Cognitive Processes Assessed by the Paced

Auditory Serial Addition Test (PASAT)

Concussions, or closed head injuries, are among the most familiar and least feared of all types of head injury. In sports like soccer and boxing, head injuries are often an insignificant concern and frequent occurrence (Gronwall, 1977). Though considered a minor concern by many, concussions have been related to significant cognitive deficits that can persist for days or years following the injury. To facilitate an understanding of the cognitive difficulties experienced following brain injury, the present study intends to analyze cognitive processes tapped by the Paced Auditory Serial Addition Test (PASAT), a test shown to be highly sensitive to the effects of brain injury. In this way, the present study hopes to both discover which individual processes are impaired that contribute to poor performance on the PASAT and to better the understanding of the loss of cognitive ability immediately following and persisting after injury in order to aid in the development of effective therapeutic programs for mild and severe cases of brain injury. This paper discusses the effects of traumatic brain injury and the methods of assessment of brain injury. In addition, the use of the PASAT as a measure of cognitive deficit following head injury and cognitive processes that are assessed by the PASAT are reviewed.

Physical and Cognitive Effects of Concussion

Mild concussions, or mild traumatic brain injuries, are diagnosed if a patient has a loss of consciousness less than thirty minutes and post-traumatic amnesia of only hours. Increases in duration of loss of consciousness and post-traumatic amnesia relate to increased severity and greater post-concussive symptoms (Lezak, 1995). With mild concussions, focal neurological deficit does not usually appear on MRI or CAT scans; however, patients most commonly exhibit symptoms which point toward damage in the frontal lobe and subcortical areas of the brain, such as irritability, affect inconsistency, and attentional deficits.

A predictable series of events frequently follows a head injury. Temporary brain stem damage is indicated by respiratory arrest, loss of consciousness, and nausea. Alteration in cerebral blood flow and decreases in activity of the reticular formation are also noted (Taylor, 1966). In mild cases, complete recovery can occur in as little as a few minutes or a couple hours (Symonds, 1937). Sometimes, the only remaining evidence of the concussion is a loss of memory of the events directly proceeding and directly following the injury, also known as post-traumatic amnesia. However, this clinical recovery may not be equitable to a recovery to normal functioning levels. In fact, many cases of traumatic brain injury result in post-concussion syndrome, a persistent condition characterized by mood swings, difficulty with concentration, memory troubles, irritability, vertigo, and persistent headaches among other symptoms.

History of Psychological Assessment of Concussive Symptoms

In the beginning of the 20th century, case studies and clinical observations made note of the irritability, easy fatiguing, slowness of processing, and difficulty with memory following a traumatic brain injury (Schilder, 1934). These observations prompted research into the assessment of impaired cognition following traumatic brain injury. Conkey (1938), in making the first quantitative assessment of psychological sequelae, found that simple functions were most readily recovered, but that more complex functions, such as speed of processing and sustained attention, were most longitudinally affected by traumatic brain injury. However, these conclusions have been criticized based on the unclear distinction between simple and complex tasks. For example, the author considered counting backwards from twenty to one a simple task, saying the days of the week in reverse order was considered a complex task.

Upon comparing mildly concussed patients within 48 hours from their injury and more severe cases five days after the injury, Ruesch (1944) found that speed of processing and the ability to sustain attention were most affected by head injury. Unfortunately, because no control group was used, the extent of differences between those with and without head injuries is unknown, leaving no point of reference. In another study by Ruesch (1945), simple visual reaction time and tachistoscopic recognition were most impaired in acute cases of head injury; however, neither age nor severity of injury, likely to be two moderators of performance on these tasks, were controlled.

Interestingly, in 1958, Dencker and Lofving tested 28 head-injured subjects with non-head-injured identical twins. Although significant differences were not found in intelligence, concentration, or reaction time, uninjured twins performed better at tachistoscopic figure/ground discrimination and paced continuous ten-choice reaction time tasks, thus indicating that speed of perception was impaired. Unfortunately, the most recent injury in this study was three years old and the average was ten years. Because many of the injuries were several years old, the immediate and clinically pertinent, reversible effects of traumatic brain injury were not researched.

