Dual-element effects in pigeons' matching-to-sample with temporal and visual stimuli

The present study examined whether the dual-element effect occurs when temporal and visual stimuli appear simultaneously in a zero-delayed, symbolic matching-to-sample task. Two groups of pigeons were first exposed to either a red or green sample stimulus, for either 30 s or 5 s. The sample was followed by the presentation of yellow and blue comparisons. For pigeons in one group, the duration of the sample was the relevant cue. Responses to the yellow comparison were reinforced if the sample was 30 s, and responses to the blue comparison were reinforced if the sample was 5 s. For the other group, sample duration was irrelevant. Responses to the yellow comparison were reinforced if the sample had been green and responses to the blue comparison were reinforced if the sample had been red. Both groups then learned a second matching task in which the sample and comparison stimuli were vertical and horizontal lines. Finally, matching performance was examined when the lines appeared together with the temporal or color elements. The results showed that the line matching task was acquired more slowly for pigeons that were first trained to attend to duration. More importantly, matching was reduced when the temporal and line elements appeared simultaneously, and the effects were similar to those obtained when visual elements are combined.