Summary

Sequential behaviour is observed in various domains of cognitive psychology, including free recall paradigms. In this chapter, within a neurocomputational framework resampling (RS) mechanisms are compared with competitive queuing (CQ) mechanisms. While both types of implementations select the most active representation, the subsequent inhibition is at the level of selection for RS models and at the level of (re)activation for CQ models. It is shown that despite the overwhelming success of CQ models in serial recall (with regard to types of sequencing error), RS models outperform CQ models with regard to interresponse times in a free recall task. Additional analyses show that decay of response suppression reduces the difference between the models. The RS model is sensitive to the size of the search set and accounts for memory selection performance in patients with Alzheimer's dementia or Huntington's disease.

Introduction

In many complex systems that exhibit sequential ordering of actions, a selection mechanism converts simultaneously activated representations into a sequence of actions. The simplest form this selection mechanism can take is one by which one action is selected and then executed, after which another action is activated (from zero), selected, and executed, and so on. However, research within psychology has demonstrated that this type of selection mechanism is inconsistent with detailed error analyses in serial recall (Henson et al., 1996) and typing (see Salthouse, 1986), as it would, for example, be unable to account for the smooth transitions between successive actions. Instead, evidence points towards a two-stage mechanism, by which in the first stage all task-appropriate representations are activated in parallel (instead of sequentially), and in the second stage representations are selected one at a time to produce its corresponding action. Although most of the initial knowledge was gathered from motor behaviour, with typing as one familiar example (see the review by Salthouse, 1986, and references therein), researchers have suggested that this two-stage mechanism may also be central to other forms of sequential behaviour, from walking through a room or grasping a mug to producing speech, preparing coffee, or even memorising words. Given the ubiquity of serial ordering in our daily lives, it may come as no surprise that models exist in which simultaneously activated representations produce serially ordered actions. Two of these models are highlighted in this chapter and relate to sequential retrieval from memory.