Properties of the threshold stimulus exposure duration (TSED) measure of visual search efficiency

Using a threshold stimulus exposure duration (TSED) method, rather than the usual response time methods, a recent study showed evidence for a two-stage visual selection process in visual search. The resulting TSED function was bilinear. In the present study, we investigated whether this bilinear pattern reflects general property of TSED functions or if it was just an artifact of specific methodological choices. Experiment 1 refined the staircase procedure of the TSED method to separate the effect of target-present and target-absent trials. Experiments 2 and 3 replaced the target-present/target-absent task with two-alternative forced-choice tasks. Results repeatedly showed a bilinear pattern in the TSED function across paradigms, with a distinct kink point separating a shallower slope at lower set sizes from a steeper slope at larger set sizes. The findings provide convincing evidence that bilinear pattern in TSED functions is generalizable property rather than a task-specific artifact. A modified Guided Search "carwash" can explain how visual search can produce bilinear TSED functions and linear RT × Set Size functions.