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Cognitive Slowing in Closed-Head Injury
BRAIN AND COGNITION ARTICLE NO.
32, 429–440 (1996)
0075
Cognitive Slowing in Closed-Head Injury F. RICHARD FERRARO University of North Dakota Mean response times (RTs) from a sample of 13 simple- and choice-reaction time studies (which included 353 Closed-Head Injury (CHI) subjects at various stages of injury and 329 Control, non-CHI, subjects; mean age of both groups, approximately 28 years) were analyzed using Brinley Plot/multiple regression analysis techniques to provide support for the observation that CHI results in a slowing of basic cognitive information processing. Across 101 experimental conditions, the best-fit equation that resulted from regressing the CHI data onto the Control data for matched conditions was Y (CHI) 5 1.54 X (Control) 2 59, and this specific regression equation accounted for approximately 89% of the variance (based on R 2 ). These results suggest that the basic cognition processes involved in simple- and choicereaction time performance were approximately 1.54 times slower in CHI individuals in this sample as compared to non-CHI individuals. This pattern of performance substantiates the observation the CHI results in a slowing of even very basic cognition information processes. 1996 Academic Press, Inc.
A prominent area of study within the literature describing closed-head injury is speed of information processing (Bleiberg, Nadler, Reeves, Garmoe, Cederquist, Lux, & Kane, 1994; Mattson, Levin, & Breitmeyer, 1994; Van Zomeren & Deelman, 1978). Many studies have examined the claim that a fundamental outcome of a closed-head injury is a reduction in the speed (i.e., slowing) at which a variety of cognitive operations can be executed. From a theoretical perspective this ‘‘general’’ slowing of cognitive processes has recently gained prominence within the field of gerontology (e.g., Cerella, 1985; Cerella, Poon, & Williams, 1980; Salthouse, 1985). When a variety of tasks and methodologies are combined and examined in a metaanalytic/multiple regression fashion, the resulting Brinley (1965) plots reveal that the relationship between the response times (RTs) of older and younger adults is a linearly increasing function which has a slope that approximates 1.5. That is, the RTs of the older adults are typically 1.5 slower than their A shortened version of this paper was presented at the 1994 meeting of the International Neuropsychological Society, Cincinnati, OH. Address reprint requests to F. Richard Ferraro, at the Department of Psychology, Box 8380, University of North Dakota, Grand Forks, ND 58202-8380. E-mail: [email protected]. 429 0278-2626/96 $18.00 Copyright 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
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younger counterparts’ RTs across the same experimental conditions. The implication of this pattern of performance was that age differences in response latency and speed could be attributed to a single, general factor (Birren, 1965; Cerella, 1985; Salthouse & Somberg, 1982). The proposal was that a general slowing of the central nervous system was the cause of the robust observation that older adults are slowing more than younger adults on virtually all speeded cognitive tasks. The increased use of the Brinley plot/multiple regression methodology stems from the mathematical and quantitative relationship that exists between young and older adults’ response latencies across a variety of speeded tasks. This mathematical function is often represented by the equation Y 5 mX (where Y represents the response latencies for younger adults, X represents the response latencies for older adults and m represents the coefficient of slowing, also referred to as the slope of the regression function, of young RT and old RT). In addition to the slope value being used to demonstrate the extent of cognitive slowing, it is also the case that the correlation coefficient calculated across task conditions common to both young and old adults should also be quite high, typically approaching r 5 11.0. The magnitude of this correlation coefficient value also provides an estimate of the fit of the data to the particular equation. For instance, Salthouse and Somberg (1982) tested young and older adults on their ability to perform a memory scanning task. Across the eight conditions in which all young and old subjects participated, the correlation coefficient between young and older adults’ mean RT performance was approximately r 5 1.99. Similarly, Hale (1990) found that the slope values for 10-, 12-, and 15-year-old children, in comparison to adult RT latencies, across several conditions, were 1.82, 1.56, and 1.00, respectively. The correlation coefficient across these three comparisons was above r 5 1.99 in each case. These two studies highlight the notion that a global mechanism can act to reduce speed of performance in older adults (see also Myerson, Ferraro, Hale, & Lima, 1992). This idea of a ‘‘general‘‘ slowing of cognitive operations has also recently been applied to other subject populations that show evidence of brain deficits. These populations have included individuals who are mentally retarded (MR; Kail, 1992) or who have been diagnosed with Alzheimer’s disease (AD; Nebes & Brady, 1992). RTs for MR individuals increased linearly as a function of the corresponding RTs for a nonretarded group of individuals, with the slope (coefficient of slowing) of the regression function ranging from 1.43 to 2.34 with the correlation coefficients ranging from r 5 1.90 to 1.99. Likewise, the RTs of individuals with AD also increased linearly, as compared to non-AD individuals, although the slope of the best fitting regression function varied depending upon the type and complexity of the tasks performed. When the tasks used did not include sentence completion and lexical decision, the correlation coefficient increased from r 5 1.64 to 1.83. The
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slope of the linear function averaged 2.32 and ranged from 2.0 to 2.9, with this greater slope value attributed to the complexity of the tasks performed. Use of the Brinley (1965) multiple regression technique has been instrumental in gaining a clearer understanding of the underlying cognitive processes across these various subject groups. This has contributed to a better understanding of the many behavioral dysfunctions exhibited by these various population groups. The implication is that the behavioral observation of a general cognitive slowing appears to be a prominent characteristic of several population groups that exhibit deficiencies with normal brain functioning. In the present study, the Brinley plot/multiple regression methodology was employed to investigate the observation that closed-head injury (CHI) individuals exhibit a slowing in their cognitive processing, as compared to non-CHI individuals. Pairs of mean RT latencies from individuals with and without CHI can be fitted to the equation described earlier (Y 5 mX), where Y represents a mean RT latency for a group of CHI individuals and X represents a mean RT latency for a group of non-CHI individuals. As mentioned this approach has been helpful in the investigation of speed of cognitive performance in groups as diverse as children, mentally retarded adults, older adults, and individuals with Alzheimer’s disease. It should be noted that the requirements of the Brinley plot/multiple regression methodology (i.e., choosing studies, subject selection, data aggregation, and analysis) will necessarily result in a wide degree of variability with regard to injury severity, time since injury, and other potentially important factors such as criteria for inclusion/exclusion of empirical studies and subject recruitment practices. A table (Table 1) of characteristics of all 13 studies has been included to assist in illuminating the characteristics of the various studies chosen. Thus, one must be cautious regarding the specific generalizability of the particular results obtained, although this is a continuing issue with the use of meta-analytic methodology (see Myerson, Wagstaff, & Hale, 1994; Perfect, 1994). There is ample evidence from the literature examining individuals with CHI to suggest that slowing of cognitive processes is a pervasive characteristic of this group. For instance, several studies have shown increases in RT (both simple and choice) in CHI, as well as RT increases as task complexity increases (Benton & Blackburn, 1958; Blackburn & Benton, 1955; Dencker & Lofving, 1958; Gronwall, 1977; Miller, 1970; Norman & Svahn, 1961). Furthermore, Van Zomeren and Brouwer (1994, p. 77) have performed a preliminary meta-analysis of cognitive slowing in CHI and revealed the predicted increase in RT in CHI individuals, as compared to that seen in non-CHI individuals. Unfortunately, these authors did not provide any sort of slowing ratio (CHI RT/non-CHI RT) or percentage of variance accounted for by the apparent linearly increasing function portrayed in their data. However, their data clearly indicate a linearly increasing function.
