Feature and conjunction processing in the auditory modality.

In five experiments, participants made speeded target/nontarget classification responses to singly presented auditory stimuli. Stimuli were defined via vocal identity and location in Experiments 1 and 2 and frequency and location in the remaining experiments. Performance was examined in two conditions inspired by visual search: In the feature condition, responses were based on the detection of unique stimulus features; in the conjunction condition, unique combinations of features were critical. Experiment 1 showed a conjunction benefit, since classifications were faster in the conjunction condition than in the feature condition. Potential confounds were eliminated in Experiments 2 and 3, which resulted in the observation of conjunction costs. In Experiments 4 and 5, we examined, respectively, whether the cost could be explained in terms of differences in interstimulus similarity and target template complexity across the main conditions. Both accounts were refuted. It seems that when the identification of particular feature combinations is necessary, conjunction processing in audition becomes an effortful process.