Lexical Effects in Phoneme Monitoring: Time-course versus Attentional Accounts

Under what conditions do lexical factors influence phoneme detection times? Experiment 1 measured subjects’ latencies to detect initial phonemes in monosyllabic and disyllabic words that were preceded by a semantically related or unrelated word. One group of subjects was instructed to pay attention to the semantic relations between words, and a second group was asked to focus on acoustic-phonetic information. A significant priming effect was found, only for monosyllabic words, and only in the first group. In Experiment 2, previously observed frequency effects (Dupoux and Mehler, 1990) disappeared when the detection task was biased towards acoustic-phonetic information. In Experiment 3, two student populations were tested with exactly the same instruction set and showed markedly different results: One group showed a consistent lexical superiority effect on monosyllabic items while the other group showed no such effect. Taken together, these results suggest that the presence or absence of lexical effects is extremely sensitive to attentional parameters that can be affected by explicit biasing instructions and/or individual differences. Importantly, these effects cannot be accounted for in terms of mean reaction time differences (where slow reaction times would be expected to lead to stronger lexical influences than fast ones). The results reported here are consistent with the view that phoneme detection can be carried out using either of two quite different routes. Implications for current models of lexical and prelexical processing are discussed.