Journal of Experimental Psychology: Human Perception and Performance 1985, Vol. II, No. 4, 475-489 Copyright 1985 by the American Psychological Association, Inc. 0096-1523/85/100.75 Interference Between Phonemes During Phoneme Monitoring: Evidence for an Interactive Activation Model of Speech Perception Joseph Paul Stemberger Indiana University Jeffrey Locke Elman and Patricia Haden University of California, San Diego We explore the recent finding (Newman & Dell, 1978) that the time needed to detect a target phoneme in a phoneme monitoring task is increased when the preceding word contains a phoneme similar to the target. Normal adult native speakers of English monitored auditorily presented sentences and responded as quickly as possible whenever they detected a specified phoneme. We found that preceding word-initial phonemes, despite being processed more quickly, increased the response latency to the following target phoneme more than did preceding word-medial phonemes. There was also an increase in response latency even when the subject could be highly certain that the similar preceding phoneme was not an instance of the target phoneme. We argue that the interference effects are due to fundamental characteristics of perceptual processing and that more time is needed to categorize the target phoneme. We present a computer simulation using an interactive activation model of speech perception to demonstrate the plausibility of our explanation. The technique of phoneme monitoring, wherein a subject monitors auditorily pre- sented stimuli for the occurrence of a partic- ular "target" phoneme, has often been used as a vehicle for studying higher level processes of speech perception, such as word frequency (Foss & Blank, 1980), transitional probability of words (Morton & Long, 1976), and lexical ambiguity (Foss, 1970). Lower level aspects of speech processing have been less extensively investigated, though questions about the basic unit of perception (segment vs. syllable vs. word; Foss & Swinney, 1973) and the effects of stress (Cutler, 1976), consonant clusters (Treiman, Salasoo, Slowiaczek, & Pisoni, 1982), and vowel length (Foss & Gernsbacher, 1983) have been addressed. Newman and This research was supported in pan by Office of Naval Research Contract N-00014-82-C-0374 to Jeffrey Elman, and by National Institutes of Health Training Grant NS 7134-06 to Indiana University. We would like to thank Carol Fowler, Gary Dell, and the anonymous reviewers for their helpful comments on an earlier version of this article. Requests for reprints should be sent to Joseph Paul Stemberger, who is now at the Department of Linguistics, University of Minnesota, Minneapolis, Minnesota 55455. Dell (1978) recently studied one aspect of these lower level processes in detail. They found that the time needed to detect a target phoneme is increased by the presence of a similar phoneme in the preceding word. The size of this increase depends on how similar the preceding phoneme is and how near it is to the target phoneme. We will explore this last phenomenon further in this article. Newman and Dell attempted to account for their results as one aspect of false-alarm- ing. They reasoned that subjects should show a tendency to make false alarms to similar segments; for example, when the target is /b/, subjects may make false alarms to /p/ and /d/, because they sound so similar to the target phoneme. They showed that their sub- jects did indeed make false alarms to /p/ in their filler sentences. However, it was clear that subjects were not overtly making false alarms to the phoneme in the previous word in the target sentences. If this had been the case, the subject's response would have oc- curred either before the subject had heard the target phoneme or so soon thereafter that the subject could not possibly be responding to the target phoneme (e.g., 50 ms after onset of the /b/); reaction times would have been 475 This document is copyrighted by the American Psychological Association or one of its allied publishers. This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.