Abstract
In absolute judgment tasks, identical stimuli are rated higher (or lower) when presented in a series of more frequent small (or large) stimuli. Using
visual stimuli differing in velocity, we show that this conventional frequency effect is largely modulated by the primacy effect-that is, by the stimuli occurring on
the early trials of a run. In Experiment 1, a frequency-like primacy effect was obtained with equal-frequent velocities. Identical velocities were rated faster when
mainly slow rather than fast ones occurred on initial trials. In Experiment 2, we contrasted the frequency effect and the primacy effect: In runs with frequent slow
velocities, mainly fast ones occurred earlier, whereas in runs with infrequent slow velocities, mainly slow ones did so, Lack of differences of ratings in the two
conditions suggests 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.
