Chapter 4 notes tb

Attention

Attention

can be considered the cognitive resources that can be allocated to various tasks. The taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalizing, and concentration of consciousness.

Selective Attention

Refers to the fact that we usually focus our attention on one or a few tasks or events at any given time.

Dichotic Listening Task

A person listens to an audiotape over a set of headphones. On the tape there are different messages, recorded as to be heard simultaneously in opposite ears. Participants in a dichotic listening task typically are played two or more different messages and asked to shadow one of them. Information is presented at a rapid rate (150 words per minute) so the shadowing task is demanding. Sometimes the tapes are recorded for binaural presentation.

binaural presentation

presenting the same two messages or sometimes just one message to both ears simultaneously

The Logic of the Dichotic Listening Task Setup

The person must concentrate on the message to be shadowed. Because the rate of presentation of information is so fast, the shadowing task is difficult and requires a great deal of mental resources. Therefore, fewer resources are available to process information from the non-shadowed, unattended message.

Cherry (1953) and Classical Study

It demonstrated that people can, with few errors, shadow a message spoken at a normal to rapid rate. When researchers later questioned these participants about the material in the unattended message, they could nearly always report accurately whether the message contained speech or noise and, if speech, whether the voice was that of a man or a woman. When the unattended message consisted of speech played backward, some participants reported noticing that some aspect of the message, which they assumed to be normal speech, was vaguely odd. Participants could not recall the content of the unattended message or the language in which it was spoken. In one variation of the procedure, the language of the unattended message was changed from English to German, but participants apparently did not notice the switch. Participants of another experiment (Moray, 1959) heard prose in the attended message and a short list of simple words in the unattended message. They failed to recognize the occurrence of most words in the unattended message, even though the list had been repeated 35 times!

Filter Theory (Broadbent)

States that there are limits on how much information a person can attend to at a given time. The person uses an attentional filter to let some information back through and block the rest. Only material that gets past the filter can be analyzed later for meaning. Thus it is selecting information for later processing. So it should not be possible to recall any of the meaning of an unattended message, as it would not be processed.

Attentional filter is based on:

some physical (basic acoustic) aspect of the unattended message: the location of its source or its typical pitch or loudness, or instance.

Broadbent's Filter Theory: Paying attention to two messages at once

It does not mean that people can never pay attention to two messages at once. Instead what is limited is the amount of information we can process at a given time. Two messages that contain little information, or that present information slowly, can be processed simultaneously. The filter thus protects us from information overload by shutting out messages when we hear too much information to process all at once.

Contradictions to the Filter Theory (Moray)

Moray (1959) discovered one of the most famous, called the cocktail party effect: Shadowing performance is disrupted when ones own name is embedded in either the attended or unattended message. Moreover, the person hears and remembers hearing their name.

Why does the Cocktail Party Effect pose a problem for the Filter Theory?

Filter theory predicts that all unattended messages will be filtered out-that is, not processed for recognition or meaning-which is why participants in dichotic listening tasks can recall little information about such messages. The cocktail party effect shows something completely different: People sometimes do hear their own name in an unattended message or conversation, and hearing their name will cause them to switch their attention to the previously unattended message. Moray concluded that only important material can penetrate the filter set up to block unattended messages. Presumably, messages containing those such as a persons name are important enough to get through the filter and be analyzed for meaning. Left unexplained, then, is how the filter knows which messages are important enough to let pass.

An alternate explanation for the name recognition finding

Note that participants did not always hear their name in the unattended channel. Thus, an alternative explanation for the name recognition finding is that the shadowing task does not always take 100% of ones attention. Therefore, attention occasionally lapses and shifts to the unattended message. During these lapses, name recognition occurs.

Treisman (1960): Argue against alternative interpretation of cocktail party effect

She played participants two distinct messages, each presented to a different ear, and asked the participants to shadow one of them. At a certain point in the middle of the messages, the content of the first message and the second message was switched so that the second continued the story line of the first and vice versa. Immediately after the two messages switched ears, many of the participants repeated one or two words from the unattended ear. If the participants processed the unattended message only when their attentional filter lapsed, it would be very difficult to explain why these lapses always occurred at the point when the two messages switched ears. To explain this result, Treisman reasoned that participants must be *basing their selection of the message to attend to at least in part on the meaning of the message-a possibility that the filter theory does not allow

Wood and Cowan (1995) Experimental Methods

In one experiment, they had 168 undergraduate students perform a dichotic listening task. Two of the groups shadowed an excerpt from "The Grapes of Wrath" (read very quickly at a rate of 175 words per minute) in the attended channel (always presented to the right ear) and were also presented with an excerpt from "2001: A space Odyssey" in the unattended channel, always presented to the left ear. Five minutes into the task, the speech in the unattended channel switched to backwards speech for 30 seconds. Previous experiments had established that under these conditions, roughly half of the participants would notice the switch and half would not. The two group differed in only how long the normal speech was presented after the backward speech: two and a half minutes for one group; one and a half minutes for the other. A third, control group of participants heard an unattended message with no backwards speech.

