Self-Terminated vs. Experimenter-Terminated Memory Search

Self-Terminated vs. Experimenter-Terminated Memory Search J. Isaiah Harbison (isaiah.harbison@gmail.com) Erika K. Hussey (erikahussey@gmail.com) Michael R. Dougherty (mdougher@umd.edu) Department of Psychology, University of Maryland at College Park College Park, MD 20742 USA Eddy J. Davelaar (eddy.davelaar@gmail.com) Department of Psychological Sciences, Birkbeck University of London Malet Street, WC1E 7HX, London, UK Abstract Open- and Closed-Interval Designs In most free-recall experiments, participants are given a preset amount of time to search memory. Recently, several studies have examined retrieval in an open-interval design in which the participant, not the experimenter, determines when to terminate memory search. The present study performs the first direct comparison between participant-terminated and experimenter-terminated retrieval. No difference was found in the number of items retrieved from memory; however, inter- retrieval times (IRTs) did differ, such that the participant- terminated paradigm did not show the hyperbolic function typically found when using the experimenter-determined, closed-interval design. We were able to account for this result by equipping a simple relative sampling model with a memory search stopping rule that assumes that giving participants a pre-set retrieval interval causes them to search longer (and tolerate more search failures) than they would in the open-interval design. The difference between the open-interval and closed- interval recall design is illustrated in Figure 1. The closed- interval design, shown in Panel A, is restricted, in that the retrieval interval participants are given is pre-determined by the experimenter. After the interval has expired, search is terminated for the participant by the experimenter or by the software program used for the experiment. One reason this design has been used is that it allows greater focus on basic processes of memory retrieval, attempting to eliminate individual differences in how long participants spend searching memory. However, it is not necessarily the case that participants search during the entire pre-determined interval. In fact, many process models that have been proposed to account for the retrieval results from the closed- interval design have assumed a stopping decision to be part of the memory search process (e.g., Raaijmakers & Shiffrin, 1981). Moreover, the closed-interval design might induce participants to search memory longer than they normally would, potentially leading to results that do not replicate when participants are free to retrieve and self-terminate memory search. The open-interval design (panel B of Figure 1) gives participants an unlimited amount of time to retrieve. The principle strength of this design is that it allows for the measurement of memory search termination decisions, including the total time spent in search—determined by the participant—and the exit latency, or the time between the final retrieval and the decision to terminate search. Both measures have proven diagnostic for evaluating memory search stopping rules (Harbison et al., 2009). The design also, arguably, has greater ecological validity: Individuals are unlikely to have a fixed external time limit when searching memory during most everyday tasks outside the lab (for an examination of termination decision in response to external demands, see Davelaar, Yu, Harbison, Hussey, & Dougherty, 2012). However, the open-interval design too has potential weaknesses: Self-termination might prime participants to put less effort into retrieval and therefore provide inadequate data for the purposes of theory testing. If Keywords: memory; free-recall; stopping rules. Terminating Memory Search At some point, any search of memory must end. Several recent studies have begun to examine how this decision is made in free recall tasks, where search is often terminated while there remain potentially retrievable items unreported (Dougherty & Harbison, 2007; Harbison, Dougherty, Davelaar, & Fayyad, 2009; Unsworth, Brewer, & Spillers, 2011). These studies used a slightly modified version of the standard list recall paradigm; the only difference is that participants terminate their own memory search. This open- retrieval interval design (henceforth, open-interval design) is in contrast to the standard, closed-retrieval-interval design (closed-interval design) that gives participants a pre- determined retrieval interval. Both the open-interval and closed-interval designs have strengths and weaknesses, but to date, they have not been directly compared. The goal of the present study is to perform this comparison and evaluate how allowing or not allowing participants to terminate their own search influences the variables used to describe memory retrieval.