Most current memory theories assume that judgments of past occurrence
are based on a unidimensional familiarity signal. In a test of this hy
pothesis, subjects studied mixed lists of pictures and words that occu
rred up to three times each. They then were given two tests: a forced-
choice frequency discrimination rest including all pairs of conditions
(e.g., picture seen twice vs. word never seen) and a numerical freque
ncy judgment rest on individual items. Forced-choice proportions for a
ll pairings (picture-picture, word-word, and picture-word) were well f
it by a one-dimensional scaling solution, suggesting a common basis of
recognition and frequency judgments for both pictures and words. Both
forced-choice and numerical judgment data indicated that familiaritie
s of pictures started lower than those of words but increased more rap
idly with repetition. Results are discussed in connection with the dis
tinction between familiarity and recall, and the possible role of resc
aling in the mirror effect.