Wood and Cowan (1995) Experimental Results

Wood and Cowan (1995) first asked whether the people who noticed the backward speech in the unattended message showed a disruption in the shadowing of the attended message. In other words, if they processed information in the unattended message, did this processing have a cost to their performance on the main task? The answer was clearly yes. Wood and Cowan counted the percentage of errors made in shadowing and noted that the percentage rose to a peak during 30 seconds of the backward-speech presentation. The effect was especially dramatic for those people who reported noticing the backward speech. Control participants, who were never presented with backwards speech showed no rise in their shadowing errors, nor did most of the participants who did not report noticing the backwards speech.

Wood and Cowan (1995) Experiment: What Caused the Shift in Attention to the backwards speech?

The finding showed that control participants and participants who did not notice the backwards speech more no more errors over the time studied. However, participants who did report hearing backwards speech made noticeably more errors, which peaked 10 to 20 seconds after the backwards speech began.

Wood and Cowan (1995) Experiment Conclusion

That the participants who noticed the backwards speech had their attention "captured" by the backwards speech, which led to poorer performance on the main shadowing task.

Conan, Cowan, and Bunting (2001) and Working-Memory Span

20% of participants with high working-memory spans detected their names in the unattended channel, compared with 65% of participants with low working-memory spans. Thus a lower working-memory capacity means less ability to actively block the unattended message.

Anne Treisman (1960): Attenuation Theory

A modified filter theory, instead of considering unattended messages blocked before they could be processed for meaning argued that some meaningful information in unattended messages might still be available, even if hard to recover.

Attenuation theory: incoming messages processing

In the first, the messages physical properties, such as pitch or loudness, are analyzed. The second analysis is linguistic, a process of parsing the messages into syllables and words. The third kind of analysis is semantic, processing the meaning of the message. Some meaningful units (such as words or phrases) tend to be processed quite easily.

Attenuation Theory to explain Cocktail Effect

Words or phrases with permanently lowered thresholds require little mental effort by the hearer to be recognized. Thus, according to Treisman's theory, the participants in Moray's experiments heard their names because recognizing their names required little mental effort.

Attenuation Theory: Primed words

Only a few words have permanently lowered thresholds. Words that have subjective importance (such as your name) or that signal danger, have permanently lowered thresholds; that is, they are recognizable even at low volumes. However, the context of a word in a message can temporarily lower its threshold. If a person hears "the dog chased the...", the word cat is primed-that is, especially ready to be recognized. Even if the word cat were to occur in the unattached channel, little effort would be needed to hear and process it. This explains why people in Treisman's experiment switched ears: Hearing the previous words in a sentence primed to participants to detect and recognize the words that followed, even when those words occurred in the unattended message.

Anne Treisman Attenuation Theory: Different Factors Affecting the Processing of the Two Messages

People process only as much information as is necessary to separate the attended message from the unattended message. If then two messages differ in physical characteristics, then we process information only to this level and easily reject the unattended message. If the two messages differ only semantically, we process both through the level of meaning and select which message to attend to based on this analysis. Processing for meaning takes more effort, however, so we do this kind of analysis only when necessary. Messages not attended to are not completely blocked out but rather weakened in much the way that turning down the volume weakens the audio signal from a stereo. Parts of the message with permanently lowered thresholds (significant stimuli) can still be recovered, even from an unattended message.

Contrasts Between Attenuation and Filter Theories

Attenuation theory allows for many different kinds of analyses of all messages, whereas filter theory allows for only one. Filter theory holds that unattended messages, once processed for physical characteristics, are discarded and fully blocked; attenuation theory holds that unattended messages are weakened but the information they contain is still available.

Deutsch and Deutsch (1963) and Norman (1968): Late-Selection Theory

This theory holds that all messages are routinely processed for at least some aspects of meaning. Attentional selection occurs after this routine processing, very late relative to the two earlier models.

Pashler's Interpretation of the Late-Selection Theory

Recognition of familiar objects proceeds unselectively and without any capacity limitations. One cannot voluntarily choose to identify or recognize something, according to these theorists. Whether there is just one sensory input or many does not affect the extent to which stimuli are analyzed or the timing of such analyses.

Bottleneck Hypothesis

Note that the filter theory hypothesizes a bottleneck-a point at which the processes a person can bring to bear on information are greatly limited-at the filter. Late-selection theory also describes a bottleneck but locates it later in processing, after certain aspects of the meaning have been extracted. All material is processed up to this point, and information judged to be most important is elaborated more fully. This elaborated material is more likely to be retained; unelaborated material is forgotten.

