Visual separability: a study on unschooled adults.

It has been suggested in previous studies that unschooled adults present serious difficulties at performing tasks which, like part verification, dimensional filtering, or orientation judgments, require them to pay attention to a specific aspect of the stimulus structure. In the present study we examined the performance of unschooled adults by using a task which does not explicitly require the subjects to attend selectively to a specific component of the stimuli. Separability either of parts or of dimensions as well as line-orientation registration were estimated by the occurrence of illusory conjunctions. Whatever the properties involved in the illusions, these occurred in unschooled adults, at about the same rate as in age-matched schooled controls. The two sets of contrasting findings suggest that a critical variable is whether or not the subjects' attentional control is required. The relevance of the present findings as regards the level of processing responsible for illusory conjunctions is discussed.