Testing the stimulus-to-response bridging function of the oddball-P3 by delayed response signals and residue iteration decomposition (RIDE).

It has been proposed that the P3b component of event-related potentials (ERPs) reflects linking of responses to target stimuli. This proposal was tested by disconnecting the temporal link between target stimuli and responses, and by applying residue iteration decomposition (RIDE) for separating the ERP components into stimulus-locked, response-locked, and "intermediate" clusters. Left or right keys had to be pressed in response to frequent (80%) and rare (20%) target letters, but responses had to wait for "go" signals (appearing in 90% of trials). Between blocks, stimulus-onset asynchronies (SOAs) from targets to go-signals varied from 0 ms to 800 ms. Rare targets with their rare responses were expected to evoke large P3bs ("oddball effect"). If related to stimulus processing only, this effect will be equally large across all SOAs and will be modeled by RIDE's stimulus-cluster. If related to response initiation only, the oddball effect will be evoked by go-signals rather than by targets and will be modeled by RIDE's response-cluster. If indicating integration of rare stimuli with their rare responses, the oddball effect will be evoked by targets but will be reduced and stretched in time across SOAs and will be modeled by RIDE's intermediate cluster. RIDE analysis confirmed this latter view, for the most part. SOA effects matched best, though not perfectly, predictions made by the stimulus-response-link view. These results call for a refined account of the oddball effect on P3b in terms of stimulus-response coupling.