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PASAT: Observed correlations with IQ
Perron. vKf;rM. Dl$ Vol. 9. so. I. pp. 179-150. Printed in Great Bntam. All rights reserved
1988
PASAT:
Copyright
observed correlations
c
0191.8869 88 53.00+0.00 1988 Pergamon Journals Ltd
with IQ
VINCENT EGAN Deparrmenr
of Psychology,
Unirersiry
of Edinburgh,
(Received
7 George Square. Edinburgh,
I 7 March
EH8
9PP. Scotland
198 7)
Summary-Relations between psychometric measures of intelligence and the clinical Paced Auditory Serial-Addition Task (PASAT) were examined in a non-clinical group of young adults. PASAT correlated with the six separate psychometric scales, and especially with an overall estimate of non-verbal intelligence (r = 0.71, P < 0.001). One-minute samples of PASAT performance were also strongly correlated with intelligence (median r = 0.62, P < 0.01). The results suggest that PASAT is correlated with general intelligence and numerical ability, contrary to previous claims.
PASAT is a test used to measure the reduction of patients’ information-processing capacity following minor to moderately severe closed head-injury (Gronwall, 1977). During the test subjects are asked to listen to a recorded series of single digits and add each number to the one presented previously. Digits are presented at a constant pace, once every 2 or 4 sec. Little demand is placed upon memory: subjects need only remember one number, add it to the next and store this currently heard digit. Once the subject knows what to do, task difficulty consists primarily in the pacing. Practice on PASAT improves performance only slightly. compared to the major improvements that follow a patient’s recovery from concussion (Gronwall, 1977). When they factor-analysed a combination of clinical measures concerned with memory impairment. Gronwall and Wrightson (1981) found that PASAT loaded chiefly on a factor of attention, concentration and information-processing capacity; and that this factor had no substantial correlation with a factor of verbal competence. This was taken to support their previous claim that PASAT was “not significantly correlated with either general intelligence or arithmetic ability”. PASAT, however, involves relatively elementary information-processing based on the speed of intake: tasks of this type have sometimes appeared to have substantial correlations with general intelligence (e.g. Nettelbeck, 1987). So is PASAT really intellect-free? 28 subjects were collected from schools and Youth Training Schemes (mean age 16 yr, 7 months (SD 9.7 months)). The spread of ability on the Standard Progressive Matrices (SPM: Raven, 1977) approximated to normality (mean IQ 101.4, SD 15.4, population range 75-120). Testing was conducted in two blocks. one concerned with IQ tests, one with PASAT. Measures obtained were the percentage accuracy on the full PASAT task, and for each I min epoch within it. Subject completed the Alice Heim 2 (AHZ: Heim, Watts and Simmonds. 1974). the Cattell Culture-Fair (CCF: Cattell, 1973) and Mill-Hill Vocabulary (MHV: in Raven, 1977) tests. 5 subjects were not present at the main testing session, and did not complete the AH2. Additional verbal, performance and total scores were derived by adding appropriate tests together (VC, PC and TC respectively). PASAT was presented as described above (Gronwall, 1977). Subjects were given unpaced practice on PASAT until they were 100% accurate. They were then given practice on a paced practice version of the task, presented in the form of a tape-loop. This familiarised them with a more quickly-paced task. Following this paced practice, subjects were given the PASAT task proper, in which subjects heard 61 digits, one every 4 sec. These were presented by cassette also. During the inter-stimulus interval subjects made their response verbally. The experimenter recorded this on a scoring key. Mean percent accuracy for PASAT was 87. I (SD 16.1); in each I-min epoch the means and standard deviations were, respectively, 92.4 (16. I), 89.1 (14.2). 84.8 (20. I) and 85.5 (18.9). These results suggest a ceiling effect. Irrespective of epoch or full task, mean percentage accuracy and standard deviation remained about the same, inplying high internal consistency for PASAT. This is supported by correlations between the four subtest epochs and full PASAT [respectively r = 0.92, 0.95, 0.93 and 0.93 (all P < O.OOl)]. PASAT’s split-half reliability was 0.96 (P < O.OGl).
