Theory of attention

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In the 1950's and 1960's the dominant theory of attention was the bottleneck theory, stating humans act as a single communication channel of limited capacity at some part in an information processing sequence. Dichotic listening tasks were devised to illustrate this theory; early studies showed that people are very good at processing only one of two physically distinct concurrent sources of information. The resource theory however assumes that attention can be regarded as a single reservoir of information processing resources. (Reason, 1990)

The idea of attention is critical when examining actions and intentions. Normans and Shallices attention to action theory argues there are two control structures; horizontal and vertical threads. Horizontal threads comprise of processing structures called schemas and vertical threads interact with the horizontal threads to provide the means by which attentional and habitual factors activate schemas. Horizontal threads govern habitual activity without the need for attentional control. (Reason, 1990)

Later on, the role in which schemas play in action slips, an error which occurs when a person does an action that is not intended (Norman, DA, 1981) will be examined as will the role of slips and mistakes with expert users of computer programs.

Slips can be categorised into; errors in the formation of an intention, faulty activation of schemas and faulty triggering (Norman, DA, 1981). To interpret the categorisation of action slips a theory known as Activation-Trigger-Schema system (ATS) must be applied. This theory assumes that action sequences are controlled by schemas (a sensori-motor-knowledge structure). According to the ATS system information passes from high order schemas to low order schemas. High order schemas or parent schemas are initiated by lower order schemas or child schemas. The ATS theory assumes that skilled action, such as that by computer users need only be specified at the highest level. Each schema has a specific condition needed for it to be triggered (Norman, DA, 1981).
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Slips resulting from error in the formation of the intention are due to errors in classifying the situation and from an ambiguous or incompletely specified intention. A type of this slip is mode errors in which the resulting action may be appropriate for the analysis of the situation but not for the actual situation. Another type of this slip is description errors, where by the relevant information is not available to form an appropriate intention this leads to performance slips such as placing the sugar lid on the coffee pot. (Norman, DA, 1981)

Slips resulting from faulty ...

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