Embed Size (px)
Citation preview
The Effect of Handedness on the Functional Asymmetries of Motor Planning and Spatial
Functions
Candidate: Eleanor Charlotte Hanson
Supervisor: Dr Deborah Serrien
Degree: BSc Psychology
1
Contents
Abstract ............................................................................................................................................... 2
Introduction ........................................................................................................................................ 2
Method ................................................................................................................................................ 8
Design ............................................................................................................................................... 8
Participants ....................................................................................................................................... 9
Measurements ................................................................................................................................... 9
Apparatus/Materials ......................................................................................................................... 9
Procedure ........................................................................................................................................ 11
Results ............................................................................................................................................... 11
Pre-Analysis ................................................................................................................................... 11
Line Bisection Task – Directional Deviations ............................................................................... 12
Line Bisection Task – Absolute Deviations ................................................................................... 12
Tapping Task - RTs ........................................................................................................................ 13
Tapping Task - IRIs ........................................................................................................................ 14
Right-Handed Group Correlations ................................................................................................. 15
Discussion .......................................................................................................................................... 16
Main Findings................................................................................................................................. 16
Spatial Functional Asymmetry and the Line Bisection Task ......................................................... 17
Motor Planning Functional Asymmetry and the Finger Tapping Task .......................................... 18
Limitations and Future Research .................................................................................................... 19
Conclusion ...................................................................................................................................... 20
References ......................................................................................................................................... 21
Appendices ........................................................................................................................................ 30
Appendix 1: Personal details and extra-curricular activity questionnaire ...................................... 30
Appendix 2: Handedness inventory ............................................................................................... 31
Appendix 3: Information sheet ....................................................................................................... 32
Appendix 4: Line bisection task instructions ................................................................................. 33
Appendix 5: Tapping task instructions ........................................................................................... 33
Appendix 6: Debrief sheet .............................................................................................................. 33
2
Abstract
Handedness reflects cerebral lateralisation of the two brain hemispheres, however certain
neural functions are also lateralised across the hemispheres and thus represent functional
asymmetries. This experiment aimed to investigate if overall cerebral lateralisation has an effect on
the functional asymmetries of motor planning, which is dominant in the left hemisphere of the brain,
and spatial functions, which is dominant in the right hemisphere of the brain. Both right- and non-
right-handed participants completed a finger tapping task to assess the motor planning functional
asymmetry and a line bisection task to assess the spatial functional asymmetry. A significant
interaction between hand used and handedness was found for reaction times (RTs) in the tapping task,
but no effect of handedness was found in the line bisection task, thus suggesting that although
handedness has an effect on the motor planning functional asymmetry it does not affect all functional
asymmetries.
Introduction
Asymmetry has been observed across biological systems (Kimura, 1973) from single-celled
organisms to human beings and in particular this has been observed in the human brain (Beaton, 1997;
Geschwind & Galaburda, 1985a). This is known as the lateralisation process and is essential in
organising brain functioning (Liu, Stufflebeam, Sepulcre, Hadden, & Buckner, 2009) as it contributes
to the development of language amongst humans as well as reasoning and it provides an “axis for
specialisation of cortical systems” (Liu, et al., 2009, p. 20499).
There are many factors (e.g. genetics, neurochemistry, environmental, etc.) that have been
argued to contribute to the lateralisation process. For example, genetic factors have been implicated
as there are prominent structural asymmetries within the brain that are present from birth (Gilmore,
et al., 2004; Witelson & Pallie, 1973) and studies of twins also reveal high heritability estimates
(Geschwind, Miller, DeCarli, & Carmelli, 2002). However, Geschwind and Galaburda (1985a,
1985c) suggested in their hypothesis that testosterone levels within the intrauterine environment cause
the brain asymmetries and therefore, there is a neurochemical factor contributing to lateralisation.
Furthermore, with regard to genetic models, no specific gene has yet been identified as the direct
cause of lateralisation but a number of genes have been implicated (Lai, Fisher, Hurst, Vargha-
Khadem, & Monaco, 2001; Sun, et al., 2005; Sun & Walsh, 2006). This has led to the theory that
perhaps numerous factors are involved in causing the lateralisation process (Liu et al., 2009) rather
than just one factor such as genetics.