Despite these and other findings, clinicians have traditionally relied on length of post-traumatic amnesia to measure the severity of a concussion. However, Lidvall, Linderoth, and Norlin (1974) found those patients with severe cases of head injury or post-concussion syndrome did not necessarily differ from other concussion sufferers in length of post-traumatic amnesia. This finding presented the need for an accurate and reliable clinical assessment of traumatic brain injury in order to react appropriately to the needs of patients and to develop rehabilitative therapies.

In 1977, Gronwall introduced the Paced Auditory Serial Addition Test (PASAT) as a measure of the severity of closed head injuries as well as a scale of recovery following a traumatic brain injury. It was found to differentiate between patients with both mild and severe cases of concussion and those with no history of concussion. Based on a series of studies, the authors concluded that concussion results in a reduced ability of information processing when the task requires processing information at an externally regulated pace. Further supporting the conclusions of Lidvall et al. (1974), the authors also concluded that even brief periods of amnesia could result in a disturbance of mental functioning which could persist even after a recovery to full consciousness.

Though the PASAT is reliable and frequently used as a diagnostic tool, recent findings have introduced concerns of emotional distress, induced by mental stress and feelings of failure, with the PASAT (Holdwick and Wingenfeld, 1999) as well as significant correlations with subject variables, such as intelligence and mathematical ability (Dreary, Langan, Hepburn, and Frier, 1997; Wiens, Fuller, and Crossen, 1997; Brittain, La Marche, Reeder, Roth, and Boll, 1991; Egan, 1988). In addition, researchers have presented opposing evidence regarding the cognitive processes that are assessed by this complex task.

The Task

Description

The PASAT requires patients to add consecutive numbers as they are presented on an auditory tape and respond orally with the accurate sum. As each digit is presented, the patient must sum that number with the digit that was presented prior to it rather than with the patient’s previous response. Additional forms of the PASAT, which vary in length of the interstimulus interval and the number of trials, have been developed for use in research and clinical practice (Sherman et al., 1997; Potter and Barrett, 1999). The standard form consists of sixty-one single digits presented in each of the four trials. The interstimulus interval of the initial trial is 2.4 seconds and decreases by 0.4 seconds on each of the subsequent trials (Gronwall, 1977). Experimenters can gauge PASAT performance on the average amount of time needed to produce an accurate response, total number of correct responses on the entire task or by trial, or total number of incorrect or omitted responses.

Demands

This intense task requires patients to comprehend auditory stimuli, verbally respond, and prevent the encoding of one’s own response while focusing on the next digit in the series. In addition, all these tasks must be performed at an externally controlled pace (Holdwick & Wingenfeld, 1999; Wiens et al., 1997; Strauss, Spellacy, Hunter & Berry, 1994). The Paced Auditory Serial Addition Test (Gronwall, 1977) is commonly used as a neuropsychological measure of vigilance or sustained attention (Lezak, 1995); however, recent studies have indicated that PASAT performance is also related to divided attention, memory, information processing speed, and mathematical ability (Sherman, Strauss, and Spellacy, 1997; Brittain, LaMarche, Reeder, Roth, and Boll, 1991; Lezak, 1995; Roman, Edwall, Buchanan, and Patton, 1991).

While most of the literature concedes to the multifaceted nature of the PASAT, the literature presents opposing results concerning the role of various cognitive processes as determinants of PASAT performance. Differences in methodology as well as participant selection may account for a significant amount of this variation. The present study will attempt to better define the cognitive processes assessed by the PASAT by focusing on the processes of working memory, dual processing, speed of digit retrieval, and speed of math fact retrieval. The present study will also compare the performance of participants with and without head injuries on each of the tasks, in an attempt to better identify specific cognitive deficits experienced by the brain-injured population.