Table I. Correlation
of PASAT with psychometric
measures
PASAT Alice Hcim 2 Total Alice Hcim 2 Verbal Scale Alice Heim 2 Numeric Scale Alice Heim 2 Perceptual Scale Standard Progressive matrices Mill-Hill Verbal (test B) Cattcll Culture-Fair Verbal Composite Score Perceptual Composite Score Total Composite Score
0.65 0.52 0.67 0.69 0.63 0.41 0.73 0.51 0.71 0.68
l
*
l
‘* ” l* l
‘* l l l
* *
lP < 0.05. l*P < 0.001.
Table I shows that PASAT correlates substantially with most measures of intelligence for the sample: for example, PASAT correlated with TC at 0.68 (P -z 0.001). Although PC correlated somewhat higher with PASAT than did VC, the differences between these correlations did not approach statistical significance. 179
180
NOTES
ASD
SHORTER
COM.MUNICATlONS
Correlating each I min epoch with the IQ measures indicated that the PASAT-IQ correlation was not simply a product of fatigue on the full 4-min task. The median correlations of the psychometric measures with the four PASAT epochs were: for VC 0.48 (P i 0.05); PC 0.64 (P < 0.00; AHN 0.63 (P < 0.01); TC 0.62 (P -c 0.01). Hence both performance and numerical measures correlated well with performance on I-min PASAT epochs. PASAT is not, as Gronwall and Wrightson (1981) claimed, uncorrelated with general intelligence or arithmetic ability, at least in normal subjects. One objection to this result may be the ceiling effect observed. This could be reduced by subjects having to do PASAT at the rate of one stimulus every 2 sec. By virtue of the reduced spread of performance, ceiling effects tend to lower correlations. With a better distribution of PASAT scores. would the correlation increase? Hunt (1983) said that “the cognitive science view is that intelligence is an abstraction and does not have a cause” (pp. 146). The relationships shown here suggest that such a view may be unduly theoretical; there is nothing abstract about the strength of the phenomena observed. His claim that, because cognitive tasks tend to correlate with IQ tests at only 0.20 or 0.30, the information-processing approach to IQ is as useful as “the search for the Holy Grail” (Hunt, 1980) also looks short-sighted: many simple experimental tasks seem to be emerging, showing rather stronger relationships with IQ measures. PASAT has been used to study concussion for I5 years. and was not considered to relate to non-clinical variation in mental abilities. Possibly other ‘non-cognitive’ measures in daily usage by experimental and clinical psychologists are also chiefly measures of the testees’ general fluid intelligence (gf). The present study enables a traditional understanding of why PASAT correlates at relatively low levels with measures of crystallised intelligence (gc) in patients who have suffered recent head-injury: in these patients gc and gfare differentially affected by the injury. Acknowledgement-Supported
by ESRC
Award
A00428424343. REFERENCES
Cattell R. (1973) h4eusuring Intelligence with rhe Culture-Fair Tests: Munuol for Scales 2 and 3. Institute for Personality and Ability Testing, U.S.A. Gronwall D. (1977) Paced auditory serial addition task: A measure of recovery from concussion. Percepr. Mor. Skills 4, 367-373. Gronwall D. and Wrightson P. (1981) Memory and information processing capacity after closed head injury. J. Neural. Neurosurg. Psychiar. 44, 889-895. Heim A. W., Watts K. P. and Simmonds V. (1974) AH2/AH3 Manual. NFER Publishing, Windsor, U.K. Hunt E. (1980) Intelligence as an information-processing concept. Br. J. Psychol. 71, 449-474. Hunt E. (1983) On the nature of intelligence. Science 219, 4581, pp. 14&146. Nettelbeck T. (1987) Inspection time and intelligence. In Speed ofln/ormafion Processing and Infelligence (Edited by Vernon P.A.). Norwood N.J. Ablex. Raven J. (1977) Manual for Rncens Progressive Marrices and Volcabulary Scales. H. K. Lewis, London.