3
There are many demonstrations of asymmetry in humans and hand preference (handedness)
is one of them. Typically, humans will repeatedly show preference for one hand over the other to
perform unimanual actions (e.g. eating using a spoon) (Somers, Shields, Boks, Kahn, & Sommer,
2015) and this reflects the asymmetry of the lateralised brain hemispheres. Handedness is therefore
an easily observable indicator of cerebral lateralisation (Peters, 1995) and there are numerous theories
behind the cause of handedness and cerebral lateralisation. In particular, theories of lateralisation and
handedness attempt to explain why most humans show a right side bias, and have shown a right side
bias at least since the Palaeolithic period (Faurie & Raymond, 2004) and across cultures (Coren &
Porac, 1977). As a result of the right side bias, approximately only 10% of the global population
exhibit left-handedness (Gilbert, & Wysocki, 1992; Perelle & Ehrman, 1994).
The genetic approach to lateralisation and handedness proposed by Annett (1985) suggests
there is a gene that codes for left cerebral dominance, therefore causing right-handedness, and this
gene is the right shift gene (RS). The two alleles of this gene are the RS+ and RS- gene with RS+
being dominant and causing left cerebral dominance, meaning that an individual would need two RS-
alleles to be left-handed. However, this recessive left-handedness allele is still advantageous and so
persists in the population (McManus, 2002). For example, theoretical work has recently found left-
handedness to be advantageous in male fighting (Billiard, Faurie, & Raymond, 2005). The RS- allele
also introduces more genetic variety and arguably causes optimal brain organisation when paired with
an RS+ allele (Annett, 1985). Annett (1993) suggests that extreme right-handedness can result in
weaknesses in cognitive processing (extreme right-handedness referring to the individuals who
possess two RS+ alleles). For example, Annett (1993) observed that extreme right-handers had less
academic success than those more towards the middle of the scale of handedness. Having two RS+
alleles has also been linked to having an increased risk of developing schizophrenia (Annett, 1997).
Additionally, McManus (1985) and Corballis (1997) suggest that cerebral dominance and
handedness is caused by one gene with one allele for dextrality and the other for a chance element
associated with either handedness rather than specifically coding for left-handedness. However, as
mentioned previously no single specific gene has been linked to cerebral dominance, and therefore
handedness, with instead several being implicated in more recent research (Sun, et al., 2005; Sun &
Walsh, 2006; Lai et al., 2001). McManus, Davison, and Armour (2013) have now suggested that there
are actually over 40 genetic loci implicated in handedness and its direction, but in particular the
LRRTM1 on chromosome 2p12 is suggested to be crucial in determining direction of handedness
(Francks et al., 2007).
4
In contrast, other research has implicated several environmental factors contributing to the
prevalence of left-handedness rather than recessive genetics. For example, Coren (1990) suggested
that maternal age was correlated with sinistrality as he observed that mothers who gave birth aged 40
and above were more likely to have a left-handed child than women who gave birth between the ages
of 17 and 24. However, McManus (1981) failed to observe this effect with a larger sample.
Additionally, another area of research has focused on the potential link between birth stress and
sinistrality, with a meta-analysis conducted by Searleman, Porac, and Coren (1989) finding that birth
stress is associated with a higher risk of sinistrality. However, this effect is only marginal and other
studies have failed to find this link (e.g. Bailey & McKeever, 2004).
Moreover, lateralised hand preferences and other neural functional asymmetries have been
found to correlate with brain structure (e.g. Amunts, Jancke, Mohlberg, Steinmetz, & Zilles, 2000;
Beaton, 1997; Moffat, Hampson, & Lee, 1998) and therefore the brain structure asymmetries could
be a contributing factor to direction of handedness. Amunts and colleagues (1996, 2000) have
observed that handedness is correlated with a deeper central sulcus, suggesting that in right-handed
individuals they have a deeper left central sulcus and left-handed individuals have a deeper right
central sulcus. Furthermore, it has been suggested that handedness affects frontal and occipital lobe
asymmetry (Bear, Schiff, Saver, Greenberg, & Freeman, 1986; Kertesz, Polk, Black, & Howell, 1990;
Weinberger, Luchins, Morihisa, & Wyatt, 1982; Zilles et al. 1996). Anstey et al. (2004) have also
found structural asymmetries in the corpus callosum, hippocampus and amygdala which are related
to handedness as the volume of these regions appears to be larger in left-handed individuals. This
implies that there are noticeable brain structural differences between right- and left-handed
individuals and this has possible connotations for causes of the lateralisation process. However, Good
et al. (2001) failed to find a neural structural correlate of handedness.
