11.2: History of Attention

There has been a large increase in research activity in the area of attention since the 1950s. This research has focused not only on attention, but also how attention is related to memory and executive functioning. Human learning and behaviour are dependent on our ability to pay attention to our environment, retain and retrieve information, and use cognitive strategies. An understanding of the development of attention is also critical when we consider that deficits in attention often lead to difficulties in school and in the work force. Thus, attention is an important topic in the study of psychology, specifically in the areas of development (see Part II of this book), learning (Part III), and psychological disorders (see the section on ADHD in Part IV). There is no doubt that an understanding of attention and related concepts is critical to our understanding of human cognition and learning.

Introduction to the History of Research on Attention

The study of attention is a major part of contemporary cognitive psychology and cognitive neuroscience. Attention plays a critical role in essentially all aspects of perception, cognition, and action, influencing the choices we make. The study of attention has been of interest to the field of psychology since its earliest days. However, many ideas about attention can be traced to philosophers in the 18th and 19th centuries, preceding the foundation of the field of psychology. The topic of attention was originally discussed by philosophers. Among the issues considered were the role of attention on conscious awareness and thought, and whether attention was directed voluntarily or involuntarily toward objects or events. The characterization of attention provided by each philosopher reflected that individual's larger metaphysical views of the nature of things and how we come to know the world. For instance, Joan Luis Vives (1492-1540) recognized the role of attention in forming memories. Gottfried Leibniz (1646-1716) introduced the concept of apperception, which refers to an act that is necessary for an individual to become conscious of a perceptual event. He noted that without apperception, information does not enter conscious awareness. Leibniz said, "Attention is a determination of the soul to know something in preference to other things". In summary, many philosophers gave attention a central role in perception and thinking. They introduced several important issues, such as the extent to which attention is directed automatically or intentionally. These topics continue to be examined and evaluated in contemporary research. Although they conducted little experimental research themselves, their conceptual analysis of attention laid the foundation for the scientific study of attention in ensuing years. The philosophical analyses of attention led to some predictions that could be tested experimentally. In addition, in the mid-1800s psychophysical methods were being developed that allowed the relation between physical stimulus properties and their corresponding psychological perceptions to be measured. Wilhelm Wundt, who established the first laboratory devoted to psychological research in 1879, was responsible for introducing the study of attention to the field. In addition, the relation between attention and perception was one of the first topics to be studied in experimental psychology. Wundt held that attention was an inner activity that caused ideas to be present to differing degrees in consciousness. He distinguished between perception, which was the entry into the field of attention, and apperception, which was responsible for entry into the inner focus. He assumed that the focus of attention could narrow or widen. This view that has also enjoyed popularity in recent years. At the end of the 19th century, Hermann von Helmholtz (1821-1894) argued that attention is essential for visual perception. Using himself as a subject and pages of briefly visible printed letters as stimuli, he found that attention could be directed in advance of the stimulus presentation to a particular region of the page, even though the eyes were kept fixed at a central point. He also found that attention was limited: The letters in by far the largest part of the visual field, even in the vicinity of the fixation point, were not automatically perceived.

William James's [1] (1890/1950) views on attention are probably the most well known of the early psychologists. In his famous Principles of Psychology (1980), James asserted that "the faculty of voluntarily bringing back a wandering attention, over and over again, is the very root of judgment, character, and will." His definition of attention is also widely quoted. According to James (1890), “It is taking possession by the mind, in clear and vivid form, of one of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others, and is a condition which has a real opposite in the confused, dazed, scatterbrained state." Moreover, according to James, the immediate effects of attention are to make us perceive, conceive, distinguish and remember, better than we otherwise could –both more successive things and each thing more clearly. It also shortens “reaction time”. James’s definition also mentions clearness, which Titchener (1908/1973) viewed as the central aspect of attention. Pillsbury (1908/1973) agreed with Titchener, indicating, “the essence of attention as a conscious process is an increase in the clearness on one idea or a group of ideas at the expense of others”. Researchers at the beginning of the 20th century debated how this increased clearness is obtained. In summary, around 1860, the philosophical approach dominated the study of psychology in general and attention especially. During the period from 1980 to 1909, the study of attention was transformed, as was the field of psychology as a whole, to one of scientific inquiry with emphasis on experimental investigations. However, given that behaviourism came to dominate psychology in the next period, at least in the United States, the study of attentional mechanisms was largely delayed until the middle of the 20th century.

