Testing a Distinctiveness Explanation of the Primacy Effect in Free Recall Using Event-Related Potentials


The primacy effect in free recall is commonly attributed to more frequent rehearsals for stimuli in the first few serial positions. Using event-related potentials (ERPs), we investigated whether the first list position also provides a distinctive feature to the stimulus, which enhances its encoding and aids retrieval on a recall test. The amplitude of the P300 elicited by stimuli that deviate physically or semantically from their context has previously been shown to correlate with the probability of later recall when participants use rote rehearsal. We reasoned that if the temporal distinctiveness of the first item in a list contributes to its enhanced recall, such a P300 subsequent memory effect should be present for this item as well. Participants studied and immediately recalled lists of 15 words including one physically deviant “isolate” while their EEG was recorded. We quantified P300 amplitude by a principal component analysis, and applied a correction for inter-trial latency jitter. The first words in a list and isolates were better recalled than regular words in the middle list positions, and the P300 elicited by these words was correlated with subsequent recall. Regular words in the middle list positions, as well as words in the second list position, did not show such a P300 subsequent memory effect. These results support a distinctiveness-based explanation of the primacy effect in free recall.

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