The simplest chronoscope: group and interindividual differences in visual reaction time.

The use of the simplest chronoscope (a falling meterstick) to measure visual reaction time (RT) in college students of both sexes is described. Tests of three hypotheses showed that (1) mean simple RT was significantly faster than long-standing population approximations and (2) a single-factor, repeated-measures, sequential-treatment analysis of variance design replicated Donders' long-standing findings that simple RT was significantly faster than choice RT; simple RT was significantly faster than discriminative RT; and that discriminative RT was significantly faster than choice RT. Also, (3) eta-squared effect size (eta2) computed on significant interindividual subject differences accounted for more variability than the eta2 effect size computed on significant differences between treatments. It was concluded that (1) the simplest chronoscope's methodology may have contributed to the significantly faster mean simple RT; (2) interindividual differences in RT should no longer be routinely ignored or eliminated; and (3) a repeated-measures analysis of variance design which tests for both group and interindividual differences can yield reaction time results of interest to both experimental and differential psychology.