Temporal relationships between eye fixations and manual reactions in visual search

Observers freely searched for, and manually responded to, the presence of a target in multistimulus displays. The stimuli were presented on a cinema screen such that each display subtended a large visual angle to encourage the use of eye movements. Times taken to initially fixate the target (T1Fs) were compared to manual response times (MRTs). The results of two experiments were qualitatively similar, despite different levels of difficulty between them. MRTs were a linear function of T1Fs, but only when fixations did not occur very early after the onset of the stimulus display. When fixations were made very soon after the onset of the display, T1Fs were independent of MRTs. The findings were described within the framework of a one-way synchronization model which was modified to accommodate attention effects in visual search. Finally, the methodology provides a novel means of quantifying the contributions of eye movements to manual acknowledgements in real-world vision-guided tasks.