Post-categorical processing and attenuation of the auditory suffix: evidence from both immediate and delayed suffixes

Recall of the final item in a spoken list is impaired by the presentation of a spoken to-be-ignored item following the list. The nature of the processes responsible for the stimulus suffix effect (as well as its magnitude) can be varied by manipulating the intrinsic characteristics of the relationship between the final list (target) item and suffix. A series of experiments show that systematic manipulation of both typicality of same-category membership of target-item and suffix (Experiment 1), and degree of synonymity between target-item and suffix (Experiment 2) result in differential attenuation in the magnitude of the suffix effect. The effect of the synonymity manipulation persists for up to twenty seconds after the presentation of the target-item (Experiment 3). That post-categorical processing of the suffix occurs provides direct support for semantic coding in short-term memory and contradicts models arguing that short-term memory is organised according to the principle of physical similarity (e.g., LeCompte and Watkins, 1993).