Memory for goals: an activation-based model.

Keywords: Memory; Problem-solving; Cognitive simulation; Goals; Towers of Hanoi; Prospective memory

1. Introduction

When people plan, react to emergencies or other interruptions, or make mental notes to do things in the future, an important process involved is the cognitive management of goals. We use the term "goal" to refer to a mental representation of an intention to accomplish a task, achieve some specific state of the world, or take some mental or physical action (contrasting with use of "goal" to mean a performance criterion; e.g., Carver & Scheier, 1998; Heath, Larrick, & Wu, 1999). Very often, a goal must be suspended or set aside temporarily and then resumed later. Suspending a goal might be necessary, for example, if it requires subgoals to be achieved first, as in hierarchical problem solving (Miller, Galanter & Pribram, 1960) and means-ends analysis (Ernst & Newell, 1969; Newell & Simon, 1972). Alternatively, progress on a goal might be blocked by the state of the world, so one may benefit from turning attention to some other task until the environment changes (e.g., Patalano & Seifert, 1997). Or, one might be interrupted in the middle of a task, prompting the formulation of an intention to resume the task later (e.g., Marsh, Hicks & Bink, 1998; Patalano & Seifert, 1994). Each of these scenarios requires the cognitive system at some point to resume a goal that had to be suspended, which in turn involves thinking back to a previous state of the world. The better the system can remember how far it had progressed toward achieving the pending goal, the more accurately and efficiently it can resume the goal. Indeed, properly resuming a task at the right step, without taking redundant actions but also without skipping steps, can be a matter of life and death in domains like aviation (Latorella, 1996).

The question addressed in this article is whether an analysis in terms of memory theory--particularly the constructs of activation and associative priming--can help us understand how the cognitive system remembers its goals. Our hope is to identify cognitive and environmental constraints on how we store goals in memory and retrieve them later. We begin with a brief history of theorizing about cognitive goal structures, to show how and why current theory retains the assumption that goal memory is structurally different from and superior to memory for other facts and events. The review prepares us to argue that this assumption is misleading and needs to be updated to make accurate predictions about goal-directed behavior.

We then develop the goal-activation model, which identifies three constraints on goal-directed behavior: the interference level, the strengthening constraint, and the priming constraint. The interference level is a mental "clutter" of residual memory for old goals, which is simply an instance of interference generally (e.g., Keppel, Postman & Zavortink, 1968; Waugh & Norman, 1965). The strengthening constraint says that the activation of a new goal must be increased to overcome proactive interference. This strengthening process is not instantaneous and therefore predicts a behavioral time lag to encode a new goal. Importantly, this lag is functionally bounded from above, because excessive strengthening raises the interference level by making that goal more likely to capture behavior in the future, when it is no longer the target. The priming constraint says that a suspended (pending) goal can only be retrieved with help from priming from some associated cue, to overcome retroactive interference from intervening goals. The priming constraint has implications for the structure of the task environment, in that the cue to which a goal is associatively linked must be available both when the goal is suspended (in order to create the link) and when the goal is resumed (in order to prime the target).

After an introduction to the goal-activation model, we describe a computational simulation that fits and predicts behavioral data from the Tower of Hanoi puzzle. This puzzle is a means-ends task that exercises the cognitive system's ability to remember old goals, and that affords a chance to test our predictions concerning time lag to encode a goal and the presence of appropriate cues in the task environment. In the General Discussion, we re-examine empirical findings--the intention-superiority effect, in particular--previously taken to support the notion that goals are stored in memory in a special state. We also use the goal-activation model to ask how the cognitive system responds to commonplace interruptions like the telephone ringing, and to suggest directions for further research in this important applied domain. Appendix A develops an algebraic version of the model and works through an example of how to use it to predict the amount of time needed to encode a goal given a particular tempo of goals arising over time. Appendix B elaborates on the computational simulation, describing processes that may be relevant to memory simulations more generally.

2. A special goal memory: from simplifying assumption to theoretical construct