Although one often reads that research on attention essentially ceased during the period of 1910-1949, attention research never disappeared completely. However, there was an increase in interest in the topic with the advent of contemporary cognitive psychology. Lovie (1983) compiled tables showing the numbers of papers on attention listed in Psychological Abstracts and its predecessor, Psychological Index, in five-year intervals from 1910 to 1960, showing that studies on the topic were conducted during these time periods. Among the important works on attention was that of Jersild (1927) who published a classic monograph, “Mental Set and Shift”.

Another significant contribution during this era was the discovery of the psychological refractory period effect by Telford (1931). He noted that numerous studies showed that stimulation of neurons was followed by a refractory phase during which the neurons were less sensitive to stimulation. Stroop (1935/1992) also published what is certainly one of the most widely cited studies in the field of psychology, in which he demonstrated that stimulus information that is irrelevant to the task can have a major impact on performance (see below for John Ridley Stroop and the impact of the Stroop Color-Word Task on research on attention). Paschal (1941), Gibson (1940) and Mowrer, Rayman and Bliss (1940) also conducted research on attention such as that on preparatory set or mental set. In sum, although the proportion of psychological research devoted to the topic of attention was much less during this time period than during preceding decades, many important discoveries were made, which have influenced contemporary research on the topic.

The period from 1950 to 1974 saw a revival of interest in the characterization of human information processing. Research on attention during this period was characterized by an interplay between technical applications and theory. Mackworth (1950) reported experiments on the maintenance of vigilance that exemplified this interaction and set the stage for extensive research on the topic over the remainder of the 20th century. This research originated from concerns about the performance of radar operators in World War II detecting infrequently occurring signals. Cherry (1953) conducted one of the seminal works in attention during this period, studying the problem of selective attention, or, as he called it, “the cocktail party phenomenon”. He used a procedure called dichotic listening in which he presented different messages to each ear through headphones. Broadbent (1958) developed the first complete model of attention, called Filter Theory (see below). Treisman (1960) reformulated Broadbent's Filter Theory into what is now called the Filter-Attenuation Theory (see below). In the early 1970s, there was a shift from studying attention mainly with auditory tasks to studying it mainly with visual tasks. A view that regards attention as a limited-capacity resource that can be directed toward various processes became popular. Kahneman’s (1973) model is the most well known of these unitary capacity or resource theories.

According to this model, attention is a single resource that can be divided among different tasks in different amounts. The basic idea behind these models is that multiple tasks should produce interference when they compete for the limited capacity resources. Also, in this time period, the first controlled experiments that used psychophysiological techniques to study attention were conducted on humans. These experiments used methods that allow brain activity relating to the processing of a stimulus, called event related potentials, to be measured using electrodes placed on the scalp. In sum, the research during this period yielded considerable information about the mechanisms of attention. The most important development was the introduction of detailed information processing models of attention. Research on attention blossomed during the last quarter of the 20th century. Multiple resources models have emerged from many studies showing that it is easier to perform two tasks together when the tasks use different stimulus or response modalities than when they use the same modalities. Treisman and Gelade (1980) also developed a highly influential variant of the Spotlight Theory called the Feature Integration Theory to explain the results from visual search studies, in which subjects are to detect whether a target is present among distracters. Priming studies have also been popular during the most recent period of attention research. In such studies, a prime stimulus precedes the imperative stimulus to which the subject is to respond; the prime can be the same as or different from some aspect of the imperative stimulus. In addition, a major focus has been on gathering neuropsychological evidence pertaining to the brain mechanisms that underlie attention. Cognitive neuroscience, of which studies of attention are a major part, has made great strides due to the continued development of neuroimaging technologies. The converging evidence provided by neuropsychological and behavioral data promises to advance the study of attention significantly in the first half of the 21st century.