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TABLE 1 Demographic and Experimental Characteristics of 13 Studies Used in the Present Analysis Subjects
Study 1: Deacon, D., & Campbell, K. B. (1993) CHI: n 5 12; M age 5 23 years, R 5 19–46; M Ed. 5 13.4 years (R 5 10– 19); M duration of coma: 32.4 days, R 5 7–25; M post-traumatic amnesia (PTA) duration: 57.4 days, R 5 30–150; M Glascow Coma Scale (GCS): 4.75, R 5 4–6; M time since injury: 4.6 years, R 5 3.1–6.9
Control: n 5 12, M age 5 25, R 5 20–38; M Ed. 5 14.4, R 5 11–21 Conditions 12 Task Auditory Choice Reaction Time (CRT) Study 2: Haut, M. W., Petros, T. V., Frank, R. G., & Haut, J. S. (1991) Subjects CHI: n 5 20 [9 postinjury . 1 year; M age 5 25.6 years; M Ed. 5 13.3 years; M WAIS-R vocab. 5 40.3; M GCS 5 5.7, M PTA 5 37.3; M time since injury: 948.3], [11 postinjury , 1 year; M age 5 24.5; M Ed. 5 13.2; M WAIS-R vocab. 5 44.0; M GCS 5 6.2, M M PTA 5 25.2, M time since injury 5 55.4 Control: n 5 16; M age 5 22.8; M Ed. 5 13.6, M WAIS-R Vocab. 5 44.5 Conditions 2 Task Category Judgement, CRT Study 3: Haut, M. W., Petros, T. V., Frank, R. G., & Lamberty, G. (1990) Subjects CHI: n 5 12; M age 5 30.1 (R 5 20–57); M Ed. 5 13.2 (R 5 12–18); M WAIS-R Vocab. 5 52.5 (R 5 21–64); M months since injury 5 48.2;M loss of consciousness 5 18.7 days Control: n 5 16; M age 5 31 (R 5 20–45); M Ed. 5 13.6 (R 5 12–15); M WAIS-R Vocab. 5 46.4 (R 5 35–57) Conditions 3 Task Sternberg Memory Scanning, CRT Study 4: MacFlynn, G., Montgomery, E. A., Fenton, G. W., & Rutherford, W. (1984) Subjects CHI: n 5 45 (28 M/17 F), M age 5 30.9 (R 5 16–55), M PTA , 48 hr
Conditions Task Subjects
Conditions Task
Subjects
Control: n 5 45; matched on age, education, sex, marital status, socio-intellectual status (no values given) 3 4-Choice CRT Study 5: Munte, T. F., & Heinze, H. J. (1994) CHI: n 5 11 (9 M/2 F); M age 5 25.1 (SD 5 5.6), R 5 17–36; M Ed. 5 9.45 (SD 5 1.96, R 5 6–12; M time since injury 5 7.72 years, (SD 5 6.18, R 5 2–18), M PTA 5 2.81 (SD 5 .87, R 5 1.4) Control: n 5 12; matched on age and education (no values given) 9 Simple Reaction Time/Choice Reaction Time (SRT/CRT), sentence verification, lexical decision, continuous word recognition Study 6: Ponsford, J., & Kinsella, G. (1992) CHI: n 5 47 (29 M/18 F); M age 5 23.4 (SD 5 7.4, R 5 16–43); M Ed. 5 11.4 (SD 5 2.1, R 5 8–17); M time between injury and assessment 5 112 days (SD 5 76.3, R 5 28–355); M PTA 5 39.6 days (SD 5 34.8, R 5 7– 168); M GCS 5 4.7 (SD 5 2.1, R 5 3–9) Controls: n 5 30 (24 M/6 F); matched on age (M 5 24.5, SD 5 5.9, R 5 16–42) and education (M 5 11.4, SD 5 1.5, R 5 9–16)
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Table 1—Continued Conditions 4 Tasks SRT/CRT Study 7: Sandson, J., Crosson, B., Posner, M. I., Barco, P. P., Valazo, C. A., & Brobek, T. C. (1988) Subjects CHI: n 5 9; M age 5 21.17 (SD 5 17.28, R 5 20–57); M Ed. 5 13.67 (SD 5 1.97, R 5 12–16); M postinjury 5 15 months (SD 5 8.05, R 5 9–30) Conditions Task Study 8: Subjects
Control: n 5 12 6 CRT Schmitter-Edgecombe, M. E., Marks, W., Fahey, J. F., & Long, C. J. (1992) CHI: n 5 20 (14 M/6 F); M age 5 29.3 (SD 5 8.23, R 5 20–51); M Ed. 5 14.05 (SD 5 2.26, R 5 9–19); M PTA 5 125 days (SD 5 121, R 5 8–360); M WAIS-R IQ 5 95.6 (SD 5 10.01); M postinjury 5 65 months (SD 5 38, R 5 19–159), all unconscious for at least 48 hr
Control: n 5 20 (14 M/6 F); M age 5 29.45 (SD 5 9.48, R 5 19–52); M Ed. 5 14.45 (SD 5 1.10, R 5 12–16); M WAIS-R IQ 5 102.8 (SD 5 8.62) Conditions 12 Tasks CRT (S-R compatibility, Sternberg memory scanning) Study 9: Schmitter-Edgecombe, M. E., Marks, W., & Fahey, J. F. (1993) Subjects CHI: n 5 18 (13 M/5 F); M age 5 31.01, SD 5 7.83, R 5 19–44); M Ed. 5 14.33, SD 5 2.40, R 5 9–18)
Conditions Tasks Subjects
Control: n 5 18 (13 M/5 F); M age 5 30.45, SD 5 8.42, R 5 21–46; M Ed. 5 14.33, SD 5 2.40, R 5 9–18 8 Lexical Decision Task (LDT), semantic priming Study 10: Shum, D. H. K., McFarland, K., & Bain, J. D. (1994) CHI: n 5 17 (12 M/5 F); M age 5 27.59 (SD 5 10.57, R 5 15–52); M Ed. 5 10.71 (SD 5 .83, R 5 9–12); M GCS 5 5.18 (SD 5 1.94, R 5 3–7); M coma length 5 24.57 days (SD 5 23.87, R 5 2–90); M time since injury 5 538.65 days, (SD 5 637.58, R 5 27–2190)
Control: n 5 13 (8 M/5 F); M age 5 27 (SD 5 11, R 5 16–49); matched on age, sex, and education Conditions 4 Task Name-matching, CRT Study 11: Stuss, D. T., Pogue, J., Buckle, L., & Bondar, J. (1994) Subjects CHI: n 5 18; M age 5 31.0 (SD 5 12, R 5 17–57); M Ed. 5 12.6 (SD 5 2.7, R 5 5–18); M coma length 5 1.1 days (SD 5 2.6, R 5 0–7); M PTA 5 10.2 days (SD 5 18.8, R 5 0–60); M GCS (6 hr after injury) 5 11.9 (SD 5 2.9, R 5 7–15); M GCS (1 day after injury) 5 12.8 (SD 5 3.1 R 5 7– 15); M GCS (1 week after injury) 5 14.2 (SD 5 1.8, R 5 8–15) Control, n 5 18; M age 5 31.0 (SD 5 13.7, R 5 16–60); M Ed. 5 11.6 (SD 5 2.2, R 5 7–17) Conditions 21 Tasks Visual discrimination (CRT) Study 12: Stuss, D. T., Stethem, L. L., Hugenholtz, H., Picton, T., Pivik, J., & Richard, M. T. (1989)
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Table 1—Continued Subjects
Conditions Tasks Subjects
Conditions Tasks