1988
PASAT:
Copyright
observed correlations
c
0191.8869 88 53.00+0.00 1988 Pergamon Journals Ltd
with IQ
VINCENT EGAN Deparrmenr
of Psychology,
Unirersiry
of Edinburgh,
(Received
7 George Square. Edinburgh,
I 7 March
EH8
9PP. Scotland
198 7)
Summary-Relations between psychometric measures of intelligence and the clinical Paced Auditory Serial-Addition Task (PASAT) were examined in a non-clinical group of young adults. PASAT correlated with the six separate psychometric scales, and especially with an overall estimate of non-verbal intelligence (r = 0.71, P < 0.001). One-minute samples of PASAT performance were also strongly correlated with intelligence (median r = 0.62, P < 0.01). The results suggest that PASAT is correlated with general intelligence and numerical ability, contrary to previous claims.
PASAT is a test used to measure the reduction of patients’ information-processing capacity following minor to moderately severe closed head-injury (Gronwall, 1977). During the test subjects are asked to listen to a recorded series of single digits and add each number to the one presented previously. Digits are presented at a constant pace, once every 2 or 4 sec. Little demand is placed upon memory: subjects need only remember one number, add it to the next and store this currently heard digit. Once the subject knows what to do, task difficulty consists primarily in the pacing. Practice on PASAT improves performance only slightly. compared to the major improvements that follow a patient’s recovery from concussion (Gronwall, 1977). When they factor-analysed a combination of clinical measures concerned with memory impairment. Gronwall and Wrightson (1981) found that PASAT loaded chiefly on a factor of attention, concentration and information-processing capacity; and that this factor had no substantial correlation with a factor of verbal competence. This was taken to support their previous claim that PASAT was “not significantly correlated with either general intelligence or arithmetic ability”. PASAT, however, involves relatively elementary information-processing based on the speed of intake: tasks of this type have sometimes appeared to have substantial correlations with general intelligence (e.g. Nettelbeck, 1987). So is PASAT really intellect-free? 28 subjects were collected from schools and Youth Training Schemes (mean age 16 yr, 7 months (SD 9.7 months)). The spread of ability on the Standard Progressive Matrices (SPM: Raven, 1977) approximated to normality (mean IQ 101.4, SD 15.4, population range 75-120). Testing was conducted in two blocks. one concerned with IQ tests, one with PASAT. Measures obtained were the percentage accuracy on the full PASAT task, and for each I min epoch within it. Subject completed the Alice Heim 2 (AHZ: Heim, Watts and Simmonds. 1974). the Cattell Culture-Fair (CCF: Cattell, 1973) and Mill-Hill Vocabulary (MHV: in Raven, 1977) tests. 5 subjects were not present at the main testing session, and did not complete the AH2. Additional verbal, performance and total scores were derived by adding appropriate tests together (VC, PC and TC respectively). PASAT was presented as described above (Gronwall, 1977). Subjects were given unpaced practice on PASAT until they were 100% accurate. They were then given practice on a paced practice version of the task, presented in the form of a tape-loop. This familiarised them with a more quickly-paced task. Following this paced practice, subjects were given the PASAT task proper, in which subjects heard 61 digits, one every 4 sec. These were presented by cassette also. During the inter-stimulus interval subjects made their response verbally. The experimenter recorded this on a scoring key. Mean percent accuracy for PASAT was 87. I (SD 16.1); in each I-min epoch the means and standard deviations were, respectively, 92.4 (16. I), 89.1 (14.2). 84.8 (20. I) and 85.5 (18.9). These results suggest a ceiling effect. Irrespective of epoch or full task, mean percentage accuracy and standard deviation remained about the same, inplying high internal consistency for PASAT. This is supported by correlations between the four subtest epochs and full PASAT [respectively r = 0.92, 0.95, 0.93 and 0.93 (all P < O.OOl)]. PASAT’s split-half reliability was 0.96 (P < O.OGl).
