Absolute identification with simple and complex stimuli

It is well known that people can perfectly identify only a handful of disti nct unidimensional stimuli, such as line lengths, but can identify thousand s of complex stimuli, such as letters and words. This result is consistent with capacity limits in identifying unidimensional stimuli but not complex stimuli. The experiments reported here tested this theoretical dissociation using Luce's (1963) Similarity Choice Model to measure the psychological d istance between stimuli in line-length-identification and letter-identifica tion tasks. The psychological distance between line-length stimuli decrease d with the number of to-be-identified stimuli; this result is concordant wi th capacity limits in unidimensional absolute identification. Surprisingly, the opposite result held in letter identification. Psychological distance between letters increased with an increased number of to-be-identified stim uli. This result indicates an opposite type of processing deficit: People p rocess letters more efficiently with more choices.