Evidence for atypical categorical speech perception in Williams syndrome

Although language processing has been described as being a relatively ‘spared’ cognitive function in individuals presenting with Williams syndrome (7q11.23 microdeletion; WS), some studies suggest possible alterations at the level of input speech processing. We explored categorical speech perception and non-speech auditory perception in six participants with WS, as well as in chronological age-matched or reading age-matched control groups. Categorical speech perception was explored for the b-d speech sound continuum, where speech sounds vary in spectral acoustic features, and for the d-t speech sound continuum, where speech sounds vary in temporal acoustic features. Non-speech perception was explored for sine-wave analogues of the b-d continuum, which are not identified as speech stimuli. We observed a significantly increased ability in WS participants to detect subtle acoustic changes between adjacent stimuli of the b-d or the d-t continuum outside the phoneme boundary, when control participants showed absence of discrimination. This is the first study to provide evidence for an atypical sensitivity towards subtle acoustic variations during speech and non-speech auditory analysis in WS. Implications for phonological processing and reading acquisition are discussed.