As part of the lateralisation process, certain brain functions also become lateralised and
therefore specialised to one hemisphere of the brain. An example of this is language processing, as
95% of right-handers (Szaflarski, Holland, Schmithorst, & Byars, 2006) and 75% of left-handers
(Pujol, Deus, Losilla, & Capdevila, 1999) have left cerebral dominance for language. However, there
is evidence that handedness can have an impact on the functional asymmetry of language because
Knecht et al. (2000) observed that the incidence of language being lateralised to the right hemisphere
of the brain increases with strength of left-handedness. This is despite language being usually
lateralised to the left hemisphere of the brain in both right- and left-handed individuals. Nonetheless,
although there is this possible lateralisation difference for language processing in left-handed
5
individuals, it has been found to have no effect on the processing conducted, particularly in relation
to verbal fluency and speed of linguistic processing (Knecht et al., 2001).
Furthermore, there is evidence that the left-hemisphere is also dominant in motor function
(e.g. Ziemann & Hallett, 2001) as motor deficits that are a result of lesions to the left-hemisphere are
more marked than the motor deficits caused by lesions to the right hemisphere (Haaland &
Harrington, 1989; Kimura, 1977; Wyke, 1966). This suggests that there is asymmetry of motor
functions, with the left hemisphere having overall cerebral dominance. In particular, Kim et al. (1993)
has found that this motor cortex functional asymmetry is more pronounced in right-handed
individuals.
Additionally, the left hemisphere has been found to be greatly correlated with right hand and
bimanual movements (involving coordination of both hands to perform an action), whereas the right
hemisphere has been found to be associated with left hand movements only (Serrien, 2009). The
corresponding contralateral dominant hemisphere in the brain (i.e. right-handers have a dominant left
motor cortex and left-handers have a dominant right motor cortex) is reflected in greater brain volume
and activation of the contralateral cortical hand area for dominant hands (Dassonville, Zhu, Uğurbil,
Kim, & Ashe, 1997; Volkmann, Schnitzler, Witte, & Freund, 1998). This suggests that left-handers
have larger brain volume and activation in the hand cortical region within the right hemisphere of the
brain and vice versa for right-handed individuals. Nonetheless, although motor cortex dominance is
contralateral to handedness, the left hemisphere is still arguably dominant overall as it is responsible
for the organisation of bimanual movements. However, White et al. (1997) observed that gross
lateralisation of the primary sensorimotor system is not linked with the preferred use of the right-hand
in humans.
Previous research on the motor planning functional asymmetry has indicated an effect of
handedness. Peters and Durding (1979) found that although the measure of interrepsonse interval
(IRI) in a tapping task revealed differences between the speed of tapping for the dominant and non-
dominant hand for both left- and right-handed participants, it was the left-handed group that had a
smaller difference between their dominant hand and non-dominant hand in comparison to the right-
handed group. Significant differences between the dominant and non-dominant hand in tapping tasks
have also been replicated in more recent research (e.g. Hubel, Reed, Yund, Herron, & Woods, 2013).
These findings indicate that the dominant hand is more efficient in both right- and left-handed
individuals. This reflects the contralateral dominance of the motor cortex but the findings still indicate
6
that handedness has an impact on the functional asymmetry because the right hemisphere is more
efficient in movement coordination of the left hand in left-handed individuals.
