People are constantly subjected to very complex situations in which a large number of stimuli compete for our attention. Even if we do not realize it, we spend a lot of time selecting the relevant from the irrelevant, separating the grain from the straw.

This is mainly because our resources to process information are very limited, so if we open the dam of our attention without any control we would end up feeling the capacity to understand what is going on around us.

In order to know how our brain works in situations as frequent as this one, a series of hypotheses were postulated throughout the 20th century that would mark the way forward. Of these, the rigid and attenuated filter model was the pioneer .

In this article, we will discuss the postulates of this classic model, placing special emphasis on the different points that information passes through from the time it is perceived by the senses until it is persistently stored in the memory.

Rigid filter model and attenuated filter model

The rigid filter model and the attenuated filter model propose a dynamic for the operation of the attention that stands out for the insertion of a filter or screening mechanism , through which the complexity of the environment would be purified and relevant things would be selected from it. It includes elements of the multi-warehouse theory on memory, whose previous knowledge is basic for the correct understanding of these models: sensory storage, short-term memory and long-term memory.

1. Sensory store

The sensory store is the first stop in the processing of information, as it is the space in which sensations from the sense organs are deposited.

The perceptive fact, through any of its different modalities (visual, acoustic, olfactory, gustatory and tactile), needs little time to be captured by the nervous system, but requires a somewhat more elaborate analysis to determine its physical properties and its nuances .

In this warehouse, which has a very large capacity but a very limited duration, an extraordinary volume of elements is deposited on the situation in which we find ourselves, although almost all of them are diluted in a few seconds (without a deep cognitive analysis). The information would be transferred from here to short-term memory, after being filtered by the attentional filter , which will be discussed in detail later on.

2. Short term memory

After the information from the senses has crossed the above-mentioned sensory store, it would be projected into short-term memory. At this point an abstraction of the sensory image is retained , a sort of interpretation of the object on which the attention was placed.

This interpretation is an inaccurate image, since has been subjected to a first process of cognitive elaboration in which some of its objective properties may have been altered.

This memory has a smaller amplitude than the sensory store, but its duration is much longer. Thus, the (now conscious) retention of this data can be prolonged for some minutes, but will tend to dissolve if it is valued as irrelevant by the receiver. In general terms, it is estimated that an individual (under normal circumstances) can retain up to seven simple elements in this processing station, the normal range being three to eleven.

Antegrade amnesia provides reliable information about the very existence of this store, and is one of the arguments most commonly used by advocates of the compartmentalization of memory. This phenomenon describes the formation of new learnings that barely last a few minutes , after which they disappear without ever being consolidated (so they would never enter the long-term storage).

3. Long-term memory

When the information has been perceived by the sense organs, sent to the sensory store and derived to the short term memory, a process of conscious analysis on its importance is produced in order to transfer it to the last station: the long term memory. It is in this place where long-distance declarative memories dwell , and to which we voluntarily resort when we wish.

Long-term memory has an indefinite duration, and can be prolonged over a lifetime. It stores a declarative crystallization of facts experienced (episodic), knowledge about the world (semantic) and acquired skills (procedural); all necessary for their emotional relevance and/or adaptive value. There are many brain regions involved in it , for which reason it is usually affected during the evolution of dementia processes.

The filter models

Once the different stores into which the memory is divided are known, and after the analysis of its process from the moment the object is captured by the senses until it is eventually stored in a lasting way, it is easier to understand the rigid and attenuated filter model. These theories were developed in order to understand the way in which a human being deals with complex situations in which very diverse information competes with each other to be perceived, processed and stored.

Thus, it explores the characteristics of selective attention: how we discriminate information from the environment when it is complex, in order to collect what is relevant and articulate suitable responses according to the context. Here we will review two pioneering hypotheses on this subject: the rigid filter (Donald Broadbent) and the attenuated filter (Anne Treisman) , both of which are the theoretical foundation on which subsequent theoretical developments (such as the late filter model or others) would be built.

To get closer to these models, the most useful thing to do is to give an example: let’s imagine that we are meeting with a friend in a bar, drinking coffee, while he tells us an interesting story. How do we focus our attention on his words if the environment is flooded with other sounds that compete with them (such as people talking, clinking of cutlery and even cars driving near where we are)?

