Exemplar effects arise in a lexical decision task, but only under adverse listening conditions

This study investigates the influence of adverse listening conditions on the occurrence of exemplar effects in repetition priming experiments that do not instruct participants to use their episodic memories. We carried out two lexical decision experiments (N = 26 participants in each experiment), in which a prime and a target represented the same word type and could be spoken by the same or a different speaker (but were always different tokens). Other than for instance an old-new judgment task, a lexical decision task does not require participants' use of episodic memory. In Experiment 1, in which participants listened to clear speech, we obtained no exemplar effects: participants recognized word repetitions spoken by the same speaker equally fast as word repetitions spoken by different speakers. In Experiment 2, we introduced an adverse listening condition by adding speech-shaped noise to the same stimuli (at pre-tested intermediate noise level of SNR +3 dB). Exemplar effects arose in this experiment. Experiment 1 yielded on average longer response times than Experiment 2. Importantly, this result contradicts the time-course hypothesis (McLennan & Luce, 2005), according to which exemplar representations should only play a role when speech processing is relatively slow. Instead, our finding supports the hypothesis that exemplar effects arise under adverse listening conditions, when participants are stimulated to use their episodic memories in addition to their mental lexicons