Combining information in different color-coding mechanisms to facilitate visual search

An earlier experiment using a yes-no procedure with a search accuracy task [A.L. Nagy, G. Thomas, Distractor heterogeneity, attention, and color in visual search tasks, Vision Research, 43 (2003) 1541-1552] showed that observers could combine information in different cardinal color mechanisms to facilitate search performance. In the experiments reported here we attempted to replicate these results with a forced-choice procedure and tested three different models of the manner in which information in different feature coding mechanisms is combined. One model was a linear summing model in which signals in different mechanisms are linearly summed in a mechanism under the control of attention. The summed signals are used to guide attention to likely targets. The second model was a nonlinear selection model in which signals in one mechanism are used to select stimuli for attention. A decision is then based on signals generated by the selected stimuli in a mechanism other than the one that is used for selection. The third model was the linear separability model, which suggests that the chromaticity of the target stimulus must be separated from the chromaticities of the distractor stimuli by a straight line in a chromaticity diagram for efficient search. Results favored the nonlinear selection model over the linear summing model and the linear separability model.