Context Sensitivity Across Multiple Time and Frequency Scales

Everyday auditory stimuli contain structure at multiple time and frequency scales. Using EEG, we demonstrate sensitivity of human auditory cortex to the content of past stimulation in unattended sequences of equiprobable tones. In 3 experiments including 79 participants overall, we found that at different latencies after stimulus onset, neural responses were sensitive to frequency intervals computed over distinct time scales. To account for these results, we tested a model consisting of neural populations with frequency-specific but broad tuning that undergo adaptation with exponential recovery. We found that the coexistence of neural populations with distinct recovery rates can explain our results. Furthermore, the adaptation bandwidth depends on spectral context - it is wider when the stimulation sequence has a wider frequency range. Our results provide electrophysiological evidence as well as a possible mechanistic explanation for dynamic and multi-scale context-dependent auditory processing in the human cortex.