Arousal Asymmetry and Cognition 1
Cognitive Consequences of Individual Differences in Arousal Asymmetry
Thomas Holtgraves
Ball State University
Keywords: arousal asymmetry, creativity, semantic networks
June 5, 2013
CORRESPONDING AUTHOR:
Thomas Holtgraves
Dept. of Psychological Science
Ball State University
Muncie, IN 47306
Email: 00t0holtgrav@bsu.edu
Arousal Asymmetry and Cognition 2
Abstract
Prior research has demonstrated that semantic organization in the right hemisphere (RH) is more
diffuse and specialized for distant semantic associates than is semantic organization in the left
hemisphere (LH). The present research explored individual differences in this regard. If the RH
is more specialized for distant semantic associates, then individuals with a more active RH
should display greater activation of distant semantic associations. Two experiments were
conducted to examine this issue. In both studies a line bisection task was used to assess arousal
asymmetry. In Experiment 1, greater RH activation was associated with the ability to generate
remote associates to three word stimuli. In Experiment 2, relatively greater RH activation was
associated with enhanced priming of distant semantic associates. Taken together, these
experiments demonstrate that arousal asymmetry is an individual difference variable that is
related to variability in semantic organization and retrieval.
Arousal Asymmetry and Cognition 3
Cognitive Consequences of Individual Differences in Arousal Asymmetry
The two hemispheres of the brain are specialized for different functions. For example,
performance on a lateralized word recognition task tends to be superior for the left hemisphere
(LH) relative to the right hemisphere (RH). In addition to hemispheric functional differentiation,
however, there also appear to be individual differences in arousal asymmetry (Levy, Heller,
Banich & Burton, 1983), that is, greater tonic activation of one hemisphere relative to the other.
Several lines of research suggest that are different cognitive and emotional tendencies associated
with the two hemispheres. Research on hemisphericity, for example, has demonstrated trait-like
preferences for different cognitive modes that are associated with each of the two cerebral
hemispheres, and that hemispheric preference can be reliably identified via performance on a
variety of biophysical tasks (Morton, 2001; 2002; 2003). Moreover, hemispheric preference is
related to variability in Corpus Callosum size with right brain oriented individuals having
substantially larger CCs than left brain oriented individuals (Morton & Rafto, 2006). Other
researchers have focused on some of the emotional concomitants of arousal asymmetry (Sutton
& Davidson, 1997; Wheeler, Davidson, & Tomarken, 1993), demonstrating, for example, an
association between LH activation and positive mood. The present research contributes to these
lines of inquiry by examining some of the cognitive consequences of individual differences in
arousal asymmetry.
Hemispheric Specialization, Semantic Priming, and Creativity
The present approach builds upon research demonstrating hemispheric functional
differences in semantic representation and retrieval. One of the earliest and most common
techniques for demonstrating hemispheric differences in semantic organization involved
semantic priming. In these studies semantic priming was found to be roughly equivalent in the
Arousal Asymmetry and Cognition 4
two hemispheres when activation was relatively automatic (short stimulus onset asynchrony
(SOA), masked primes, etc., Neely, 1991) and the prime target pairs were strongly related and
members of the same semantic category (e.g., sofa-chair) (Chiarello, Burgess, Richards, &
Pollock, 1990; Richards & Chiarello, 1995). However, when the stimuli were not associated or
weakly associated category members (e.g., lamp-chair), priming tended to occur only in the RH
and not in the LH (Chiarello, 1985; Chiarello et al., 1990; Chiarello, Maxfield, & Swann, 1996).
These findings suggest that there is passive activation of weakly related category
members within the right but not the left hemisphere (Chiarello, 1998). Further support for this
idea was provided by Beeman and colleagues who demonstrated hemispheric differences in
summation priming (Beeman, Friedman, Grafman, Perez, Diamond, & Lindsay, 1994). They
presented three word primes prior to presenting a target (e.g., scratch). The primes were either
weakly related (cat, attack, paws) or unrelated to a target (church, grease, hurdle), with the target
lateralized to either the right or the left hemisphere. They found greater summation priming in
the RH than in the LH for the weakly related primes, suggesting that the RH is specialized for
the detection of more distant semantic associates.