Sensitivity of the PASAT to Severity of Concussion

Research has shown that patients with recent concussions tend to perform well below average on the PASAT (Gronwall and Sampson, 1974; Stuss, Stethum, Hugenholtz, & Richard, 1989); however, scores seem to normalize within thirty to sixty days following a mild concussion (Leininger, Gramling, & Farrell, 1990). When the head injury is more severe or post-concussion syndrome develops, performance on the PASAT can remain below average for a sustained period of time (Stuss et al., 1989; Gronwall and Wrightson, 1974).

Strauss et al. (1994) found that the PASAT accurately identified 55% of participants with closed head injuries. To participate in this study, participants must have had at least a year old injury. Eighteen subjects in this study had a mild head injury and ten had a moderate head injury. Given that most mild head injuries seem to fully recover within one year following injury, those with the histories of mild head trauma may not have demonstrated any impairment of performance on the PASAT. The inability of the PASAT to identify a large percentage of those with head injuries in this sample may have been strongly influenced by this factor.

Levin et al. (1987) came across an intriguing relationship between the mechanism of head injury and PASAT performance. This study found that two-thirds of patients with closed head injuries performed more poorly on the PASAT than those without concussive histories. In one of the samples, one-third of the participants had acquired a head injury as the result of assault and fifteen percent by means of a motor vehicle accident. Approximately half of each of the other two samples had sustained a head trauma as the consequence of a motor vehicle accident, while only one person had sustained a head injury by assault. Though the head-injured patients in the former group did not differ from controls on PASAT performance, the head-injured patients in the latter two groups did differ from controls.

A possible explanation for these results may lie in the mechanism of head injury. Motor vehicle accidents are associated with a greater intensity of acceleration and deceleration forces on the brain as well as a more severe rotation of the head. Due to the cerebral strain implied in this movement, greater subcortical movement would be involved (Gennarelli, 1986). It appears that these results may demonstrate the specified sensitivity of the PASAT to subcortical damage. Roman, Edwall, Buchanan, & Patton (1991) suggested that future research account for the type of head injury to provide more evidence to either support or contradict this explanation.

Although it appears that the type of head injury plays a critical role in PASAT performance, duration of post-traumatic amnesia (PTA) and loss of consciousness (LOC) do not seem to moderate performance. Both Stuss et al. (1989) and Sherman et al. (1997) found that the PASAT accurately differentiated between participants with closed head injuries and those in a control group; however, results indicated that the PASAT was insensitive to the severity of the concussion, as determined by LOC and PTA. On the whole, the literature indicates that the PASAT reliably distinguishes between those with and without concussion; however, the research correlating the mechanism of head injury and severity of head injury is scarce and contradictory.

Contributing Cognitive Factors to PASAT Performance

Both research and clinical practice have questioned which cognitive functions are assessed by the PASAT and which functions are the strongest predictors of PASAT performance. In order for a diagnostician to make inferences about a patient's level of cognitive functioning, it is important that they understand the processes assessed by a given neuropsychological measure as well as the level of contribution of each of the component processes.

While most of the literature concurs about the multifaceted nature of the PASAT, the literature presents opposing results concerning the role of various cognitive processes as determinants of performance on the PASAT. Differences in methodology as well as participant selection may account for a significant amount of this variation. The present study will attempt to better define the cognitive processes assessed by the PASAT by focusing on the processes of sustained attention, working memory, dual processing, speed of digit retrieval, and speed of math fact retrieval. The present study will also compare the performance of participants with and without head injuries on each of the tasks, in an attempt to better identify specific cognitive deficits experienced in the brain-injured population.

Sustained Attention

The PASAT demands the ability to sustain attention to successfully gather and process appropriate information from the auditory tape for extended periods of time. Those who have sustained head injuries exhibit distinct deficits in this form of attention, which is indicated by below average performance on the Digit Symbol Subtest and Cancellation Tests (Lezak, 1995). In a study of 441 patients, Sherman et al. (1997) found moderate correlations between the PASAT and tests of focused attention, such as the WAIS-R Digit Symbol Subtest and the Cancellation Test. Though these tests do require patients to maintain attention, these tasks tap different abilities than the PASAT by requiring other abilities like hand-eye coordination. It would likely be more accurate to correlate PASAT performance to performance on the first half versus second half of a speed of math fact retrieval test (as described later in this section) in order to maintain consistency in the tasks' demands.