CHI: n 5 70 [study 1: n 5 26 (20 M/6 F); M age 5 30.9 (SD 5 11.9, R 5 17–57); M Ed. 5 12.0 (SD 5 2.7, R 5 7–20); M GCS 5 13.7 (SD 5 2.2, R 5 7–15); M coma duration 5 5.5 days (SD 5 16.4, R 5 0–75); M PTA 5 20.4 days (SD 5 36, R 5 0–135); study 2: n 5 22 (15 M/7 F); M age 5 29.5 (SD 5 12.6, R 5 16–57); M Ed. 5 14.4 (SD 5 3.2, R 5 9–20); study 3: n 5 22 (14 M/8 F); M age 5 26.6 (SD 5 11.7, R 5 15–61); M Ed. 5 11.8 (SD 5 1.7, R 5 9–15); M GCS 5 11.2 (SD 5 3.5, R 5 5–15; M coma duration 5 13.0 days (SD 5 3.2, R 5 6–24); M PTA 5 31.4 (SD 5 47.5, R 5 1–178)] Control: n 5 70 [study 1: n 5 26 (20 M/6 F); M age 5 29.7 (SD 5 12.4, R 5 16–20; M Ed. 5 13.2 (SD 5 3.0, R 5 5–20); study 2: n 5 22; M age 5 27.7 (SD 5 11.6, R 5 16–54); M Ed. 5 15.5 (SD 5 2.6, R 5 11–20); study 3: n 5 22; M age 5 27.0 (SD 5 12.5, R 5 16–63); M Ed. 5 12.5 (SD 5 1.6, R 5 9–17)] 15 SRT/CRT Study 13: Van Zomeren, A. H., & Deelman, B. G. (1978) CHI: n 5 54 [(n 5 27 mild CHI; M age 5 22.8; M level of unconsciousness 5 .60 min); n 5 15 moderate CHI; M age 5 19.7; M level of unconsciousness 5 1 hr–7 days); n 5 12 severe CHI; M age 5 23.4; M level of unconsciousness .7 days)] Control: n 5 45, M age 5 22 2 SRT/4-choice RT
Note: CHI, closed-head injury; CRT, choice reaction time; ED., education; F, female; GCS, Glascow Coma Scale; LDT, lexical decision task; M, male,; n, number of subjects; PTA, post-traumatic amnesia; R, range; SD, standard deviation; SRT, simple reaction time; WAIS-R, Wechsler Adult Intelligence Scale—Revised; Vocab., vocabulary.
There is also evidence that traumatic brain injury (e.g., CHI) and aging affect information processing and brain structure in similar ways (Stuss, Stethem, Picton, Leech, & Pelchat, 1989b). Aging and traumatic brain injury result in behavioral slowing and widespread brain damage. The brain damage in CHI is diffuse and as a consequence often results in a global slowing of cognition. Thus, not only is CHI linked to behavioral slowing, this link is characteristic of behavioral slowing exhibited by older (presumably nonCHI) adults. If CHI results in a significant slowing of cognitive processing, and if this slowing is similar to the slowing exhibited by older adults, then the slope value of the regression equation should approximate 1.5. Although this interpretation of behavior is not new to studies of subjects with CHI, the present investigation is the first application of the above-mentioned Brinley plots and regression techniques in RT performance to a sample of studies taken from the CHI literature (see also Van Zomeren & Brouwer, 1994). The appli-
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cation of this methodology will allow for a determination of the magnitude, at a very general level, of this pervasive cognitive slowing. METHODS Across the 13 studies chosen, a total of 682 individuals (353 CHI and 329 non-CHI Control) were involved. A sample of published studies (see Table 1) dealing with CHI was selected using the following criteria: (1) the studies chosen employed either simple reaction time (SRT) or choice reaction time (CRT) tasks, (2) a comparable control group was present, and (3) a sufficient number of experimental conditions were present in each experiment (at least two). Based on these criteria, a total of 13 studies that contained a total of 101 experimental conditions were chosen (i.e., 101 pairs of CHI/non-CHI pairs of mean RTs). A summary of studies used in the present experiment are listed in Table 1. This table includes information pertaining to a number of subjects, sex of subjects, other demographic information (education level, age), information relevant to individuals with CHI (Glascow Coma Scale and post-traumatic amnesia chronological information), as well as number of experimental conditions and tasks employed.
RESULTS
Across the 13 studies, the mean RTs for each of the 101 experimental conditions were tabulated between the CHI and the non-CHI (Control) individuals. These points were then plotted on (X, Y) coordinates and the bestfitting regression equation (CHI data regressed onto the corresponding nonCHI Control data) was fitted to these 101 points. The best-fitting regression equation that resulted from the methods outlined above was as follows: Y (CHI) 5 1.54 X (Control) 2 59 and this function accounted for approximately 89% of the total variance (R 2 ). The resulting linearly increasing function of this particular data is presented in a Brinley (1965) plot displayed in Fig. 1. DISCUSSION
The empirical and theoretical literature on CHI suggests that CHI results in a slowing of information processing. To provide evidence in support of this observation, meta-analytic/multiple regression techniques (based on Brinley, 1965) were performed on a sample of 13 studies and the best-fit regression equation was fit through 101 points which corresponded to 101 experimental conditions experienced by both the CHI and the non-CHI individuals. The results of the present study revealed that the CHI individuals’ simple- and choice-reaction time performance is approximately 1.54 times slower than an age-matched non-CHI Control group of individuals. That is, the RTs from individuals with CHI increased linearly as a function of the RTs from non-CHI individuals with a slope of 1.54. Similar meta-analytic/multiple regression techniques are common in studies dealing with normal healthy elderly adults as well as individuals diagnosed with Alzheimer’s disease, with the results used to determine the extent
FIG. 1. Response times (in msec) of closed-head injury individuals as a function of control individuals on 101 different experimental conditions.