Overall, then, these studies suggest that both hemispheres activate closely related
semantic information, but that they differ in the nature of that activation. The LH engages in
close semantic coding, activating a restricted set of meanings and quickly settling on a dominant
meaning. In contrast, the RH engages in more diffuse semantic coding, activating many
different meanings and leaving them activated for a longer period of time. These differences are
consistent with a variety of neurological data regarding differences between the right and left
hemisphere (e.g., Jung-Beeman, 2005).
Arousal Asymmetry and Cognition 5
Although there is support for greater activation of distant semantic associates in the RH
relative to the LH, the possibility that individuals with a more active RH might display course
semantic coding to a greater extent than others has not been examined. There is one line of
research, however, that suggests the existence of such a link. Specifically, there is research
demonstrating a relationship between dispositional RH activation and proneness to paranormal
beliefs, and it has been argued that this link is caused by the coarse semantic processing
properties of the RH. For example, Pizzagalli and colleagues demonstrated stronger indirect
priming in the RH for individuals with strong paranormal beliefs relative to nonbelievers
(Pizzagalli, Lehmann, & Brugger, 2001) as well as greater RH activation (Beta waves assessed
with resting EEG) for strong paranormal believers relative to nonbelievers (Pizzagalli et al.,
2000). Relatedly, Taylor, Zach, and Brugger (2002) reported significant correlations between
magical ideation scores and a leftward shift in a line bisection task (and hence greater right
hemisphere activation). It’s possible, then, that the link between RH activation and paranormal
beliefs is partly a function of the tendency of the RH to engage in course semantic processing.
Assessing Arousal Asymmetry
One method for assessing arousal asymmetry is to compare alpha-band EEG readings for
the right and left hemispheres (e.g., Davidson, Ekman, Saron, Senulis, & Friesen, 1990).
However, faster and less cumbersome techniques have been developed that involve behavioral
tasks. One well-known measure in this regard is the line bisection task. With a line bisection
task, participants are asked to locate the center of a line by marking the line to indicate what they
perceive to be the middle point. The logic of the task is that participants tend to over-attend to a
stimulus when it is processed by the more active hemisphere. Hence, when bisecting a line, those
with a more active RH will tend to bisect to the left of the midpoint (because they over-attend to
Arousal Asymmetry and Cognition 6
the left side); those with a more active LH bisect to the right of the midpoint. An alternative
procedure is to ask participants to indicate which half of an evenly bisected line is larger
(sometimes referred to as the Landmark task), a task that is entirely perceptual. Some evidence
for the validity of line bisection task comes from the observation that people with RH damage
consistently under-perceive the left side of a line and hence err to the right of center when
making line judgments (Cappa, Guariglia, Messa, Pizzamiglio, & Zoccollotti, 1991; Damasio &
Damasio, 1980; Vallar & Perani, 1986). In contrast, intact controls tend to err to the left side
reflecting an overall RH attention bias, referred to as pseudoneglect (Jewell & McCourt, 2000).
Electrophysical/imaging research suggest that this is due to the role of the RH in early visual
attention (Çiçek, Deouell,& Knight, 2009).
Importantly, however, there is considerable individual variability in line bisection
performance (Manning, Halligan, & Marshall, 1990), and this variability is associated with
differential hemispheric activation (Bjoertomt, Cowey, & Walsh, 2002; Oliveri, Bisiach,
Brighina, Piazza, La Bua, Buffa, & Fierro, 2001).
Most relevant for the current research,
Marsh, Fogle, Simon-Dack, Davis, Lemann, Parkison, & Holtgraves (2012) and Nash,
Mcgregor, & Inzlicht (2010) have demonstrated that participants whose line bisection
performance indicated greater RH activation displayed significantly lower alpha (an inverse
indicator of cerebral activity) in the RH (but not LH) relative to other participants. Moreover,
research has demonstrated that individual differences associated with negative affect (He, Chai,
Zhang, Yu, Chen, & Wang, 2010) and motivation (Nash, Mcgregor, & Inzlicht (2010 ) are
significantly related to performance on the line bisection task. Regarding the former, He et al.
report a significantly greater leftward bias in Generalized Anxiety participants relative to healthy
participants. Regarding the latter, Nash et al., demonstrated an increased rightward line bisection
Arousal Asymmetry and Cognition 7
bias for high (but not low) self-esteem participants when they were challenged (paralleling EEG
measures of prefrontal asymmetry when challenged). Hence, individual differences and
situational variables associated with hemispheric asymmetries can be detected with line bisection
tasks.
