Effects of similarity, difficulty, and nontarget presentation on the time course of visual attention.

Long-lasting interference from an initial visual target on a subsequent one has been measured in two paradigms: rapid serial presentation of targets and nontargets at a single location, and simple presentation of two spatially separated targets. We note that comparisons between these paradigms might be invalid, since interference in each paradigm can be attributed to a different source: demands on selective attention, or demands to switch locations. We use a novel target presentation that both minimizes selection demands and eliminates location switching, yet we still find long-lasting interference. We suggest that all three paradigms discussed tap a common attentional limit. We also examine effects of similarity between targets, and effects of discrimination difficulty on the initial target. We find that similarity effects are more pronounced when nontargets are present, and we find no effect of discrimination difficulty on subsequent interference.