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of the information processing slowing in these populations. Studies dealing with normal healthy aging individuals (Myerson et al., 1992) have indicated that this slowing factor is close of 1.50, suggesting that normal healthy aged individuals’ reaction time performance is approximately 1.50 times slower than their younger counterparts. Similarly, when this technique is applied to RT data collected from Alzheimer’s disease (AD) individuals (Nebes & Brady, 1992), the slowing factor for AD individuals, as compared to agematched non-AD individuals, is 2.0 to 2.9. The present results, in addition to substantiating claims that CHI results in a general cognitive slowing of information processing, also offer some implications and recommendations for future clinical and experimental research within the area of CHI. First, it appears clear in continuing to use reaction time (both simple and choice RT) as a dependent measure in CHI research. The usefulness of using RT in empirical studies was recently documented by Mahurin and Pirozzolo (1986) regarding aging and dementia research. They came to the conclusion that ‘‘RT measurement offers increased clinical precision in the neuropsychological assessement of age-related dementia’’ (p. 345). This conclusion is supported in the present study, and the implication is that in future studies of CHI it would be advisable to continue to include measures of simple and choice RT as a means of assisting with assessment and diagnostic issues. Of course, RT measures would not be the only measures taken from CHI individuals. Rather, RT tasks would compliment the various clinical and neuropsychological measures and tests already performed. In this way, the RT measures would serve as converging evidence for clinical observations (i.e., slowed thought, slowed information processing). Second, the fact that the CHI subjects (as a group) in the present experiment evidenced a cognitive slowing of approximately 1.54 suggests that CHI dramatically slows down even very basic cognitive processes (e.g., simple- and choice-reaction time). Furthermore, this rate of cognitive slowing is a level often observed in individuals much older (e.g., cognitive slowing ratios of 1.50 or greater are often associated with individuals 65 years of age and older (Myerson et al., 1992)). The average age of the CHI individuals in the present study was approximately 28 years. Because the slowing ratio associated with the CHI individuals in the present study was 1.54 it does lead to questions of why this slowing value is at this level and what underlying mechanisms are responsible for this level of slowing. Practical answers to these questions come from a recent paper by Stuss et al. (1986b). These authors found that ‘‘the deficit in both aging and traumatic brain injury (TBI) is not only a generalized neuronal slowing but a more specific impairment in attentional control processes, exhibited as a deficit in focused attention’’ (p. 161). Thus, the implication is that CHI individuals are deficient in their attentional abilities and these deficiencies contribute to their cognitive slowing in cognitive performance and behavior (see Van Zomeren & Brouwer, 1994).
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However, to say that CHI is a form of advanced aging is a very premature statement and further studies are needed to pinpoint the exact nature of this information processing slowing in this particular population. However, the present results provide an estimate of the magnitude of this cognitive slowing. Third, if the present results are correct and if CHI results in a cognitive slowing in cognitive performance that resembles that of an older adult, rehabilitation strategies and programs should likely be modified in order to accommodate the CHI individual who is experiencing this type to cognitive slowing. In summary, it was observed that individuals with CHI evidenced a slowing in basic cognitive processes (simple- and choice-reaction time) of 1.54, meaning that their mean RT performance was approximately 1.54 times slower than non-CHI individuals performing the same tasks. Future studies dealing with the cognitive performance of individuals with CHI should continue to employ reaction-time-based tasks. Such tasks are easy to perform and yield critical data regarding the underlying information processing deficits characteristic of individuals with CHI. Finally, the application of Brinley plot/multiple regression meta-analytic techniques appear useful in examining the extent of cognitive slowing in individuals with CHI (see also Van Zomeren & Brouwer (1994) for converging evidence regarding this observation). REFERENCES Note: Studies marked with a * were used in the meta-analysis. Benton, A. L., & Blackburn, H. L. 1958. Practice effects in reaction time tasks in brain-injured patients. Journal of Abnormal and Social Psychology, 54, 109–113. Birren, J. E. 1965. Age changes in speed of behavior: Its central nature and physiological correlates. In A. T. Welford & J. E. Birren (Eds.), Behavior, aging and the nervous system. Springfield, IL: Charles C. Thomas. Pp. 191–216. Blackburn, H. L., & Benton, A. L. 1955. Simple and choice reaction time in cerebral disease. Confinia Neurologica, 15, 327–338. Bleiberg, J., Nadler, J., Reeves, D., Garmoe, W., Cederquist, J., Lux, W., & Kane, R. 1994. Inconsistency as a marker of mild head injury. Presented at the meeting of the International Neuropsychological Society, Cincinnati, OH. Brinley, J. F. 1965. Cognitive sets, speed and accuracy of performance in the elderly. In A. T. Welford & J. E. Birren (Eds.), Behavior, aging and the nervous system. Springfield, IL: Charles C. Thomas. Pp. 114–149. Cerella, J. 1985. Information processing rates in the elderly. Psychological Bulletin, 98, 67– 83. Cerella, J., Poon, L. W., & Williams, D. M. 1980. Age and the complexity hypothesis. In L. W. Poon (Ed.), Aging in the 1980’s. Washington, DC: American Psychological Association. Pp. 332–340. *Deacon, D., & Campbell, K. B. 1991. Effects of performance feedback on p300 and reaction time in closed-head injured outpatients. Electroencephalography and Clinical Neurophysiology, 78, 133–141. Dencker, S. J., & Lofving, B. A. 1958. A psychometric study of identical twins discordant for closed head injury. Acta Psychiatrica Neurologica Scandinavica, 33, 122. Gronwall, D. M. A. 1977. Paced auditory serial-addition-task: A measure of recovery from concussion. Perceptual and Motor Skills, 44, 367–373.