Working Memory

Working memory is a type of short-term memory that highlights dynamic memory processes rather than stationary, temporary storage. Often, it includes recitation of novel information and a specific manipulation of that information. Sometimes defined as a different attentional subprocess (Mateer, 1999), working memory has been defined as the ability "to hold information in the mind, to internalize information, and to use that information to guide behavior without the aid of or in the absence of reliable external cues." (Goldman-Rakic, looking for page number) In this definition, working memory relies on the ability to maintain attention while ignoring internal and external distractions (Lezak, 1995). Because the PASAT demands that examinees mentally retain relevant numbers, process the germane digits, while inhibiting the encoding of their own responses, the PASAT can easily be seen as an assessment of working memory. Lezak (1995) claims that deficits of working memory may be the only notable mental change following a head injury. Based on performance on the Brown-Peterson Technique (or Consonant Trigrams), Stuss et al. (1989) also concluded that tests of short-term memory deficits are most sensitive to the effects of head injury. Moderate correlations have been found between the PASAT and tests of working memory, such as the WAIS-R Arithmetic Subtest and the Consonant Trigrams (Sherman et al., 1997).

Using the Rey Auditory Verbal Learning Test (AVLT), Dreary et al. (1991) correlated memory ability to PASAT performance on two trials, one with a four-second interstimulus interval and another with a two-second interstimulus interval. With the two-second trial, memory ability was mildly correlated with PASAT performance. For two trials, the AVLT 4 and AVLT 5, the correlations reached moderate significance. Interestingly, the four-second trial was associated with strong correlations for seven trials, the AVLT trials 1-6 and AVLT 30. These findings indicate that the demands of the PASAT may change with varying interstimulus intervals. Perhaps, the interstimulus interval of four seconds facilitates the forgetting of items in short-term memory; however, with faster trials, the information is processed at accelerated rates, which reduces the likelihood of items in short-term memory to decay.

Another measure, the WAIS-R Letter-Number Sequencing Subtest, is less commonly used and is a more rigorous test of working memory. Participants are read a list of numbers and letters in a mixed sequence, asked to mentally separate the numbers from the letters, and then, asked to repeat the numbers back in ascending order and the letters back in alphabetical order. Past research has not correlated performance on this subtest to overall PASAT scores or analyzed the impact of brain injury on this ability to successfully perform these operations.

Though these studies illuminate the significant correlations between memory and PASAT performance, other studies have concluded that the relationship between PASAT performance and memory capacity is insignificant. Egan (1988) observed that because participants only need to remember one number and add it to the next number heard, the PASAT places little strain on memory. Gronwall and Wrightson (1981) found that the PASAT could not predict patient difficulties with consolidation and memory retrieval. The strong contradictions presented in the literature suggest a need for more research describing the relationship between memory strength and PASAT performance.

Dual Processing

Dual processing refers to the ability to simultaneously maintain and perform separate operations on two sets of information. The PASAT requires participants to separate their responses from the auditory stimuli and process each set of information accordingly, thus testing for this ability.

In Part A of the Trail Making Test (Halstead-Reitan Neuropsychological Test Battery), participants are asked to connect a series of numbers in a connect-the-dot fashion. In Part B, participants are asked to connect an alternating series of numbers and letters to one another (i.e. 1 to A to 2 to B to 3 to C and so on) on a worksheet as quickly as possible. In so doing, the dual processing ability of alternating between two sets of information is assessed. Research has indicated that the Trail Making Test, particularly Part B, distinguishes between those with and without concussions, thus implying that this ability is impaired by head injury (Cicerone, 1997).

