Applied History of Psychology/History of Research on 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 (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 (see below). 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).

Timeline

 * Pre-1880s: Franciscus Donders uses mental chronometry (the study of the temporal sequencing of information processing in the brain) to study attention with reaction time experiments. Wundt develops a research program to justify experimental psychology as a separate discipline; he uses introspection as a method of gathering information into psychological processes.
 * 1880s-1890s: At the Leipzig institute, using well-defined, quantitative, and easily reproducible experimental methodology, Wundt conducts studies on: sensation and perception, reaction times, attention and feeling, and association.
 * 1894: Helmholtz defines what is now known as ‘covert attention’ during a visual perception task. Scientific study of covert attention did not re-surface until the 1950s.
 * 1900-mid 1950s: Due to the popularity of behaviorism in psychology (emphasizing the association between a stimulus and a response, but without identifying the cognitive operations that lead to that response), research on attention is neglected.
 * 1924: Electroencephalography (EEG) is invented, which will become important in later neurological studies of attention.
 * 1935: John Ridley Stroop, in his article entitled Studies of interference in serial verbal reactions, discovers the Stroop effect (slower reaction times and an increase in mistakes when a word is printed in a color differing from the color expressed by the word's semantic meaning)
 * 1946: Magnetic Resonance Imaging (MRI) is invented, which will become important in later neurological studies of attention.
 * 1950s: Research psychologists (including Donald Broadbent) renew their interest in attention in a shift from positivism to realism in psychology, deemed as the cognitive revolution (admitted that unobservable cognitive processes can be studied scientifically).
 * 1952: Broadbent begins to publish his research findings from dichotic listening experiments on speaking and listening simultaneously, listening to synchronous messages, and failures of attention in selective listening.
 * 1953: Colin Cherry first describes the Cocktail Party Effect (the ability to focus our listening attention on a single talker talker among a mixture of conversations and background noises, and to pay attention to a stimulus that grabs our attention suddenly, such as our names).
 * 1957: Broadbent develops his mechanical model of attention.
 * 1958: Broadbent becomes clinical director of the Applied Psychology Unit at Cambridge. His book, Perception and Communication, is published, which describes his filter model of attention (an early selection model). This model was highly influential but was criticized for being too “inflexible”.
 * 1960s: Advent of information processing as the dominant perspective in cognitive psychology. Stroop’s work was rediscovered.
 * 1964: Use of Stroop Color-Word task as a measure of attentional and linguistic processes rose quickly
 * 1969:Treisman proposed her Attenuation Theory, which addresses how unattended information may get through to consciousness (not explained by Broadbent’s original model).
 * 1971: Broadbent’s second book on the topic of attention, Decision and Stress, is published, using his filter model as a starting point in his new theory, and taking into account findings from Cherry, Treisman, and others.
 * 1975: Broadbent wins a Distinguished Scientific Contribution award from the APA for being the first person to systematically study humans as an information-processing system and using a structure that could be investigated by experiment.
 * 1980: Treisman and Gelade publish their seminal paper which was the basis for Treisman’s Feature Integration Theory.
 * 1988: Treisman interprets the pop-out effect as evidence for a pre-attentive mechanism in perception. (Pre-attentive processes are based on perceptual analyses that simply signals the presence of a difference in the visual scene, rahter than on the action of focused attention.)
 * 1993: Following Broadbent’s death, numerous tributes and obituaries are published in his honour, and to recognize that his elaboration of the idea of the human organism as an information-processing system lead to a systematic study of attention.

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. However, less is known about the man behind this landmark cognitive task. In the following section, a biography of John Ridley Stroop, the creator of the Stroop Color-Word task and discoverer of the Stroop Effect, will be outlined.

John Ridley Stroop was born near Murfreesboro, Tennessee, on March 21, 1897. His middle name derived from a preacher whom his parents admired, and Stroop was known by that name both personally and professionally all through his life (MacLeod, 1992). Stroop was the second youngest of six children. As an infant, Stroop was not expected to live, which led his parents to shelter him during his childhood. Unlike the other the family members, he was not required to do heavy physical work on the family farm (MacLeod, 1991a).

Stroop's initial schooling was at Kitrell County School, where he graduated at the top of his elementary school class. He continued his education in nearby Nashville at David Lipscomb High School, graduating in 1919. In 1921, he obtained a diploma from David Lipscomb Junior College, where he was selected to be Valedictorian. On December 23, 1921, during his second year in college at the age of 24, Stroop married Zelma Dunn, great niece of Mr. David Lipscomb. Over the next seven years, they had three sons. To be able to support his growing family, Stroop taught at David Lipscomb College and worked as a janitor and as a librarian while in graduate school (MacLeod, 1992).