The Present Research
Two experiments were conducted to examine individual differences in arousal
asymmetry and its likely relation to differences in the activation of semantic associates. In both
experiments arousal asymmetry was assessed with a computerized line perception task. The first
experiment examined the relationship between arousal asymmetry and the ability to generate
remote associates to three word stimuli. The second experiment examined differences in
summation priming (Beeman et al., 1994) as a function of arousal asymmetry. If the RH is
specialized for distant semantic associates as prior research suggests, then individuals with a
more active RH should display greater activation of distant semantic associates relative to other
individuals.
Experiment 1
In this study the relationship between arousal asymmetry and the ability to generate
distant semantic associates was examined. To do this, participants completed a version of the
line bisection task and attempted to solve remote associates problems (modeled after the Remote
Associates Task, Mednick, 1962), a widely used measure of creative thinking and insight. For
the latter task, participants were asked to produce a solution word (e.g., air) in response to three
stimulus words (e.g., force, line, mail). It was expected that individuals with a more active RH
would be better at this task than would others.
Method
Arousal Asymmetry and Cognition 8
Participants. Participants (N = 78; 48 Females) were undergraduate students enrolled in
Introductory Psychology courses who participated for partial course credit. All participants
spoke English as their first language. The data from four participants (two males and two
females) were excluded because they failed to provide judgments on at least two of the ten
critical lines. In preliminary analyses there were no main effects or interactions involving
participant sex and this variable was excluded from subsequent analyses.
Materials. A computerized line perception task was developed for the current research.
The line bisection task consisted of 20 bisected lines presented on the computer screen. Ten of
the lines were bisected in the middle and constituted the critical trials. Filler trials included 5
lines that were bisected 1/16 in. to the right and 5 lines that were bisected 1/16 in. to the left.
Lines not bisected in the center were included so as to identify participants who were responding
randomly (no participants were excluded due to random responding) and to prevent participants
from realizing that all stimuli were the same and responding randomly without given a true
decision (Luh, 1995). The 20 lines were presented (four each) in lengths of 2 in., 3 in., 4 in., 5
in., and 6 in. Degree of RH activation was defined as the number of times a participant chose the
left half of an equally bisected line.
A 20 item associates test was constructed for this study. Ten of these items were
compound associates and consisted of sets for which the solution created a compound word (e.g.,
cream, skate, water – ice). These sets were randomly selected from a list provided by Bowden
and Jung-Beeman (2003) and were of moderate difficulty (in the Bowden and Jung-Beeman
study the mean percentage of these items that were solved was 54.7%). The other ten items were
remote associates and had solutions that were conceptually related but did not need to form
compound words (e.g., strike, same, tennis – match). These items were randomly selected from
Arousal Asymmetry and Cognition 9
the items used in Bowers, Regehr, Balthazard, and Parker (1990) and were more difficult than
the compound problems with a reported solution rate of 21.9%. All items are included as
supplementary material.
Finally, because of some suggestions in the literature regarding a correlation between
handedness and arousal asymmetry (Hellige, 1993) it was deemed wise to assess handedness and
treat it as a covariate. Hence, participants completed the Edinburgh measure of handedness
(Oldfield, 1971).
Procedure. Participants first completed the Edinburgh measure of handedness (Oldfield,
1971), followed by the line bisection task and then the associates test. For the latter two tasks
participants were seated approximately 57 cm in front of a computer screen and their head
stabilized and held in position with the UHCOTech HeadSpot. Participants were told that lines
would appear on the screen, and that each of these lines was bisected at a point near (but not
exactly at) the middle. They were told to look at each line and indicate which of the two halves
of the line they perceived to be the longest. Participants proceeded through the task at their own
pace and stimulus presentation order was randomized for each participant. Participants then
completed the 20 item associates task. For this task, the three stimulus words were presented on
the screen for up to 15 sec., during which participants were to type a word that was common to
all three. Presentation order was randomized for each participant.
