Dissociable ERP profiles for processing rules vs instances in a cognitive sequencing task

Abstract

A hotly debated question in cognitive neuroscience is whether individual instances of perceptual sequences, and the rules that describe them, are processed by the same brain mechanisms. We tested the hypothesis that such rules and instances are processed by dissociable brain mechanisms. We analyzed event-related brain potentials (ERPs) evoked during cognitive sequencing tasks that assessed surface (instance) vs abstract (rule) structure learning. Sequence instances ABCBAC and DEFEDF have different serial order or surface structure, but share the same rule or abstract structure, 123213. Nine healthy subjects were first trained to learn a set of surface and abstract structures in sequences of visually presented stimuli. During the subsequent ERP recording, for surface and abstract structures, they then discriminated between acceptable and unacceptable sequences, based on the pre-learned regularities. Abstract structure processing evoked a late positivity around 500 ms, which was not seen in the surface structure processing, supporting our hypothesis of dissociable processes. We discuss implications for the rule vs instance debate, and similarities between this late positivity and the P600 observed in previous studies of syntactic processing.