Effects of attention condition (divided vs. focused) and of type of non-target on target detection. Data from Johnston and Wilson (1980).

According to Deutsch and Deutsch (1967), only important inputs lead to responses. As the task used by Treisman and Geffen (1967) required their participants to make two responses (i.e., shadow and tap) to target words in the shadowed message, but only one response (i.e., tap) to targets in the non-shadowed message, the shadowed targets were more important than the non-shadowed ones.

Treisman and Riley (1969) responded by carrying out a study in which exactly the same response was made to all targets. Participants stopped shadowing and tapped when they detected a target in either message. Many more target words were detected on the shadowed message than the non-shadowed one.

Neurophysiological studies provide support for early-selection theories (see Luck, 1998, for a review). Woldorff et al. (1993) used the task of detecting auditory targets presented to the attended ear, with fast trains of non-targets being presented to each ear. Event-related potentials (ERPs; see Chapter 1) were recorded from attended and unattended stimuli. There were greater ERPs to attended stimuli 20-50 milliseconds after stimulus onset. Thus, there is more processing of attended than unattended auditory stimuli starting from the initial activation of the auditory cortex.

Johnston and Heinz's theory

Johnston and Heinz (1978) proposed a flexible model of attention incorporating the following assumptions:

• The more stages of processing that take place prior to selection, the greater the demands on processing capacity.

• Selection occurs as early in processing as possible to minimise demands on capacity.

Johnston and Wilson (1980) tested these assumptions. Pairs of words were presented together dichotically (i.e., one word to each ear), and the task was to identify target words consisting of members of a designated category. The targets were ambiguous words having two distinct meanings. If the category was "articles of clothing", then "socks" would be a possible target word. Each target word was accompanied by a non-target word biasing the appropriate meaning of the target (e.g., "smelly"), or a non-target word biasing the inappropriate meaning (e.g., "punches"), or by a neutral non-target word (e.g., "Tuesday").

When participants did not know which ear targets would arrive at (divided attention), appropriate nontargets facilitated the detection of targets and inappropriate non-targets impaired performance (see Figure 5.3). Thus, when attention had to be divided, the non-target words were processed for meaning. When participants knew all the targets would be presented to the left ear, the type of non-target word had no effect on target detection. Thus, non-targets were not processed for meaning in this focused attention condition, and so the amount of processing received by non-target stimuli is only as much as is necessary for task performance.

Section summary

The analysis of unattended auditory inputs can be greater than was originally thought. However, the full analysis theory of Deutsch and Deutsch (1963) seems dubious. The most reasonable account of focused auditory attention may be along the lines suggested by Treisman (1964), with reduced or attenuated processing of sources of information outside focal attention. The extent of such processing is probably flexible, being determined in part by task demands (Johnston & Heinz, 1978). Styles (1997, p. 28) made a telling point: "Discovering precisely where selection occurs is only one small part of the issues surrounding attention, and finding where selection takes place may not help us to understand why or how this happens.

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