In order to explore what happens in our brain in everyday situations such as this, the authors used an experimental procedure known as dicotic listening , which consists of the simultaneous emission of two different messages through each of the auditory channels (with the help of headphones). The participant would remain seated listening to its content (numbers, words, etc.), and after the presentation would point out what he thinks he has perceived.

With this simple method we could explore the dynamics of selective attention , one of the expressions of this executive function, which consists of choosing a relevant stimulus and omitting the irrelevant ones when both are presented at the same time. It is a basic skill for the development of daily life activities, together with sustained attention (or vigilance) and divided attention (efficient approach to two or more important tasks at the same time).

While it is true that both Broadbent and Treisman agreed on the basics, such as the existence of a sensory store and the process of transmitting information from short-term memory to long-term memory, they showed some discrepancies related to the concept of “filtering”. In both cases its existence was considered as a previous phase of screening of the stimulating complexity , but different views were maintained related to its degree of permeability (as will be seen later).

1. Rigid filter model

The use of a filter could resemble, in Broadbent’s own words, the “neck of a bottle”. Although the stimulating field in which we are located may be very complex, our cognitive abilities only allow a discrete percentage of it to be processed and analyzed without exceeding the resources available to us. For this purpose, the filter would act as a sieve for environmental diversity to translate it into clear, operational and manageable terms.

This filter would be located, according to the author (although later questioned from the Deutsch and Deutsch late filter frame), right at the end of the sensory store and before the short-term memory . In this way, the stimuli would be processed in series, and never in parallel (which implies that the information is analyzed one at a time and never simultaneously). This filter would facilitate a selection of the relevant and the irrelevant, so that the former would transcend to short-term memory and the latter would be radically omitted.

According to Broadbent, the screening criterion would be the physical property of the stimulus , such as the pitch or volume of the human voice, as well as the unpredictability with which it breaks into the perceptual field. In any case, from these variables the individual would choose what is relevant, while the rest of the elements would be completely ignored without being attended to or understood.

Broadbent provided empirical evidence by means of dicotic listening, through an experimental condition that consisted in the emission of a brief list of numbers in each of the test subject’s ears . For example, if the left ear heard the sequence 947 and the right ear heard 246, only one or the other would be remembered (but never information that combined the two sources or all the items included in the test). He concluded that each of the ears would function as an independent channel, with only one ear chosen and the other completely omitted.

2. Attenuated filter model

The attenuated filter was proposed by Treisman, following his attempts to replicate Broadbent’s findings. Between the proposals of these two authors there is a basic difference, located precisely in the qualities of the filter as an inserted element within information processing.

Treisman considered that there was no absolute blocking of the unattended stimulus , but that it was processed in some way despite the person trying to focus on what was relevant. The unattended messages would see their salience reduced, but they would not disappear.

Like Broadbent, he used dicotic listening to test his hypothesis. In this case, he used verbal messages (sentences with meaning), but divided the information segments in a particular way.

For example, through the left ear two messages would be played in succession without logical connection (like “I caught a coat we caught four fish”), while in the right ear would sound another very similar in structure (“we went fishing because it was cold”). In such a case, the person would say to hear “I took a coat because it was cold” or “we went fishing and caught four fish”, demonstrating that he or she had attended to both messages at the same time.

The explanation of this finding for Treisman was that the filter does not completely cancel out the unattended message , but that it continues to be processed at some level and can go on to hog the attention if it brings congruence to what was being perceived up to that very moment. He also showed, for example, that people remembered basic aspects of the “ignored” information, even using Broadbent’s own paradigm (changes in the volume of the voice, timbre, tone or sex of the speaker; as well as the reproduction of the name of the subject being evaluated).

Thus, certain conditions of the individual (such as life experience or future expectations), would be responsible for attributing perceptual relevance to the stimulus. In addition, the filter would act by weakening the less relevant messages, but these would not be completely inhibited (as suggested by the rigid filter). There would therefore be a basic processing at a semantic level (of a precategorical type) with which the selection tasks would be optimised without saturating the cognitive system.

Bibliographic references:

  • Driver, J. (2001). A selective review of selective attention research from the past century. British Journal of Psychology, 92, 53-78.
  • Lee, K. and Choo, H. (2011). A critical review of selective attention: An interdisciplinary perspective. Artificial Intelligence Review, 40(1), 27-50.

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