Information Processing Speed

Sherman et al. (1997) and Dreary et al. (1991) assessed the role of information processing speed in PASAT performance. Contrary to the indications of Gronwall and Wrightson (1981), the results indicated nonsignificant correlations between the PASAT and reaction time tasks, which led the researchers to conclude that the PASAT does not measure speed of information processing. This finding was further substantiated by Potter and Barrett’s (1999) study in which electrophysiological measures were used to detect the relationship between the demands of the PASAT and the allocation of cognitive resources, including speed of cognitive processing. Their results indicated that head-injured patients do not exhibit signs of lagging cortical responses. This conclusion agrees with other previously described research arguing that head injuries related to lowered PASAT performance seem to be subcortical. From this information, the authors concluded that the lowered performance on tasks measuring the ability to shift attention as well as the ability to perform the task in a timely manner, such as the WAIS-R Digit Symbol Subtest, were due to an impaired allocation of the available mental resources, as opposed to a slowing of information processing.

Speed of Digit Retrieval

The PASAT requires that participants attend to a series of numbers and recall the numbers heard in the list. In order for this act to be successfully completed, digits must be stored in a way that they can be easily and accurately retrieved. The present study proposes that this memory skill may play a distinct role in PASAT performance as participants sort through the digits they have heard. In order to assess for this ability, the present study created an experimental task that measures how quickly participants can identify which digits appear on an original list of double digits that appear serially on a computer screen.

Speed of Math Fact Retrieval

Mathematical ability has also been found to correlate strongly with PASAT scores (Egan, 1988; Sherman et al., 1997); however, the tests used to assess this ability, such as the WAIS-R Arithmetic Subtest, rely heavily on other cognitive abilities, such as working memory. In order to determine whether the mathematical ability to retrieve addition facts like those presented in the PASAT uniquely contributes to PASAT performance, the present study developed another experimental task to pinpoint this ability. In this task, participants must add two single-digit numbers that appear side by side on a computer screen and orally produce an accurate sum as quickly as possible. By presenting the digits in this manner, without arithmetical signs, the present study hopes to mimic the way that participants mentally perceive addition facts when taking the PASAT.

Time Component

Based on an array of studies, Gronwall (1974) concluded that the externally determined pace of the PASAT played a key role in the decreased performance of those with head injuries, thus suggesting that an exercise like the PASAT that was not externally paced would not be as impaired in brain-injured populations. In general, externally paced assessment tools have been shown to be more sensitive to the effects of brain injury than self-paced tasks (Baribeau, Ethier, & Braun, 1989; Raskin er al., 1998; Cicerone, 1997). Many studies, using a four-second interstimulus interval, have found that there was no significant difference between those with and without head injury on the task. The present study intends to create another task similar to the PASAT that will have a five-second interdigit interval to further clarify this question to distinguish the cognitive abilities to perform the mathematical operations on the PASAT from the externally paced time factor.

Moderators of PASAT Performance

Gender and Race

PASAT performance has not been shown to be influenced by gender. Brittain et al. (1991) found that males (146.8 correct responses on average) earned higher scores than females (145.2 correct responses on average); however, it is important to note that the authors deemed this amount negligible and unimportant. Similarly, Roman et al. (1991) concluded that gender did not significantly impact PASAT performance. Wiens et al. (1997) found that Hispanic, Asian, and Native American males do better than their female counterparts; however, for African Americans and Caucasians, the opposite was true. The authors conducted an analysis of variance that accounted for education level, age, and WAIS-R FSIQ, which found no main effects for race. From these results, the authors concluded that the observed differences probably resulted from these other factors. Because only a small number of minorities participated in this study, the authors hesitated to draw any conclusions and suggested further research with larger samples.

Age and IQ

Most studies indicate that both age and intelligence contribute to PASAT performance. Weins et al. (1997) found that older participants performed worse than younger participants and those with higher WAIS-R FSIQ (Full-Scale Intelligence Quotient) scores had stronger PASAT performance than those with lower FSIQ scores. Additionally, they found that as age increased (20-29, 30-39, and 40-49 year olds) within each range of WAIS-R FSIQ scores (80-89, 90-99, 100-109, 110-119, 120-129, and 130+), the number of correct responses on the PASAT decreased. The results also indicated a greater range of PASAT scores in the lower IQ groups than the higher.