Finally, significant advances have also been made toward expanding the theories and methods of attention to address a range of applied problems. Two major areas can be identified. The first one concerns ergonomics in its broadest sense, ranging from human-machine interactions to improvement of work environments such as mental workload and situation awareness. The second major area of application is clinical neuropsychology, which has benefited substantially from adopting cognitive models and experimental methods to describe and investigate cognitive deficits in neurological patients. There is also work being done on the clinical application of attentional strategies (e.g., mindfulness training) in the treatment of a wide range of psychological disorders (see section on mindfulness).

John Ridley Stroop and The Stroop Effect

For over half a century, the Stroop effect has been one of the most well known standard demonstrations in undergraduate psychology courses and laboratories. In this cognitive task, participants asked to name the color of the ink in which an incompatible color word is printed (e.g., to say “red” aloud in response to the stimulus word GREEN printed in red ink) take longer than when asked to name the color in a control condition (e.g., to say "red" to the stimulus XXXXX printed in red ink). This effect, now known as the Stroop effect, was first reported in the classic article “Studies of Interference in Serial Verbal Reactions” published in the Journal of Experimental Psychology in 1935. Since then, this phenomena has become one of the most well known in the history of psychology.

Stroop’s article has become one of the most cited articles in the history of experimental psychology. It has more than 700 studies seeking to explain some nuance of the Stroop effect along with thousands of others directly or indirectly influenced by this article (MacLeod, 1992). However, at the time of its publication, it had relatively little impact because it was published at the height of Behaviourism in America (MacLeod, 1991). For the next thirty years after its publication, almost no experimental investigations of the Stroop effect occurred. For instance, between 1935 and 1964, only 16 articles are cited that directly examined the Stroop effect. In 1960s, with the advent of information processing as the dominant perspective in cognitive psychology, Stroop's work was rediscovered. Since then, the annual number of studies rose quickly, until by 1969 the number of articles settled in at just over 20 annually, where it appears to have remained (MacLeod, 1992).

Donald Broadbent and Dichotic Listening

Donald E. Broadbent has been praised for his outstanding contributions to the field of psychology since the 1950s, most notably in the area of attention. In fact, despite the undeniable role that attention plays in almost all psychological processes, research in this area was neglected by psychologists for the first half of the twentieth century (Massaro, 1996). During that time, behaviourists ignored the role of attention in human behaviour. Behaviourism was characterized by a stimulus-response approach, emphasizing the association between a stimulus and a response, but without identifying the cognitive operations that lead to that response (Reed, 2000). Subsequently, in the mid-1950s, a growing number of psychologists became interested in the information-processing approach as opposed to the stimulus response approach. It was Broadbent’s elaboration of the idea of the human organism as an information-processing system that lead to a systematic study of attention, and more generally, to the interrelation of scientific theory and practical application in the study of psychology.

Dichotic Listening Experiments

In 1952, Broadbent published his first report in a series of experiments that involved a dichotic listening paradigm. In that report, he was concerned with a person’s ability to answer one of two messages that were delivered at the same time, but one of which was irrelevant.

The participants were required to answer a series of Yes-No questions about a visual display over a radio-telephone. For example, the participant would be asked “S-1 from G.D.O. Is there a heart on Position 1?” Over,” to which the participant should answer “G.D.O. from S-1. Yes, over.” Participants in groups I, II, III, and IV heard two successive series of messages, in which two voices (G.D.O and Turret) spoke simultaneously during some of the messages. Only one of the voices was addressing S-1, and the other addressed S-2, S-3, S-4, S-5, or S-6. Participants were assigned to the following five groups:

• Group I: instructed to answer the message for S-1 and ignore the other on both runs
• Group II: instructed on one run to only answer the message from G.D.O. andon the second run was provided with a visual cue before the pairs of messages began for the name of the voice to be answered
• Group III: were given the same directions as Group I on one run, and on the other run had the experimenter indicate the correct voice verbally after the two messages had reached the “over” stage
• Group IV: had the correct voice indicated in all cases, but in one run it was before the messages began (like in Group II) and in the other run it was after the messages had finished (like in Group III)
• Group V: under the same conditions as Group I, heard the same recordings as Groups I, II, III and IV, but then also heard a two new recordings. One recording had a voice that addressed S-1 and a voice that addressed T-2, T-3, T-4, T-5, orT6 (thus the simultaneous messages were more distinct than for the other groups). The other recording had this same differentiation of messages, but also had both voices repeat the call-sign portion of the message (i.e., “S-1 from G.D.O., S-1 from G.D.O.)