Results and Discussion
Scores on the total associates test varied between 1 and 11 (out of a maximum possible
score of 20) with a mean of 6.01 (SE = .32). Scores on the line bisection task (number of times
left side was chosen as larger) varied between 0 and 10 (out of a maximum possible score of 10)
with a mean of 5.62 (SE = .24). Consistent with past research (Bowers & Heilman, 1980), there
Arousal Asymmetry and Cognition 10
was a left side (RH) bias (i.e., pseudoneglect) as indicated by an overall mean of 5.62 that was
significantly different from the scale midpoint of 5, t(73) = 5.62, p < .05).
The relationship between performance on the line bisection task and the associates test
was analyzed using both correlational techniques and mean differences. In terms of the former,
partial correlations (with handedness treated as a control variable) between line bisection
performance and associates test performance were computed. There was a significant positive
correlation between line bisection performance and the overall associates test, r = .31, p < .01.
Hence, the more frequently the left side was chosen as larger the greater the number of associates
that were correctly generated. Subsequent analyses indicate that this relationship was significant
for the compound items (r = .32, p < .01) but not for the non-compound items (r = .153, p < .20).
Next, on the basis of a median split, participants were classified as RH active if they
chose the left side of the equally bisected line on seven or more trials (N = 29; 15 females).
Performance on the associates test was analyzed with a 2 (Active Hemisphere; Right Active,
Non-Right Active) X (2) (Stimulus Type; Compound, Non-compound) Analysis of Covariance
(ANCOVA) with repeated measures on the second factor and scores on the Edinburg handedness
measure treated as a covariate. The covariate was significant in this analysis, F(1, 70) = 9.7, p <
.01. There was a marginally significant main effect for hemisphere, F(1,70) = 3.62, p = .06.
Right hemisphere active participants performed marginally significantly better on the associates
test (M = 6.74; SE = .49) than did Non-Right Hemisphere Active participants (M = 5.53; SE =
.40). In this study, then, increasing RH tonic activation, as assessed with the line bisection task,
was associated with an increased ability to generate associates that were related to each of three
words in a stimulus set.
Arousal Asymmetry and Cognition 11
Experiment 2
This experiment examined performance on a summation priming task as a function of
individual differences in arousal asymmetry as assessed with performance on the line bisection
task. The summation priming task was a modification of the task used by Beeman et al. (1994).
In their study, three word primes were presented simultaneously in the center of the screen,
followed by a target that was presented to either the left visual field (LVF) and hence initially
processed by the RH, or to the right visual field (RVF) and hence initially processed by the LH.
In the present study, the targets were presented centrally rather than being lateralized to the right
or left hemisphere, and performance on the lexical decision task was examined as a function of
individual differences in arousal asymmetry. If the RH is specialized for detecting diverse
semantic associates as demonstrated by Beeman et al. (1994), then it follows that individuals
who display greater arousal in the RH should show relatively greater priming effects with this
task. Hence, although an overall summation priming effect was expected, it was also expected
that participants with a more active RH would show greater summation priming effects than
others.
Method
Participants. Participants (N=130; 86 Females) were undergraduate students enrolled in
Introductory Psychology courses who participated for partial course credit. All participants spoke
English as their first language. The data from two participants was excluded because of missing
judgments on at least two of the ten critical lines in the line bisection task.
Materials. The line bisection task was the same one used in Experiment 1 (10 critical
evenly bisected lines and 10 filler lines). The materials for the summation priming task were the
summation (N = 24) and unrelated (N = 24) triads taken from Beeman et al. (1994). The
Arousal Asymmetry and Cognition 12
summation sets involved three words (e.g., cat, attack, paws) weakly related to the target (e.g.
scratch); the unrelated sets involved three words that were unrelated to the target. Two lists of
prime – target pairs were constructed and constituted two versions of the task. Participants were
randomly assigned one of the two versions. The lists were mirror images of each other: if the
target was preceded by the summation primes in one list it was preceded by the unrelated primes
in the other list. In this way, across the experiment, each of the 48 targets was preceded by the
summation primes and unrelated primes an equal number of times.
