The time course of response suppression: No evidence for a gradual release from inhibition

Abstract

Most models of serial recall postulate that recalled items are suppressed and thus temporarily rendered unavailable. Response suppression can explain several results, for example the small number of erroneous repetitions and people's reluctance to report repeated items. Although it is clear that response suppression is not permanent (thus permitting renewed recall of an item on the next trial), nothing is known about its time course. We report two experiments that measured the time course of response suppression with a multiple cued‐retrieval response‐deadline method. Emphasis was on the extent of repetition inhibition for lists that contained a repeated item. Regardless of whether presentation was rapid (Experiment 1; 150 ms/item) or slow (Experiment 2; 500 ms/item), (a) the standard pattern of repetition inhibition and erroneous repetitions occurred and (b) repetition inhibition remained constant across increasing retrieval time. This suggests that the release from response suppression is a discrete, list‐wide effect rather than a continuous, gradual wearing off. The latter conclusion is consistent with the operation of the SOB model (Farrell & Lewandowsky, 2002) but not with models that postulate complete suppression with gradual wearing off.

Notes

Correspondence should be addressed to Matthew Duncan, School of Psychology, University of Western Australia, Crawley, WA 6009, Australia. Email: [email protected]

We thank Leo Roberts for his assistance during data collection. Preparation of this paper was facilitated by a large grant from the Australian Research Council to the second author.

Aside from response suppression, a guessing bias has also been offered as an explanation of repetition inhibition (Greene, 1991; Mewaldt & Hinrichs, 1973). On this view, people are simply reluctant to repeat themselves, and if forced to guess, they will be more likely to produce an unrecalled item rather than a repetition. Although corrections for guessing bias can greatly reduce or eliminate repetition inhibition (e.g., Greene, 1991; Mewaldt & Hinrichs, 1973), it does not eliminate the effect. Inhibition effects persist after corrections for guessing, particularly when vocabulary size is small (see Hinrichs, Mewaldt, & Redding, 1973; Walsh & Schwartz, 1977). Repetition inhibition also persists when guesses and low confidence responses are removed from the analysis altogether (Henson, 1998a, Experiment 3). Finally, guessing cannot explain why people do not always consciously report a bias against guessing repeated items (Walsh & Schwartz, 1977), why errors in recall of repeated items are often omissions (Jahnke, 1972), or the fact that participants are known to detect repetitions in lists (Henson, 1998a). Thus, a guessing bias cannot be the sole explanation of repetition inhibition (see Henson, 1998a, for a more detailed discussion).

To prevent misconceptions, we mention two potential implications that do not follow from our conclusion: First, we do not suggest that suppression is the sole cause of repetition inhibition. Second, we do not exclude the possibility that some repetition blindness phenomena observed with RSVP reflect encoding failures.

Concerning the former, there are aspects of repetition inhibition that response suppression alone cannot explain. For example, the extent of repetition inhibition is known to depend on separation of repeated items at input. When repetitions are adjacent or separated by only one other item, inhibition is reduced or reverses into facilitation (Henson, 1998a), an effect explained by people noticing the immediate repetitions and “tagging” the item for repeated report (Henson, 1998a). These results imply that other factors, including people's guessing strategies, contribute to repetition inhibition effects.

Concerning the latter, although there are extensive similarities between repetition blindness and other forms of repetition inhibition, the similarity breaks down in certain cases. The main issue is whether repetition blindness should be considered a special case of repetition inhibition. A common conclusion is that inhibition effects represent output processes (e.g., Armstrong & Mewhort, 1995; Crowder, 1968a; Greene, 1991; Henson, 1998a; Jahnke, 1969a). However, it has been argued that the retrieval demands of serial recall confound input and output processes (Fagot & Pashler, 1995). Furthermore, there are instances where inhibition appears to be a perceptual failure independent of output processes (Kanwisher, Kim, & Wickens, 1996). This had led to the conclusion that repetition blindness is a perceptual phenomenon distinct from other forms of inhibition (see Henson, 1998a). However, neither of these two issues compromises our main conclusion, that repetition inhibition provides a legitimate empirical index of response suppression.

Although in SEMs simulations the wearing off is discretised over subsequent responses for the sake of simplicity, Henson clearly identifies the process as time‐based (see Henson, 1998b, Appendix B). In the Primacy model (Page & Norris, 1998), a mechanism for gradual release has not been explicitly implemented, but the authors state that modelling the pattern of erroneous repetitions would require the amount of response suppression “… to weaken during the course of further recall,….” (Page & Norris, 1998, pp. 765).

We found an extremely high level of repetition facilitation for one individual who was consequently removed from the analysis. We comment on the reasons for this participant's high facilitation and its relevance to Experiment 2 in the Discussion.

This regression analysis confounds between‐ and within‐participant variability, which is often inadvisable (e.g., Lorch & Myers, 1990). The data from both experiments were therefore also analysed using hierarchical regression (Busing, Meijer, & van der Leeden, 1994), which estimates regression parameters for each participant separately and ascertains statistical significance based on their overall pattern. In both experiments, the hierarchical regression analyses supported the same conclusions as the simple regressions: For ease of interpretation, we report only the latter.