Attention to overlapping objects: detection and discrimination of luminance changes.

Selective attention to 1 of 2 overlapping objects was assessed in a cuing paradigm. Participants detected or identified targets that appeared in 1 of 6 possible target locations (3 on each object). Significant cuing effects for the simple detection of such targets using both reaction time and sensitivity measures of performance were found. Cuing effects were consistently greater when the participants were required to identify some aspect of the target even when the tasks (detection vs. identification) were equated for overall performance level. These differences in cuing effects between tasks were much reduced if the target locations were no longer grouped into 2 objects. It is suggested that identical stimuli can elicit differing attentional mechanisms depending on task type (rather than task difficulty) and that these mechanisms differ in the nature of the representation of the visual world.