Stroop’s university years were spent at George Peabody College (now part of Vanderbilt University) in Nashville. There, he received his BS in 1924, his MA in 1925, and his PhD in 1933. His doctoral degree was in Experimental Psychology with a minor in Educational Psychology and an elective in Education. Stroop’s dissertation research was carried out under the supervision of Dr. Joseph Peterson, a former president of the American Psychological Association, at the Jesup Psychological Laboratory. Stroop developed these color-word tasks partly because the naming-reading comparison was of interest to Dr. Peterson in his individual differences research (MacLeod, 1991a). However, his real interest was on interference between conflicting processes. His research followed studies being conducted at the time on interference or inhibition but using materials that were similar in nature to those employed in color naming-word reading studies (Stroop, 1935). For instance, Stroop referred in his article to studies on color-word naming that were conducted by John James McKeen Cattell (1886), who at the instigation of his doctoral supervisor, Wilhelm Wundt, investigated differences in reaction times to naming objects, the properties of those objects, as well as the corresponding words. Catell reported that reading words took less time than naming the objects or properties, the latter including color (Macleod, 1991b). However, it was not until Stroop's research that anyone thought to combine the word and object/property dimensions, creating the now famous situation of response conflict (MacLeod, 1991). Stroop’s PhD dissertation went to become his classic paper, which over the years became one of the most cited articles in the history of the Journal of Experimental Psychology.

Stroop teaching career began long before the completion of his doctoral degree. He was principal at a Mississippi Consolidated School in 1921-1922. Then, he returned to David Lipscomb College. There, he began as an instructor in Mathematics and English (1922–1923), and then switched to Modern Languages (1924–1928). Between 1928 and 1932, he was Professor of Psychology and Education, serving as Dean of the Faculty for the 1928-1929 academic year. After completing his PhD, Stroop conducted research for the Tennessee Educational Commission (1933–1934), then serving briefly as a special instructor in Psychology and Education at Tennessee Polytechnic Institute. He returned to David Lipscomb College, where he taught for almost his entire 40-year career.

After completing his PhD, Stroop had planned to continue his line of research. However, when Dr. Peterson died in 1935, Stroop never again conducted research in psychology. As Macleod (1992) noted, it was probably this event more than any other that led Stroop to discontinue his psychological research. His wife also wrote in her biographical sketch of him: "His major professor at Peabody, Dr. Joseph Peterson, invited him to collaborate with him on a research project furthering the study of [Stroop] 's doctorate thesis. Dr. Peterson's unexpected death prevented such from happening. This was probably the changing of his work as he became more involved in teaching the Bible and writing in that field." (in MacLeod, 1991a). Stroop published just four papers in psychology throughout his career. One concerned with group versus individual judgments (1932), and the other three related to color-word processing including his classic paper (1935), a critique of work on the color-word issue (1935), and a test of a possible explanation of the Stroop effect (1938). Although his research career ended following the publication of these papers, Stroop remained in psychology and chaired his department from 1948 until 1964. After this period, Stroop's interest shifted away from psychology, and he devoted his attention to his religion for the rest of his life.

Stroop was a Christian who preached every Sunday in and around Nashville, often taking a train out into the country and being paid with a chicken or a bag of potatoes. He also kept a card file indicating for each Sunday where he had spoken and what his topic had been (MacLeod, 1991a). Moreover, Stroop taught bible classes in college in addition to teaching psychology. He was known to colleagues and students as both Dr. Stroop and Brother Stroop. Stroop’s major contributions were in the area of biblical studies. He wrote seven books based on his biblical teachings, beginning with Why Do People Not See the Bible Alike? published in 1949 and ending with Restoration Ideas on Church Organization published in 1966. His major work was a trilogy entitled God’s Plan and me, which was published in 1950s. He received awards for these books, which were popular as textbooks in Christian schools. The bible then rather than psychology was Stroop’s life work. John Ridley Stroop retired in 1967. He spent 1967-1968 as Dean of Ohio Valley College in Parkersburg, Virginia, after which he took up the position of Emeritus Professor of Biblical Studies at David Lipscomb College (MacLeod, 1991a). He died on September 1, 1973 at the age of 76.

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).

The discovery of the Stroop Effect and the development of this Color-Word task has had a lasting impact on cognitive psychology. As MacLeod (1991a) has noted, “There are few phenomena in psychology so robust that they appear in virtually every introductory text and are known by researchers in almost every sub-area of the discipline. The Stroop effect is one of these rare phenomena. John Ridley Stroop was a pioneer, instrumental in providing one of the tools most valued by cognitive psychologists. A half century later, the task that bears his name continues to be a challenging puzzle for experimental psychologists to solve. (MacLeod, 1991a)” This landmark cognitive task has been widely used to index attentional and linguistic processes. Understanding the Stroop effect may ultimately lead us to a fuller comprehension of how attention works and of the place of attention in a more general theory of cognition.

