A clarification of self-terminating versus exhaustive variances in serial and parallel models

A recent study published in Perception & Psychophysics (Donnelly, Found, & Muller 1999) employs response time (RT) variances (in the form of standard deviations) in addition to mean RTs. Variances can contribute greatly to mo del testing. However, there is a danger of perpetuating the kinds of logica l and methodological errors that have tong attended research employing mean RTs alone. Mis commentary clarifies the theoretical and methodological iss ues, points out some new results concerning variability in search processes , and indicates how to resolve the global and specific challenges associate d with identifying psychological mechanisms.