Table I. Correlation
of PASAT with psychometric
measures
PASAT Alice Hcim 2 Total Alice Hcim 2 Verbal Scale Alice Heim 2 Numeric Scale Alice Heim 2 Perceptual Scale Standard Progressive matrices Mill-Hill Verbal (test B) Cattcll Culture-Fair Verbal Composite Score Perceptual Composite Score Total Composite Score
0.65 0.52 0.67 0.69 0.63 0.41 0.73 0.51 0.71 0.68
l
*
l
‘* ” l* l
‘* l l l
* *
lP < 0.05. l*P < 0.001.
Table I shows that PASAT correlates substantially with most measures of intelligence for the sample: for example, PASAT correlated with TC at 0.68 (P -z 0.001). Although PC correlated somewhat higher with PASAT than did VC, the differences between these correlations did not approach statistical significance. 179
180
NOTES
ASD
SHORTER
COM.MUNICATlONS
Correlating each I min epoch with the IQ measures indicated that the PASAT-IQ correlation was not simply a product of fatigue on the full 4-min task. The median correlations of the psychometric measures with the four PASAT epochs were: for VC 0.48 (P i 0.05); PC 0.64 (P < 0.00; AHN 0.63 (P < 0.01); TC 0.62 (P -c 0.01). Hence both performance and numerical measures correlated well with performance on I-min PASAT epochs. PASAT is not, as Gronwall and Wrightson (1981) claimed, uncorrelated with general intelligence or arithmetic ability, at least in normal subjects. One objection to this result may be the ceiling effect observed. This could be reduced by subjects having to do PASAT at the rate of one stimulus every 2 sec. By virtue of the reduced spread of performance, ceiling effects tend to lower correlations. With a better distribution of PASAT scores. would the correlation increase? Hunt (1983) said that “the cognitive science view is that intelligence is an abstraction and does not have a cause” (pp. 146). The relationships shown here suggest that such a view may be unduly theoretical; there is nothing abstract about the strength of the phenomena observed. His claim that, because cognitive tasks tend to correlate with IQ tests at only 0.20 or 0.30, the information-processing approach to IQ is as useful as “the search for the Holy Grail” (Hunt, 1980) also looks short-sighted: many simple experimental tasks seem to be emerging, showing rather stronger relationships with IQ measures. PASAT has been used to study concussion for I5 years. and was not considered to relate to non-clinical variation in mental abilities. Possibly other ‘non-cognitive’ measures in daily usage by experimental and clinical psychologists are also chiefly measures of the testees’ general fluid intelligence (gf). The present study enables a traditional understanding of why PASAT correlates at relatively low levels with measures of crystallised intelligence (gc) in patients who have suffered recent head-injury: in these patients gc and gfare differentially affected by the injury. Acknowledgement-Supported
by ESRC
Award
A00428424343. REFERENCES
Cattell R. (1973) h4eusuring Intelligence with rhe Culture-Fair Tests: Munuol for Scales 2 and 3. Institute for Personality and Ability Testing, U.S.A. Gronwall D. (1977) Paced auditory serial addition task: A measure of recovery from concussion. Percepr. Mor. Skills 4, 367-373. Gronwall D. and Wrightson P. (1981) Memory and information processing capacity after closed head injury. J. Neural. Neurosurg. Psychiar. 44, 889-895. Heim A. W., Watts K. P. and Simmonds V. (1974) AH2/AH3 Manual. NFER Publishing, Windsor, U.K. Hunt E. (1980) Intelligence as an information-processing concept. Br. J. Psychol. 71, 449-474. Hunt E. (1983) On the nature of intelligence. Science 219, 4581, pp. 14&146. Nettelbeck T. (1987) Inspection time and intelligence. In Speed ofln/ormafion Processing and Infelligence (Edited by Vernon P.A.). Norwood N.J. Ablex. Raven J. (1977) Manual for Rncens Progressive Marrices and Volcabulary Scales. H. K. Lewis, London.