Primacy and frequency effects in absolute judgments of visual velocity

In absolute judgment tasks, identical stimuli are rated higher (or lower) w hen presented in a series of more frequent small (or large) stimuli. Using visual stimuli differing in velocity, we show that this conventional freque ncy effect is largely modulated by the primacy effect-that is, by the stimu li occurring on the early trials of a run. In Experiment 1, a frequency-lik e primacy effect was obtained with equal-frequent velocities. Identical vel ocities were rated faster when mainly slow rather than fast ones occurred o n initial trials. In Experiment 2, we contrasted the frequency effect and t he primacy effect: In runs with frequent slow velocities, mainly fast ones occurred earlier, whereas in runs with infrequent slow velocities, mainly s low ones did so, Lack of differences of ratings in the two conditions sugge sts that the two effects canceled each other. In Experiment 3, when mainly frequent velocities occurred earlier, the conventional frequency effect was obtained. We conclude that the conventional frequency effect represents a combination of the primacy effect and the pure frequency effect.