Factors Depicting a Message's Importance

A message's importance depends on many factors, including its context and the personal significance of certain kinds of content (such as your name). Also relevant is the observers level of alternes. Generally, the attentional system functions to determine which of the incoming messages is the most important; this messages is the one to which the observer will respond.

How well does evidence for the late-selection theory measure up?

Pashler (1998) argues that the bulk of the evidence suggests it is undeniably true that information in the unattended channel sometimes receives processing for meaning. At the same time, it appears true that most results thought to demonstrate late selection could be explained in terms of either attentional lapses (to the attended message) or special cases of particularly salient or important stimuli grabbing attention. In any event, it seems unlikely that unattended messages are processed for meaning to the same degree as are attended messages.

Daniel Kahneman (1973) Metaphor of Attention

He viewed attention as a set of cognitive processes for categorizing and recognizing stimuli. The more complex the stimulus, the harder the processing, and therefore the more attentional resources are required. People have some control over where they direct their mental resources, however: They can also choose what to focus on and where to allocate their attentional resources.

Daniel Kahneman (1973) Model of Attention

Essentially, this model depicts the allocation of mental resources to various cognitive tasks. Many factors influence this allocation of capacity, which itself depends on the extent and type of mental resources available. The availability of mental resources, in turn, is affected by the overall level of arousal, or state of alertness.

Daniel Kahneman (1973) Model of Attention: Level of Arousal

Argued that one effect of being aroused is that more cognitive resources are available to devote to various tasks. Paradoxically, however, the level of arousal also depends on a tasks difficulty. This means that we are less aroused while performing easy tasks, than we are at performing more difficult tasks. We therefore bring fewer cognitive resources to easy tasks, which fortunately, require fewer resources to complete.

Daniel Kahneman (1973) Attention Model: Allocation Policy

Arousal thus affects our capacity (the total sum of our mental resources) for tasks. Note that this policy is affected by an individuals enduring dispositions, momentary interactions, and the evaluation of the demands on ones capacity . Essentially this model predicts that we pay more attention to things we are interested in, are in the mood for, or have judged important. The more effort expended the more attention we are using.

Daniel Kahneman (1973) Attention Model: Effort

Effort is only one factor that influences performance on a task, however. Greater effort or concentration results in better performance on some tasks-those that require limited processing, performance of which is constrained by mental resources or capacities allocated to it.

Daniel Kahneman (1973) Attention Model: Data Limited Performance

The task depends entirely on the quality of the incoming data, not on mental effort or concentration. Norman and Bobrow pointed out that both kinds of limitations affect our ability to perform any cognitive task.

Automaticity and the Effects of Practice

As we become well-practiced doing something, that act takes less of our attention to perform.

What affects the capacity a task requires?

One factor is the difficulty of the task. Another important issue that affects the capacity a task requires is the individuals familiarity with the task. Practice is thought to decrease the amount of mental effort a task requires.

John Ridley Stroop (1935): The Stroop Effect

Participant were presented with a series of colour bars (red, blue, green, brown, purple) printed in conflicting colours (for example, the word red printed in green ink). Participants were asked to name, as quickly as possible, the ink colour of each item in the series. When shown bars, they did so quickly, with few errors and apparently little effort. Things changed dramatically, however, when items consisted of words that named colours other than that of the ink in which the item was printed. Participants stumbled through these lists, finding it difficult to read the words formed by the letters.

The Difficulty of the Stroop Test

The difficulty stems from the following: Adult, literate participants have had so much practice reading that the task requires little attention and is performed rapidly. In fact, according to Stroop, literate adults read so quickly and effortlessly that not reading words is hard. Thus, when confronted with items consisting of words, participants couldn't help reading them. We describe this kind of response-one that requires no attention and cannot be inhibited- as automatic. Indeed, the most common theoretical account of the the Stroop Effect is that for literate adults reading is automatic and its products, which conflict with the ink colour on a Stroop Trial, interfere with a participants ability to name the ink colour.

Posner and Snyder (1975): Automatic Processing

Posner and Snyder (1975) offered three criteria for cognitive processing to be called automatic processing: (1) it must occur without intention; (2) it must occur without involving conscious awareness; and (3) it must not interfere with other mental activity.

Schneider and Shiffrin (1977): Automatic Processing Experiment

Schneider and Shiffrin (1977) examined automatic processing of information under well-controlled laboratory conditions. They asked participants to search for certain targets, either letters or numbers, in different arrays of letters or numbers called frames. Previous work had suggested that when people search for targets of one type (such as numbers) in an array of a different type (such as letters), the task is easy. Numbers against a background of letters seem to pop out automatically. In fact, the number of non target characters in an array, called distractors, makes little difference if the distractors are of a different type from the targets. When the target and the distractors are of the same type, the number of distractors does not make a difference*.