Due to the variability seen in PASAT scores, the authors suggested that the PASAT may have good sensitivity to traumatic brain injury in populations with average to above-average IQ levels, but not those in the low to low-average IQ levels. These findings could indicate that the PASAT taps different abilities for those with higher versus lower intelligence levels (Weins et al., 1997). Based on observations that participants of higher intelligence tend to selectively skip every other number on faster trials, thus doubling the interstimulus interval and sidestepping the processes that the PASAT intends to measure, it could be concluded that those of higher intelligence seek and employ strategies in the test and that this higher level cognitive ability is impaired following brain injury. Because this task is intellectually challenging, it is also possible that, regardless of concussive history, the task is too challenging and leads to overall poorer performance in populations of lower intelligence.

Dreary et al. (1991) correlated IQ with PASAT performance on both a four-second and two-second trial. The results indicated significant correlations between Verbal Subtest performance (Information, Vocabulary, Arithmetic, Comprehension, and Similarities), Performance Subtest performance (Picture Completion, Block Design, Object Assembly, and Digit Symbol), and overall combined scores (WAIS Performance IQ, WAIS Verbal IQ, and WAIS Full Scale IQ). The largest correlations existed between WAIS Performance IQ and WAIS FSIQ and performance on the PASAT's two-second trial.

Studies by Egan (1988) and Brittain et al. (1991) also revealed a strong positive relationship between PASAT performance and intelligence, but contradict previous findings set forth by Gronwall and Wrightson (1981), who found no relationship between intellectual ability and PASAT performance. One possible explanation for the different conclusions drawn by these studies may lie in the method of IQ assessment. Some studies use the WAIS FSIQ for intelligence estimates, others use selected portions of the WAIS, and some studies use less popular scales, such as the NAART (North American Adult Reading Test) and Alice Heim 2.

Mathematical Ability and Education Level

Because the PASAT requires that participants add single digits to one another, the mathematical skill of adding is required. For this reason along with others, Gronwall (1977) indicated that the PASAT should only be used with participants between the ages of 14 and 55, who can competently and readily retrieve addition facts from rote memory. Gronwall and Wrightson (1981) found no significant correlation between mathematical ability and PASAT performance; however, in a sample of young adults (mean age = 16.58 years), Egan (1988) found that the PASAT was strongly correlated with mathematical ability, determined by the Alice Heim 2 Numeric Scale. Sherman et al. (1997) also found that mathematical ability, gauged by the WAIS-R Arithmetic Subtest, contributed to performance on both the 1.6-second and two-second trials of the PASAT in a sample with a mean age of 32.7 years. However, the Arithmetic Subtest is not a pure measure of mathematical ability as it also emphasizes working memory.

In addition, Stuss et al. (1987), Weins et al. (1997), and Cicerone (1997) also found that mathematical ability contributes to an examinee’s performance on the PASAT. Further, these authors noted that those with some college perform markedly better than high school students. With presentation rates of less than two seconds, the differences between the two groups become more distinct. Intelligence may have confounded this data as those attending a university are, on average, likely to be more intelligent than high school students. (Still searching for more information on the relationship between IQ and educational level… maybe I’m looking in the wrong places.)

Present Study

Given that the PASAT relies heavily on the ability to process auditory stimuli and perform a series of mathematical operations, neuropsychological measures of dual processing and speed of math fact retrieval are expected to correlate most strongly with PASAT performance. In accordance with prior research, the present study predicts moderate a correlation between working memory and PASAT performance. Low to moderate correlations are expected between the PASAT and the speed of digit retrieval task. The present study also predicts that tests of working memory and dual processing will best distinguish between participants with and without head injuries.

Due to the controversy presented in the literature, the study also intends to further investigate the impact of number of concussions, persistent post-concussive symptoms, and the kind of injury on PASAT performance. The present study hypothesizes that the existence of persistent post-concussive symptoms and type of injury (car-related versus not car-related) will influence PASAT performance. With increased severity and duration of post-concussion symptoms, PASAT performance is expected to decrease. With regard to the findings presented by Roman et al. (1991), the present study predicts that those in car-related accidents will perform more poorly than those injuries associated with sports or falls.

