Processing of Unexpected Stimulus Timing in Linguistic and Non-Linguistic Sequences

Abstract

Timing, and ergo rhythm, are intrinsic features of language that help facilitate real-time speech comprehension. However, work exploring how variable timing is processed in speech is limited. This dissertation addresses this gap in literature by exploring the tenets of how temporal variability is cognitively processed, particularly in the context of real-time stimulus processing. This research is one of the first works to examine temporal variations in linguistic and other acoustically complex contexts. Using electroencephalography (EEG) and behavioural methods, participants were tested on their perception of temporal variations within a continuous stream of either simple tones, complex waves, or syllables. Two timing deviants were presented that occurred early or late compared to other stimuli in the sequence. Event-related potentials (ERPs) were recorded for each stimulus type across three experiments. A fourth experiment tested participant recognition memory for syllable order. Results showed differential processing between the two timing deviants. Unexpectedly earlier tokens elicited larger pre-attentive responses compared to late, suggesting a saliency for the earlier tokens that was not present for the delayed ones. This pattern was observed across all three levels of acoustic and linguistic complexity. Compared to sequences with no timing deviants or an early timing deviant, unexpectedly late tokens were more detrimental to memory, suggesting a negative impact of delays on verbal recognition. Thus, not only were early and late timing variations processed differently, but delays in continuous sequences were also more cognitively taxing for working memory. The results reported in this dissertation contribute to existing knowledge by enriching our understanding of the fundamentals of how aspects of prosodic timing may affect attention and memory. Additionally, it provides new insights into how speech synthesis can be used in neurolinguistic research by tracking how neurophysiological responses change with increasing acoustic complexity and linguistic familiarity.