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.

Broadbent was born May 6, 1926, in Birmingham, England (American Psychological Association, 1976). He was originally interested in the natural sciences, and thus, when he joined the Royal Air Force (RAF) in 1944, he began his study of aeronautical engineering. As he spent time in the RAF he observed that human difficulties often arose from psychological, as opposed to physical, causes (Craik & Baddeley, 1995). More specifically, he noted that communication difficulties, such as problems listening to a specific stream of auditory information when presented with numerous streams, were frequently caused by inefficient processes of attention, perception, or memory, rather than by failures of hearing or technical equipment (Craik, 2000). Upon this observation, Broadbent’s interests changed from the subject of engineering to that of psychology.

At that time, however, the field of psychology was virtually unheard of in his home country of England. It was not until Broadbent travelled across the Atlantic to the United States for flying training that he discovered that psychology was being widely studied in North America (APA, 1976). After some time working in the personnel selection branch of the RAF, he began to study experimental psychology at Cambridge. Fortunately for Broadbent, and for scores of future psychologists, the psychology department at Cambridge was an especially suitable place for him due to its natural sciences orientation and its emphasis on practical application (Craik & Baddeley, 1995). Headed by Sir Frederic Bartlett, the department was enthusiastic to apply the cybernetic ideas of the late K .J. W. Craik, with the aim of understanding human behaviour in terms of control systems, to practical problems and psychological theory in general (APA, 1976). By sheer accident, but with fortunate advantage to the field of psychology, Broadbent’s interests in experimental psychology and practical application allowed him to find his place in the Applied Psychology Unit at Cambridge.

It was during his 25 years, from 1958 to 1974, as director of the Applied Psychology Unit that Broadbent was able to study and define models related to his interests in the effects of environmental stressors on cognitive performance, problems related to the detection and understanding of speech, and problems of selective listening and attention (Craik & Baddeley, 1995). Up to that time, most research had shown that noise did not influence performance on psychological tasks. Broadbent wondered, however, if noise would adversely influence performance on untraditional psychological tests (APA, 1976). For instance, he discovered that noise did have an effect on the vigilance tasks invented by N. H. Mackworth, however, these tasks were deliberately long and repetitive, making them tedious to study.

During that time, Broadbent also looked at the problems caused by communicating with gunnery and air control systems, in which many channels of speech communication were delivered at one time. In contrast to the vigilance studies, he found that this problem allowed for short and quick experiments, which contributed favourably to his study of attention and noise (APA, 1976). His work on communication systems indicated that most people spend their lives surrounded by many different types of stimuli, however, they cannot respond or describe the majority of them.

Not only were Broadbent’s contributions to experimental psychology noteworthy for attention research, they also contributed to belief in the need for societal relevance in research (Craik, 2000). It is perhaps through his background in natural sciences and engineering, and his subsequent practical work with the RAF on noise and communication, that Broadbent developed a particular admiration for applied psychological work. In addition, he had an informal speaking style when presenting lectures and essays, as well as used commonplace analogies to represent complicated ideas, which allowed society as a whole to consume his theories. For instance, when initially stated, his mechanical model of attention consisted of a Y-tube, in which two separate channels of ping-pong balls merge in a central channel protected by a filter that allows only one ball to enter (Massaro, 1996). Such an analogy clearly illustrated the limitations of human attention when attempting to attend to two auditory channels at the same time. As stated by Craik and Baddeley, “[Broadbent’s] psychology was intended for society and its problems, not merely for the dwellers in ivory towers” (1995, pp. 303).

After his death in 1993, numerous tributes and biographical acknowledgements were written in Broadbent’s honour. Above all, he is remembered for the unmistakable image that he projected of himself, as “the man, the scholar, the scientist, the philosopher of science, and of his commitments to empirical psychology, to explicit models or theories, and to the application of psychological knowledge to real-word problems” (Massaro, 1996, pp. 141). It is with this clear image in mind that a new generation of psychologists set forth, using Broadbent’s principles of experimental psychology as tools for practical application and research in the area of attention, and more broadly, all psychological processes that influence humankind.

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. and on 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, or T-6 (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 othere 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.

Anne Treisman (née Taylor) was born on February 27, 1935 in Wakefield, Yorkshire, England (Anon, 1991). Through the war years, Treisman lived with her family in a village near Rochester, Kent, where her father, Percy Taylor, worked as chief education officer. Forced by the English educational system to choose only three subjects to study throughout secondary school, Treisman’s studies focused on the language arts, a choice which would shape much of her post-secondary pursuits (Anon, 1991).