Procedure. Participants completed, in order, the Edinburgh handedness inventory
(Oldfield, 1971), the line bisection task and the summation priming task. The first two tasks were
identical to those used in Experiment 1. For the priming task, participants first heard a 500-Hz
tone and saw an orienting screen with a fixation cross in the center for 250 ms. The three prime
words (stacked in a vertical order) then appeared in the center of the screen for 2000 ms. This
was followed by a 300 ms screen with a fixation cross accompanied by a 500-Hz tone. The
target was then presented in the center of the screen. Participants were instructed to indicate, as
quickly as possible, whether or not the target was a word. The manual response options consisted
of two keys on a response box marked Yes/No. Participants were instructed to push the Yes key
if the letter string was a word and the No key if the letter string was not a word.
Participants had 3000 ms to respond. For 48 trials (24 summation prime trials and 24 unrelated
prime trials) the target was a word and hence the correct answer was yes. To ensure that
participants did not develop the expectation that the target string was always a word, there were
48 non-word trials in which the target string was a pseudo-word (e.g., pister, clins, smates) and
hence the correct answer was no. The format of the non-word trials was identical to that of the
48 critical trials. Immediately after making a judgment, feedback (correct/incorrect and response
Arousal Asymmetry and Cognition 13
time) was provided on the screen for 1500 ms. Feedback was provided in order to motivate
participants. Presentation order was randomized for each participant.
Results and Discussion
As in Experiment 1, a participant was considered to be right hemisphere activate (N = 56)
if she or he judged the left side to be longer on seven or more trials, and scores on the
handedness measure were treated as a covariate. Overall accuracy for this experiment was
96.4% and did not differ as a function of prime (96.1% vs. 96.8%), F < 1, or hemisphere
activation (96% vs. 96.8%), F < 1.
The overall priming effect was reliable as participants were significantly faster judging
targets following primes (M = 538 ms; SE = 6.73) than following unrelated words (M = 555 ms;
SE = 7.24), F(1,125) = 8.52, p < .01. The handedness covariate was significant, F(1,125) = 4.16,
p < .05 and there was no difference in response time as a function of hemisphere activation,
F(1,125) = 1.92, p > .15. However, as expected, there was a significant Hemisphere X Prime
interaction, F(1,125) = 6.45, p < .05, and the difference between unrelated and summation
primes was significant for right active participants (M = 569; SE = 10.99 vs. M = 544; SE =
10.21), F(1,54) = 14.65, p < .001, but not for non-right active participants (M = 541; SE = 9.67
vs. M = 533; SE = 8.98), F< 1. In other words, participants with a more active RH demonstrated
distant semantic priming; other participants did not.
An alternative analysis was conducted in which only strongly right-handed participants
(defined as participants with a score of 0 on the left-hand scale of the Edinburgh) were included
and handedness as a covariate was dropped. The Hemisphere X Prime interaction remained
significant in this analysis, F(1, 57) = 7.73, p < .01. As in Experiment 1, correlation analyses
were also conducted. In this case the correlation between priming (mean response time for the
Arousal Asymmetry and Cognition 14
unrelated trials minus mean response time for the summation trials) and performance on the line
bisection task (number of trials the left side was selected as larger) was computed. This
relationship was in the predicted direction but not significant (r = .14, p < .14).
General Discussion
The present research was designed to investigate some of the cognitive consequences of
individual differences in arousal asymmetry. Prior research has demonstrated that semantic
organization is more diffuse in the RH than in the LH. Specifically, when weakly related or
nonassociated primes are used, stimuli presented initially to the RH typically produce greater
priming than stimuli presented initially to the LH. The present research sought to test the
hypothesis that there is an individual difference corollary to this effect. Specifically, it was
expected that people with a more active RH should be more likely to display the RH course
semantic effects typically found in divided field studies. The present studies provide some
support for this extension. Experiment 1 suggests that greater RH activation may be associated
with an enhanced ability to generate remote associates to three word stimuli. And in Experiment
2, participants demonstrating greater RH activation displayed enhanced priming of distant
semantic associates relative to other participants. Taken together, these experiments demonstrate
that arousal asymmetry is an individual difference variable that is related to variability in
semantic organization and retrieval.
