Broadbent's filter model of attention

Broadbent's filter model is an early selection theory of attention.

Description


Donald Broadbent developed the filter model as an extension of William James’ multi-storage paradigm. Broadbent proposed the notion that a filter acts as a buffer on incoming sensory information to select what information gains conscious awareness. The attended information will pass through the filter, while unattended information will be completely blocked and ignored. The filter acts on stimuli solely on their physical characteristics, such as location, loudness, and pitch.

During World War II the rapid development of machinery did not arise without complications. It was common for radar operators to have difficulties communicating with several pilots at once, as all of their voices were broadcast over one loud speaker. This overloading of perceptual input fueled Broadbent's curiosity of how stimuli capture our attentional resources.

In the filter model, initial processing of stimuli occurs pre-attentively on the basis of their physical features, and is housed in a temporary sensory store. Unlike the physical properties, Broadbent believed semantic features, due to their complexity, would impose a limited capacity on the temporary storehouse of incoming stimuli. For this reason, he postulated a filter then acts on the stimuli, to determine what will be processed further and filter out irrelevant stimuli. Information selected to pass through the filter is then available for short-term memory and manipulation of the selected information, prior to storage in long-term memory.

The development of the filter model was the first theoretical account relating psychological phenomena to information processing concepts of mathematics and computer science. As so, Broadbent provided a computer metaphor in which information-processing at the micro level acted in series, while at the macro level it operated in a parallel fashion. As attention can be directed by physical properties or by an organism's drives, this reveals a parallel processing manner at the macro level, while still processing information semantically at a micro level. Further, goal-directed behaviour requires attention to be controlled; hence a high degree of selectivity is put forth in the information-processing stream. When developing his model, Broadbent emphasized the splitting of incoming stimuli to attended or unattended channels. Channel selection is guided through attention. If one is attempting to attend to a stimulus based on their current goals, they will employ voluntary attention; whereas if a sensory event catches one's attention, reflexive attention will be employed. During his experimentation, Broadbent made use of the dichotic listening test. This task has been used extensively to test numerous psychological phenonomena such as response times of specific auditory information, as well as testing for attended and unattended information presented to a participant. It is widely used as it is a non-invasive method of testing cerebral dominance. In a typical dichotic listening task, the participant is wearing a headphone, which will have differing stimuli presented in each ear piece. The participant is instructed to attend (attended channel) the information coming from one of the ear pieces and neglect (unattended channel) the information presented from the other. Following the listening period, the participants are tested on whether they recall any information presented in the unattended channel. Early research using dichotic listening tasks provided empirical evidence of participants’ ability to correctly recall information to the attended channel, and poor recalling in the unattended channel. Caution must be taken when considering the results of dichotomous listening tests as the majority of people have a right ear advantage for verbal stimuli. This means that information presented to the right ear has a better chance of gaining conscious awareness than information presented to the left ear.

Modern views of Broadbent's model
As psychological research has improved immensely since Broadbent’s time, more sophisticated measures indicate that we do have an attentional filter, though it is integrated into a broader cognitive system. This system compensates for the controversies of limited parallel processing in Broadbent's original findings. A major component of the system entails sensory memory, which is broken down into iconic memory and echoic memory. The aforementioned represent visual and auditory memory respectively, which function preattentively. Given the existence of such a preattentive memory store makes it possible for preattentive stimuli to work in a serial manner. Research on iconic memory has provided a visual hierarchy of the visual system, which indicates specific neurons are activated before stimulus recognition, supporting Broadbent's theory of preattentive processing. Additionally, research has shown that physical features of a stimulus guide attentional selection. It has been found consistently that observers correctly separate relevant from irrelevant stimuli due to physical rather than semantic features, indicating selection channels are heavily influenced by physical features. According to the modality effect, echoic memory has an advantage over iconic memory. Research has shown that the auditory system is more apt to objective interpretation than the visual system, as auditory organization is less ambiguous than the visual organization. This indicates that auditory information is first processed for its physical features, and then combined with visual information features. Moreover, allocation of attention is a product of both voluntary and reflexive attention. Goals and behaviours drive attention but may be influenced by an exogenous stimulus of particular stimulus strength, which varies by situation. Such research evidence confirms Broadbent's notion of voluntary attentional mechanisms. More recent research finds that Broadbent's model neglected to address the time requirements of shifting attention. However, he did distinguish that internal and external stimuli can cause shifts of attention, though he did not consider that internally and externally driven shifts of attention may have differing time courses.

