Version: v2, Published online: 2017
Retrieved March 23, 2019, from https://www.rep.routledge.com/articles/thematic/attention/v-2
4. Broadbent’s filter theory and the early/late selection debate
No treatment of attention has been more influential than that given by Donald Broadbent in his 1958 book Perception and Communication. Prior to Broadbent’s work the influence of behaviourism was such that the postulation of mental entities not immediately connected with publicly observable stimuli or publicly manifest behaviour was regarded with suspicion. Purely cognitive phenomena were rarely explored scientifically. Broadbent’s book played an important role in establishing such phenomena as reputable explananda for scientific psychology, by showing how the mathematical theories that were then being developed for the quantification of information could be applied to the project of explaining them.
Broadbent advocated a picture in which mental phenomena are taken to depend on the passage of information between different processing channels that pass through the brain. He argued that such a picture needed to include a theory of the way in which bottlenecks in the capacity of those channels can be managed:
The fact that any given channel has a limit is a matter of central importance to communication engineers, and it is correspondingly forced on the attention of psychologists who use their terms
(Broadbent 1958: 5)
Since the management of bottlenecks in information processing capacity was, according to Broadbent, the function of attention, his claim that psychology needed to take note of channel capacities had the effect of reintroducing the phenomenon of attention to the psychologist’s research agenda.
In the theory that Broadbent develope attention serves to manage a bottleneck that occurs when a large-capacity processing system feeds into a smaller-capacity processing system. This basic picture was common to almost all of the theorists in the decades immediately following Broadbent’s work. For these theorists the first task for a theory of attention was to say which sorts of processing are handled by the large capacity system and which by the small. The hope was that knowing this would enable us to locate the bottleneck of attention at one particular point in the brain’s information processing hierarchy.
Broadbent’s own view was that the large-capacity system—operating before the attentional bottleneck—is responsible only for the detection of simple physical properties, whereas the small-capacity system—operating after attention—is responsible for the detection of semantic features, and for the recognition of those stimuli for which there is identifying information stored in memory. This was known as the ‘early selection’ view. Broadbent’s principal rivals were the ‘late selectionists’, who held that almost all processing is done ‘pre-attentively’ by the large capacity system. According to their view the only processing that takes place after the attentional bottleneck is the processing by which already processed stimuli are brought to consciousness (Deutsch and Deutsch 1963). In its extreme form this early selectionist view leads to a version of epiphenomenalism (see Epiphenomenalism), since it implies that the occurrence of conscious awareness is separate from and subsequent to, all of the processing that makes any difference to the determinants of behaviour and thought.
The empirical study of attention in the decades following Broadbent’s work was dominated by the debate between those who followed Broadbent in his ‘early selectionist’ view and those who adopted the ‘late selectionist’ rival.
Since the early selectionists held that the brain’s capacity for extracting semantic information from stimuli was small, and was allocated by the paying of attention, they supposed that people would be unaware of any of the semantic properties of those stimuli to which they were not attending. Evidence consistent with this hypothesis was easy to find. Colin Cherry had shown, in 1953, that if headphones are used to present an experimental participant with two streams of speech, one in each ear, and if the participant gives all of his attention to one of these streams, then that participant will be unable to report anything about the content of the unattended stream, and will not even know whether hat stream was speech or nonsense. This ignorance of the semantic properties: Properties such as pitch – can be detected for all speech, whether or not attention is being directed elsewhere. All of this is just as the early-selection theory would predict.
On the other side of this debate the late selectionists supposed that the semantic processing of stimuli would go on, whether or not one is paying attentionto those stimuliThey also supposed that the representations resulting from such processing would have an effect on the subject’s subsequent performance, but that they would do so unconsciously. Evidence consistent with this hypothesis was also found. It was shown that people take longer to respond if the picture to which they are responding shares a semantic property with a picture that has recently been ignored (Driver and Tipper 1989). It was also claimed, although this was more controversial, that semantic properties to which attention has not been paid can elicit a slight change in skin conductivity (indicating fear or anticipation) in people who have previously been given a small electric shock whenever a word having that semantic property was presented (Corteen and Dunn 1974; Dawson and Schell 1982).
Both sides in this debate could point to experimental results that the rival theory struggled to explain. The attempts to resolve this dispute between the early and late selection theories eventually lead to a stalemate, and alternative conceptualizations of the phenomena were sought.
Mole, Christopher. Broadbent’s filter theory and the early/late selection debate. Attention, 2017, doi:10.4324/9780415249126-V042-2. Routledge Encyclopedia of Philosophy, Taylor and Francis, https://www.rep.routledge.com/articles/thematic/attention/v-2/sections/broadbents-filter-theory-and-the-early-late-selection-debate.
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