Such divided attention effects are assumed to be caused by one or more aspect of processing that is limited, and are explained in terms of the amount of information that can be processed per unit time (e.g., a trial), referred to as capacity. Studies of visual perception have shown that for some tasks, increasing the number of relevant stimuli reduces performance, whereas for other tasks, increasing the number of relevant stimuli has no effect on performance. Tasks that depend on only feature contrast can follow a separate unlimited-capacity processing pathway and therefore do not incur divided attention effects. According to this theory, tasks that require object processing must follow a limited-capacity pathway and therefore incur divided attention effects. A multiple pathway processing theory can account for these and a large body of previous results. We found no evidence of a separate spatial limitation. Using a visual search task with the extended simultaneous-sequential method to reveal capacity limitations, we found evidence of limited-capacity processing of object properties and unlimited-capacity processing of feature contrast. Extant results in the literature are collectively inconsistent with both simple object-based theories and simple space-based theories of divided attention. Object-based theories assert that processing information from multiple objects is limited, whereas space-based theories assert that processing information from multiple locations is limited. Divided attention effects have been observed across a variety of stimuli and perceptual tasks, which have given rise to both object-based and space-based theories of divided attention.
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