For groups I and II, it is important to note that the overall proportion of failures to answer the correct message correctly was 52%. Results from Groups III and IV indicated that delaying knowledge of the correct voice until the message is completed makes that knowledge almost useless. More specifically, Broadbent (1952) stated:

“The present case is an instance of selection in perception (attention). Since the visual cue to the correct voice is useless when it arrives towards the ends of the message, it is clear that process of discarding part of the information contained in the mixed voices has already taken place…It seems possible that one of the two voices is selected for response without reference to its correctness, and that the other is ignored…If one of the two voices is selected (attended to) in the resulting mixture there is no guarantee that it will be the correct one, and both call signs cannot be perceived at once any more than both messages can be received and stored till a visual cue indicates the one to be answered”. (p. 55)

In 1954, Broadbent used the same procedure as discussed above with slight modifications. In that case, he found information that indicated the positive impact that spatial separation of the messages has on paying attention to and understanding the correct message. The dichotic listening paradigm has been utilized in numerous other publications, both by Broadbent and by other psychologists working in the field of cognition. For example, Cherry (1953) investigated how we can recognize what one person is saying when others are speaking at the same time, which be described as the “cocktail party problem” (p. 976). In his experiment, subjects listened to simultaneous messages and were instructed to repeat one of the messages word by word or phrase by phrase.

Information-Processing and the Filter Model of Attention

Cognitive psychology is often called human information processing, which reflects the approach taken by many cognitive psychologists in studying cognition. The stage approach, with the acquisition, storage, retrieval, and use of information in a number of separate stages, was influenced by the computer metaphor and the way people enter, store, and retrieve data from a computer (Reed, 2000). The stages in an information-processing model are:

• Sensory Store: brief storage for information in its original sensory form
• Filter: part of attention in which some perceptual information is blocked out and not recognized, while other information is attended to and recognized
• Pattern Recognition: stage in which a stimulus is recognized
• Selection: stage that determines what information a person will try to remember
• Short-Term Memory: memory with limited capacity, that lasts for about 20-30 seconds without attending to its content
• Long-Term Memory: memory that has no capacity limit and lasts from minutes to a lifetime

Using an information-processing approach, Broadbent collected data on attention (Reed, 2000). He used a dichotic listening paradigm (see above section), asking participants to listen simultaneously to messages played in each ear, and based on the difficulty that participants had in listening to the simultaneous messages, proposed that a listener can attend to only one message at a time (Broadbent, 1952; Broadbent, 1954). More specifically, he asked enlisted men in England's Royal Army to listen to three pairs of digits. One digit from each pair was presented to one ear at the same time that the other digit from the pair was presented to the other ear. The subjects were asked to recall the digits in whatever order they chose, and almost all of the correct reports involved recalling all of the digits presented to one ear, followed by all the digits presented to the other ear. A second group of participants were asked to recall the digits in the order they were presented (i.e., as pairs). Performance was worse than when they were able to recall all digits from one ear and then the other.

To account for these findings, Broadbent hypothesized that the mechanism of attention was controlled by two components: a selective device or filter located early in the nervous system, and a temporary buffer store that precedes the filter (Broadbent, 1958). He proposed that the filter was tuned to one channel or the other, in an all-or-nothing manner. Broadbent’s filter model, described in his book Perception and Communication (1958), was one of the first information-processing models to be examined by psychologists.

Shortly after, it was discovered that if the unattended message became highly meaningful (for example, hearing one’s name as in Cherry's Cocktail Party Effect, as mentioned above), then attention would switch automatically to the new message. This result led to the paradox that the content of the message is understood before it is selected, indicating that Broadbent needed to revise his theory (Craik & Baddeley, 1995). Broadbent did not shy away from this task. In fact, he saw all scientific theories as temporary statements, a method of integrating current evidence in a coherent manner. According to Craik and Baddeley, (1995), although Broadbent always presented his current theories firmly and persuasively, he never took the position of obstinately defending an outmoded theory. When he published his second book on the topic, Decision and Stress (1971), he used his filter model as the starting point, to which he applied modifications and added concepts “to accommodate new findings that the model itself had stimulated” (Massaro, 1996, pp. 141). Despite its inconsistencies with emerging findings, the filter model remains the first and most influential information-processing model of human cognition.

