The US version of the d2, a cancellation task of attention, purports to measure selective attention, inhibition, processing speed, rule compliance and quality of performance. The d2 and the Wechsler Adult Intelligence Scale-Revised (WAIS-R) were administered to a normative sample of 506 US college students (59% male; mean age 20.7 years, range 18-32; 79% Caucasian). Statistically significant (p<.05), yet minimal correlations were demonstrated between the Picture Completion (PC) subtest and the d2 percentage of errors (E%; r=-.28), total performance (TN-E; r=.16), concentration performance (CP; r=-.25), and fluctuation of performance across trials (FR; r=-.14). Similarly, small, yet significant (p<.05) correlations were found between the Information (INF) subtest and the d2 E% (r=-.17), CP (r=.16), and FR (r=-.13). These results complement investigations of normal German samples included in Brickenkamp & Zillmer's (in press) review, as well as providing evidence for discriminant validity of the d2.

Selective attention is the capacity to focus on one or two important stimuli while suppressing awareness of competing distractions (Van Zomeren & Brouwer, 1994). A related construct of vigilance or sustained attention refers to the capacity to maintain an engaging activity over a period of time (Brickenkamp & Zillmer, 1998). Cancellation tasks, such as Bells (Gauthier, et al., 1989) and the Star task (Wilson, et al., 1987) have been developed to assess selective attention and vigilance. The d2 Test of Attention is considered to be the standard instrument for measuring concentration speed and attention in Germany in both clinical and applied settings (Brickenkamp & Zillmer, 1998). First published in 1962 and currently in its 8th German edition, the d2 has recently been adapted for use in English speaking populations with US normative data (Brickenkamp & Zillmer, 1998). Unlike traditional adminstrations of other cancellation tasks, the d2 measures consistency and speed of performance across the test condition.

While the US version of the d2 represents a promising measure of sustained attention and vigilance, its discriminant validity has not yet been demonstrated. Similar to contrasts between the d2 and the Hamburg-Wechsler Intelligence Test for Adults (Hamburg-Wechsler-Intelligenztest für Erwachsene; HAWIE) in German samples demonstrated by Brickenkamp (1962), it was predicted that d2 constructs would be relatively independent of psychometric intelligence.

Participants

Participants included 506 college students who were recruited from Drexel University in Philadelphia, PA. They were recruited from several Introductory Psychology classes and received course credit for their participation. Participants ranged in age from 18 to 32 years (mean=20.7; SD=3.1). The sample was 59% male with the following ethnic representation: Caucasian (77%), Asian American (14%), and African American (9%).

Materials

d2 test of Attention. The d2 is a timed test of selective attention. The items are composed of the letters "d" and "p" with one, two, three or four dashes arranged either individually or in pairs above and below the letter. The subject is given 20 seconds to scan each line and mark all "d's" with two dashes. There are 14 lines of 47 characters each for a total of 658 items. Measures of performance include total number of items processed (TN), percentage of errors (E%), an index of concentration performance (CP) TN - errors (TN - E), and fluctuation rate across trials (FR).

Wecshler Adult Intelligence Scale- Revised. Picture Completion and Information subtests of the WAIS-R were selected to assess intelligence.

Design & Procedure

Variables of interest and the constructs they purport to measure are summarized in Table 1. The d2 and subtests of the WAIS-R were also administered per standard protocol (Brickenkamp & Zillmer, 1998; Wechsler, 1981). Variables of interest were analyzed using Pearson's correlation technique.

Table 1: Description of the variables of interest from the d2 and WAIS-R subtests.

Variables of Interest	Description	Constructs Measured
d2
TN	Total Items Processed	Attentional allocation, processing speed, amount of work completed and motivation
E%	Percentage of Errors	Inhibitory control, rule compliance, carefulness
CP	Concentration Performance	Speed and accuracy of performance
TN - E	Total Items Scanned minus Error Scores	Quantity of work completed after correction for errors
FR	Fluctuation Rate	Consistency of performance across trials
WAIS-R
INF	Information Subtest Scaled Score	Verbally mediated crystallized knowledge
PC	Picture Completion Subtest Scaled Score	Attention to visuospatial details, scanning

Statistically significant (p<.05), yet minimal correlations were demonstrated between the Picture Completion (PC) subtest and the d2 percentage of errors (E%; r=-.28), total performance (TN-E; r=.16), concentration performance (CP; r=-.25), and fluctuation of performance across trials (FR; r=-.14). Similarly, small, yet significant (p<.05) correlations were found between the Information (INF) subtest and the d2 E% (r=-.17), CP (r=.16), and FR (r=-.13). Results are summarized in Table 2.

As predicted, the minimal correlations found demonstrate contrasts between the d2 and subtests of the WAIS-R. This suggests that intelligence and d2 measures are relatively independent of one another. This index of discriminant validity distinguishes the d2 as a promising test of selective attention. Results complement those found in the German version of the d2 when compared to the HAWIE in the European normative sample.

Although the correlations between the d2 and intelligence measures were minimal, they were statistically significant. This indicates that attention and intelligence share some, albeit small, portion of the variance. Performance on intelligence measures require varying degrees of selective and sustained attention.

The current investigation has improved upon Brickenkamp's (1962) and Hellwig's (1975) investigations of the d2 and intelligence measures by incorporating a larger sample size (n=38; n=240; n=506, respectively). However, the sample employed for the current investigation represents a homogenous group in terms of age, geographic location, level of education and socio-economic status (SES). Therefore these results may be of restricted range. They are, however, are consistent with correlations to the HAWIE and Culture Fair Intelligence Test (Catell & Weiss, 1971) which drew from more heterogeneous German samples. Additional research using more heterogeneous US samples and complete administrations of the Wechsler scales is suggested.

Brickenkamp, R. (1962). Aufmerksamkeits-Belastungs-Test (Test d2). [The d2 test of Attention.] (1st ed.). Göttingen: Hogrefe.

Brickenkamp, R. & Zillmer, E. (1998). The d2 Test of Attention. (1st US ed.). Seattle, WA: Hogrefe & Huber Publishers.

Catell, R. B. & Weß, R. H. (1971). Grundintelligenztest- Skala 3. [Culture Fair Test (CFT 3).] Göttingen: Hogrefe.

Helliwig, H. J. (1975). Zur Differenzierung von Intelligenztest- und Konzentrationsleistungen. [The differentiation of performance in intelligence- and concentration tests.] Unpublished dissertation, Technical University of Berlin.

Wechsler, D. (1981). The Wechsler Adult Intelligence Scale, Revised. San Antonio, TX: The Psychological Corporation.

Van Zomeren, A. H., Brouwer, W. H. (1994). Clinical neuropsychology of attention. New York, NY: Oxford University Press.

The authors are appreciative of contributions of Barbara Holda, Daniel Rosenberg, and Yoon Joon Hong Lint. We are also gratefully acknowledge the efforts of 506 Drexel University undergraduates who participated in this investigation.

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