Serial recall and presentation schedule: A micro‐analysis of local distinctiveness

Abstract

According to temporal distinctiveness theories, items that are temporally isolated from their neighbours during presentation are more distinct and thus are recalled better. Event‐based theories, which deny that elapsed time plays a role at encoding, explain isolation effects by assuming that temporal isolation provides extra time for rehearsal or consolidation of encoding. The two classes of theories can be differentiated by examining the symmetry of isolation effects: Event‐based accounts predict that performance should be affected only by pauses following item presentation (because they allow time for rehearsal or consolidation), whereas distinctiveness predicts that items should also benefit from preceding pauses. The first experiment manipulated inter‐item intervals and showed an effect of intervals following but not preceding presentation, in line with event‐based accounts. The second experiment showed that the effect of following interval was abolished by articulatory suppression. The data are consistent with event‐based theories but can be handled by time‐based distinctiveness models if they allow for additional encoding during inter‐item pauses.

Notes

Correspondence should be addressed to Stephan Lewandowsky, School of Psychology, University of Western Australia, Crawley, W.A. 6009, Australia. Email: [email protected]

We thank Leo Roberts for his assistance during data collection. This research was supported by a Large Grant from the Australian Research Council to the first author and an associated Linkage Grant awarded to both authors, and by grants 88/S15050 from BBSRC (UK) and grants R000239002 and R000239351 from ESRC (UK).

The randomisation procedure was checked by computing average serial positions for each cell of the pre × post grid (aggregating across trials and participants). Perfect randomisation would correspond to a serial position of exactly 5 in each cell (given that positions 2, 4, 6, 8 were considered). The observed average across all cells in the grid was 4.98, with a standard deviation of 0.20. It follows that serial position was adequately controlled and could not affect the regression analysis.

As a further check, the number of cell entries in the pre × post grid was subjected to a χ² analysis. The randomisation procedure should have prevented any association between the pre and post durations. Accordingly, although the test statistic was significant, χ²(25) = 274.8, p < .0001, the degree of association between the two types of interval was low (Cramer's V = .107). Because χ² is notoriously sensitive to sample size, Cramer's V is considered a better measure of association (e.g., Howell, 2002).

One might argue that the subjective grouping of the list into chunks of three items, which is suggested by the serial position curves and the transposition gradients, could somehow obscure or counteract an effect of pre. However, we consider this unlikely: One of the critical serial positions (position 4) was at the beginning of a subjective group and one was at the end (position 6). Hence subjective grouping had an equal chance to override an effect of pre as well as post—we nonetheless only observed an effect of post.