New scores for the Category Test: measures of interference for subtests 5 and 6

The Category Test is a well-known neuropsychological instrument used to assess concept formation and higher executive abilities. The present study investigated the utility of additional scores for the Category Test. We used principles developed in cognitive psychology to create several new measures for subtests 5 and 6 of this test. These scores were primarily designed to be sensitive to interference effects of learning decision rules from subtest 2, subtest 3, and subtest 4. The new scores as well as the total error scores from subtests 5 and 6 were used to discriminate subjects with documented brain injury from subjects who were neurologically normal based on neuroimaging and neurologic evaluation. The Category Test was given following Reitan's (1979) instructions, with the exception that no additional prompting was given to participants who struggled early with the test in order to reduce the "executive" guidance of the examiner. Because any "interference" from earlier subtests on performance of subtest 5 and subtest 6 should be related to mastery of these earlier subtests, the normal group was matched to the brain-impaired group on which subtest(s) they learned. This resulted in four learning groups: (a) learned subtests 3 and 4; (b) learned subtest 4 but not 3; (c) learned subtest 3 but not 4; and (d) failed to learn either subtest. ANOVA analyses revealed that the three measures of interference were significantly greater in the brain-damaged group than in the normal controls. Also, specific interference measures were related to specific prior subtest mastery, thus providing support for a proactive interference effect. In addition, we have evidence that our new measures may be selectively sensitive to frontal system dysfunction.