Reduced Efficiency and Capacity Limitations in Multidimension Signal Recognition

The first part of Experiment I showed that subjects recognized difficult frequency and intensity signals significantly less well when these were presented together than when they were presented alone. It was estimated that contingent variability resulting from other dimension signal and response context occurring on the same trial accounted for a third of the reduction, and capacity limitations for the remainder. Efficiency on the two dimensions presented together was found to be related and two data subsets were identified for which no efficiency reduction occurred. In the second part of Experiment I subjects recognized correlated frequency and intensity signals and showed a significant improvement in performance over either dimension performed alone. The gain in efficiency was well predicted by the “integration” model of Green and Swets (1966) from one- but not from two-dimension performance. The result suggested that the reduction in efficiency associated with capacity limitations was a function not of the number of signals but of the number of difficult decisions. Experiment II replicated the first part of Experiment I with easy signals. Efficiency was the same whether the signals were presented together or alone. The result indicated that the reduction in efficiency with difficult signals was not due to response interference or to failures of post-recognition retention. The implications of the results for models of attentional capacity are discussed.