ENDOGENOUS COVERT SPATIAL ORIENTING IN AUDITION - COST-BENEFIT ANALYSES OF REACTION-TIMES AND EVENT-RELATED POTENTIALS

The present study examines mechanisms of endogenous covert spatial ori enting in audition as revealed by event-related brain potentials (ERPs ) and reaction times (RTs). In one experimental condition, subjects we re instructed to respond to any target tone irrespective of whether it was presented in a valid (spatially predictive cue), neutral (uninfor mative cue), or invalid (misleading cue) trial. In another experimenta l condition, only target tones presented at a cued position required a response-that is, subjects could completely ignore tones presented at the uncued ear. Cue validity had an effect on RT, which consisted in benefits for valid trials and in costs for invalid trials relative to the RTs in neutral trials. There were also distinct ERP effects of cue validity in the 100-300 msec time range. These ERP effects were enlar ged in the condition in which uncued tones could be ignored. The effec ts of cue validity on RTs and ERPs demonstrated covert orienting in au dition both for stimuli requiring an overt response and also for stimu li that did not require a behavioural response. It is argued that this attentional selection is located at intermediate stages of informatio n processing, rather than at peripheral stages such as basic sensory-s pecific processing or response selection.