Brain and Cognition 64 (2007) 201–207
www.elsevier.com/locate/b&c
Processing spatial–temporal information in recent-onset
schizophrenia: The study of short-term memory and
its susceptibility to distraction
Caroline Cellard
a,b,*
, Sébastien Tremblay
b
a,b
, Catherine Lehoux
b,c
, Marc-André Roy
b
a
École de psychologie, Université Laval, Québec, Canada G1K 7P4
Centre de recherche Université Laval Robert Giffard, Beauport, Canada
c
Hôtel-Dieu de Lévis, Lévis, Québec, Canada
Accepted 3 March 2007
Available online 25 April 2007
Abstract
Memory impairment is a core feature in schizophrenia (SZ). The aim of this study was to investigate short-term memory (STM) and
its sensitivity to distraction with visual–spatial material. This study comprised 23 recent-onset SZ patients and 23 healthy controls. The
degree of disruption upon recall from interleaving irrelevant items within a sequence of to-be-remembered items—the sandwich effect
[Hitch, G. J. (1975). The role of attention in visual and auditory suffix effects. Memory and Cognition, 3, 501–505]—was examined.
STM performance, whether in the presence or absence of distraction, was poorer and markedly more vulnerable to disruption in SZ.
Our results suggest that processing spatial information in STM is susceptible to interference in SZ.
Crown copyright Ó 2007 Published by Elsevier Inc. All rights reserved.
Keywords: Schizophrenia; Spatial information; Short-term memory; Serial memory; Distraction; Selective attention; Recent-onset
1. Introduction
Many researchers view attentional control and shortterm memory (STM) processing dysfunctions in schizophrenia (SZ) as core features of the disorder. However,
most, if not all, of the work on STM and its interaction
with selective attention has focused on processing of verbal
items. Yet, processing of spatial information seems to be
particularly affected in SZ (Park & Holzman, 1992) and
it is not clear whether dysfunctional attentional processes
are responsible, at least in part, for the observed deficits
in spatial STM (see Lee & Park, 2005, for a discussion).
In the current study, we examine the capacity to remember
temporal–spatial information over the short-term and its
susceptibility to distraction within a paradigm well established in experimental cognitive psychology: the sandwich
*
Corresponding author. Address: École de psychologie, Université
Laval, Québec, Canada G1K 7P4. Fax: +418 656 3646.
E-mail address: caroline.cellard@crulrg.ulaval.ca (C. Cellard).
paradigm (Hitch, 1975; Tremblay, Nicholls, Parmentier,
& Jones, 2005).
The interplay of STM and selective attention is usually
investigated through the manipulation of distraction, either
present or absent when a sequence of to-be-remembered
(TBR) items is learned. Oltmanns and Neale (1975) developed a procedure known as the Digit Span Distractibility
Test (DSDT), in which irrelevant items (digits said in a
female voice) are interleaved with TBR items (digits read
in a male voice). If, for serial recall of spoken lists, irrelevant items are interpolated between TBR items, there is a
significant increase in recall errors for SZ patients as well
as for healthy participants (e.g., Corrigan & Green, 1991;
Harvey & Pedley, 1989; Oltmanns, 1978; Oltmanns &
Neale, 1975; Rund, 1989). However, this limitation is more
pronounced in SZ. Typically, SZ patients recall fewer items
than controls whether the TBR list is presented with or
without interleaved distractors but the presence of distractors has a much greater impact on recall for SZ patients.
Indeed, for a list of six digits, the magnitude of disruption
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C. Cellard et al. / Brain and Cognition 64 (2007) 201–207
can reach up to 46% in the recall performance of SZ
patients and up to 26% for healthy subjects (Frame & Oltmanns, 1982; see Spring, Weinstein, Freeman, & Thompson, 1991, for a meta-analysis).
In the study of normal cognition, a procedure similar to
that of the DSDT is referred to the sandwich effect paradigm (e.g., Hitch, 1975). The mere interpolation of auditory irrelevant items within a sequence of TBR items
produces a robust but small deleterious effect upon serial
recall (e.g., Baddeley, Papagno, & Andrade, 1993; Nicholls
& Jones, 2002). The so-called sandwich effect has recently
been replicated with lists of visual–spatial items (Tremblay
et al., 2005), using the dot task, regarded as a good analogue of the typical verbal serial recall task and a procedure
that minimizes the possibility that spatial information be
verbally recoded (see Jones, Farrand, Stuart, & Morris,
1995). When seeking if a verbal memory phenomenon
can be reproduced in the spatial domain it is critical to
ensure that the TBR information is truly spatial and nonverbal.
