The neural coding of speech across human languages

PROJECT SUMMARY
The basic mechanisms underlying comprehension of spoken language are unknown. We are only beginning to
understand how the human brain extracts the most fundamental linguistic elements (consonants and vowels)
from a complex and highly variable acoustic signal. Traditional theories have posited a ‘universal’ phonetic
inventory shared by all humans, but this has been challenged by other newer theories that each language has
its own unique and specialized code. An investigation of the cortical representation of speech sounds across
languages can likely shed light on this fundamental question. Previous research has implicated the superior
temporal cortex in the processing of speech sounds. Most of this work has been entirely carried out in English.
The recording of neural activity directly from the cortical surface from individuals with different language
experience is a promising approach since it can provide both high spatial and temporal resolution. Here, we
propose to examine the mechanisms of phonetic encoding, by utilizing neurophysiological recordings obtained
during neurosurgical procedures. High-density electrode arrays, advanced signal processing, and direct
electrocortical stimulation will be utilized to unravel both local and population encoding of speech sounds in the
lateral temporal cortex. We will examine neural encoding of speech in patients who are monolingual and bilingual
in Mandarin, Spanish, and English, the most common spoken languages worldwide and feature important
contrastive differences of pitch, formant, and temporal envelope. We will test a novel hypothesis that speech
processing across languages will reflect a general auditory encoding of relevant phonetic properties, but that
processing is modified by language-specific “tuning”. A cross-linguistic approach to the neural encoding of
speech will powerfully advance our understanding of how the brain processes sound pattern variability within
and across languages. This will provide fundamental insights into the shared mechanisms of auditory processing
and experience-dependent plasticity in humans. The results may have significant implications for the
development of new diagnostic and rehabilitative strategies for language and neurological disorders (e.g.,
aphasia, dyslexia, autism). Furthermore, this proposal strives to achieve a broader view of diversity and
inclusion in the neuroscience of language.

Grant Number: 5U01NS117765-05
NIH Institute/Center: NIH
Principal Investigator: Edward Chang