Hierarchical modulation of auditory prediction error signaling is independent of attention

The auditory system is tuned to detect rhythmic regularities or irregularities in the environment which can occur on different timescales, i.e. regularities in short (local) and long (global) timescale which could conflict or converge. While MMN and P3b are thought to index local and global deviance, respectively, it is not clear how these hierarchical levels interact and to what extent attention modulates this interaction. We used a hierarchical oddball paradigm with local (sequence-level) and global (block-level) violations of regularities in 5-tone sequences, in attended and unattended conditions. Amplitude of negativity in the N2 timeframe and positivity in the P3b timeframe elicited by the final tone in the sequence were analyzed in a 2*2*2 factorial model (local status, global status, attention condition). We found a significant interaction between the local and global status of the final tone on the N2 amplitude (p .05), together demonstrating that lower-level prediction error is modulated by detection of higher-order regularity but expressed independently of attention. Regarding P3b amplitude, we found significant main effect of global status (p<.001, η p 2 = .42), and an interaction between global status and attention (p < .001, η p 2 = .70). Thus, higher-level prediction error, indexed by P3b, is sensitive to global regularity violations if the auditory stream is attended. The results demonstrate the capacity of our auditory perception to rapidly resolve conflicts between different levels of predictive hierarchy as indexed by MMN modulation, while P3b represents a different, attention-dependent system.