Location and color as cuing dimensions in contingent classification

The contingent classification task is one in which stimuli in a classification task are simultaneously cued by the addition of another dimension so that the classification is reduced to a discrimination of only two stimuli. The contingencies are arranged so that the cuing dimension itself provides no response information. Four experiments were carried out in which location and color were the cuing dimensions for contingent stimuli that were either letters or lines. These stimuli were considerably more difficult to perceive than those used in earlier experiments. Location provided effective contingent classification for both letters and lines, but color was ineffective with both types of stimuli. It is suggested that in order for a cuing dimension to provide effective contingent classification, its levels must in effect provide information channels, much as modalities do. Location seems to have a special status in providing such visual channels, whereas color does not. Discriminability of the levels on the cuing dimension cannot be dismissed as a factor in the different effectiveness, since the two locations were more discriminable than were the two colors. Since color was maximally discriminable, however, location still has a special status in that it can provide greater discriminability, even possibly through its ability to act as a channel.