Selective attention and pigeons' multiple necessary cues discrimination learning.

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 eight pigeons on a simultaneous 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 pigeons had CLHD (circle, large, horizontal, dark) as the positive stimulus (S+), whereas others had SSVL (square, small, vertical, light) as the S+. All eight pigeons acquired the MNC discrimination, suggesting that they had attended to all four dimensions. Learning rate was similar to all four dimensions, with learning along the orientation dimension being a bit faster than along the other three dimensions. The more dimensions along which the S-s differed from the S+, the faster was learning, suggesting an added benefit from increasing perceptual disparities between the S-s and the S+. Of particular note, evidence of attentional tradeoffs among the four dimensions was much weaker with the simultaneous task than with the successive task. We consider several reasons for this empirical disparity.