In contrast, it has been suggested that the right hemisphere of the brain is crucial in various
spatial functional processing, for example monitoring (Fink et al., 1999). This indicates a right
hemisphere cerebral dominance for spatial functions (Corbetta, Kincade, Ollinger, McAvoy, &
Shulman, 2000; Coull, Nobre, & Frith, 2001). This can be demonstrated in a study conducted by
Rotondaro, Merola, Aiello, Pinto, and Doricchi (2015) as they observed that during a line bisection
task participants usually marked the line to the left of the objective centre, an observation known as
pseudoneglect (Brooks, Della Sala, & Darling, 2014; Longo & Lourenco, 2007; Manning, Halligan,
& Marshall, 1990) which corresponds to the behavioural attentional bias (Zago et al., In Press). This
effect reflects the right hemisphere dominance for spatial functions (Bowers & Heilman, 1980).
Neuroimaging studies have also found that the line bisection task activates the right frontal
and posterior occipito-parietal-temporal regions (Zago et al., In Press), therefore supporting the
evidence for right hemisphere dominance for the spatial functional asymmetry. However, Vogel,
Bowers, and Vogel (2003) observed that having a right hemisphere dominance for spatial tasks was
only observed in right-handed participants and that there was no hemispheric preference for the left-
handers with regards to spatial tasks. Based on this finding, Somers et al. (2015) suggested the
bilaterality of spatial functions in left-handers explains why left-handers demonstrate less accurate
spatial skills than right-handers. They propose this is reflected in tasks such as mental rotation tasks,
but they fail to specify as to how the bilaterality reduces the accuracy of a left-hander’s performance
in the task. However, the negative impact of bilaterality on spatial tasks is contested as other research
has demonstrated that bilaterality of spatial functions is an advantage in mental rotation tasks (Zacks,
2008). Furthermore, Burnett, Lane, and Dratt (1982) found that extreme left- and right-handers had
worse spatial skills than mixed or moderately right-handed individuals. However, left hemisphere
lateralisation for spatial functions in left-handed individuals has also been observed (Flöel, Buyx,
Breitenstein, Lohmann, & Knecht, 2005).
Additionally, spatial attention has also been linked strongly to the right hemisphere of the
brain as part of the lateralisation process (Harvey, Milner, & Roberts, 1995; Marshall et al., 1997;
Weintruab & Mesulan, 1987) and Flöel et al. (2005) found that the link between attentional
dominance and handedness is similar to the way language dominance is linked with handedness. In
particular, spatial functions processing has been linked to the right superior temporal cortex (Karnath,
Ferber, & Himmelback, 2001). Furthermore, a correlation has been observed between the strength of
7
pseudoneglect in the line bisection task and the volume of white matter connections that are
responsible for linking together the parietal cortex and the frontal cortex, specifically in the right
hemisphere of the brain (De Schotten et al., 2011). These findings could aid in the explanation of why
the left side of space is favoured by the right hemisphere and is demonstrated as pseudoneglect in
spatial tasks such as a line bisection task.
The literature reveals that as part of the lateralisation process, various cognitive functions are
also lateralised to one hemisphere of the brain, thus creating functional asymmetries. However,
research has also started to find that overall hemisphere dominance, as reflected by handedness, can
have impacts on these functional asymmetries (e.g. language, Knecht et al., 2000). This study
therefore aimed to investigate if handedness, in the form of a dominant contralateral brain
hemisphere, affects the two functional asymmetries of motor planning (conducted in the left
hemisphere, e.g. Ziemann & Hallett, 2001) and spatial functions (conducted in the right hemisphere,
e.g. Fink et al., 1999). The motor planning functional asymmetry was assessed using a finger tapping
task. The spatial functional asymmetry was assessed using a line bisection task. However, in order to
investigate this, it was necessary to first find a reliable measure of direction of handedness.
There are two main methods to classify handedness (Brown, Roy, Rohr, Snider, & Bryden,
2004). These are directly, via preference measures (e.g. Waterloo Handedness Questionnaire (WHQ),
Steenhuis & Bryden, 1989) or indirectly, via performance measures which are used to infer direction
of handedness (Corey, Hurley, & Foundas, 2009) such as the Wathand Box Test (WBT) (Bryden,
Pryde, & Roy, 2000b). However, recent research now suggests it is equally important to acquire a
measure of strength of handedness referring to whether an individual is consistently handed or
inconsistently handed (Prichard, Propper, & Christman, 2013), as handedness consistency has been
found to link strongly with genetic models of handedness (Hardie & Wright, 2014). Consistency of
handedness refers to the number of tasks performed by each hand (Hardie & Wright, 2014), therefore
an individual who performs all tasks with the right hand is a consistent right-hander and a person who
uses different hands for different tasks is an inconsistent hander.
