Previous studies have suggests that auditory cortex – a part of the brain that typically processes sound – is not ‘idle’ in Deaf individuals, but instead may respond to input from other sensory modalities such as vision and touch. Such crossmodal plasticity (CP) is traditionally thought to have a negative effect on clinical outcomes of cochlear implantation (CI). This has notably resulted in clinicians discouraging parents from teaching sign language to Deaf children for fear that the use of a visual language will cause the ‘auditory’ cortex to respond to vision instead, and that this will hinder auditory cortex from responding to a spoken language following auditory restoration.
However, there is little scientific evidence to support this notion, and little evidence to support a direct causal link between sign language, CP, and CI outcomes. Second, there is evidence that supports the opposite view – that CP is actually beneficial to outcomes, and that learning sign language encourages the language parts of the brain to develop properly, resulting in better outcomes. Consequently, preventing Deaf children from learning sign language could be having the opposite intended effect, causing worse CI outcomes along with other outcomes associated with not being able to communicate efficiently, such as poor mental health and quality-of-life. It is therefore crucial to examine the link between sign language usage in Deaf individuals, CP, and CI outcomes in more detail to determine how they are linked, if at all.
This project determines whether CP occurs in Deaf individuals who use sign language as their primary means of communication, and if so, in what parts of auditory cortex. Understanding the nature of CP in congenitally Deaf individuals is the first step to being able to understand: i) the relationship between CP and CI outcomes, which could form the basis of a predictor for CI outcomes; and ii) whether sign language is detrimental to such outcomes. Specifically, the project asks: 1) Does CP occur in auditory cortex of congenitally Deaf individuals; 2) Does CP occur in early parts of auditory cortex (consequently having a knock-on effect for all auditory processing), or only in later parts of auditory cortex (i.e. in areas associated with language processing)? 3) To what extent are auditory and language areas involved in processing sign language in congenitally Deaf individuals?