It was at Cambridge University that Treisman first discovered the pleasures of intellectual exchange. Studying modern languages, she obtained a first class BA with distinction, which earned her a research scholarship (Anon, 1991; Treisman, 2006). However, faced with the prospect of research on a relatively unknown author, Treisman decided to use her scholarship to obtain a second BA in psychology instead. Under the supervision of Richard Gregory, Treisman completed this second degree in one extra year (Anon, 1991). Gregory’s influence on Treisman was profound; in this year, she was introduced to various methods of exploring the mind through experiments in perception, igniting in her the enthusiasm for research that she maintains to this day (Anon, 1991).

In 1957, Treisman began working toward her DPh at Oxford University, under the supervision of Carolus Oldfield (Anon, 1991). She conducted research on aphasia and considered pursing a career in clinical psychology. However, Treisman soon realized that she lacked the appropriate training to effectively help patients and, unwilling to simply use her patients as subjects in graduate research, Treisman’s clinical career aspirations faded. Around the same time, information theory was shifting psychologists’ view of the mind from the traditional behaviourist view of the mind as a switchboard to that of an active processor of information (Goldstein, 2005). Donald Broadbent and Colin Cherry had recently published groundbreaking papers introducing selective listening (also known as the “cocktail party problem”), which launched the cognitive revolution (Broadbent, 1954; Cherry, 1953). Broadbent’s Filter Model of selective attention (1958), also referred to as an early selection model, proposed that unattended information is filtered out early in the process of auditory perception, that is, before incoming information is analyzed to determine its meaning. While this theory was tremendously influential, and could account for much of the cocktail party problem, it has been criticized for being too “inflexible” (e.g., this theory could not explain why unattended information occasionally gets through to consciousness). Guided by Donald Broadbent's book Perception and Communication (1958), Treisman began using a two-channel tape recorder (that she had been using to test aphasics) to conduct research on auditory attention in the normal population (Anon, 1991). After three years of research, she married Michel Treisman, another Oxford graduate student. Two years later, in 1962, she completed her thesis on selective attention and speech perception that earned her the DPh degree (Treisman, 2006).

Treisman spent the next four years working in the Medical Research Council Psycholinguistics Research Unit, conducting more research in selective listening (Anon, 1991). In 1964, Treisman proposed an influential theory that addressed some of the “inflexibility” of Broadbent’s Filter model. This was Treisman’s Attenuation Theory, whereby processing of unattended information is attenuated or reduced, rather than completely filtered out, accounting for the fact that unattended information sometimes reached consciousness. Further, her model proposed that information processing occurs in a hierarchical manner, with processing of physical characteristics occurring at an early stage (e.g., pitch, or tone of voice) and semantic processing at a later point (Treisman, 1964, 1969).

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.

In the early 1980s, neuroscientists were discovering that the primate visual cortex contained areas where neurons were specifically tuned to selective features (e.g., orientation, luminance, colour, shape etc.) (Gazzaniga et al., 2002). These findings perplexed the neuroscience community who was now faced with the question of how the brain solves the “binding problem” (i.e., how does the visual system recombine these disconnected features into unified wholes). Treisman approached this problem by testing patients with selective attention problems. She and her colleagues were first to demonstrate that the binding problem could present itself in everyday life and that one of its solutions involved spatial attention (Treisman and Schmidt, 1982; Goldstein, 2005). Treisman’s theory has had a tremendous impact, providing a starting point for a great number of experiments in the areas of cognitive psychology, vision science, imaging, neuropsychology and cognitive neuroscience.

In 1984, Treisman was made Fellow of the Canadian Institute for Advanced Research in their program of artificial intelligence (Treisman, 2006). The fellowship allowed Treisman to collaborate closely with computer scientists who approached the study of perception from a different angle. Two years later, Treisman and Kahneman moved to the University of California, Berkeley, where they were both professors in the Psychology Department (Treisman, 2006). In 1989, Treisman was elected a Fellow of the Royal Society, London, and in 1990, she was awarded the Howard Crosby Warren medal of the Society for Experimental Psychologists. In 1993, Treisman accepted a position as a professor in the Psychology Department at Princeton University in New Jersey, where she still conducts research to this day. Along with her numerous graduate students, Treisman continues to tackle some of the more challenging questions in cognitive psychology.

Treisman continues to receive numerous prestigious awards recognizing her invaluable contributions to the study of perception and attention, including the William James Fellowship of the American Psychological Society (2002) and a D.Sc., granted honoris causa, from the University of British Columbia (2004). Clearly, Anne Treisman has been a key figure in the establishment of cognitive psychology as a science, and a significant contributor to its evolution.

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

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., colour, 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., colour 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).

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.