From deviance to meaning: frontal temporal interaction in the processing of unexpected events

Deviance detection refers to the ability to detect changes from an expected regularity. This ability allows us to monitor and react to the environment when the unexpected happens. Extensive laboratory studies have been conducted to understand the underlying neural mechanisms and cognitive processes in deviance detection, however, the functional roles of brain regions involved in deviance detection remain unclear. The current thesis aims at studying the spatiotemporal dynamics of brain activity in deviance detection by measuring Event-related Optical Signal (EROS). EROS is a relatively new brain imaging method which has relatively good spatial and temporal resolutions to allow the spatiotemporal dissociation of brain responses. Specifically, three experiments were conducted to study the interactions of the frontal and temporal cortices in 1) detecting semantic and syntactic violations, 2) representing regularities, and 3) detecting audiovisual deviance. The first experiment investigated brain responses to semantic and syntactic violations in sentence comprehension. Similar temporal followed by frontal cortex activities were elicited by both semantically and syntactically anomalous words. However, the temporal activity corresponding to a semantic anomaly was more ventral than that corresponding to a syntactic anomaly. The second experiment investigated the brain response to the counterpart of deviance detection – regularity detection. Sequences of auditory tones governed by three contingency rules were presented. Temporal and fronto-parietal network activities were observed according to the processing requirements of the contingency rules. This result suggests that the brain can simultaneously hold different models of the stimulus contingency within the information processing stream, but that these representations are held at different levels, both in terms of latency and location of the brain responses. The last experiment extended the investigation of brain responses in deviance detection from unimodal to multimodal sensory systems. By using a set of control conditions, brain responses to audiovisual deviance iii detection were separated from those of audiovisual integration. More interestingly, interactions of audiovisual integration and audiovisual deviance detection were revealed. The results from these experiments and previous EROS studies suggest that deviance detection is a common property among various cognitive processes and involves similar basic cognitive components in the frontal and temporal cortices.