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Can You Trust Your Ears? (Audio Illusions)

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A bottleneck restricts the rate of flow, as, say, in the narrow neck of a milk bottle. The narrower the bottleneck, the lower the rate of flow.

Broadbent's, Treisman's, and Deutsch and Deutsch Models of Attention are all bottleneck models because they predict we cannot consciously attend to all of our sensory input at the same time.

This limited capacity for paying attention is therefore a bottleneck and the models each try to explain how the material that passes through the bottleneck is selected.

Donald Broadbent is recognized as one of the major contributors to the information processing approach, which started with his work with air traffic controllers during the war. In that situation a number of competing messages from departing and incoming aircraft are arriving continuously, all requiring attention.

The air traffic controller finds s/he can deal effectively with only one message at a time and so has to decide which is the most important. Broadbent designed an experiment (dichotic listening) to investigate the processes involved in switching attention which are presumed to be going on internal in our heads.

Broadbent (1958) argued that information from all of the stimuli presented at any given time enters a sensory buffer. One of the inputs is then selected on the basis of its physical characteristics for further processing by being allowed to pass through a filter. Because we have only a limited capacity to process information, this filter is designed to prevent the information-processing system from becoming overloaded.

The inputs not initially selected by the filter remain briefly in the sensory buffer, and if they are not processed they decay rapidly. Broadbent assumed that the filter rejected the non-shadowed or unattended message at an early stage of processing.

Broadbent >wanted to see how people were able to focus their attention (selectively attend), and to do this he deliberately overloaded them with stimuli - they had too many signals, too much information to process at the same time.

One of the ways Broadbent achieved this was by simultaneously sending one message (a 3-digit number) to a person's right ear and a different message (a different 3-digit number) to their left ear. Participants were asked to listen to both messages at the same time and repeat what they heard. This is known as a 'dichotic listening task'.

Broadbent was interested in how these would be repeated back. Would the participant repeat the digits back in the order that they were heard (order of presentation), or repeat back what was heard in one ear followed by the other ear (ear-by-ear). He actually found that people made fewer mistakes repeating back ear by ear and would usually repeat back this way.

Resultsfrom this research led Broadbent to produce his 'filter' model of how selective attention operates. Broadbent concluded that we can pay attention to only one channel at a time - so his is a single channel model.

In the dichotic listening task each ear is a channel. We can listen either to the right ear (that's one channel) or the left ear (that's another channel). Broadbent also discovered that it is difficult to switch channels more than twice a second.

So you can only pay attention to the message in one ear at a time - the message in the other ear is lost, though you may be able to repeat back a few items from the unattended ear. This could be explained by the short-term memory store which holds onto information in the unattended ear for a short time.

Broadbent thought that the filter, which selects one channel for attention, does this only on the basis of PHYSICAL CHARACTERISTICS of the information coming in: for example, which particular ear the information was coming to, or the type of voice.

According to Broadbent the meaning of any of the messages is not taken into account at all by the filter. All SEMANTIC PROCESSING (processing the information to decode the meaning, in other words understand what is said) is carried out after the filter has selected the channel to pay attention to. So whatever message is sent to the unattended ear is not understood.

Because we have only a limited capacity to process information, this filter is designed to prevent the information-processing system from becoming overloaded.

The inputs not initially selected by the filter remain briefly in the sensory buffer store, and if they are not processed they decay rapidly. Broadbent assumed that the filter rejected the non-shadowed or unattended message at an early stage of processing.

Evaluation of Broadbent's Model

1. Broadbent's dichotic listening experiments have been criticized because:

The early studies all used people who were unfamiliar with shadowing and so found it very difficult and demanding. Eysenck & Keane (1990) claim that the inability of naive participants to shadow successfully is due to their unfamiliarity with the shadowing task rather than an inability of the attentional system.

Participants reported after the entire message had been played - it is possible that the unattended message is analyzed thoroughly but participants forget.

Analysis of the unattended message might occur below the level of conscious awareness. For example, research by Von Wright et al (1975) indicated analysis of the unattended message in a shadowing task. A word was first presented to participants with a mild electric shock. When the same word was later presented to the unattended channel, participants registered an increase in GSR (indicative of emotional arousal and analysis of the word in the unattended channel).

More recent research has indicated the above points are important: e.g. Moray (1959) studied the effects of practice. Naive subjects could only detect 8% of digits appearing in either the shadowed or non-shadowed message, Moray (an experienced 'shadower') detected 67%.

2. Broadbent's theory predicts that hearing your name when you are not paying attention should be impossible because unattended messages are filtered out before you process the meaning - thus the model cannot account for the 'Cocktail Party Phenomenon'.

3. Other researchers have demonstrated the ' cocktail party effect' (Cherry, 1953) under experimental conditions and have discovered occasions when information heard in the unattended ear 'broke through' to interfere with information participants are paying attention to in the other ear. This implies some analysis of meaning of stimuli must have occurred prior to the selection of channels. In Broadbent's model the filter is based solely on sensory analysis of the physical characteristics of the stimuli.

Treisman's Attenuation Model

Selective attention requires that stimuli are filtered so that attention is directed. Broadbent's model suggests that the selection of material to attend to (that is, the filtering) is made early, before semantic analysis.

