Cognitive Psychology - The processes involved in attention.

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Cognitive Psychology (PSY323M1)

Lecture 4. The processes involved in attention.

Reading: Chapter 5 Eysenck & Keane; Styles, E.A. (1997). The psychology of attention. Psychology Press, Hove

Cognitive Lab: Eriksen task in Superlab folder

Your objectives are to-:

i). Understand the notion of attentional selection and attempts to pinpoint the location (i.e. 'early', 'late' or 'flexible') of the attentional filter in the information processing chain.

ii). Assess the utility of the different metaphors that aid our understanding of visual selective attention.

iii). Understand current thinking regarding the fate of 'unattended' stimuli, and in particular the results derived from the 'negative priming' paradigm.

iv). Be cognisant of the processes involved in visual search, with particular emphasis on Treisman's (1980) Feature Integration Theory.

v). Be able to describe some of the major disorders of attention.

When you are having a conversation in the coffee bar, a place that is notoriously noisy, you are most often so engrossed that you remain oblivious to the noise all around you. Likewise, when you are looking for someone in a crowd, especially if they are well known to you and the crowd isn't too large, it is most often a relatively effortless task to pick them out. How do we pick out and concentrate on that one sound source from among all others as we track a conversation? And how do we manage to identify that one object in space from among all the other objects? That is, what mechanisms or processes govern our ability to focus our attention on one source of information and exclude all the other sources?

Of course, we do not always have the luxury to pay full attention to a conversation because as often as not we are required do other things at the same time - like drive a motor car, negotiate our way along a crowded pavement or find that friend amidst the crowd. So how do we manage to divide our attention so that we can carry out multiple tasks at the same time? The fact that it is a normal human activity, indeed an expectation of all but the most intellectually feeble, is captured rather well in Lyndon Johnson's denouncement of Gerald Ford as someone 'who couldn't fart and chew gum at the same time'!

Focussed Attention

An early worker in this area, Cherry (1953), presented different messages simultaneously to each ear, and asked subjects to repeat the message they heard in one ear - a task known as 'shadowing'. He found that they remained unaware of the fact that the ignored message was actually in a foreign language or in reversed speech. Broadbent (1958), carried out a number of similar studies using a dichotic listening task in which a different series of digits were presented simultaneously to each ear. So for example, 2 was presented to the left ear and 5 to the right, then 9 to the left and 3 to the right, 1 to the left and 4 to the right and so on. The results showed that rather than recall the digits in the order in which they were presented ( 2,5,9,3,1,4 in this example), subjects recalled by ear of presentation (2,9,1 and 5,3,4 in this example). These results led Broadbent (op cit.), to propose that all stimuli are registered in parallel, and at a very early stage in the information processing chain stimuli are selected, or allowed to pass through a filter, where further processing of the selected stimuli takes place. Stimuli that are not selected may be held in a buffer for possible later processing. The physical characteristics of the stimuli provide the basis for the selection process. So on both Cherry's (op cit.) and Broadbent's (op cit.), task the basis of selection was the ear of presentation. The advantage of an attentional system organised in this way is that the capacity limited mechanisms deployed to further process information (e.g. mechanisms involved in memory or language), are not overloaded. The ignored information in Cherry's (op cit.), study did not receive any further processing so they remained unaware of the nature or content of that information. This is an early selection account of attention and it may be summarised as follows -:

A. All stimuli gain access to sensory mechanisms and are briefly held in store.

B. Where there is more than one message, a selection is made on the basis of the physical characteristics of the message and it is passed on to other mechanisms for further processing. The ignored message is held in store until the system is ready to handle it, if that is required.

C. This filtering process is necessary so that the limited capacity part of the system doesn't become totally overwhelmed by the available information.

However, later work challenged this account of attention. For example, Allport, Antonis and Reynolds (1972), presented a passage of prose to one ear and a series of words to the other ear. The subjects task was to shadow the passage of prose. They found that recall of the words was very poor. In contrast if subjects were presented with pictures, rather than words, whilst shadowing the passage of prose, they were later able to identify up to 90% of them. This suggested that the filter may not be as rigid as originally proposed and that if the stimuli were sufficiently dissimilar (in this case visual versus auditory) the information in the non-shadowed channel may indeed be processed.

Also, Von Wright, Anderson and Stenman (1975), performed a two-stage experiment in which words were firstly presented to subjects. Some of the words were accompanied by an electric shock. In the second part of the experiment subjects were required to perform a shadowing task in which these words, together with words that had not been associated with shock, comprised the stimuli for the 'ignored' message. They found that the shock associated words were associated with an increased galvanic skin response, suggesting that the words had not been filtered out during performance of the shadowing task. Words with a similar meaning or similar sound produced the same effect suggesting that attentional selection may occur quite 'late' in the information processing chain. Results like these suggested to Deutsch and Deutsch (1963), that attentional selection occurs after the identity of stimuli have been established. Their 'late selection' account of attention can be summarised as follows -:

A. All stimuli are fully analysed.

B. The selection bottleneck occurs near the response end of the chain of processing.

C. The most important or relevant information is the determinant of the response.

Treisman and Geffen (1967), asked their subjects to perform a shadowing task, but to tap a pencil on the table if they heard a target word in either message. If late selection theory was correct, then since the identity of all stimuli were established before selection, the subjects ought to have been as good at detecting the targets on the non-shadowed as on the shadowed ear. However the results showed that only 8% of the targets on the ignored channel were detected as opposed to 87% on the shadowed channel. These results provided strong evidence in favour of Treisman's (1963), model of attention which proposes a much more flexible location for the 'bottleneck'. Her theory can be summarised as follows -:

A. The processing bottleneck is much more flexible.

B. Information is processed through a hierarchy in which the information is first analysed in terms of its physical characteristics, then syllabic pattern, words, grammatical structure etc.

C. If the system encounters capacity-limits then the information is not fully analysed all the way to the top of the hierarchy, but stops at the point where further processing is no-longer viable.

The Eriksen Paradigm

The early work in the field of attention was concerned mostly with auditory attention. Eriksen and his associates investigated visual spatial attention. The task he used for the purpose required subjects to respond, in the simplest case, to two stimuli. For example they had to press button one if the target was an A and button 2 if it was a B. The subjects were cued as to where on a computer screen the target would appear. Most often an asterisk was displayed in the middle of the screen for 500ms so that the subjects could fixate on that point before the target letter was presented. So the task was a very simple one to perform.
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However, the target was not always presented in isolation. On some trials the target was accompanied by distractor letters presented adjacent to the target on either side. What he found was that the exact location of the distractors, and whether they were the same or different from the target, affected subjects reaction times. If the distractors were the same as the target (e.g. in the compatible condition, A A A), reaction time was not affected. If the distractors were different from the target (e.g. A B A, the incompatible condition), then reaction time was slowed, but only if ...

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