Evaluating the contribution of parallel processing of color and shape in a conjunction search task

Traditionally, researchers interpret the difficulty in conjunction search as difficulty in binding features. In the present study, we used a behavioral-computational approach to assess if parameters from feature search could predict performance in a color-shape conjunction search task. We also investigated whether pooling-mediated processing in peripheral regions was a key-limiting factor in performance in conjunction search by manipulating display arrangements across different experiments. The results indicated that parameters in homogeneous search displays can indeed be used to successfully predict performance in conjunction search displays. This finding is noteworthy because it indicates that the visual system must be extracting the same information from the display in feature and conjunction search tasks (i.e., the target-distractor similarity) using color and shape. Furthermore, there was no compelling evidence that pooling-mediated processing was the primary constraint on performance in this conjunction search task. A model-comparison approach compared the accuracy of different distractor rejection architectures in predicting performance in conjunction search tasks. The winning model showed participants engaging hierarchically with the display, selecting and rejecting distractor subsets based on a single defining feature. Taken in the context of previous research on heterogeneous search performance, the current results imply that the inherent demands of search for a conjunction of color and shape compel participants to adopt this targeted search strategy.