Adaptive processing of spoken language: flexible communication in health, disease and disorder

Speech is the most important and complex sound that we hear every day. Impairments of speech comprehension have a devastating effect on our social and intellectual lives and are insufficiently treated by sensory prostheses (e.g. hearing aids for age-related hearing loss), or rehabilitation (e.g. speech therapy for developmental language disorders, or aphasia). To understand and ameliorate these difficulties we take inspiration from the success of healthy listeners who can achieve successful comprehension despite many everyday challenges. We comprehend speech produced with a marked accent, or heard in a noisy environment, demonstrating robustness of sensory processing. Linguistic robustness is illustrated when we correctly interpret unfamiliar words in sentences or infer the correct meaning of ambiguous words like “bark” or “bank”. The brain systems that achieve resilient speech understanding in the face of these challenges may be responsible for comprehension impairments when they are damaged. If, conversely, these brain systems remain available to impaired listeners then they may permit new forms of rehabilitation. We work with a range of clinical populations with sensory and language impairments to test these hypotheses and to develop new methods of detecting speech comprehension impairments, discovering their underlying causes and suggesting new interventions.

Understanding speech quickly and accurately is a fundamental human ability and the foundation for all our social, educational, and economic achievements. This programme of research explores the computational and neurobiological mechanisms that explain the success of speech perception, comprehension and learning in healthy individuals. By revealing mechanisms that enable listeners to successfully comprehend despite everyday sensory challenges (e.g. noisy or degraded speech) and linguistic challenges (e.g. unfamiliar or ambiguous words) we gain insights into adaptive neural mechanisms that support the acquisition of language skills, their maintenance and retention in adulthood, and the resilience or rehabilitation of language skills after brain injury or disease. This work is important due to the prevalence of language disorders in development and in later life (e.g. following stroke or neurodegeneration), and the severe consequences of language disorders for educational outcomes, economic and social success, and lifelong well-being.

Recent research has established two key mechanisms that contribute to successful speech processing in challenging listening situations: (1) predictive computations by which listeners integrate prior knowledge and sensory signals to arrive at optimal interpretations of noisy and ambiguous speech, and (2) neural oscillations that track the rhythm and timing of connected speech. We are exploring these mechanisms as explanations of deficits observed in developmental language disorders, and in neurodegenerative or post-stroke aphasia. Ongoing work seeks to expand our understanding of these predictive and oscillatory computations in other aspects of speech processing including speech production, and higher-level lexical or semantic processing of speech. Our work combines brain imaging (fMRI, MEG) and brain stimulation (TMS, tACS) to determine the causal mechanisms by which neural activity leads to successful spoken language understanding, and to develop new behavioural and neural methods for exploring individual differences in these mechanisms. Findings have application to the development of new diagnostic methods and for language interventions in the classroom, home or clinic.