In SZ, there is a relative dearth of studies on spatial
STM, especially for temporal–spatial information and the
effect of visual–spatial distraction. From reviewing the literature, it seems consistent across studies that spatial
STM is impaired (but see Salame, Danion, Peretti, & Cuervo, 1998, for a different view), though the variability in the
procedures is considerable. There is ample evidence that
processing of spatial information is dysfunctional as
observed in variants of delayed response and delayed perceptual discrimination tasks (e.g., Park & Holzman, 1993;
Tek et al., 2002). Typically, in such tasks, a target is briefly
displayed, followed by a delay, and then, participants have
to respond by locating or detecting the target. Those tasks
are very different to serial recall procedures in terms of
memory load and response requirements. With regard to
serial recall or sequence reproduction of spatial material
(e.g., the Corsi block task), most researchers have observed
marked deficits (Fleming et al., 1997; Fraser, Park, Clark,
Yohanna, & Houk, 2004; Stone, Gabrieli, Stebbins, & Sullivan, 1998), while some others failed to find a significant
difference between SZ patients and controls (see Clare,
McKenna, Mortimer, & Baddeley, 1993). However, the
balance of evidence weighs strongly for a genuine impairment, and thus supports the claim that the deficit in STM
processing is not restricted to verbal material (see, e.g.,
Chey, Lee, Kim, Kwon, & Shin, 2002).
According to Fischer (2001) there are two key components in spatial serial recall procedures that contribute to
the memory load: serial order and spatial location. This
observation also applies to verbal serial recall, which
requires processing item and order information. In the case
of spatial material, the location of the blocks (Corsi block
task) or dots (dot task) represents item information. Using
a computerized version of the Corsi block task, Dreher and
his collaborators (2001) developed variants of the task that
selectively tap either on spatial recall (item) or temporal
recall (order). They obtained a significant difference in per-
formance between the SZ group and the healthy subjects
on the spatial but not on the temporal version of the task.
The latter pattern of results observed in the spatial domain
suggests that item memory is altered in SZ rather than
order memory (see also Fraser et al., 2004); which parallels
with the finding that order memory is preserved in verbal
serial recall (Elvevag, Weinberger, & Goldberg, 2001).
To our knowledge, the impact of visual–spatial distraction on STM for visual–spatial information has never been
tested in SZ. In the case of verbal serial recall, there is
ample evidence that SZ patients are more sensitive to distraction than controls. One key question is whether this
pattern of distraction with recall also extends to spatial
STM. Based on what is probably the most influential
model of STM, the so-called Working Memory (WM)
model (Baddeley, 2003; see also Baddeley & Hitch, 1974),
one could expect to find a different pattern of distraction
for spatial STM. A key assumption of the WM model is
that STM is divided into separate subsystems such as the
visual–spatial sketchpad and the phonological loop
(respectively responsible for processing visual images and
verbal material). This view is based around the premise
that the cognitive architecture is divided into separate modules, such as verbal or spatial components. However, there
is accumulating evidence, that, at least for processing serial
order, spatial and verbal STM are functionally equivalent.
Both show similar serial position curves, with primacy and
marked recency effects (e.g., Jones et al., 1995; Smyth &
Scholey, 1996) and are sensitive to interference effects or
distraction (e.g., Tremblay, Macken, & Jones, 2001;
Tremblay et al., 2005). In order to test whether the susceptibility of STM to distraction, for spatial material, is more
pronounced in SZ than in healthy controls, we propose to
employ the visual–spatial version of the sandwich paradigm. This will allow us to determine whether the type of
deficits reported for verbal STM (e.g., Corrigan & Green,
1991; Harvey & Pedley, 1989; Oltmanns, 1978; Oltmanns
& Neale, 1975; Rund, 1989) is also found with spatial
material, that is, a greater impact of distraction in patients
with SZ in comparison with healthy controls. In addition,
we chose to test the previously mentioned hypotheses with
recent-onset participants to minimize the risk of a prevalence bias (i.e. the tendency for prevalent cases being more
likely to include an overproportion of more severe cases
more likely to show more severe neuropsychological
impairment; Lehoux et al., 2003; Roy et al., 2003).
2. Method
2.1. Participants
The total sample included 46 participants [23 recentonset SZ patients (19 males, 4 females) and 23 healthy controls (19 males, 4 females)] (see Table 1). All patients were
outpatients suffering from SZ [paranoid (n = 19), undifferentiated (n = 3), disorganized (n = 1)] with a mean duration of illness of 26 months. They were all treated with