Anne Treisman and Feature Integration Theory

Anne Treisman is one of the most influential cognitive psychologists in the world today. For over four decades, she has been has using innovative research methods to define fundamental issues in the area of attention and perception. Best known for her Feature Integration Theory (1980, 1986), Treisman’s hypotheses about the mechanisms involved in information processing have formed a starting point for many theorists in this area of research.

In 1967, while Treisman worked as a visiting scientist in the psychology department at Bell Telephone Laboratories, she published an influential paper in Psychological Review that was central to the development of selective attention as a scientific field of study. This paper articulated many of the fundamental issues that continue to guide studies of attention to this day. While at Bell, Treisman’s research interests began to expand (Anon, 1991). Although she remained intrigued by the role of attention on auditory perception, she was now also fascinated by the way this construct modulates perception in the visual modality.

In the following years, Treisman returned to Oxford, where she accepted a position as University lecturer in the Psychology Department and was appointed a Fellow of St. Anne’s College (Treisman, 2006). Here, she began to explore the notion that attention is involved in integrating separate features to form visual perceptual representations of objects. Using a stopwatch and her children as research participants, she found that the search for a red ‘X’ among red ‘Os’ and blue ‘Xs’ was slow and laborious compared to the search for either shape or colour alone (Gazzaniga et al., 2002). These findings were corroborated by results from testing adult participants in the laboratory and provided the basis of a new research program, where Treisman conducted experiments exploring the relationships between feature integration, attention and object perception (Triesman & Gelade, 1980).

In 1976, Treisman’s marriage to Michel Treisman ended. She remarried in 1978, to Daniel Kahneman, a fellow psychologist who would go on to win the Nobel Prize for Economics in 2002. Shortly thereafter, Treisman and Kahneman accepted positions at the University of British Columbia, Canada. In 1980, Treisman and Gelade published a seminal paper proposing her enormously influential Feature Integration Theory (FIT). Treisman’s research demonstrated that during the early stages of object perception, early vision encodes features such as color, form, and orientation as separate entities (in "feature maps") (Treisman, 1986). Focused attention to these features recombines the separate features resulting in correct object perception. In the absence of focused attention, these features can bind randomly to form illusory conjunctions (Treisman & Schmidt, 1982; Treisman, 1986). Feature integration theory has had an overarching impact both within and outside the area of psychology.

Feature Integration Theory Experiments

According to Treisman’s Feature Integration Theory perception of objects is divided into two stages:

1. Pre-Attentive Stage: The first stage in perception is so named because it happens automatically, without effort or attention by the perceiver. In this stage, an object is analyzed into its features (i.e., color, texture, shapes etc.). Treisman suggests that the reason we are unaware of the breakdown of an object into its elementary features is that this analysis occurs early in the perceptual processes, before we have become conscious of the object. Evidence: Treisman created a display of four objects flanked by two black numbers. This display was flashed on a screen for one-fifth of a second and followed by a random dot masking field in order to eliminate residual perception of the stimuli. Participants were asked to report the numbers first, followed by what they saw at each of the four locations where the shapes had been. In 18 percent of trials, participants reported seeing objects that consisted of a combination of features from two different stimuli (i.e., color and shape). The combinations of features from different stimuli are called illusory conjunctions (Treisman and Schmidt, 1982). The experiment also showed that these illusory conjunctions could occur even if the stimuli differ greatly in shape and size. According to Treisman, illusory conjunctions occur because early in the perceptual process, features may exist independently of one another, and can therefore be incorrectly combined in laboratory settings when briefly flashed stimuli are followed by a masking field (Treisman, 1986).
2. Focused Attention Stage: During this second stage of perception features are recombined to form whole objects. Evidence: Treisman repeated the illusory conjunction experiment, but this time, participants were instructed to ignore the flanking numbers, and to focus their attention on the four target objects. Results demonstrated that this focused attention eliminated illusory conjunctions, so that all shapes were paired with their correct colours (Treisman and Schmidt, 1982). The experiment demonstrates the role of attention in the correct perception of objects.