The mask-onset delay paradigm and the availability of central and peripheral visual information during scene viewing.

We employed a variant of the mask-onset delay paradigm in order to limit the availability of visual information in central and peripheral vision within individual fixations during scene viewing. Subjects viewed full-color scene photos with instructions to search for a target object (Experiment 1) or to study them for a later memory test (Experiment 2). After a fixed interval following the onset of each eye fixation (50-100 ms), the scene was scrambled either in the central visual field or over the entire display. The intact scene was presented when the subject made an eye movement. Our results reconcile different sets of findings from prior research regarding the masking of central and peripheral visual information at different intervals following fixation onset. In particular, we found that when the entire display was scrambled, both search and memory performance were impaired even at relatively long mask-onset intervals. In contrast, when central vision was scrambled, there were subtle impairments that depended on the viewing task. In the 50-ms mask-onset interval, subjects were selectively impaired at identifying, but not in locating, the search target (Experiment 1), while memory performance (Experiment 2) was unaffected in this condition, and hence, the reliance on central and peripheral visual information depends partly on the viewing task.