Cracking the Speech Code: The Neural and Perceptual Encoding of the Speech Signal – SpeechCode

Human language had been, for a long time, viewed as an abstract, discrete and symbolic mental system divorced from its physical implementations. While fruitful and productive when describing the mature language faculty, this view left open the question of how such a system might be acquired from a limited, concrete and continuous physical input, such as speech—a logical conundrum known as the ‘linking problem’. The current project proposes to break new ground by linking the earliest language acquisition mechanisms to basic auditory perception. Recent advances in the understanding of the neural coding and information processing properties of the mammalian auditory system make the time ripe for such a rethinking of the logical problem of language acquisition. Indeed, the speech signal encoded by the auditory system serves as the input for language learning. Importantly, auditory processing transforms this signal by organizing it into different representational patterns. The project investigates the general hypothesis that these transformations have a direct impact on language learning. The general objective of the project is thus to understand how the developing auditory system encodes the speech signal, providing representations that contribute to language acquisition. The project is thus organized around two, closely related specific objectives: (i) to analyze and characterize speech and other speech-like signals in terms of computational and mathematical principles of neural coding and information processing in the auditory system; and (ii) to identify and describe early perceptual abilities present at the onset of language development allowing human infants to recognize speech as a relevant signal for language acquisition. To achieve these objectives, the project is grounded in an integrative view of the mind and the brain, synthesizing hitherto rarely combined disciplines, such as language acquisition research, psychoacoustics and the study of neural coding. It provides a novel approach to foundational questions such as “Why is language special?” through the cross-fertilization of developmental cognitive neuropsychology, psychophysics and information theory. The project, which will run for a duration of 36 months and involves three leading research laboratories, the LPP, the LSP and the LPS, is broken down into two tasks. The first, corresponding to the first objective involves the computational modeling of speech and speech-like signals, such as the native language, an unfamiliar language, monkey calls and sine-wave speech. The second, corresponding to the second objective, comprises electrophysiological (EEG) and metabolic (near-infrared spectroscopy) measures of newborn infants’ brain responses to these sound categories, thereby assessing the role of prenatal experience as well as the specificity of the early neural specialization for speech and language processing. The expected result is a theoretical and empirical breakthrough in the understanding of how our auditory and cognitive systems develop to sustain speech and language. By identifying the physical and acoustic properties of speech that trigger language-related processing and the neural mechanisms underlying these, the current project opens up the way for the future development of new applications supporting individuals with speech processing and language impairments.