Chapter Review Summary
People are often oblivious to unattended inputs; they are unable to tell if an unattended auditory input was coherent prose or random words, and they often fail altogether to detect unattended visual inputs, even though such inputs are right in front of the viewer’s eyes. However, some aspects of the unattended inputs are detected. For example, people can report on the pitch of the unattended sound and whether it contained human speech or some other sort of noise. Sometimes they can also detect stimuli that are especially meaningful; some people, for example, hear their own name if it is spoken on the unattended channel.
These results suggest that perception may require the commitment of mental resources, with some of these resources helping to prime the detectors needed for perception. This proposal is supported by studies of inattentional blindness, studies showing that perception is markedly impaired if the perceiver commits no resources to the incoming stimulus information. The proposal is also supported by results showing that you perceive more efficiently when you can anticipate the upcoming stimulus (and so can prime the relevant detectors). In many cases, this anticipation is spatial—if, for example, you know that a stimulus is about to arrive at a particular location. This priming, however, seems to draw on a limited-capacity system, and so priming one stimulus or one position takes away resources that might be spent on priming some other stimulus.
Your ability to pay attention to certain regions of space has encouraged many researchers to compare attention to a spotlight beam, with the idea that stimuli falling “within the beam” are processed more efficiently. However, this spotlight analogy is potentially misleading. In many circumstances, you do seem to devote attention to identifiable regions of space, no matter what falls within those regions. In other circumstances, though, attention seems to be object-based, not space-based, and so you pay attention to specific objects, not specific positions.
Perceiving, it seems, requires the commitment of resources, and so do most other mental activities. This provides a ready account of divided attention: It is possible to perform two tasks simultaneously only if the two tasks do not in combination demand more resources than are available. Some of the relevant mental resources are task-general, and so are called on by a wide variety of mental activities. These include the response selector and executive control. Other mental resources are task-specific, required only for tasks of a certain type.
Divided attention is clearly influenced by practice, and so it is often easier to divide attention between familiar tasks than between unfamiliar tasks. In the extreme, practice may produce automaticity, in which a task seems to require virtually no mental resources but is also difficult to control. One proposal is that automaticity results from the fact that decisions are no longer needed for a well-practiced routine; instead, one can simply run off the entire routine, doing on this occasion just what one did on prior occasions.