Task difficulty and cognitive deficits in schizophrenia.

Abstract

Investigators of schizophrenic cognition often produce 2 or more tasks of differing difficulty levels by manipulating a variable that affects the accuracy of both normal and schizophrenic individuals; the investigators find that the variable also affects the difference between the groups in accuracy and conclude that the variable taps a schizophrenic differential deficit. An alternative hypothesis is that task differences in true-score variance artifactually produce the finding. For free-response tasks, group differences tend to be larger when difficulty is near 50%. The authors illustrate a new method of controlling this artifact by selecting items for hard and easy tasks on opposite sides of 50% difficulty and equidistant from it. Using this design with an anagram task, they found that schizophrenic and normal individuals differ no more on hard anagrams than on easy ones, and they propose the design for testing hypotheses concerning schizophrenic deficit on tasks that differ in difficulty.

The Stroop task and attention deficits in schizophrenia: A critical evaluation of card and single-trial Stroop methodologies.

“…However, this approach has been criticized on a number of grounds, including statistical (e.g., regression-to-the-mean effects; Chapman & Chapman, 1973) and subject-characteristic issues (e.g., systematic unmatching on unknown variables; Meehl, 1971). Although not entirely optimal (see, e.g., Chapman & Chapman, 1989;Miller, Chapman, Chapman, & Collins, 1995), the possibility of a generalized deficit was examined by following the suggestions of Chapman et al (1994) to determine whether patients perform differently on two tasks from what would be predicted on the basis of general performance level.…”

Oculomotor and manual indexes of incidental and intentional spatial sequence learning during middle childhood and adolescence

“…Thomas and Nelson (2001) used proportional change in RTs, and Thomas and colleagues (2004) used the diVerence between z scores on random trials and z scores on sequence trials. Interpretation of diVerence scores between groups on experimental versus control conditions can be problematic when there are baseline diVerences among groups (Chapman, Chapman, Curran, & Miller, 1994;Faust, Balota, Spieler, & Ferraro, 1999;Knight & Silverstein, 2001;MacDonald & Carter, 2002;Miller, Chapman, Chapman, & Collins, 1995;Salthouse & Hedden, 2002). DiVerent ways of handling baseline diVerences can result in diVerent interpretations.…”

Configural processing in autism and its relationship to face processing

“…Furthermore, simply focusing on interactions, for example, group (autistic and control) × condition (gender and individual) with RT as the dependent measure may be subject to scaling problems that result merely from differences in baseline performance between the groups rather than from a real interaction between group and the conditions of interest. These analytical problems are well-recognized and have plagued the literature previously, for example, in the domain of schizophrenia (Miller, Chapman, Chapman, & Collins, 1995). In an attempt to be cognizant of these potential scaling problems, we not only use the median (to offset the influence of outliers) for each cell for each individual but also more importantly, the percentage change across the experimental conditions is calculated and compared across groups to control for differences in the absolute base RT.…”