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Reaction time after head injury: Fatigue, divided and focused attention, and consistency of performance. Journal of Neurology, Neurosurgery, and Psychiatry, 52, 742–748. Stuss, D. T., Stethem, L. L. Picton, T. W., Leech, E. E., & Pelchat, G. 1986b. Traumatic brain injury, aging, and reaction time. Canadian Journal of Neurological Sciences, 16, 161– 167. Van Zomeren, A. H., & Brouwer, W. H. 1994. Clinical neuropsychology of attention. New York: Oxford Univ. Press. *Van Zomeren, A. H., & Deelman, B. G. 1978. Long-term recovery of visual reaction time after closed-head injury. Journal of Neurology, Neurosurgery, and Psychiatry, 41, 452– 457.
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Cognitive Slowing in Closed-Head Injury F. RICHARD FERRARO University of North Dakota Mean response times (RTs) from a sample of 13 simple- and choice-reaction time studies (which included 353 Closed-Head Injury (CHI) subjects at various stages of injury and 329 Control, non-CHI, subjects; mean age of both groups, approximately 28 years) were analyzed using Brinley Plot/multiple regression analysis techniques to provide support for the observation that CHI results in a slowing of basic cognitive information processing. Across 101 experimental conditions, the best-fit equation that resulted from regressing the CHI data onto the Control data for matched conditions was Y (CHI) 5 1.54 X (Control) 2 59, and this specific regression equation accounted for approximately 89% of the variance (based on R 2 ). These results suggest that the basic cognition processes involved in simple- and choicereaction time performance were approximately 1.54 times slower in CHI individuals in this sample as compared to non-CHI individuals. This pattern of performance substantiates the observation the CHI results in a slowing of even very basic cognition information processes. 1996 Academic Press, Inc.
A prominent area of study within the literature describing closed-head injury is speed of information processing (Bleiberg, Nadler, Reeves, Garmoe, Cederquist, Lux, & Kane, 1994; Mattson, Levin, & Breitmeyer, 1994; Van Zomeren & Deelman, 1978). Many studies have examined the claim that a fundamental outcome of a closed-head injury is a reduction in the speed (i.e., slowing) at which a variety of cognitive operations can be executed. From a theoretical perspective this ‘‘general’’ slowing of cognitive processes has recently gained prominence within the field of gerontology (e.g., Cerella, 1985; Cerella, Poon, & Williams, 1980; Salthouse, 1985). When a variety of tasks and methodologies are combined and examined in a metaanalytic/multiple regression fashion, the resulting Brinley (1965) plots reveal that the relationship between the response times (RTs) of older and younger adults is a linearly increasing function which has a slope that approximates 1.5. That is, the RTs of the older adults are typically 1.5 slower than their A shortened version of this paper was presented at the 1994 meeting of the International Neuropsychological Society, Cincinnati, OH. Address reprint requests to F. Richard Ferraro, at the Department of Psychology, Box 8380, University of North Dakota, Grand Forks, ND 58202-8380. E-mail: [email protected]. 429 0278-2626/96 $18.00 Copyright 1996 by Academic Press, Inc. All rights of reproduction in any form reserved.
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younger counterparts’ RTs across the same experimental conditions. The implication of this pattern of performance was that age differences in response latency and speed could be attributed to a single, general factor (Birren, 1965; Cerella, 1985; Salthouse & Somberg, 1982). The proposal was that a general slowing of the central nervous system was the cause of the robust observation that older adults are slowing more than younger adults on virtually all speeded cognitive tasks. The increased use of the Brinley plot/multiple regression methodology stems from the mathematical and quantitative relationship that exists between young and older adults’ response latencies across a variety of speeded tasks. This mathematical function is often represented by the equation Y 5 mX (where Y represents the response latencies for younger adults, X represents the response latencies for older adults and m represents the coefficient of slowing, also referred to as the slope of the regression function, of young RT and old RT). In addition to the slope value being used to demonstrate the extent of cognitive slowing, it is also the case that the correlation coefficient calculated across task conditions common to both young and old adults should also be quite high, typically approaching r 5 11.0. The magnitude of this correlation coefficient value also provides an estimate of the fit of the data to the particular equation. For instance, Salthouse and Somberg (1982) tested young and older adults on their ability to perform a memory scanning task. Across the eight conditions in which all young and old subjects participated, the correlation coefficient between young and older adults’ mean RT performance was approximately r 5 1.99. Similarly, Hale (1990) found that the slope values for 10-, 12-, and 15-year-old children, in comparison to adult RT latencies, across several conditions, were 1.82, 1.56, and 1.00, respectively. The correlation coefficient across these three comparisons was above r 5 1.99 in each case. These two studies highlight the notion that a global mechanism can act to reduce speed of performance in older adults (see also Myerson, Ferraro, Hale, & Lima, 1992). This idea of a ‘‘general‘‘ slowing of cognitive operations has also recently been applied to other subject populations that show evidence of brain deficits. These populations have included individuals who are mentally retarded (MR; Kail, 1992) or who have been diagnosed with Alzheimer’s disease (AD; Nebes & Brady, 1992). RTs for MR individuals increased linearly as a function of the corresponding RTs for a nonretarded group of individuals, with the slope (coefficient of slowing) of the regression function ranging from 1.43 to 2.34 with the correlation coefficients ranging from r 5 1.90 to 1.99. Likewise, the RTs of individuals with AD also increased linearly, as compared to non-AD individuals, although the slope of the best fitting regression function varied depending upon the type and complexity of the tasks performed. When the tasks used did not include sentence completion and lexical decision, the correlation coefficient increased from r 5 1.64 to 1.83. The
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slope of the linear function averaged 2.32 and ranged from 2.0 to 2.9, with this greater slope value attributed to the complexity of the tasks performed. Use of the Brinley (1965) multiple regression technique has been instrumental in gaining a clearer understanding of the underlying cognitive processes across these various subject groups. This has contributed to a better understanding of the many behavioral dysfunctions exhibited by these various population groups. The implication is that the behavioral observation of a general cognitive slowing appears to be a prominent characteristic of several population groups that exhibit deficiencies with normal brain functioning. In the present study, the Brinley plot/multiple regression methodology was employed to investigate the observation that closed-head injury (CHI) individuals exhibit a slowing in their cognitive processing, as compared to non-CHI individuals. Pairs of mean RT latencies from individuals with and without CHI can be fitted to the equation described earlier (Y 5 mX), where Y represents a mean RT latency for a group of CHI individuals and X represents a mean RT latency for a group of non-CHI individuals. As mentioned this approach has been helpful in the investigation of speed of cognitive performance in groups as diverse as children, mentally retarded adults, older adults, and individuals with Alzheimer’s disease. It should be noted that the requirements of the Brinley plot/multiple regression methodology (i.e., choosing studies, subject selection, data aggregation, and analysis) will necessarily result in a wide degree of variability with regard to injury severity, time since injury, and other potentially important factors such as criteria for inclusion/exclusion of empirical studies and subject recruitment practices. A table (Table 1) of characteristics of all 13 studies has been included to assist in illuminating the characteristics of the various studies chosen. Thus, one must be cautious regarding the specific generalizability of the particular results obtained, although this is a continuing issue with the use of meta-analytic methodology (see Myerson, Wagstaff, & Hale, 1994; Perfect, 1994). There is ample evidence from the literature examining individuals with CHI to suggest that slowing of cognitive processes is a pervasive characteristic of this group. For instance, several studies have shown increases in RT (both simple and choice) in CHI, as well as RT increases as task complexity increases (Benton & Blackburn, 1958; Blackburn & Benton, 1955; Dencker & Lofving, 1958; Gronwall, 1977; Miller, 1970; Norman & Svahn, 1961). Furthermore, Van Zomeren and Brouwer (1994, p. 77) have performed a preliminary meta-analysis of cognitive slowing in CHI and revealed the predicted increase in RT in CHI individuals, as compared to that seen in non-CHI individuals. Unfortunately, these authors did not provide any sort of slowing ratio (CHI RT/non-CHI RT) or percentage of variance accounted for by the apparent linearly increasing function portrayed in their data. However, their data clearly indicate a linearly increasing function.