Schneider and Shiffrin (1977) Experimental Conditions

In the varied-mapping condition, the set of target letters or numbers, called the memory set, consisted of one or more letters or numbers, and the stimuli in each frame were also letters or numbers. Targets in one trial could be distractors in subsequent trials. So participants might search for a J in one trial, then search for an M on a second trial, with a J distractor included. In this condition, the task was expected to be hard and require less capacity.

Schneider and Shiffrin (1977) Experimental Varied Factors

The first was frame size-that is, the number of letter and numbers presented in each display. This number was always between 1 and 4. Slots not occupied by a letter or number contained a random dot pattern. Second was the frame time-that is, the length of time each array was displayed. This varied from approximately 20 milliseconds to 800 milliseconds. Third was the memory set-that is, the number of targets the participant was asked to look for in each trial.

Schneider and Shiffrin (1977) Experiment: Consistent-Mapping Condition Results

Thought to require only automatic processing (because the targets and distractors were not the same type of stimuli), participants performance varied only with the frame time, not with the number of targets search for (memory set) or the number of distractors present (frame size). This means that participants were just as accurate in searching for one as for four targets and searching among one, two, or four items in a frame. Accuracy depended only on the length of time the frames were displayed.

Schneider and Shiffrin (1977) Experiment: Varied-Mapping Condition Results

Thought to require more than automatic processing (because the targets and distractors could both be letters or both numbers, and because targets on one trial could become distractors on another), participants performance in detecting the target depended on all three variables: memory set size (number of targets searched for), frame size (number of distractors present), and frame time.

Schneider and Shiffrin (1977) Experimental Results

Automatic Processing, they asserted is used for easy tasks with familiar terms. It operates in parallel (meaning it can operate simultaneously) with other processes) and does not strain capacity limitations. This kind of processing is done in the consistent-mapping condition: Because the targets "popped out" from the background, little effort or concentration was required. That searching for four targets was as easy as searching for one illustrates the parallel nature of this kind of processing: several searches can be conducted simultaneously.

Schneider and Shiffrin (1977): Controlled Processing

Is used for difficult tasks and ones that involve unfamiliar processes. It usually operates serially (with one set of information processed at a time), requires attention, is capacity limited, and is under conscious control. Occurred in the varied-mapping condition (where targets and distractors could alternate across different trials). More generally, controlled processing is what we use with non routine or unfamiliar tasks.

Divided Attention

If attention is a flexible system for allocating resources, and if tasks differ in the amount of attention they require, then people should be able to learn to perform two tasks at once (known as divided attention).

Spelke, Hirst, and Neisser (1976): Dual-Task Performance

Two Cornell University students were recruited as participants. Five days a week, for 17 weeks, working in 1 hour sessions, these students learned to write words dictated while they read short stories. Their reading comprehension was periodically tested. After 6 weeks of practice, their reading rates approached their normal speeds. Also by the end of 6 weeks, their scores on the reading comprehension tests were comparable whether they were only reading stories (and thus giving their reading task their full attention) or reading stories while writing down dictated words. Further investigation revealed that participants could also categorize the dictated words by meaning and discover relations among the words without sacrificing reading speed or comprehension.

Alternation Hypothesis for Dual-Task Performance Experiment

Many Psychologists were surprised that the participants in the this study could process information about meaning without conscious attention, and some offered alternative explanations for the findings. One hypothesis is that participants alternated their attention between the two tasks, attending first to the story, and then to the dictation, and then back to the story, and so on. The authors argued that the fact that participants reading speeds were comparable whether or not they were taking dictation suggests that if they were alternating their attention, they were doing so without any measurable lag.

Speke, Hirst, Reeves, Caharack, and Neisser (1980) Evidene against Alternation Hypothesis for Dual-Task Performance Experiment

Found evidence against this alternation hypothesis. Their participants were trained in ways similar to those used by Spelke et al. (1976). All participants copied dictated words while reading. Some participants read short stories, presumably containing some redundant material and therefore requiring relatively little attention. Other participants read encyclopedia articles, thought to contain less redundant material and thus to require more concentration. After they reached normal reading speeds and reading comprehension during dictation, the participants tasks were switched: Those who were reading short stories were now given encyclopedia articles, and those trained using encyclopedia articles now read short stories. Six of the seven participants performed comparably with the new reading material, indicating that the participants were probably not alternating their attention between the two tasks. If they were, then to learn to take dictation while reading short stories should not transfer well to doing so while reading encyclopedia articles.

