Attentional tradeoffs in the pigeon.

We deployed the Multiple Necessary Cues (MNC) discrimination task to see if pigeons can simultaneously attend to four different dimensions of complex visual stimuli. Specifically, we trained nine pigeons (Columba livia) on a go/no go discrimination to peck only 1 of 16 compound stimuli created from all possible combinations of two stimulus values from four separable visual dimensions: shape (circle/square), size (large/small), line orientation (horizontal/vertical), and brightness (dark/light). Some of the pigeons had CLHD (circle, large, horizontal, dark) as the positive stimulus (S+), whereas others had SSVL (square, small, vertical, light) as the S+. We recorded touchscreen pecking during the first 15 s that each stimulus was presented on each training trial. Discrimination training continued until pigeons' rates of responding to all 15 negative stimuli (S-s) fell to less than 15% of their response rates to the S+. All pigeons acquired the MNC discrimination, suggesting that they attended to all four dimensions of the multidimensional stimuli. Learning rate was similar for all four dimensions, indicating equivalent salience of the discriminative stimuli. The more dimensions along which the S-s differed from the S+, the faster was discrimination learning, suggesting an added benefit from increasing perceptual disparities of the S-s from the S+. Finally, evidence of attentional tradeoffs among the four dimensions was seen during discrimination learning, raising interesting questions concerning the possible control of behavior by elemental and configural stimuli.