Methods

Participants

Participants will be undergraduate university students who voluntarily participate as a requirement for an introductory psychology course. Participants will be excluded if they have a history of psychoactive substance use in the twenty-four hours prior to the experiment, have any primary neurological disorders, or are taking any sedative or hypnotic medications, as these factors may affect performance.

Materials

A battery consisting of established as well as experimental neuropsychological measures will be used. The following established neuropsychological tests are included: the Paced Auditory Serial Addition Test (PASAT), the WAIS-R Digit Span Subtest, the Trail Making Test, Parts A and B, and the WAIS-R Letter-Number Sequencing Subtest. A tape player was used to administer the PASAT. All the other tasks require copies of the assessments, score sheets, a stopwatch, and writing utensils.

In addition to the aforementioned neuropsychological measures, participants will also complete the following two experimental tasks, which aim to pinpoint speed of retrieval of recently learned stimuli and speed of retrieval of previously learned stimuli, respectively, by recording reaction time. Both programs were created using a computer program, SuperLab 1.68, which has a voice key function that records response time when auditory input from the microphone is perceived.

The first experimental task, the Speed of Digit Retrieval Test, required participants to attend to seven double digits presented serially in 14-point font on a 17-inch computer screen. An interstimulus interval of two hundred milliseconds was allotted between the presentation of each stimulus. After viewing this series of numbers, participants will be shown another series of six numbers, each individually appearing on the screen, and will be asked to orally respond with, "Yes," or "No," to indicate whether each number was presented on the original list. Of the digits that will appear on this list, one will have been the first on the serially presented list, one will have been the last, one will have been middle, and the other three will be novel. Stimuli will disappear from the list as soon as an auditory response is recorded from the headset. One practice trial will be provided, which will be followed by thirty experimental trials. Average reaction time will be recorded by SuperLab, and the experimenter will note accuracy.

In the other experimental task, the Speed of Math Fact Retrieval Test, participants will be shown a series of paired single digits in 14-point font on a 17-inch computer screen, asked to sum the two numbers, and required to orally produce an accurate response. A total of eighty-six pairs of single digits appeared on the screen in random order. The first five will be considered practice trials. The stimuli will remain on the screen until SuperLab records an auditory response. Average response will be recorded by SuperLab and the experimenter will note the number of errors.

The participants will also complete a third experimental task, which will be formatted identically to the PASAT. However, only one trial consisting of sixty-one digits will be presented at the rate of one number every five seconds. The auditory stimuli will be presented on a cassette tape recorded by the experimenter.

Participants will also complete a medical questionnaire to assess for significant medical history, psychiatric history, neurological history, and concussive history. In addition, it will assess for factors expected to influence performance, such as the use of sedative and hypnotic medications, psychoactive substances, and alcohol consumption. To assess for current anxiety and depression, the Beck Anxiety Inventory (BAI) and the Beck Depression Inventory (BDI) will also be administered.

Procedure

After reading and signing the informed consent form, participants will respond to the medical questionnaire and complete the BAI and BDI. At this point, because the PASAT and the other neuropsychological measures are cognitively challenging, and as a result, can lead to frustration and a negative affect, participants will be prefaced that most people find these tasks challenging and that they are not expected to get all of the answers correct. Throughout the instructions, during practice trials, and between trials and measures, positive feedback, such as "Good!" and "You are doing fine," will be provided to encourage continued participation and relieve feelings of failure. Participants will also be informed that short breaks will be provided as needed.

The measures were randomized for each participant to control for order effects. Instructions from the WAIS manual were used to administer the Digit Span Subtest and Letter-Number Sequencing Subtest. Gronwall’s (1977) instructions were used to administer the PASAT. All other instructions were developed by the experimenter.

Before leaving the experiment, the experimenter provided the participants with an information sheet, which further clarified the experiment and provided the participants with a number to call in case they experienced any discomfort following the experiment.

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