Poster E126, Monday, March 26, 2:30-4:30 pm, Exhibit Hall C
Predictability and Repetition in Sound: Characterising the Sustained EEG Response to Regularity
Rosy Southwell1, Candida Tufo1, Maria Chait1; 1University College London
We use sequences of tone-pips, which rapidly change in frequency in either a regular (REG) or random (RAND) pattern. We have previously shown that the brain closely tracks the level of regularity in these stimuli; manifest as a substantial, sustained increase in passive electroencephalography (EEG) responses to REG as compared to matched RAND. We also vary the number of unique frequencies (alphabet size) within each sequence, previously finding the smaller the alphabet, the larger the brain response. Notably, this pattern of results, where predictable sounds are associated with an increase in responses, is opposite to that predicted from neural adaptation or repetition suppression. A large body of work in audition shows suppression of neural responses to successive tone pips presented at the same frequency. Here, we use REG and RAND with a wider range of alphabet sizes from 1 to 20, to reconcile these opposing effects of predictability within a single paradigm. As alphabet size decreases, rendering the sequence more predictable, will the sustained response continue to increase, or will adaptation effects start to dominate? We find that for alphabet size = 1, the sustained response is indeed lower than for larger alphabets, with evidence for rapid adaptation as early as the fourth repetition. However, the EEG response does eventually build to a sustained level which is significantly higher than for alphabet size = 20. Our results point to a system for automatic monitoring of predictability in the auditory environment which is distinct from, but concurrent with, repetition suppression.
Topic Area: PERCEPTION & ACTION: Audition