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TABLE 1 Demographic and Experimental Characteristics of 13 Studies Used in the Present Analysis Subjects
Study 1: Deacon, D., & Campbell, K. B. (1993) CHI: n 5 12; M age 5 23 years, R 5 19–46; M Ed. 5 13.4 years (R 5 10– 19); M duration of coma: 32.4 days, R 5 7–25; M post-traumatic amnesia (PTA) duration: 57.4 days, R 5 30–150; M Glascow Coma Scale (GCS): 4.75, R 5 4–6; M time since injury: 4.6 years, R 5 3.1–6.9
Control: n 5 12, M age 5 25, R 5 20–38; M Ed. 5 14.4, R 5 11–21 Conditions 12 Task Auditory Choice Reaction Time (CRT) Study 2: Haut, M. W., Petros, T. V., Frank, R. G., & Haut, J. S. (1991) Subjects CHI: n 5 20 [9 postinjury . 1 year; M age 5 25.6 years; M Ed. 5 13.3 years; M WAIS-R vocab. 5 40.3; M GCS 5 5.7, M PTA 5 37.3; M time since injury: 948.3], [11 postinjury , 1 year; M age 5 24.5; M Ed. 5 13.2; M WAIS-R vocab. 5 44.0; M GCS 5 6.2, M M PTA 5 25.2, M time since injury 5 55.4 Control: n 5 16; M age 5 22.8; M Ed. 5 13.6, M WAIS-R Vocab. 5 44.5 Conditions 2 Task Category Judgement, CRT Study 3: Haut, M. W., Petros, T. V., Frank, R. G., & Lamberty, G. (1990) Subjects CHI: n 5 12; M age 5 30.1 (R 5 20–57); M Ed. 5 13.2 (R 5 12–18); M WAIS-R Vocab. 5 52.5 (R 5 21–64); M months since injury 5 48.2;M loss of consciousness 5 18.7 days Control: n 5 16; M age 5 31 (R 5 20–45); M Ed. 5 13.6 (R 5 12–15); M WAIS-R Vocab. 5 46.4 (R 5 35–57) Conditions 3 Task Sternberg Memory Scanning, CRT Study 4: MacFlynn, G., Montgomery, E. A., Fenton, G. W., & Rutherford, W. (1984) Subjects CHI: n 5 45 (28 M/17 F), M age 5 30.9 (R 5 16–55), M PTA , 48 hr
Conditions Task Subjects
Conditions Task
Subjects
Control: n 5 45; matched on age, education, sex, marital status, socio-intellectual status (no values given) 3 4-Choice CRT Study 5: Munte, T. F., & Heinze, H. J. (1994) CHI: n 5 11 (9 M/2 F); M age 5 25.1 (SD 5 5.6), R 5 17–36; M Ed. 5 9.45 (SD 5 1.96, R 5 6–12; M time since injury 5 7.72 years, (SD 5 6.18, R 5 2–18), M PTA 5 2.81 (SD 5 .87, R 5 1.4) Control: n 5 12; matched on age and education (no values given) 9 Simple Reaction Time/Choice Reaction Time (SRT/CRT), sentence verification, lexical decision, continuous word recognition Study 6: Ponsford, J., & Kinsella, G. (1992) CHI: n 5 47 (29 M/18 F); M age 5 23.4 (SD 5 7.4, R 5 16–43); M Ed. 5 11.4 (SD 5 2.1, R 5 8–17); M time between injury and assessment 5 112 days (SD 5 76.3, R 5 28–355); M PTA 5 39.6 days (SD 5 34.8, R 5 7– 168); M GCS 5 4.7 (SD 5 2.1, R 5 3–9) Controls: n 5 30 (24 M/6 F); matched on age (M 5 24.5, SD 5 5.9, R 5 16–42) and education (M 5 11.4, SD 5 1.5, R 5 9–16)
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Table 1—Continued Conditions 4 Tasks SRT/CRT Study 7: Sandson, J., Crosson, B., Posner, M. I., Barco, P. P., Valazo, C. A., & Brobek, T. C. (1988) Subjects CHI: n 5 9; M age 5 21.17 (SD 5 17.28, R 5 20–57); M Ed. 5 13.67 (SD 5 1.97, R 5 12–16); M postinjury 5 15 months (SD 5 8.05, R 5 9–30) Conditions Task Study 8: Subjects
Control: n 5 12 6 CRT Schmitter-Edgecombe, M. E., Marks, W., Fahey, J. F., & Long, C. J. (1992) CHI: n 5 20 (14 M/6 F); M age 5 29.3 (SD 5 8.23, R 5 20–51); M Ed. 5 14.05 (SD 5 2.26, R 5 9–19); M PTA 5 125 days (SD 5 121, R 5 8–360); M WAIS-R IQ 5 95.6 (SD 5 10.01); M postinjury 5 65 months (SD 5 38, R 5 19–159), all unconscious for at least 48 hr
Control: n 5 20 (14 M/6 F); M age 5 29.45 (SD 5 9.48, R 5 19–52); M Ed. 5 14.45 (SD 5 1.10, R 5 12–16); M WAIS-R IQ 5 102.8 (SD 5 8.62) Conditions 12 Tasks CRT (S-R compatibility, Sternberg memory scanning) Study 9: Schmitter-Edgecombe, M. E., Marks, W., & Fahey, J. F. (1993) Subjects CHI: n 5 18 (13 M/5 F); M age 5 31.01, SD 5 7.83, R 5 19–44); M Ed. 5 14.33, SD 5 2.40, R 5 9–18)
Conditions Tasks Subjects
Control: n 5 18 (13 M/5 F); M age 5 30.45, SD 5 8.42, R 5 21–46; M Ed. 5 14.33, SD 5 2.40, R 5 9–18 8 Lexical Decision Task (LDT), semantic priming Study 10: Shum, D. H. K., McFarland, K., & Bain, J. D. (1994) CHI: n 5 17 (12 M/5 F); M age 5 27.59 (SD 5 10.57, R 5 15–52); M Ed. 5 10.71 (SD 5 .83, R 5 9–12); M GCS 5 5.18 (SD 5 1.94, R 5 3–7); M coma length 5 24.57 days (SD 5 23.87, R 5 2–90); M time since injury 5 538.65 days, (SD 5 637.58, R 5 27–2190)
