Effects on P3 of spreading targets and response prompts apart

- P3 amplitudes evoked by rare stimuli get reduced when responses are delayed.
- Response prompts were presented 0-500 ms after target onsets, in 100 ms steps blockwise.
- The oddball effect on P3 was already reduced at 0.1 s SOA.
- The reduction reflected a monotonic decrease of response-locked P3 portions across SOAs.

When key-press responses to targets have to be withheld until the presentation of response prompts, target-evoked P3 amplitudes are reduced and so is the P3 difference between rare and frequent targets (the oddball effect on P3). Recently we showed that this even applied when go-signals followed targets by 100 ms. Here we aimed at replicating this result with more fine-grained temporal resolution in 100 ms steps from 0 ms to 500 ms, and dissecting the P3 complex to stimulus- and response-related portions by applying residue iteration decomposition (RIDE). Frequent and rare target stimuli (in random series) were followed by go signals (and occasional no-go signals), with block-wise fixed stimulus-onset asynchronies (SOAs) from 0 ms to 500 ms. Target-evoked P3 amplitudes decreased monotonically across SOAs. Part of this decrease might have been due to an overlapping Contingent Negative Variation (CNV) prior to go signals, increasing across SOAs. When CNV was subtracted out by forming rare-frequent difference waveforms, oddball-P3 was largest at SOA 0, smallest at SOA 500, and equally large at SOAs 100-400. According to RIDE, it was P3's response-related part that was increased at SOA0. These results may be interpreted in terms of the stimulus-response-link reactivation hypothesis of P3.