Hypothesis explanation of automatic performance in dual-task experiment

One of the two tasks (for example, the dictation task) is being performed automatically. According to one of Posner and Snyder's (1975) criteria for automaticity-that processing not interfere with other mental activity-taking dictation in this study might be considered automatic. However, participants were clearly aware that words were being dictated, and they typically recognized about 80% of the dictated words on tests immediately following trials. Moreover, participants clearly intended to copy the dictated words. Therefore, taking dictation does not meet Posner and Snyder's (1975) last two criteria: lack of intention and lack of conscious awareness.

Speke, Hirst, Reeves, Caharack, and Neisser (1980) Evidence against Automaticity Hypothesis

Participants trained to copy complete sentences while reading were able to comprehend and able to recall those sentences, suggesting that the participants had processed the dictation task for meaning. This in turn suggests they paid at least some attention to the dictation task, given that most psychologists believe automatic processing occurs without comprehension.

Speke, Hirst, Reeves, Caharack, and Neisser (1980) Dual-Task Experiment: Combining two separate tasks

A third explanation favoured, is that the participants learned to combine two separate tasks: reading and taking dictation. That is, practice with these two specific tasks caused the participants to perform these tasks differently from the way they did them first. This implies that if wither one of these tasks were combined with a third (such as shadowing prose), additional practice would be needed before the two tasks could be done together efficiently. Practice thus appears to play an enormous role in performance and is one important determinant of how much attention any task requires.

Pashler (1993): Practice and Task Performance Experiment

Even with lots of practice, however, some sets of tasks are hard to do together at the same time. Pashler (1993) reported on studies from his and other laboratories that examined the issue of doing two things at once with greater depth. The participant is asked to work on two tasks. The first is a tone choice response task, in which on each trial the participant is presented with either low- or a high-pitched tone one is instructed to respond "low" or "high" as quickly as possible. Response times are recorded, and the participant is often given feedback regarding speed and accuracy. The second task involves visual presentation of a letter, and the participant is instructed to press one of several response keys that correspond to the letter presented.

Pashler (1993): Practice and Task Performance Experimental Results

The interval between the presentation of the tone (S1) and the letter (S2) is systemically varied. At long intervals participants show no interference and appear to perform the two tasks successively, finishing their response to the first task before beginning to work on the second task. However, as the interval between the presentation of S1 and S2 gets shorter and shorter, the time to complete the second task gets longer and longer. The hypothesized explanation is that while the participant is working on the first task, he cannot devote any attention to make progress on the second.

Psychological Refractory Period (PRP)

The slow response time to the second stimulus, S2, at shorter intervals between the presentation of S1 and S2. Pashler (1993) considered three distinct possibilities to where the bottle neck here lies: at the stage of perception of the stimulus (A), at the stage of making a response (C), or at a stage in which a response is selected or chosen (B). In fact, the work of Pashler and his colleagues supports the theory of Welford (1952), who argued that for this last possibility (B) and who coined the term psychological refractory period. Pashler (1993) also found evidence that retrieving information from memory caused a bottleneck and disrupted attention to the second task.

Gordon Logan and Joseph Etherton (1994/1996): The Attention Hypothesis of Automatization

Work by Gordon Logan and Joseph Etherton has sought to tie together many concepts we have talked about in this chapter. These researchers propose what they call an attention hypothesis of automatization, which states that attention is needed during the practice phase of a task and determines what gets learned during practice. Attention also determines what will be remembered from the practice. Logan and colleagues (1996) put it this way: "Learning is a side effect of attending: People will learn about the things they attend to and they will not learn much about things they do not attend to". Specifically, Logan and his colleagues argued that attention affects what information gets encoded into a memory and what information is later received.

Mike Tombu and Pierre Jolicoeur (2003) Alternative Hypothesis to bottleneck account of the Psychological Refractory Period: Capacity Sharing Model

Offered an alternative to the bottleneck account of the psychological refractory period, however. Rather than that attention must be divided into an all-or-none fashion between two tasks, they argued that it can be shared in a more flexible manner. That is, while performing an attention-demanding phase of task 1, people can choose to allocate some attention to a demanding phase of a second task. Their account predicts that when people choose to share some attention between two tasks, performance on the first task will be impaired relative to when all attention is devoted to it. Research from their lab supports this capacity sharing model

Logan and Etherton (1994) Experiments

Presented university student participants with a series of two-word displays and asked them to detect particular target words (for example, words that names metals) as fast as possible. For some participants, the word pairs remained constant over trials. Other participants saw word pairs that varied from trial to trial. The question was: Would participants in the first condition gain an advantage in performance because the words were consistently paired?

Logan and Etherton (1994) Experiments: Would participants in the first condition gain an advantage in performance because the words were consistently paired?