Control: n 5 13 (8 M/5 F); M age 5 27 (SD 5 11, R 5 16–49); matched on age, sex, and education Conditions 4 Task Name-matching, CRT Study 11: Stuss, D. T., Pogue, J., Buckle, L., & Bondar, J. (1994) Subjects CHI: n 5 18; M age 5 31.0 (SD 5 12, R 5 17–57); M Ed. 5 12.6 (SD 5 2.7, R 5 5–18); M coma length 5 1.1 days (SD 5 2.6, R 5 0–7); M PTA 5 10.2 days (SD 5 18.8, R 5 0–60); M GCS (6 hr after injury) 5 11.9 (SD 5 2.9, R 5 7–15); M GCS (1 day after injury) 5 12.8 (SD 5 3.1 R 5 7– 15); M GCS (1 week after injury) 5 14.2 (SD 5 1.8, R 5 8–15) Control, n 5 18; M age 5 31.0 (SD 5 13.7, R 5 16–60); M Ed. 5 11.6 (SD 5 2.2, R 5 7–17) Conditions 21 Tasks Visual discrimination (CRT) Study 12: Stuss, D. T., Stethem, L. L., Hugenholtz, H., Picton, T., Pivik, J., & Richard, M. T. (1989)
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Table 1—Continued Subjects
Conditions Tasks Subjects
Conditions Tasks
CHI: n 5 70 [study 1: n 5 26 (20 M/6 F); M age 5 30.9 (SD 5 11.9, R 5 17–57); M Ed. 5 12.0 (SD 5 2.7, R 5 7–20); M GCS 5 13.7 (SD 5 2.2, R 5 7–15); M coma duration 5 5.5 days (SD 5 16.4, R 5 0–75); M PTA 5 20.4 days (SD 5 36, R 5 0–135); study 2: n 5 22 (15 M/7 F); M age 5 29.5 (SD 5 12.6, R 5 16–57); M Ed. 5 14.4 (SD 5 3.2, R 5 9–20); study 3: n 5 22 (14 M/8 F); M age 5 26.6 (SD 5 11.7, R 5 15–61); M Ed. 5 11.8 (SD 5 1.7, R 5 9–15); M GCS 5 11.2 (SD 5 3.5, R 5 5–15; M coma duration 5 13.0 days (SD 5 3.2, R 5 6–24); M PTA 5 31.4 (SD 5 47.5, R 5 1–178)] Control: n 5 70 [study 1: n 5 26 (20 M/6 F); M age 5 29.7 (SD 5 12.4, R 5 16–20; M Ed. 5 13.2 (SD 5 3.0, R 5 5–20); study 2: n 5 22; M age 5 27.7 (SD 5 11.6, R 5 16–54); M Ed. 5 15.5 (SD 5 2.6, R 5 11–20); study 3: n 5 22; M age 5 27.0 (SD 5 12.5, R 5 16–63); M Ed. 5 12.5 (SD 5 1.6, R 5 9–17)] 15 SRT/CRT Study 13: Van Zomeren, A. H., & Deelman, B. G. (1978) CHI: n 5 54 [(n 5 27 mild CHI; M age 5 22.8; M level of unconsciousness 5 .60 min); n 5 15 moderate CHI; M age 5 19.7; M level of unconsciousness 5 1 hr–7 days); n 5 12 severe CHI; M age 5 23.4; M level of unconsciousness .7 days)] Control: n 5 45, M age 5 22 2 SRT/4-choice RT
Note: CHI, closed-head injury; CRT, choice reaction time; ED., education; F, female; GCS, Glascow Coma Scale; LDT, lexical decision task; M, male,; n, number of subjects; PTA, post-traumatic amnesia; R, range; SD, standard deviation; SRT, simple reaction time; WAIS-R, Wechsler Adult Intelligence Scale—Revised; Vocab., vocabulary.
There is also evidence that traumatic brain injury (e.g., CHI) and aging affect information processing and brain structure in similar ways (Stuss, Stethem, Picton, Leech, & Pelchat, 1989b). Aging and traumatic brain injury result in behavioral slowing and widespread brain damage. The brain damage in CHI is diffuse and as a consequence often results in a global slowing of cognition. Thus, not only is CHI linked to behavioral slowing, this link is characteristic of behavioral slowing exhibited by older (presumably nonCHI) adults. If CHI results in a significant slowing of cognitive processing, and if this slowing is similar to the slowing exhibited by older adults, then the slope value of the regression equation should approximate 1.5. Although this interpretation of behavior is not new to studies of subjects with CHI, the present investigation is the first application of the above-mentioned Brinley plots and regression techniques in RT performance to a sample of studies taken from the CHI literature (see also Van Zomeren & Brouwer, 1994). The appli-
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cation of this methodology will allow for a determination of the magnitude, at a very general level, of this pervasive cognitive slowing. METHODS Across the 13 studies chosen, a total of 682 individuals (353 CHI and 329 non-CHI Control) were involved. A sample of published studies (see Table 1) dealing with CHI was selected using the following criteria: (1) the studies chosen employed either simple reaction time (SRT) or choice reaction time (CRT) tasks, (2) a comparable control group was present, and (3) a sufficient number of experimental conditions were present in each experiment (at least two). Based on these criteria, a total of 13 studies that contained a total of 101 experimental conditions were chosen (i.e., 101 pairs of CHI/non-CHI pairs of mean RTs). A summary of studies used in the present experiment are listed in Table 1. This table includes information pertaining to a number of subjects, sex of subjects, other demographic information (education level, age), information relevant to individuals with CHI (Glascow Coma Scale and post-traumatic amnesia chronological information), as well as number of experimental conditions and tasks employed.
