Selective Attention Essay, Research Paper
Kahneman and Treisman (1984, p.55) have succinctly described the main disagreement between
early selection and late selection theories of attention: ‘The classic question of attention theory
has always been whether attention controls the build-up of perceptual information, or merely
selects among the responses associated with currently active percepts.’ Early selection theories
hold that attention serves to select which one of a number of stimuli will be further semantically
processed and stored in long term memory. On the other hand, more recent late selection theories
maintain that selective attention operates after all stimuli are semantically processed. This essay
briefly examines and discusses the main findings and criticisms that have caused the transition
from early selection models to late selection models of attention. Apart from these two extreme
positions, theories that combine aspects of both theories are also discussed. The essential
question which, if answered, would provide evidence on whether stimuli are semantically
processed before or after selection is what people know about the unattended information. If the
subject does not know the meaning of unattended information, this would mean that it has been
discarded before it has been processed for meaning. One of the first approaches to this question
was attempted by Cherry (1953, in Parkin, 1999) who carried out an experiment in which
subjects were required hear two different messages simultaneously, one in each ear, but only pay
attention to one of them. To make sure that subjects were not attending to the other message,
they were asked to shadow the attended message, that is to recite aloud everything they heard.
Subjects could report the physical characteristics of the voice in the unattended message, but not
its meaning. Cherry concluded that selective attention completely overshadows the meaning of
unattended stimuli. Broadbent’s (1958, in Eysenck & Keane, 1995) ‘filter’ model of attention
was based on a similar experiment. Subjects were presented dichotically with pairs of digits and
were instructed to shadow whichever message they preferred. A strong preference was shown for
attending ear-by-ear. Broadbent theorised that stimuli are selected according to their physical
attributes and unattended messages are not semantically processed and discarded. According to
Broadbent, switching attention from one stimulus to another is also quite difficult. These two
previous experiments had numerous weaknesses. In Cherry’s experiment subjects were asked
about information in non-shadowed messages after they had completed the shadowing phase.
This information may have been perceived and processed, but forgotten later. In Broadbent’s
experiment there was no particular meaning to be extracted from the pairs of digits presented, so
there was no sufficient evidence to draw conclusions about semantic processing. Moreover, it
was later made clear that it is possible to easily switch attention from one ear to another, when
the meaning of the unattended message was relevant to the shadowed message. Experiments by
Grey and Wedderburn (1960, in Parkin, 1999) and Treisman (1964, in Parkin, 1999)
demonstrated that subjects select which message to attend to by following the meaning of a
sentence. This suggests that humans can select a stimulus according to its meaning not only its
physical cues. This could directly provide evidence for a late-selection model. However,
Treisman (1960, in Kahneman and Treisman, 1984) accounted for this finding with the
‘attenuator’ model, which is still an early selection theory. She proposed that the filter described
by Broadbent is actually more flexible and the unattended message can be partly semantically
processed. Treisman’s attenuation theory was a good alternative to the filter model, as it could
explain the new findings. However, it has been criticised for lack of clarity and for being a halfmeasure. Since subjects’ attention appears to be directed according to the meaning of a sentence,
one could also claim that they can actually fully process stimuli for meaning before selection. In
the area of visual attention, Johnston and Dark (1986, in Eysenck & Keane, 1995) presented
evidence that unattended visual stimuli undergo little or no semantic processing. However,
counter evidence comes from recent studies with subjects suffering from simultagnosia. Patients
are unable to attend to more than one object at any given time, even when objects are close
together. However, when an unattended word is semantically related to the attended word,
patients can report both words (Caslett & Suffran, 1991, in Allport, 1993). Experiments on which
early-selection models have been based appear problematic. Many authors (e.g. Deutsch &
Deutsch, 1963, in Eysenck, 1995; Parkin, 1999) have argued that the shadowing task is too
demanding for the subjects to be able to process the unattended stimuli in a way equivalent to
real world conditions. It should also be noted that theories for attention were developed on the
basis of either auditory or visual experiments solely, although it was not evident that the same
mechanisms are employed in all types of attention. Following the findings by Gray and
Wedderburn (1960, in Parkin, 1999), Deutsch and Deutsch (1963, in Eysenck & Keane, 1995)
formed the first account of a late selection theory, proposing that all stimuli are fully analysed
and attention merely selects the most important stimulus to respond to. However, it was difficult
to provide evidence for this position, as an experiment by Treisman and Riley (1989, in Eysenck
& Keane, 1995) showed that subjects detected much less target words in non-shadowed
messages. More evidence for late selection came from studies on subliminal perception. Some
studies have shown that an unnoticed aspect of a stimulus, can influence subjects’ behaviour
(Parkin, 1999). This indicates that unattended features of stimuli can be semantically processed.
However, there is still no evidence that unattended messages are fully analysed. In the face of
lack of evidence for the Deutsch and Deutsch theory, Johnston and Heinz (1978, in Parkin, 1999;
1978, in Eysenck & Keane, 1995) proposed a less rigid model in which selection is possible both
before and after semantic processing of information. They assumed that there is a limited central
capacity, which is carefully allocated to various tasks including reasoning, auditory attention,
visual attention and other functions. Early selection was considered to consume fewer resources
than late selection. Thus, when a task involves physical cues early selection should be preferred.
However, there is evidence that dissimilar tasks, for example visual attention and auditory
attention, interfere less with each other when performed simultaneously than more similar tasks
do (e.g. Allport, 1972; Brooks, 1967, both in Parkin, 1999). Relevant evidence from
neuropsychological studies (review by Allport, 1993) seems to suggest that rather separate
mechanisms control different kinds of attentional tasks. The concept of a central capacity,
therefore, appears ill defined. It is still possible, however, that we can process information
semantically both before and after selection according to the task demands on the capacity of the
processing system, which, according to Welford’s (1952,in Eysenck & Keane, 1995) well
supported ‘bottleneck’ idea, is unable to make two decisions about the appropriate responses to
two different stimuli at the same time. The evidence and theories mentioned in this essay lead to
the conclusion that humans can detect meaning in unattended stimuli. There is no evidence,
however, that this semantic processing is as complete as the processing of attended stimuli.
Nevertheless, it could also be said that this conclusion is a rough generalisation, as there is no
clear indication that there is a unique attentional mechanism responsible for attending all kinds of
stimuli. Visual attention, for example may be controlled by different mechanisms than auditory
attention. There is still no theory that provides a clear and testable explanation for all the known
evidence and localises attentional selection. The main reason for this difficulty is that it is almost
impossible to devise an experiment that will localise selection without interfering with the
subjects’ natural functioning. REFERENCES Allport, A. (1993). ‘Attention and Control: Have
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H.C. & Hunt, R.R. (1993). Fundamentals of cognitive psychology (5th ed). Brown &
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handbook (3rd ed.), Erlbaum, Hove Kahneman, D. & Treisman, A.(1984). ‘Changing Views of
Attention and Automaticity. In Parasuraman, R. & Davies, D.R. (Eds.). Varieties of attention.
Academic P. Orlando Kinchla, R.A.(1992).’Attention’. Annual Review of Psychology. 43: 71142 Parkin, A.J.(1999).Essential Cognitive Psychology. Draft 23-3-99. University of Sussex.
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