Exploring the relationship between visual search and visual discrimination

The present study examined the effect of set size and target-distractor discriminability on contrast and orientation search performance in central vision for six observers. Set size was manipulated through display set size and the target-distractor discriminability was defined as the ratio of target-distractor difference to the corresponding discrimination threshold. Results agreed with studies in peripheral vision and showed a constant set size effect across different domains of the study (the accuracy domain and the time domain) and different dimensions of stimuli (contrast and orientation). The slopes of the set size effect were also similar to the prediction of the decision integration hypothesis, suggesting that an attentional effect in the decision process was sufficient to account for the set size effect in central vision. Results also showed that the target-distractor discriminability was a determining factor for simple visual search performance. The search duration threshold versus target-distractor discriminability functions were comparable for stimuli within or across stimulus dimensions.