The problem of serial order in visuospatial short-term memory

How do we remember the order of a novel sequence of items? Much research has examined
how people remember sequences of verbal stimuli (e.g., digits in a phone number), and several
mechanisms of serial order have been proposed to underlie memory for such sequences. Less
research has examined how people remember the order of sequences of visuospatial stimuli (e.g., a
series of spatial locations), and the mechanisms of serial order underlying such sequences remain
unspecified. This thesis explores the extent to which memory for sequences of visuospatial stimuli
is explicable in term of mechanisms proposed to underlie memory for verbal sequences.
Contemporary models of verbal short-term memory represent serial order either by: (I) using a
competitive queuing sequence planning and control mechanism, by (2) position marking, by (3) a
primacy gradient of activation, by (4) incorporating response suppression, and by (5)
implementing output interference, or through some combination of these mechanisms. Empirical
evidence suggests that all five mechanisms must coexist in any adequate model of serial order
memory for verbal sequences.
In this thesis, I argue that extant data indicating functional similarities between verbal and
visuospatial serial order memory support the idea that visuospatial sequences are planned and
controlled using a competitive queuing mechanism. However, direct evidence for the role of the
four remaining mechanisms of serial order in visuospatial short-term memory is currently lacking. I
present a series of twelve experiments examining memory for visuospatial sequences, combined
with computational modelling work, which sought direct evidence for the role (or lack thereof) of
the different mechanisms of serial order.
The outcomes of the experiments and computational modelling work suggest that the serial
order of a visuospatial sequence is represented by a competitive queuing system, equipped with a
primacy gradient, positional markers, and response suppression. The results therefore buttress the
notion that verbal and visuospatial short-term memory rely on some common mechanisms for the
representation and generation of serial order.