Perceptual Aberration and Schizotypy: A Cautionary Note

A group of 345 undergraduates completed scales assessing levels of perceptual aberration (Perceptual Aberration Scale¹) and magical ideation (Magical Ideation Scale; MIS⁶) as part of a mass testing protocol. Students were then selected for further participation in the study on the basis of their PAS scores. The “high PAS” group included 24 individuals who scored more than one standard deviation above the mean on the PAS (PAS>10). The “low PAS” group included 27 participants who scored low on the scale (PAS=1 or 2). Written informed consent was obtained from all participants.

Each of the 51 participants completed the Degraded Stimulus Continuous Performance Test (DSCPT).⁷ The DSCPT is a computerized test of attention with a high information-processing load. It involves the visual presentation of a series of degraded (i.e., highly blurred) digits at the rate of one per second. Subjects are instructed to push a button every time the target digit appears. Hit rate over 480 trials was used as the measure of attention.

For the analysis, participants were divided into high and low PAS groups. They were also divided into three equal groups based on their MIS scores (high, mid-range, and low). A two-way analysis of variance (ANOVA; PAS×MIS) was calculated for the hit rate measure of DSCPT performance.

Perceptual aberration scores were highly correlated with MIS scores (r=0.74, df=50, P<0.001), indicating that participants who scored high on the PAS also tended to score high on the MIS. Therefore only a few individuals were in the “low PAS/high MIS” and the “high PAS/low MIS” groups (Table 1).

In a two-way ANOVA (PAS×MIS) with attentional scores as the dependent variable, there was a significant main effect for PAS (F=9.14, df=1, 45, P=0.004), indicating that high-PAS participants showed significantly lower hit rates on the DSCPT than low PAS participants. This is consistent with previous findings on cognitive test performance. However, there was also a main effect for MIS, indicating that mid-range and high MIS scores predicted a better DSCPT hit rate than low MIS scores, and there was a significant interaction effect between PAS and MIS scores (F=3.91, df=2,45, P=0.027).

Low PAS/high MIS participants performed best, and high PAS/low MIS participants performed worst. Although few individuals were in these two categories, when they were excluded from analysis of the total participant group, the PAS main effect disappeared. See Table 1 for these results.

The results of this small study appear to support the hypothesis that high PAS scores, when used alone, are not an optimal criterion for measuring the larger construct of schizotypy. High-schizotypy participants showed poorer performance on the DSCPT than low-schizotypy participants when the only criterion for schizotypy was PAS score; however, this association did not hold when another criterion of schizotypy, MIS, was added. This result suggests that even though PAS scores are correlated fairly highly with measures of other facets of schizotypy, high PAS scores also may reflect something unrelated to schizotypy in some individuals. This other factor, rather than schizotypy, may be responsible for the poor attentional performance by high PAS groups.

The sample for this study was small. Subjects with high PAS and low MIS scores (or vice versa) were few. Past research has attested to the multidimensionality of schizotypy. We do not believe that our findings threaten the validity of the multidimensional schizotypy construct in any way. Our findings are merely cautionary. They suggest that use of multiple measures in selection of schizotypic subjects may be preferable to the use of a single criterion such as perceptual aberration.