Grouping in short-term verbal memory: is position coded temporally?

The nature of the mechanisms that code item position in serial short-term verbal recall was investigated with reference to temporal grouping phenomena--effects that arise when additional pauses are inserted in a presented list to form groups of items. Several recent models attempt to explain these phenomena by assuming that positional information is retained by associating items with contextual information. According to two of the models--the Phonological Loop model (Hitch, Burgess, Towse, & Culpin, 1996) and the OSCAR model (Brown, Preece, & Hulme, 2000)--contextual information depends critically on the timing of item presentation with reference to group onset. By contrast, according to the Start-End model (Henson, 1998) and a development from it, which we label the Oscillator-Revised Start-End model (Henson & Burgess, 1997), contextual information is independent of time from group onset. Three experiments examined whether coding of position is time dependent. The critical manipulation was to vary stimulus-onset asynchrony from one group to the next in the same list. Lists of consonants were presented visually, but with vocalization in Experiment 1, auditorily in Experiment 2, and auditorily with articulatory suppression in Experiment 3. The pattern of order errors consistently favoured the predictions of the time-independent models over those of the time-dependent models in that across-group transpositions reflected within-group serial position rather than time from group onset. Errors involving intrusions from previous lists also reflected within-group serial position, thereby extending support for the time-independent models.