Figure 511

Memory performance as a function of strength of the correct response and time available to respond. Based on data in Hay and Jacoby (1996).

Jacoby (1996) argued that action slips would be most likely when the correct response was not the strongest one, and when the response had to be made rapidly. That was what they found (see Figure 5.11).

Why is the research by Hay and Jacoby (1996) of major importance? As they pointed out, "Very little has been done to examine action, slips by directly manipulating the likelihood of their occurrence in experimental situations. In the research presented here, we not only manipulated action slips, but also teased apart the roles played by automatic and intentional responding in their production" (p. 1332).

Schema theory

According to schema theory (Norman, 1981; Sellen & Norman, 1992), actions are determined by hierarchically organised schemas or organised plans. The highest-level schema represents the overall intention or goal (e.g., buying a present), and the lower-level schemas correspond to the actions involved in accomplishing that intention (e.g., taking the train to the nearest shopping centre). A schema determines action when its level of activation is sufficiently high and when the appropriate triggering conditions exist (e.g., getting into the train when it stops at the station). The activation level of schemas is determined by current intentions and by the immediate environmental situation. According to this schema model, action slips occur for various reasons:

• Errors in the formation of an intention.

• Faulty activation of a schema, leading to activation of the wrong schema or to loss of activation in the correct schema.

• Faulty triggering of active schemas, leading to action being determined by the wrong schema.

Reason's (1979) action slips can be related to this theoretical framework. For example, discrimination failures can lead to errors in the formation of an intention, and storage failures for intentions can produce faulty triggering of active schemas.


One of the positive characteristics of recent theories is the notion that errors or action slips should not be regarded as special events produced by their own mechanisms. They emerge from the interplay of conscious and automatic control, and are thus "the normal by-products of the design of the human action system" (Sellen & Norman, 1992, p. 318). On the negative side, the notion that behaviour is determined by either the automatic or conscious mode of control is simplistic. There are considerable doubts about the notion of automatic processing, and it is improbable that there is a unitary attentional system. More needs to be discovered about the factors determining which mode of control will dominate. It is correctly predicted by contemporary theory that action slips should occur most often with highly practised activities, because it is under such circumstances that the automatic mode of control is most likely to be used. However, the incidence of action slips is much greater with trivial actions than with those regarded as important. For example, many circus performers carry out well practised actions, but the danger element ensures they make minimal use of the automatic mode of control. It is not clear that recent theories are equipped to explain such phenomena.

Behavioural efficiency

It might be argued that people would function more efficiently if they placed less reliance on automatic processes and more on the central processor. However, automated activities can be be disrupted if too much attention is paid to them. For example, it can be harder to walk down a steep spiral staircase if attention is paid to the leg movements involved. Moreover, Reason's diarists produced an average of only one action slip per day, which does not indicate that their usual processing strategies were ineffective. Indeed, most people seem to alternate between the automatic and attention-based modes of control very efficiently.

Action slips result from a failure to shift from automatic to attention-based control at the right time. Although theoretically important, action slips usually have a minimally disruptive effect on everyday life. However, there may be some exceptions, such as absent-minded professors who focus on their own profound inner thoughts rather than on the world around them.

Section summary

Action slips have been investigated by means of diary studies, in which participants keep daily records of their slips. Various categories of action slip have been identified, but they all involve highly practised activities. Highly practised skills do not require detailed attentional monitoring except at critical decision points. Failures of attention at such decision points cause many action slips. Failure to remember what was done a few seconds previously is responsible for many other action slips.

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