Mechanisms of multidimensional grouping, fusion, and search in avian texture discrimination

The influence of dimensional organization on pigeon texture perception was examined in a simultaneous conditional discrimination procedure. Six experienced pigeons were reinforced for pecking at a small block of target elements randomly located within a larger array of distracter elements in each texture stimulus. Target/distracter differences in color, size, orientation, and combinations of these dimensions were examined. In Experiment 1, the influence of target/distractor similarity on performance was investigated by using different forms of unidimensional and conjunctively organized texture stimuli made of two and three dimensions. Targets in feature displays, in which the two regions consistently differed along a single dimension, were located more accurately than targets in conjunctive displays, where a combination of values from all dimensions defined each region. In Experiment 2, a tradeoff between response speed and accuracy was found in the pigeons' processing of conjunctive displays. In Experiment 3, the number of distracters differentially influenced the localization of feature and conjunctive targets. Overall, the pigeons' reactions to these feature and conjunctive stimuli paralleled those of humans, suggesting that functionally equivalent mechanisms may mediate the perceptual grouping, search, and discrimination of textured multidimensional stimuli in both species.