Treisman's (1964) model retains this early filter which works on physical features of the message only. The crucial difference is that Treisman's filter ATTENUATES rather than eliminates the unattended material. Attenuation is like turning down the volume so that if you have 4 sources of sound in one room (TV, radio, people talking, baby crying) you can turn down or attenuate 3 in order to attend to the fourth.

The result is almost the same as turning them off, the unattended material appears lost. But, if a non-attended channel includes your name, for example, there is a chance you will hear it because the material is still there.

Treisman agreed with Broadbent that there was a bottleneck, but disagreed with the location. Treisman carried out experiments using the speech shadowing method. Typically, in this method participants are asked to simultaneously repeat aloud speech played into one ear (called the attended ear) whilst another message is spoken to the other ear.

In one shadowing experiment, identical messages were presented to two ears but with a slight delay between them. If this delay was too long, then participants did not notice that the same material was played to both ears.

When the unattended message was ahead of the shadowed message by up to 2 seconds, participants noticed the similarity. If it is assumed the unattended material is held in a temporary buffer store, then these results would indicate that the duration of material held in sensory buffer store is about 2 seconds.

In an experiment with bilingual participants, Treisman presented the attended message in English and the unattended message in a French translation. When the French version lagged only slightly behind the English version, participants could report that both messages had the same meaning.

Clearly, then, the unattended message was being processed for meaning and Broadbent's Filter Model, where the filter extracted on the basis of physical characteristics only, could not explain these findings. The evidence suggests that Broadbent's Filter Model is not adequate, it does not allow for meaning being taken into account.

Treisman's ATTENUATION THEORY, in which the unattended message is processed less thoroughly than the attended one, suggests processing of the unattended message is attenuated or reduced to a greater or lesser extent depending on the demands on the limited capacity processing system.

Treisman suggested messages are processed in a systematic way, beginning with analysis of physical characteristics, syllabic pattern, and individual words. After that, grammatical structure and meaning are processed.

It will often happen that there is insufficient processing capacity to permit a full analysis of unattended stimuli. In that case, later analyses will be omitted. This theory neatly predicts that it will usually be the physical characteristics of unattended inputs which are remembered rather than their meaning.

To be analyzed, items have to reach a certain threshold of intensity All the attended/selected material will reach this threshold but only some of the attenuated items. Some items will retain a permanently reduced threshold, for example your own name or words/phrases like 'help' and 'fire'. Other items will have a reduced threshold at a particular moment if they have some relevance to the main attended message.

Evaluation of Treisman's Model

1. Treisman's Model overcomes some of the problems associated with Broadbent's Filter Model, e.g. the Attenuation Model can account for the 'Cocktail Party Syndrome'.

2. Treisman's model does not explain how exactly semantic analysis works.

3. The nature of the attenuation process has never been precisely specified.

4. A problem with all dichotic listening experiments is that you can never be sure that the participants have not actually switched attention to the so called unattended channel.

Further Information

Listen to a BBC radio 4 programme: Donald Broadbent and the Cocktail Party.

References

Broadbent, D. (1958). Perception and Communication. London: Pergamon Press.

Cherry, E. C. (1953). Some experiments on the recognition of speech with one and with two ears. Journal of the Acoustical Society of America, 25, 975-979.

Eysenck, M. W. & Keane, M. T. (1990). Cognitive psychology: a student's handbook. Hove: Lawrence Erlbaum Associates Ltd.

Moray, N. P. (1959). Attention in dichotic listening: Affective cues and the influence of instructions. Quarterly Journal of Experimental Psychology, 11, 56-60.

Treisman, A., 1964. Selective attention in man. British Medical Bulletin, 20, 12-16.

Von Wright, J. M., Anderson, K., & Stenman, U. (1975). Generalization of conditioned GSRs in dichotic listening. In P. M. A. Rabbitt & S. Dornic (Eds.), Attention and performance (Vol. V, pp. 194-204). London: Academic Press.

How to reference this article:

McLeod, S. A. (2008). Selective attention. Retrieved from www.simplypsychology.org/attention-models.html

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A bottleneck restricts the rate of flow, as, say, in the narrow neck of a milk bottle. The narrower the bottleneck, the lower the rate of flow. Broadbent's, Treisman's, and Deutsch and Deutsch Models of Attention are all bottleneck models because they predict we cannot consciously attend to all of our sensory input at the same time.

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1) From the study by Moray into dichotic listening explain what a shadowing task is.
2) Outline one control that was used in the study into dichotic listening conducted by Moray.
3) Outline 2 conclusions that can be drawn from the study into dichotic listening conducted by Moray.

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An identification paradox exists.
the content of the rejected message is ignored and blocked from conscious perception, but the block does not prevent a response to one's own name.
1) All verbal content in the rejected message is LOST, when attention is focused on the message in one ear.
2) The message is rejected even when it is repeated many times.
3) Subjectively important messages can penetrate the block.
4) It is very difficult to make neutral material important enough to penetrate the block.

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Study 1: no evidence of words from rejected message being recognised.
Study 2: the presence of a name can cause the instruction to be heard.
Study 3: Participants couldn't be primed to respond to digits, as they were not important enough to break through the attentional barrier.

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Study 1: unrecorded
Study 2: 12 participants
Study 3: 2 groups of 14

Opportunity sample of undergraduates and research workers

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To test dichotic listening findings:
1) amount of information recognised in the rejected message.
2) effect of hearing one's name in the unattended message
3) effect of instructions to identify a specific target in the rejected message.