In two experiments, we examined the effects of manipulating the densit
y of stimuli on comparison difficulty in a comparative judgment task.
In Experiment 1, subjects were slower at judging the relative size of
a pair when the members were adjacent items in the linear order than w
hen the members were separated by items of intervening magnitudes. In
Experiment 2, the advantage of choosing the larger rather than the sma
ller of two large stimuli (e.g., the congruity effect) increased when
the linear order included many small items. In contrast, the advantage
of choosing the smaller of two small items increased when the linear
order included many large items. The applicability of the range-freque
ncy theory (Parducci, 1965) to these results is discussed.