Symposium: Fast dynamic encoding of the sound landscape: regularities, deviance and categories
Thursday, Sep 10, 2015
How the brain discovers regularities in sound sequences
1UCL Ear Institute, University College London, London, United Kingdom
Sensitivity to patterns is fundamental to sensory processing, in particular in the auditory system, since most auditory signals only have meaning as successions over time. Accumulating evidence from the MMN literature suggests that the brain is tuned to the statistics of sensory stimulation. However, the process through which these statistical regularities are discovered - how the brain finds regularities within the ongoing input - has eluded investigation. In my presentation I will review recent brain imaging and psychophysics findings in my lab that suggest that the auditory brain is a well-tuned ‘pattern seeker’, continuously scanning the unfolding auditory input for regularities, even when listeners’ attention is focused elsewhere. Our data demonstrate that listeners are remarkably sensitive to the emergence of complex patterns within rapidly evolving sound sequences, performing on par with an ideal observer model. Brain responses reveal online processes of evidence accumulation - dynamic changes in tonic activity precisely correlate with the expected precision or predictability of ongoing auditory input –both in terms of deterministic (first-order) structure and the entropy of random sequences. Source analysis demonstrates an interaction between primary auditory cortex, hippocampus and inferior frontal gyrus in the process of ‘discovering’ the regularity within the ongoing sound sequence. The results are consistent with precision based predictive coding accounts of perceptual inference and provide compelling neurophysiological evidence of the brain's capacity to encode high order temporal structure in sensory signals.