Information processing Consensus

Broadbent (1958) argued that much of cognition consists of a sequential series of processing stages. When a stimulus is presented, basic perceptual processes occur, followed by attentional processes that transfer some of the products of the initial perceptual processing to a short-term memory store. Thereafter, rehearsal serves to maintain information in the short-term memory store, and some of the information is transferred to a long-term memory store. Atkinson and Shiffrin (1968; see also Chapter 6) put forward one of the most detailed theories of this type.

This theoretical approach provided a simple framework for textbook writers. The stimulus input could be followed from the sense organs to its ultimate storage in long-term memory by successive chapters on perception, attention, short-term memory, and long-term memory The crucial limitation with this approach is its assumption that stimuli impinge on an inactive and unprepared organism. In fact, processing is often affected substantially by the individual's past experience, expectations, and so on.

We can distinguish between bottom-up processing and top-down processing. Bottom-up or stimulus-driven processing is directly affected by stimulus input, whereas top-down or conceptually driven processing is affected by what the individual contributes (e.g., expectations determined by context and past experience). As an example of top-down processing, it is easier to read the word "well" in poor handwriting if it is presented in the sentence context, "I hope you are quite_", than when it is presented on its own.

The sequential stage model deals primarily with bottom-up or stimulus-driven processing, and its failure to consider top-down processing adequately is its greatest limitation.

During the 1970s, theorists such as Neisser (1976) argued that nearly all cognitive activity consists of interactive bottom-up and top-down processes occurring together (see Chapter 4). Perception and remembering might seem to be exceptions, because perception depends heavily on the precise stimuli presented (and thus on bottom-up processing), and remembering depends crucially on stored information (and thus on top-down processing). However, perception is influenced by the perceiver's expectations about to-be-presented stimuli (see Chapters 2, 3, and 4), and remembering is influenced by the precise environmental cues to memory that are available (see Chapter 6).

By the end of the 1970s, most cognitive psychologists agreed that the information-processing paradigm was the best way to study human cognition (see Lachman et al., 1979):

• People are autonomous, intentional beings interacting with the external world.

• The mind through which they interact with the world is a general-purpose, symbol-processing system ("symbols" are patterns stored in long-term memory which "designate or 'point to' structures outside themselves"; Simon & Kaplan, 1989, p. 13).

• Symbols are acted on by processes that transform them into other symbols that ultimately relate to things in the external world.

• The aim of psychological research is to specify the symbolic processes and representations underlying performance on all cognitive tasks.

• Cognitive processes take time, and predictions about reaction times can often be made.

• The mind is a limited-capacity processor having structural and resource limitations.

• The symbol system depends on a neurological substrate, but is not wholly constrained by it.

Many of these ideas stemmed from the view that human cognition resembles the functioning of computers. As Herb Simon (1980, p. 45) expressed it, "It might have been necessary a decade ago to argue for the commonality of the information processes that are employed by such disparate systems as computers and human nervous systems. The evidence for that commonality is now over-whelming." (See Simon, 1995, for an update of this view.)

The information-processing framework is continually developing as information technology develops. The computational metaphor is always being extended as computer technology develops. In the 1950s and

1960s, researchers mainly used the general properties of the computer to understand the mind (e.g., that it had a central processor and memory registers). Many different programming languages had been developed by the 1970s, leading to various aspects of computer software and languages being used (e.g., Johnson-Laird, 1977, on analogies to language understanding). After that, as massively parallel machines were developed, theorists returned to the notion that cognitive theories should be based on the parallel processing capabilities of the brain (Rumelhart, McClelland, & the PDP Research Group, 1986).

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