Summary:
Divided attention refers to the ability to divide ones attention between two or more tasks. The focused attention models explain how all our inputs are focused on one task at any one time, however it is clear from looking at everyday life that we are able to divide our attention, successfully being able to complete more than one task at the same time.
Divided attention refers to the ability to divide ones attention between two or more tasks. The focused attention models explain how all our inputs are focused on one task at any one time, however it is clear from looking at everyday life that we are able to divide our attention, successfully being able to complete more than one task at the same time. There are two main explanations of divided attention, one is the modular theories and the one I will be focusing on; the capacity model by Kanheman.
Kanheman (1973) put forward the capacity/resource allocation model of attention. This is one of the best known models and suggests that humans have a limited amount of processing capacity and whether two or more tasks can be performed together successfully depends on how much demand they make on this limited capacity processor. This idea of a limited capacity is very probable and has been clear to be the case from earlier research carried out on divided attention.
As well as the capacity, external factors such as heat, noise, anxiety and lack of sleep may also affect performance on tasks related to attention (Revelle). Findings such as these do support the capacity models of attention.
According to Kanheman different tasks require a different amount of processing. So, easy tasks will require little processing capacity and leave plenty available for carrying out another task at the same time, whereas more difficult tasks require a lot more processing capacity, so maybe can only be carried simultaneously with another task which doesn't require so much. The amount of capacity that a task requires depends on a number of things such as its difficulty and past experience of the task. If past experience of the task is increased, and practise is undertaken the same process which may once have required a lot of processing soon becomes automatic, meaning that it can be carried out with less processing. Underwood can account for this in his findings, as he carried out an attention tasks on participants with one group having practised the task, so the skilled participants and another group who had not practiced the task. He found that the experienced shadowers recalled a great deal more from the unattended channel than inexperienced ones.
In addition arousal is seen as very important in determining how much capacity is available. When one is alert and aroused, it has been found that more resources are available meaning that attention can be divided between two tasks, however when we become tired, less resource availability makes the capacity needed to complete a simple task more, making it less likely that we can divide our attention.
Kanheman believes that the central processor allocation policy controls the whole attention system by flexibly allocating attentional resources to various tasks. The central processor has a limited pool of attention resources. Kanheman calls the process of determining how much capacity is available "effort" and this effort is involved in how the capacity is allocated. If the overall effort required exceeds that of the limited capacity of the central processor, so the overall demands on the central processor are too large then it must decide which task is the most important, and must disregard the less important task. It is in this decision making process where the momentary intentions and enduring dispositions come into play (see figure a below). Momentary dispositions refer to "voluntary shifts in attention", for instance making a conscious effort to listen to a message playing through one ear as oppose to the other and enduring dispositions refers to the rules for allocating capacity which are outside of ones voluntary control; for instance, hearing your name being mentioned in a nearby conversation and so shifting you attention. These both affect the central processor when making decisions about tasks.
This theory of attention is very popular and has a lot of support. For instance, it can account for dual task studies such as those carried out by Bourke et al. in these, Bourke gave his participants four very different tasks and measured the degree at which each one interfered with the others. He found that the tasks did interfere with each other, with the random generator task interfering the most and the tone task interfering the least. These finding support the prediction of Kanheman's theory that dual task performance should depend on the demands of the task on the total available capacity.
However other studies have found less support for this, such as that carried out Hegarty et al. which found evidence that other factors other than demands on central capacity are important in determining dual task performance. Also results from another study carried out by Segal and Fusella(1970) cannot be accounted for. In this, they asked participants to detect a faint visual or auditory stimulus while at the same time forming an either auditory or visual mental image. They found that the auditory task impaired performance on the auditory signal detection task more than the visual task did. The capacity model by Kanheman would say that this is because the auditory task is more difficult than the visual task.
However after carrying out a visual detection task, they found out that the auditory task was less disruptive than the imagery task. So it seems as there is no difference in difficulty between the two tasks, but perhaps the fact that the tasks that interfered with each other were the similar ones was the problem. The reason for this interference seems to be that tasks of the same modality were competing with each other for the same cognitive processors and Kanheman's model cannot account for this.
On the other hand, the model does incorporate Johnston and Wilson's (1980) flexible attention theory in which it is said that the central processor accounts for the flexibility of the allocation of attentional resources. It is also in general more flexible than the earlier filter theories which assume there is only one single channel. Kanheman was able to explain the findings from dichotic listening tasks. He suggested that shadowing a message through one ear required all of the attentional capacity, so leaving very little for the unshadowed ear. He also could account for some participants being able to recall the unshadowed message with the idea of enduring dispositions.
Despite these very positive points, many of Kanheman's key terms are not clearly defined. He is not specific about how much capacity there actually is and it is very difficult to define "arousal." The Yerkes and Dodson law also found something that didn't correspond with Kanheman's theory. It was found that although performance does increase as arousal does, this only happens up to a certain point, after which point increasing arousal is associated with a decreased performance. Whereas Kanheman's theory suggests that arousal continues to increase performance up to any point.
Lastly, the theory has been criticised as being a circular argument by Allport (1980). He says that it is too easy to explain the findings from dual task experiments in terms of central capacity. So if two tasks can be performed simultaneously it's because they don't exceed the central capacity and if they cannot be performed then it is because the combined effort needed to accomplish the tasks exceeds the capacity. This may be the case, but there is no independent definition of the central processing capacity. So, task difficulty cannot be defined. The argument is circular as difficult tasks require more attention and tasks that require more attention are difficult.
In conclusion, the central capacity theory although being an advance on earlier theories, cannot account for the effects of task similarity on dual task performance and it has been accused of being descriptive rather than explanatory (Allport).
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