A NEW PERFORMANCE-CURVE METHOD FOR THE DETECTION OF SIMULATED COGNITIVE IMPAIRMENT

Objectives. To evaluate a new performance-curve method for detecting s imulated cognitive impairment. Design. The method was based on quantit ative analysis of choice reaction times in a series of eight matching- to-sample tasks of graded complexity, in which participants were requi red to identify which of two comparison stimuli was identical to a sim ultaneously presented sample stimulus. The stimuli consisted of arrays of letters, the number of letters ranging from 1 to 10 in the eight t asks. Methods. Mean reaction times of a standardization group of 20 he althy young adults were used to construct regression equations to desc ribe the behaviour of three test groups: 20 healthy individuals instru cted to perform to the best of their ability (non-simulators), 20 heal thy individuals instructed to simulate cognitive impairment incurred a s a result of a head injury (simulators), and 25 patients with a histo ry of closed head injury (patients). Results. There was a linear relat ionship between individual participants' latencies and the mean latenc ies of the standardization sample; the patient group showed steeper sl opes, and the simulators higher intercepts, than the non-simulator gro up. A univariate measure of performance, based on the proportionate in crease in latency corresponding to a standard increase in the standard ization group's latency was able to identify 14/20 simulators while mi sclassifying 2/20 non-simulators and 2/25 patients. Other measures, in cluding the number of errors made in the choice reaction time task and in recognition memory tasks, and a performance-curve measure based on Raven's Standard Progressive Matrices, were less successful in identi fying simulators. Conclusions. This new performance-curve method may p rove to be a useful addition to tests currently used to diagnose simul ated cognitive impairment in clinical and medicolegal settings.