The answer was yes, but only when the specifics of the target detection task forced the participants to pay attention to both words in the display. If, for example, the experimenters coloured one of the two words green and asked participants only to decide whether the green word in a stimulus display was a target word on each trial, then participants did not gain an advantage from consistent pairings of words and indeed later recalled fewer of the distractor words. Apparently the colour cue made it easy for participants to ignore the second word in the display. To ignore something means not to pay attention to it, and thus apparently little gets learned about it. Even with extensive practice (five sessions), participants in the consistent pairing condition were unlikely to learn which words had been paired if they had no reason to pay attention to the distractor word.

Strayer and Johnston (2001): Interference Simulation Experiment #1

In their first experiment, they had research participants perform a pursuit-tracking task: They used a joystick to move a cursor on a computer to keep it positioned over a moving target. At various intervals the target flashed either red or green, a signal to the driver to push a break button on the joy stick (red) or ignore the flash (green). Participants performed first the driving tracking task by itself, then performed the dual-task portion of the study: either listening to a radio broadcast or talking on a cell phone with a confederate of the experimenters. Listening to the radio broadcast did not cause people to miss red lights or react to them more slowly then they had when performed the pursuit task by itself (the single-task condition). However, talking on the phone did cause both problems.

Strayer and Johnston (2001): Interference Simulation Experiment #2

Had participants talk on a cell phone, either shadowing lists of words the confederate read to them or else performing a word-generation task. In the latter task, the participant listened to the word the confederate read (for example, the word cream) and then had to generate a new word that began with the last letter of the word read (would then say a word beginning with the letter m). For some participants the pursuit task was easy, with few unpredictable changes, whereas for others it was more difficult, with many such changes. Shadowing words did not lead to reliable decrements in performance. However, generating words did, and the decrement was especially pronounced when the task was difficult.

Strayer and Johnston (2001): Interference Simulation Tasks Experimental Observations

There is evidence that in-person conversations are modulated by driving difficulty, so that as the demands of driving increase, participation of all participants in a conversation decreases. By contrast, at least one of the participants in a cellular phone conversation is unaware of current driving conditions and may even be unaware the cell-phone user is driving.

Strayer and Johnston (2001): Interference Simulation Tasks Experiment Summary

Research on divided attention suggests that there are serious limits on the number of things we can actually do at once. It may seem that we can do things simultaneously in the real world, when in many cases we do both tasks by rapidly switching our attention back and forth between the two. Of course, when those individual tasks become more demanding, it becomes harder and harder to do them simultaneously.

Spatial Attention

Attention plays a large role in how efficient you are in your visual search, and in the types of things that aid and impair your performance. Spatial Cues act in directing attention to a particular area in space. Spatial attention involves both in the context of spatial cueing paradigm, and in the context of visual search.

Posner and Colleagues Experiment: Spatial Cueing

They asked observers to fixate on a plus sign in the middle of the screen. An arrow cue then appeared above the fixation, and it pointed to the right, to the left, of had two heads (one pointing left and one pointing right). Observers were told to move attention, but not their eyes, in the direction indicated by the one-headed arrow cue. In the case of the two-headed arrow cue, they were told to leave attention (and their eyes) at the fixation sign. A simple target (a square) then appeared on the screen, and observers were asked to hit a key when they detected the target. On 80% of trials with a one-headed cue, the target appeared in the same location indicated by the cue; this was called a valid trial. On 20% of trials with a one-headed cue, the target appeared in the location opposite to that indicated by the cue; this was called an invalid trial. Finally, in the case of two-headed cues, targets were equally likely to appear on either side. This was called a neutral trial.

Posner and Colleagues Experimental Results

The results indicated that observers were fastest in the validity cued condition and slowest in the invalidity cued condition. Posner and colleagues interpreted these results as showing that performance was facilitated on valid trials (relative to neutral trials), presumably because observers shifted attention to the location of the target prior to its appearance. Likewise, there was an important cost (relative to natural trials) to having shifted attention to the wrong location on the invalid trials. They developed a spotlight metaphor of attention and suggested that attention can be likened to a spotlight that enhances the efficiency of detection of events within its beam. The spotlight metaphor is therefore an important way to characterize input attention, as it affects the ease with which stimuli can be brought into the system for processing.

Anne Treisman and Gelade (1980) Experiment: Visual Search Model; (Panel A)

In one experiment, they presented participants with a series of simple objects (such as letters) that differed in several features (such as colour and shape). Participants were asked to search for a particular object, for example, a blue letter Z. If the item being searched for differed from the background items in the critical feature (such as blue item against all black items, as in panel A), the target listen seemed to pop out of the display, and the number of background items did not affect participants response times. This pattern of results served as evidence that the detection of individual features is automatic-that is, it does not require attention and can be performed in parallel across the entire display. In other words, all items in the display can be searched at once under these conditions.

