Abstract:

In daily conversation listeners with normal speech-language and hearing function effortlessly decipher speech signals that in fact vary tremendously depending on phonetic context, talker characteristics and background noise. The remarkable efficiency in speech comprehension has been explained in terms of normalization, context effect, and top-down influence of cognition. Although most listeners perform equally well in relatively easy tasks, individual differences seem to emerge with an increase in task difficulty. It is largely unknown what mechanisms are responsible for the listener variability. The present study hypothesizes that cognitive function (as measured in working memory span) and perceptual flexibility (as measured in context effect) account for variance in normal-hearing individuals' performance on difficult listening tasks.

In Experiment 1, one hundred healthy young individuals performed the following tasks: a complex working memory task, three phonetic context effect tasks (2 spectral contrast and 1 temporal contrast tasks), and three speech tasks (minimal pair discrimination, sentence verification, and phrase transcription). Listener performance in minimal pair discrimination was predicted by working memory capacity and context effect sizes, whereas performance in phrase transcription was predicted by only working memory capacity.

In Experiment 2, individuals were classified into different groups based on the size of their observed context effects. It was hypothesized that temporal context effect size would predict speech comprehension performance and that the strength of prediction would vary depending on the rate of speech (e.g., very fast vs. very slow). Contrary to the hypothesis, listeners with smaller context effect sizes performed better. In stead, working memory capacity predicted listener performance in more difficulty conditions (i.e., fast and slow rates) without predicting performance in an easy condition (i.e., regular rate). The results demonstrate how cognitive processes and perceptual abilities can differentially contribute to speech perception and comprehension.