Attention
Attention is commonly understood as the ability to attend to some things while ignoring others. Attention is controllable, selective, and limited. It is the progression by which external stimuli form internal representations that gain conscious awareness. Attention is part of nearly every waking moment for humans, as it is the focusing of one’s thoughts. Selective attention utilizes cognitive processes to focus on relevant targets on input, thoughts or actions while neglecting irrelevant sources of input. This is the basis for how we attend to specific stimuli. Voluntary attention, otherwise known as top-down attention, is the aspect over which we have control, enabling us to act in a goal-directed manner. In contrast, reflexive attention is driven by exogenous stimuli redirecting our current focus of attention to a new stimulus, thus it is a bottom-up influence. These two divisions of attention are continuously competing to be the momentary foci of attention. Selection models of attention theorize how specific stimuli gain our awareness. Early selection models emphasize physical features of stimuli are attended to, while late selection models argue that semantic features are what determine our current focus of attention.

Early selection models of attention
Psychological research regarding attention is largely governed by the processes of which stimuli are selected to enter our conscious awareness. Selection models are utilized by researchers to propose when stimulus information is attended to. Early selection models state that a stimulus is selected to be attended to prior to coming in contact with the filter. A filter can be regarded as the selector of relevant information. Information which is relevant to a particular situation will be attended to, while irrelevant attention is then unattended to. Broadbent supported this early selection theory. The basic idea proposes that perception of the stimulus is not required prior to selecting its relevance.

Late selection models of attention
Late selection models are those which state that incoming information is not selected for by a filter specifically, but later in the information processing sequence. With these models, both attended and unattended information passes through the filter. The filter merely acts as an information attenuator, as in it intensifies the pertinent information, and attenuates the intensity of the stimuli deemed to be unimportant . Information inputs are processed equivalently, until semantic encoding and analysis can be performed. This notion implies that internal decisions of stimuli relevance must be made, before allowing it to gain conscious awareness.

Attenuation model of attention
Anne Treisman, a graduate student of Broadbent’s, was not fully convinced by the notion of a filter performing decisions as to what stimuli gain conscious awareness. She proposed an alternative mechanism, the attenuation theory, in which the filter acts as an attenuator of information, either increasing or decreasing attentional capacities towards it. This slight modification has the unattended channel passing through all processing stages, only weakened rather than completely blocked. As the unattended channel includes weakly attended to information, to gain conscious awareness this information must surpass a threshold, which Treisman believed was determined by the words' meaning. Important words (such as one’s name) would have a low threshold, to easily gain awareness, whereas unimportant words (such as "lamp") would have a higher threshold to prevent them from gaining awareness inappropriately. In this way, the threshold for each word acts as a filtering mechanism, relying on semantic features.

Memory selection model of attention
Deutsch, Deutsch and Norman were not fully convinced by Broadbent’s selection criteria based solely on physical features of a stimulus. The cocktail party effect influenced researchers to look further than physical selection features, to semantic selecting features. The cocktail party effect is an example of how unattended information can gain one’s awareness. Suppose you were at a social gathering having a conversation with some friends, when you hear someone mention your name and it grasps your attention. This unattended-to information somehow gained your awareness. This fueled the development of the memory selection model, which shares the same basic principle of early selection models that stimulus features are selected via their physical properties. Attended and unattended information passes through the filter, to a second stage of selection on the basis of semantic characteristics or message content. Items which are selected are incorporated into short-term memory and awareness. The second selection mechanism, rather than the filter, decides what information gains our awareness.

Multimode model of attention
Additional research proposes the notion of a moveable filter. The multimode theory of attention combines physical and semantic inputs into one theory. Within this model, attention is assumed to be flexible, allowing different depths of perceptual analysis. Which feature gathers awareness is dependent upon the person’s needs at the time. Switching from physical and semantic features as a basis for selection yields costs and benefits. Stimulus information will be attended to via an early selection through sensory analysis, then as it increases in complexity, semantic analysis is involved, compensating for attention's limited capacity. Shifting from early to late selection models reduces the significance of stimuli rendering one's attention, though it increases breadth of attention. Research has found that semantic selection requires a greater attentional resources than physical selection.

Capacity model of attention
Daniel Kahneman took a different approach to describing attention, by describing its division, rather than selection mechanisms. He describes attention as a resource in which energy or mental effort is required. Mental effort is used while engaging in performing any mental task, and the greater the complexity, the greater the effort needed to solve a task. Kahneman believes there are three basic conditions which needed to be met for proper completion of a task. By combining total attentional capacity, momentary mental effort, and appropriate allocation policy of the attentional capacity, a person will exert enough mental effort to overcome mental tasks. The key component is allocating enough attention, as a resource, to the task at hand. Kahneman also noted that arousal influences the total attentional capacity in any given situation. In addition, his model incorporates the ideas of voluntary and reflexive attention, which affect allocation policy. In order to direct attention appropriately, one must attend to relevant information, while neglecting irrelevant information to prevent becoming distracted. This mental effort theory proposed by Kahneman provides an overview of the influences and interdependencies of attention allocation, which is meant to supplement attention selection models.