Temporal bisection with trial referents.

In temporal bisection, the subject is required to compare the similarity of a probe duration with two referent durations. Two bisection experiments with human subjects are reported in which performance under three referent conditions was compared. In two of the conditions, no-referent and fixed-referent, the referent pair was constant throughout the session and was varied between sessions. In the no-referent condition, samples of the referents were presented at the beginning of a block of trials, but not on the probe trials. In contrast, in the fixed-referent condition, the referent pair was presented on each probe trial. In the third referent condition, roving-referent, the referent pair was also presented on each probe trial, but the values of the pair varied during a session rather than between sessions. The pseudologistic Model (PLM; Killeen, Fetterman, & Bizo, 1997) provided an excellent account of the data from all referent conditions and indicated that (1) the scalar variability was located in the perception of the probe and was independent of the structure of the bisection task, (2) the role of the referents was to set the criterion, (3) the probe was compared with the criterion rather than with the referents, and (4) the comparison of the probe with the criterion occurred even when trial referents were available.