Stimulus offset P3 and temporal resolution of uncertainty.

Stimulus offset evoked potentials were recorded to short (1 250 ms) and long (2 500 ms) tones in the context of the odd-ball paradigm. In one condition, the short tone was presented frequently with a probability of 0.85 and the long tone with a probability of 0.15, and in a second condition, the probabilities of tone presentation were reversed. Offset P3s were obtained only to short and not to long rare tones, indicating that resolution of uncertainty rather than stimulus probability or task relevance is responsible for eliciting this late positive component in the context of this experiment.