RESULTS
Across the 13 studies, the mean RTs for each of the 101 experimental conditions were tabulated between the CHI and the non-CHI (Control) individuals. These points were then plotted on (X, Y) coordinates and the bestfitting regression equation (CHI data regressed onto the corresponding nonCHI Control data) was fitted to these 101 points. The best-fitting regression equation that resulted from the methods outlined above was as follows: Y (CHI) 5 1.54 X (Control) 2 59 and this function accounted for approximately 89% of the total variance (R 2 ). The resulting linearly increasing function of this particular data is presented in a Brinley (1965) plot displayed in Fig. 1. DISCUSSION
The empirical and theoretical literature on CHI suggests that CHI results in a slowing of information processing. To provide evidence in support of this observation, meta-analytic/multiple regression techniques (based on Brinley, 1965) were performed on a sample of 13 studies and the best-fit regression equation was fit through 101 points which corresponded to 101 experimental conditions experienced by both the CHI and the non-CHI individuals. The results of the present study revealed that the CHI individuals’ simple- and choice-reaction time performance is approximately 1.54 times slower than an age-matched non-CHI Control group of individuals. That is, the RTs from individuals with CHI increased linearly as a function of the RTs from non-CHI individuals with a slope of 1.54. Similar meta-analytic/multiple regression techniques are common in studies dealing with normal healthy elderly adults as well as individuals diagnosed with Alzheimer’s disease, with the results used to determine the extent
FIG. 1. Response times (in msec) of closed-head injury individuals as a function of control individuals on 101 different experimental conditions.
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of the information processing slowing in these populations. Studies dealing with normal healthy aging individuals (Myerson et al., 1992) have indicated that this slowing factor is close of 1.50, suggesting that normal healthy aged individuals’ reaction time performance is approximately 1.50 times slower than their younger counterparts. Similarly, when this technique is applied to RT data collected from Alzheimer’s disease (AD) individuals (Nebes & Brady, 1992), the slowing factor for AD individuals, as compared to agematched non-AD individuals, is 2.0 to 2.9. The present results, in addition to substantiating claims that CHI results in a general cognitive slowing of information processing, also offer some implications and recommendations for future clinical and experimental research within the area of CHI. First, it appears clear in continuing to use reaction time (both simple and choice RT) as a dependent measure in CHI research. The usefulness of using RT in empirical studies was recently documented by Mahurin and Pirozzolo (1986) regarding aging and dementia research. They came to the conclusion that ‘‘RT measurement offers increased clinical precision in the neuropsychological assessement of age-related dementia’’ (p. 345). This conclusion is supported in the present study, and the implication is that in future studies of CHI it would be advisable to continue to include measures of simple and choice RT as a means of assisting with assessment and diagnostic issues. Of course, RT measures would not be the only measures taken from CHI individuals. Rather, RT tasks would compliment the various clinical and neuropsychological measures and tests already performed. In this way, the RT measures would serve as converging evidence for clinical observations (i.e., slowed thought, slowed information processing). Second, the fact that the CHI subjects (as a group) in the present experiment evidenced a cognitive slowing of approximately 1.54 suggests that CHI dramatically slows down even very basic cognitive processes (e.g., simple- and choice-reaction time). Furthermore, this rate of cognitive slowing is a level often observed in individuals much older (e.g., cognitive slowing ratios of 1.50 or greater are often associated with individuals 65 years of age and older (Myerson et al., 1992)). The average age of the CHI individuals in the present study was approximately 28 years. Because the slowing ratio associated with the CHI individuals in the present study was 1.54 it does lead to questions of why this slowing value is at this level and what underlying mechanisms are responsible for this level of slowing. Practical answers to these questions come from a recent paper by Stuss et al. (1986b). These authors found that ‘‘the deficit in both aging and traumatic brain injury (TBI) is not only a generalized neuronal slowing but a more specific impairment in attentional control processes, exhibited as a deficit in focused attention’’ (p. 161). Thus, the implication is that CHI individuals are deficient in their attentional abilities and these deficiencies contribute to their cognitive slowing in cognitive performance and behavior (see Van Zomeren & Brouwer, 1994).
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However, to say that CHI is a form of advanced aging is a very premature statement and further studies are needed to pinpoint the exact nature of this information processing slowing in this particular population. However, the present results provide an estimate of the magnitude of this cognitive slowing. Third, if the present results are correct and if CHI results in a cognitive slowing in cognitive performance that resembles that of an older adult, rehabilitation strategies and programs should likely be modified in order to accommodate the CHI individual who is experiencing this type to cognitive slowing. In summary, it was observed that individuals with CHI evidenced a slowing in basic cognitive processes (simple- and choice-reaction time) of 1.54, meaning that their mean RT performance was approximately 1.54 times slower than non-CHI individuals performing the same tasks. Future studies dealing with the cognitive performance of individuals with CHI should continue to employ reaction-time-based tasks. Such tasks are easy to perform and yield critical data regarding the underlying information processing deficits characteristic of individuals with CHI. Finally, the application of Brinley plot/multiple regression meta-analytic techniques appear useful in examining the extent of cognitive slowing in individuals with CHI (see also Van Zomeren & Brouwer (1994) for converging evidence regarding this observation). REFERENCES Note: Studies marked with a * were used in the meta-analysis. Benton, A. L., & Blackburn, H. L. 1958. Practice effects in reaction time tasks in brain-injured patients. Journal of Abnormal and Social Psychology, 54, 109–113. Birren, J. E. 1965. Age changes in speed of behavior: Its central nature and physiological correlates. In A. T. Welford & J. E. Birren (Eds.), Behavior, aging and the nervous system. Springfield, IL: Charles C. Thomas. Pp. 191–216. Blackburn, H. L., & Benton, A. L. 1955. Simple and choice reaction time in cerebral disease. Confinia Neurologica, 15, 327–338. Bleiberg, J., Nadler, J., Reeves, D., Garmoe, W., Cederquist, J., Lux, W., & Kane, R. 1994. Inconsistency as a marker of mild head injury. Presented at the meeting of the International Neuropsychological Society, Cincinnati, OH. Brinley, J. F. 1965. Cognitive sets, speed and accuracy of performance in the elderly. In A. T. Welford & J. E. Birren (Eds.), Behavior, aging and the nervous system. Springfield, IL: Charles C. Thomas. Pp. 114–149. Cerella, J. 1985. Information processing rates in the elderly. Psychological Bulletin, 98, 67– 83. Cerella, J., Poon, L. W., & Williams, D. M. 1980. Age and the complexity hypothesis. In L. W. Poon (Ed.), Aging in the 1980’s. Washington, DC: American Psychological Association. Pp. 332–340. *Deacon, D., & Campbell, K. B. 1991. Effects of performance feedback on p300 and reaction time in closed-head injured outpatients. Electroencephalography and Clinical Neurophysiology, 78, 133–141. Dencker, S. J., & Lofving, B. A. 1958. A psychometric study of identical twins discordant for closed head injury. Acta Psychiatrica Neurologica Scandinavica, 33, 122. Gronwall, D. M. A. 1977. Paced auditory serial-addition-task: A measure of recovery from concussion. Perceptual and Motor Skills, 44, 367–373.
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