Effects of Stimulus Number and Target-to-Distractor Ratio on the Performance of Random Array Letter Cancellation Tasks

Cancellation tests are commonly used in the clinical assessment of visuospatial function, but there has been little study of task characteristics influencing performance. This study was designed to assess factors which affect cancellation performance. Sixteen healthy subjects sequentially performed four random-array letter cancellation tasks. The forms contained 50 and 100 stimuli and target:distractor (T/D) ratios of 1:4 and 1:9 with target letter “A” and randomly selected letter distractors. The primary performance measure was calculated as the number of correctly cancelled targets divided by the time to complete the task, corrected for accuracy. This measure revealed a strong effect of T/D ratio (p< .0001), with performance adversely affected by higher proportion of distractors. There was no effect of stimulus number. This suggests that T/D ratio should be considered in cancellation test design and interpretation.     

When a Lot of Knowledge Is a Dangerous Thing The Debilitating Effects of Plan Complexity on Verbal Fluency

Three experiments examined the relationships among plan complexity, access to planned actions, and verbal fluency while pursuing a persuasion goal. Consistent with theoretical expectations, complex planners were less fluent than less complex planners under high access conditions. Persons whose access was raised were less fluent than those whose access was not raised. A second experiment showed that reduced fluency was not induced by lowering of self-confidence. The third experiment replicated the findings of the second experiment and demonstrated that the questioning procedure used to raise access in the first two experiments produced increases in plan complexity as suggested by theory. These findings are discussed in terms of their implications for the study of strategic communication.