended on neural systems available in other primate brains. In this paper, we will demonstrate how our understanding of speech perception, one important facet of language, has profited from work in nonhuman primate studies. Streams and hierarchies in nonhuman primate auditory cortex'What' and 'where' pathways in vision and audition A decade ago, it was suggested that auditory cortical processing pathways are organized dually, similar to those in the visual cortex ( Fig. 1 the primary sensory areas into posterior parietal cortex, another pathway into anterior temporal cortex. As in the visual system 6 , the posterior parietal pathway was hypothesized to subserve spatial processing in audition while the temporal pathway subserved the identification of complex patterns or objects. Per the directions of their projections in the auditory system, these pathways were referred to as the postero-dorsal and antero-ventral streams, respectively.Anatomical tract tracing studies in monkeys support separate anterior and posterior projection streams in auditory cortex 7,8 . The long-range connections from the surrounding belt areas project from anterior belt directly to ventrolateral prefrontal cortex (PFC) an...

It has been proposed that the identification of sounds, including species-specific vocalizations, by primates depends on anterior projections from the primary auditory cortex, an auditory pathway analogous to the ventral route proposed for the visual identification of objects. We have identified a similar route in the human for understanding intelligible speech. Using PET imaging to identify separable neural subsystems within the human auditory cortex, we used a variety of speech and speech-like stimuli with equivalent acoustic complexity but varying intelligibility. We have demonstrated that the left superior temporal sulcus responds to the presence of phonetic information, but its anterior part only responds if the stimulus is also intelligible. This novel observation demonstrates a left anterior temporal pathway for speech comprehension.

Emotional signals are crucial for sharing important information, with conspecifics, for example, to warn humans of danger. Humans use a range of different cues to communicate to others how they feel, including facial, vocal, and gestural signals. We examined the recognition of nonverbal emotional vocalizations, such as screams and laughs, across two dramatically different cultural groups. Western participants were compared to individuals from remote, culturally isolated Namibian villages. Vocalizations communicating the so-called “basic emotions” (anger, disgust, fear, joy, sadness, and surprise) were bidirectionally recognized. In contrast, a set of additional emotions was only recognized within, but not across, cultural boundaries. Our findings indicate that a number of primarily negative emotions have vocalizations that can be recognized across cultures, while most positive emotions are communicated with culture-specific signals

A core difficulty in developmental dyslexia is the accurate specification and neural representation of speech. We argue that a likely perceptual cause of this difficulty is a deficit in the perceptual experience of rhythmic timing. Speech rhythm is one of the earliest cues used by infants to discriminate syllables and is determined principally by the acoustic structure of amplitude modulation at relatively low rates in the signal. We show significant differences between dyslexic and normally reading children, and between young early readers and normal developers, in amplitude envelope onset detection. We further show that individual differences in sensitivity to the shape of amplitude modulation account for 25% of the variance in reading and spelling acquisition even after controlling for individual differences in age, nonverbal IQ, and vocabulary. A possible causal explanation dependent on perceptual-center detection and the onset-rime representation of syllables is discussed.