Criteria interactions across visual attributes.

Judgmental interference in dual tasks has been demonstrated in conditions where the detection or discrimination of different contrast increments applied to two stimuli presented simultaneously or in sequence. The present work demonstrates such interference for changes along two distinct visual features, namely contrast and orientation, when simultaneously applied to the same or to two distinct objects (Gabor-patches). The interference reveals itself in the use of quasi-equal decision criteria for both dimensions, in conflict with an optimal behavior requiring that criteria be proportional to the sensitivities for the distinct changes. The quasi-equality of the criteria assessed for contrast and orientation changes implies the equality of the internal noises characterizing the respective detection process, hence suggesting that they are limited at the decision level. Among the conceptual consequences of this limitation are the existence of a meta-attribute decisional dimension (tantamount to that of a "central executive system") and the questionable merits of probability summation over spatial channels. In addition, the data show a significant sensitivity drop in the dual- with respect to the single-task conditions, all the more so when the modulated features belong to two objects rather than to the same object. While the sensitivity drop in dual tasks is the standard trademark of distributed attention, it is argued that decisional interference is yet another aspect of it.