In contrast to exemplar and decision bound models of categorization, the memory and contrast models described here do not assume that long-term representations of stimulus magnitudes are available. Instead, stimuli are categorized using only their differences from a few recent stimuli. To test this alternative, sequential effects were examined in a binary categorization of 10 tones varying in frequency. Stimuli up to two trials back in the sequence had a significant effect on the response to the current stimulus. Further, the effects of previous stimuli interacted with one another. A memory and contrast model, where only ordinal information about the differences between the current stimulus and recent preceding stimuli is utilized, best accounted for these data.
Erratum: The state probability for state 6 in Table 2 (p. 420) should be ".108" not ".018".
This paper won the APA Division of Experimental Psychology 2005 New Investigator Award in Learning, Memory, and Cognition.