The present results have implications for several areas of research. First, the concept of
hemisphericity suggests that there are different thinking and behavior styles associated with
which of the two hemispheres predominates for an individual. One cognitive dimension of
hemisphericity is the association of the right brain with global processing and the left brain with
local processing. The activation and generation of distant semantic associates, as examined in the
Arousal Asymmetry and Cognition 15
two experiments reported here, can be considered instances of global processing. Hence, the
present finding of more distant semantic processing being associated with greater RH activation
is consistent with this conceptualization of hemisphericity. Although research on hemisphericity
fell out of favor for a period of time due to the lack of reliable tasks for assessing left-brain vs.
right-brain orientation, newer assessment techniques and conceptualizations (e.g. Morton, 2001,
2002, 2003) have provided some empirical support for this concept.
Second, the present findings provide some support for a mechanism that may underlie the
relationship between RH activation and a proneness to paranormal beliefs. Past research has
demonstrated that people with a proneness to paranormal beliefs demonstrate enhanced RH
activity (Pizzagalli et al., 2000). But why? It has been suggested that a proneness to paranormal
beliefs may reflect a more active network of loose semantic associations, in other words course
semantic coding (Pizzagalli, Lehmann, & Brugger, 2001). The present results provide some
empirical support for this reasoning by demonstrating an association between dispositional RH
activation and the ability to generate and comprehend distant semantic associates. Further
research could examine this more directly by examining the relationship between paranormal
belief proneness and course semantic coding in the two hemispheres as assessed with the tasks
used in the current research.
Third, the tendency for the RH to engage in more diffuse processing suggests that it may
play a particularly important role in certain types of creativity. Although the empirical literature
on the neural correlates underlying creativity is relatively unclear (Dietrich & Kanso, 2010),
there have been some studies reporting RH specialization, in particular the right superior
temporal gyrus (STG), for convergent creativity, especially in terms of the experience of insight
(Bowden, Jung-Beeman, Fleck, & Kounios, 2005; Jung-Beeman, Bowden, Haberman, Frymiare,
Arousal Asymmetry and Cognition 16
Arambel-Liu, Greenblatt, Reber, & Kounios, 2004; Kounios, Frymiare, Bowden, Fleck,
Subramaniam, Parrish, & Jung-Beeman, 2006). For example, participants in the Jung-Beeman et
al. study attempted to solve verbal problems (i.e., generating semantic associates) and indicated
whether they were solved with or without insight. Imaging results demonstrated that problems
solved with insight were associated with increased activity in the right hemisphere anterior
superior temporal gyrus. EEG readings in a second experiment demonstrated a burst of gamma
activity in the same area immediately prior to insight solution. This area is associated with the
making of connections between distant semantic associates and hence is consistent with the
present findings.
The present results suggest several additional issues for further research. One issue is
whether functional differentiation and arousal asymmetry would combine in an additive manner.
For example, Levine, Banich, & Koch-Weser (1984) demonstrated a right visual field (RVF)/LH
advantage on a word recognition task and a left visual field (LVF)/RH advantage on a face
recognition task. However, individuals differed with respect to the size and direction of these
advantages; individuals with a more active LH showed a stronger LH advantage for the word
recognition test, and a smaller RH advantage for the face recognition task, relative to participants
with a more active RH. Also, Tamagni, Mantei, & Brugger (2009) examined emotion word
recognition as a function of both visual field presentation and individual differences in
hemispheric attention (assessed with a line bisection task). Superior recognition of negatively
valenced over positively valenced words occurred for participants who were left bisectors (and
hence individuals who rely more on RH functions). Moreover, these individuals displayed better
overall recognition accuracy for words presented to the LVF than words presented to the RVF.
Applying this to the present research, if the targets in Experiment 2 were lateralized to the right
Arousal Asymmetry and Cognition 17
or left visual field rather than presented centrally, the expectation would be that even though
there would be an overall tendency for superior RH performance (functional differentiation),
individuals with a more active RH would display this effect to a greater extent than others.
Arousal Asymmetry and Cognition 18
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Author notes
The author wishes to thank Adam Felton, Kevin Cappaert, and Joe Waters for their assistance in
collecting data used in this study. This research was partially supported by a grant from the Ball
State University Aspire grants program.