Electrophysiological correlates of accurate mental image formation in auditory perception and imagery tasks

Event-related potentials (ERPs) were recorded while listeners made intonation judgments about target notes that terminated a sequence of heard notes (bottom-up task) or a sequence of imagined notes (top-down task). We hypothesized that the neural processes underlying the accurate formation and evaluation of mental images would behave similarly in both tasks. In the imagery condition, the amplitude of the N100 component of the auditory evoked potential in response to the target tone was smaller for those listeners who formed more accurate mental images. It was comparable in amplitude to the N100 evoked when all of the notes leading to the target were heard, consistent with a process of habituation of the N100 in the auditory cortex due to the formation of a sequence of mental images. The P3a response - a marker of deviance detection - to mistuned targets was also found in the imagery condition and it was larger for listeners who formed more accurate images. Additionally, the influence of long-term implicit memory for tonal structure of Western music on the acuity of mental images was examined by comparing responses to leading tone (contextually unstable) and tonic (contextually stable) targets. Images were more accurate for targets that were related more closely to the established tonal context. The results suggest that successful top-down activation of pitch representations activates the same neural processes that underlie the N100 response to perceived notes, and that the engagement of these processes underlies successful detection of mistuning as indexed by the P3a component.