Anne Treisman and Gelade (1980) Experiment: Visual Search Model; (Panel C)

In another condition, participants were asked to search for an object with a combination of features. For example, in panel C you were asked once again to search for the blue Z, but in this case the blue Z was hidden amongst other items that included both other blue letters (that were not Z's) and other Z's (that were not blue). In this condition, search was much more difficult and participants response times varied with the number of background items. That is, locating the target item took longer the more distractor items were in the display. It was argued that search in this case was difficult because the observer not only had to find the features "Z" and "colour blue", but also had to make both of those features were on the same object. In other words, the panel C participants were asked to perform a conjunction search. In order to perform a conjunction search, observers require controlled, nonautomatic processing.

Feature Integration Theory

The general idea is that we perceive objects in two distinct stages. In the first stage, which is pre-attentive, or automatic,we register features of objects, such as their colour and shape. This allows us to detect or recognize all objects that can be identified on the basis of a single feature. In the second stage, attention allows us to "glue" the features together in a unified object. This stage is necessary in order to identify complex objects, or to detect objects that share features with other background objects

Treisman and Schmidt (1982): Illusory Conjunctions

Showed that when attention is diverted or "overloaded" participants make "gluing" errors

Treisman and Schmidt (1982): Illusory Conjunctions Experiment

In the experimental demonstration of this phenomena, participants saw two black digits displayed on either side of a row of three larger coloured letters, presented briefly (for 200 milliseconds). They were asked to pay attention to and recite the black digits, with the experimenter emphasizing the importance of accuracy. Participants were also asked, after they had reported the digits, report the positions, colours, and names of any letters they had seen. They were asked to report information only about which they were highly confident. Participants were able to provide correct information on letters 52% of the time, but in 39% of the trials they reported illusory conjunctions (such as a red X instead of either a blue X or a red T). In other words, when mentally taxed, people mistakenly combined features in illusory conjunctions.

Treisman and Schmidt (1982): Illusory Conjunctions Experiment Summary of Results

Perceiving individual features takes little effort or attention, whereas "gluing" features together into cohort objects requires more.

Change Blindness

The inability to notice large changes to scenes when the scene is somehow disrupted.

Inattentional Blindness

The phenomenon of not perceiving a stimulus that might be literally right in front of you, unless you are paying attention to it.

Daniel Simons: Inattentional Blindess Experiment

Participants were asked to follow either the white team or the black team and to count the number of times the team they were watching passed a basketball (easy condition) or to keep track separately of both the number of bounce passes and the number of aerial passes made by the target team (hard condition). At a little under a minute into the presentation, two unexpected events occurred: "After 44-48s of this action, either of two unexpected events occurred: in the Umbrella-Woman Condition, a tall women holding an umbrella walked from off camera on one side of the action to the other, left to right. The actions of the players, and this unexpected event, were designed to mimic the stimuli used by Neisser and colleagues. In the Gorilla Condition, a shorter woman wearing a gorilla costume that fully covered her body walked through the action in the same way. In either case, the unexpected event lasted 5s, and the players continued their actions during and after the event".

Simons and Chabris (1999): Inattentional Blindess Experiment Results

After viewing the entire videotape, students wrote down their counts and then were asked to describe anything unusual they had seen on the video. Questions beaus increasing specific and finally asking if they saw any of the 2 conditions walk across the screen? Overall 46% of participants failed to notice either the umbrellas woman or the gorilla. Only 44% of participants ever reported seeing a gorilla, although this number was much greater for the subjects watching the black team, who presumable shared more visual features with the gorilla (dark colour) than did the white team. Simons and Chabris (1999) concluded that unexpected events can be overlooked.

Simons and Chabris (1999): Inattentional Blindess Experiment Results Summary

Presumably, we perceive only those events to which we attend, especially if the unexpected event is dissimilar to the focus of our attention, and if our attention is tightly focused somewhere else.

Neuroscientific Studies of Attention

Cognitive neuroscientists are interested in examine which areas of the human brain are active when a person is attending to a stimulus or event. Researchers have long speculated the parietal lobe of the brain is one such location.

Posner and Raichle (1994): Systems of Visual Attention Experiment

A participant is seated in front of a visual display, fixing on a central point. On either side of the point are two boxes. On each trial, one box brightens or an arrow appears, indicating on which side of the screen the participant should expect the see the next stimulus. The purpose of this cue is to encourage the participant to focus their attention at a particular location. The participants task is to respond as fast as possible when he detects the stimulus. Sometimes no cue is given, and at other times an invalid cue is given, to assess the benefit of having attention focused in either the valid or invalid location.

