Discussion
The present study examined the effects of cognitive load and emotional
faces on WM performance using modified Aospan. The primary hypothesis of
the current study was to examine how the distractors with different
levels of cognitive load may affect the WM performance of emotional
facial processing. The second objective was to examine the effect of
emotional faces on WM performance. Overall the results confirmed proper
manipulation of different distraction tasks as participants performed
better in the low level of distraction than the high level of
distraction. This also confirms the design that cognitive load was lower
in the low than the high level of distraction and participants consumed
less WM resources when performing the mathematical equations with fewer
operands than larger operands. Utilizing varying levels of mathematical
equations is effective in manipulating different amount of cognitive
load, and these different levels of cognitive load affect performance of
WM span.
Regarding the impact of cognitive load on WM performance, it was found
that when participants were presented with distractor of low cognitive
load, WM performance was not affected. However, in exposure to
distractor of high cognitive load WM was significantly impeded. The
cognitive load of distracting tasks in the modified Aospan are divided
into three levels, with the difference in performance of WM span between
difficult and control condition being the most prominent. In other
words, the difficult distracting task taxes the highest cognitive
resources thereby diminishing the WM span performance to the greatest
degree. This result is consistent with the previous studies (Allen et
al., 2017; Lavie, 2005; O’toole et al., 2011) contradictory that
increasing the cognitive load of the distractor has a vast impact in WM
performance. When there are two or more incoming stimuli that need to be
processed, priority must be assigned to one or the other at a given
time. To allocate cognitive resources appropriately between the two
competing resources, the WM model (Baddeley & Hitch, 1974) explains
that a critical component named the central executive plays a pivotal
role in this moment (Baddeley, 2012). The central executive acts as a
guide for the delegation of resources and attention allocation of
resources to manage and maintain information in mind during the task.
Under low cognitive load, this component is working adequately but when
cognitive load increases, the WM is affected reflecting the limited
capacity of attentional resources and WM span.
The present findings are also consistent with the assumption of the TBRS
model which suggests that WM functions to temporarily store items and
process information, and these function are fueled by limited
attentional resources (Geday, Kupers, & Gjedde, 2007; Vergauwe,
Barrouillet, & Camos, 2009). The TBRS model also states that the
cognitive load of a given event corresponds to the proportion of time
(Geday et al., 2007). In terms of the complex span paradigm, the TBRS
model explains that the recall performance of storage component should
be a function of the cognitive load of the processing component of the
span task. This trade-off is due to the limited-capacity mechanism of WM
suggested by Baddeley (2012). The present findings are in line with
their suggestion in terms of the limited-capacity nature of WM. It is
suggested that both the processing component (mathematical equations
solving) and storage component (serial recall of emotional faces)
require visuospatial WM, another component proposed by the WM model.
This component provides a virtual environment for physical simulation,
calculation, visualization and optical memory recall. It is a part of
the WM that holds information during the initial processing to produce
the recollection of an image such as a place or a face. Therefore, the
current results revealed a trade-off between the two processes
(emotional facial processing and calculation). This is consistent with
the proposal of the limited-capacity mechanism of WM. As a result, the
higher the cognitive load is, the lower the levels of performance are.
Regarding the effect of emotional faces on WM performance, the results
showed no significant effect of emotional face on WM performance.
Although previous studies such as Craig et al. (2014) lend support to
the happiness superiority effect, wherein positive facial stimuli were
found to be processed more quickly than negative and neutral ones in
their visual search task. However, such effect was not apparent in the
current study as the type of emotional stimuli being processed did not
affect the WM performance. In an explanatory manner, participants were
not influenced by the emotions of facial stimuli (bottom-up attention)
when preforming the task. In fact, a study has investigated the
strategies used in complex span paradigm and found using strategies such
as imagery (Bailey, Dunlosky, & Kane, 2011). They found that
participants used encoding strategies such as chunking of verbal
letters. In this study, although the non-verbal emotional faces can
prevent participants from rehearsing or chunking, they plausibly employ
alternative methods to facilitate WM performance. For example, they have
associated a name for each emotional face based on its features to help
with their memory performance.
A key limitation of the current study is that participants were not
asked to report the emotionality of the facial stimuli they were exposed
to, it remains inconclusive as to whether emotions have no impact on WM
or that the participants did not perceive the stimuli as emotionally
arousing. Future studies should address this by asking participants to
rate the emotionality of the stimuli in the experiment. As the study has
only used three different types of emotional faces. The non-significant
results might have been attributed to this. In support of this
assumption, previous studies (e.g., Craig et al., 2014; O’toole et al.,
2011) have used other emotional stimuli such as threat related stimuli.
It was found that threatening or angry faces elicited a bigger effect
(also known as Anger Superiority Effect) on capturing attention compared
to general happy or sad faces. In future studies, more salient emotional
facial stimuli are recommended. If the emotionality of faces is more
prominent, participants may elicit stronger emotional responses toward
them. As the current results are not consistent with the TBRS model
(Barrouillet et al., 2004), the modified version of Aospan in the
present study with varying cognitive load can be further verified by the
TBRS model in the future to address the following questions. First, it
has been found that affective state of individuals may either improve or
diminish the WM performance, however, few studies (e.g. Yang, Yang, &
Isen, 2013) have examined the effects of current mood state on WM using
complex span paradigm. Second, the current modified Aospan used
emotional facial stimuli as to-be-remembered items, future studies may
employ emotional words, aversive or appetitive stimuli to investigate
whether these non-verbal but meaningful stimuli have effects on WM
performace because these stimuli are of evoluationarily importance.
In conclusion, the current study modified the Aospan in which changed
the to-be-remembered items to emotional faces and varied the cognitive
load by means of different levels of mathematical equations. In
consideration of the non-verbal nature of emotional facial stimuli, the
time limit plus 3 SD was applied for differences in ability of
individuals. The effect of emotional faces on WM performance was
non-significant. Instead, the results reveal a main effect of cognitive
load on WM performance. These findings add evidence to the TBRS model.
Acknowledgements
We thank Aospan for providing us the software for data collection.
Compliance with ethical standards
All procedures performed in our experiments involving human participants
were in accordance with the ethical standards of the institutional
and/or national research committee and with the 1964 Declaration of
Helsinki and its later amendments or comparable ethical standards. The
experiment reported here was approved by the Local Ethical Committee of
the University of Salford.
Informed consent
Informed consent was obtained from all individual participants included
in the study.
Conflict of interest
The authors declare that the research was conducted in the absence of
any commercial or financial relationships that could be construed as a
potential conflict of interest.