Sensory Neglect Phenomenon

Clinical neurologists have documented the phenomenon of sensory neglect (sometimes called hemineglect) in patients who have parietal lobe damage. These patients often ignore or neglect sensory information located in the visual field opposite the damaged hemisphere. Thus if an area of the right parietal lobe is the damage site (as it often is), the patient overlooks information in the left visual field. This neglect may include, for example, neglecting to wash one side of the face or body, neglecting to brush on one side of the mouth, or eating from only one side of the plate. In clinical studies, patients showing hemineglect have been studied in more detail. Typically, they are presented with stimuli and asked to copy them. For example, when a patient with a lesion of the right parietal lobe is asked to copy simple line drawings such as a clock or a house, he omits details on the left. Note that in both cases the left part of the drawing is missing, something the patient did not appear to notice.

Hemineglect and Clinical Work Studies

Clinical work has established that hemineglect is attentional, rather than sensory (Banich, 1997). Were it simply a sensory deficit, we would expect patients to turn their gaze to the part of the visual field they were missing-in other words, to be aware of their visual information is incomplete. Indeed, some patients have just this type of deficit, and they do compensate by just such strategies. In contrast, patients with hemineglect seem unaware of one size of their body and disinclined to try to attend to information from that side. In extreme cases, patients with hemineglect can deny that some of their limbs belong to them. In one case study, a patient through hospital staff had cruelly played a severed leg in his bed; he tried to throw it to the floor, but the rest of his body followed his leg.

Brain Regions Associated with Attention

Although the parietal lobe is one main brain region known to be associated with attention, it is not the only one. Areas of the frontal lobe as well play a role in peoples ability to select motor responses and develop plans.

Networks of Visual Attention

Much of our brain processes of attention has centred on visual attention. Researchers have identified more than 32 areas of the brain that become active during visual processing of an unattended stimulus.

Posner and Raichle (1994): Systems of Visual Attention Experimental Results

They argued that to perform this task a person needs to execute three distinct mental operations. She first must disengage her attention wherever it was previously directed. Brain activity in the posterior parietal lobe is heightened during this process. Once disengaged, attention must be refocused on the spatial location of the new to-be-attended stimulus. Posner and Raichle called this the move operation. They reported that patients with brain damage in the superior colliculus, a major structure of the midbrain, have difficulty moving their attention from one location to another. Finally, according to Posner and Raichle, when attention is redirected, neural processing of the new location is enhanced; stimulus information presented at the to-be-attended location is emphasized, and the brain circuitry underlying this operation (the pulvinar, located in the thalamus) becomes more active. As you might expect, patients with damage to the pulvinar do not show the enhanced processing of which other people are capable when attending to a stimulus in a particular location.

Posner and Raichle (1994): Systems of Visual Attention Experimental Results Summary

The idea that attention consists of several different processes that operate independently has received some support from clinical psychological studies of children and adults with ADHD. An estimated 3% to 5% of the general school age population has some form of ADHD, with the disorder approximately three ties more likely in boys than in girls. Barkley's (1998) classic work suggests that ADHD clients suffer not so much from the inability to be alert or to devote mental resources to a task as from the inability to sustain vigilance on dull, boring, repetitive tasks. The major deficit in ADHD children is an inability to inhibit ongoing response, an inability that may be a part of Posner and Raichle's enhance operation.

Posner and Raichle's (1994) Attentional Networks and Underlying Brain Areas of Distinct Cognitive Processes

Their description of attentional networks postulated that distinct areas of the brain underlie distinct cognitive processes, with three different attentional networks that recruit individual cognitive processes (such as moving or disengaging). These are the alerting network, responsible for achieving and maintaining an alert state; the orienting network, which selects information from sensory input; and the executive control network, which resolves conflicts among different responses. The alerting network is associated with the frontal and parietal regions of the right hemisphere; the orienting network with areas of both the parietal and frontal areas; and the executive control network with the frontal lobes, especially the prefrontal cortex.

Event-Related Potentials (ERPs) and Selective Attention

Cognitive neuropsychologists have reported some fairly dramatic findings suggesting that information is processed very differently in attended versus unattended channels. Some of this work relies on measures such as a series of electrical potential recordings (electroencephalogram, or EEG) taken from the scalp of a participant. For technical reasons, researchers often average electrical potential recorded 1 millisecond after presentation of a stimulus, 2 milliseconds after a stimulus, and so forth. This procedure results in a measure called an event-related potential (ERP).

Banich (1997) Event-Related Potentials (ERPs) Study

Participants are asked to listen to one channel and to count long duration tones. Short duration tones and long duration tone are both presented in each channel, attended and unattended. Researchers keep track of the ERPs to each stimulus. Results from many studies show that ERPs differ as a function of whether a stimulus was attended to. The amplitude of waveforms is usually much larger for the attended than for the unattended stimulus. This difference usually begins 80 milliseconds after presentation of the stimulus, which is enough time for information to travel from the sensory receptors in the ears to the cerebral hemispheres, suggesting that the effect occurs in the brain, not in the ears.