This study used the Flinders Handedness Survey (FLANDERS) (Nicholls, Thomas,
Loetscher, & Grimshaw, 2013), which is a preference measure of handedness derived from the
inventory created by Provins and Cunliffe in 1972. The FLANDERS inventory was developed to
overcome the criticisms of length, response format, instructions and factorial structure which the
authors applied to other inventories. While similar to the Edinburgh Handedness Inventory (EHI)
(Oldfield, 1971) and the Annett Handedness Inventory (Annett, 1970) in length, the FLANDERS
8
inventory also aims to categorise participants into left-, right- and mixed-handers. However, rather
than using a Likert scale (which is used in the WHQ) to rate answers, or a strong/weak handedness
answer method (as in the EHI), which have instructions that are commonly misunderstood (Fazio,
Coenen, & Denney, 2012), the FLANDERS inventory provides three options to answer with, ‘left’
or ‘right’ or ‘either’, as in Annett’s (1970) and Provins and Cunliffe’s (1972) inventories. However,
the FLANDERS inventory added more specific instructions with regards to the ‘either’ answer in
order to prevent uncertainty about what this response actually meant. This is because previous studies
have found that certain populations were more likely to respond ‘either’ than others (e.g. Annett,
1970). In the FLANDERS inventory, “Participants were asked to tick the ‘either’ box only when one
hand is truly no better than the other” (Nicholls et al., 2013, p. 2915). For the categorisation of
participants into left-handers, right-handers and mixed-handers this inventory is valid and reliable as
the questions have good correlations with hand performance and other tests of lateral preference
(Nicholls et al., 2013). However, if an experiment has handedness as the main area of interest a longer
more in depth questionnaire would be more appropriate.
The FLANDERS inventory (Nicholls et al., 2013) was used to categorise participants in to
right- and non-right-handers. In the finger tapping task the reaction times (RTs) and IRIs were
recorded for each group but also for the hand used with reference to the dominant and non-dominant
hand of each participant. The line bisection task was administered using the same stimuli as in
Rotondaro et al.’s (2015) study. In this task, the participants’ absolute and directional deviations from
the objective centre were recorded for lines of varying lengths and compared across the two groups.
The directional deviations were used to investigate the pseudoneglect demonstrated by the different
groups. It was expected that handedness, and therefore cerebral laterality, would affect the functional
asymmetries of motor planning and spatial functions, thus resulting in significant differences between
the scores of right-handed and non-right-handed participants and a significant interaction between
handedness and the task. Any potential correlations were also investigated between the tasks
themselves and between the tasks and handedness inventory scores for the right-handed group.
Method
Design
This study used a repeated measures experimental design to test two independent variables
and record four dependent variables using two tasks: the line bisection and finger tapping tasks. The
line bisection task had two levels; one level being the group of participants (non-right-handed or right-
handed individuals) and the other level being the length of the line (either 2cm, 10cm or 20cm). The
finger tapping task also had two levels; one level was group as in the other task (non-right-handed or
9
right-handed individuals) and the other level was hand used, referring to either the dominant or non-
dominant hand. To test the effects of these tasks and their manipulations, the dependent variables for
the line bisection task were the directional deviations (used to indicate pseudoneglect) and absolute
deviations. The dependent variables for the tapping task were the RTs and the IRIs. All four dependent
variables were analysed separately.
Participants
A convenience sample of 50 participants was recruited via an online research participation
scheme (https://nottingham.sona-systems.com/Default.aspx?ReturnUrl=/) from the population of
undergraduates from the University of Nottingham. Upon completion, all participants received 0.5
course credits through the same participation scheme. Of these 50 undergraduates, there were 6 males
and 44 females. Furthermore, within this sample 37 participants were right-handed (4 males and 33
females), 9 participants were left-handed (2 males and 7 females) and 4 participants were mixed-
handed (0 males and 4 females). The mixed-handed participants and left-handed participants were
combined to form a non-right-handed group. Their ages ranged from 18 to 25 years of age (M = 19.5,
SD = 1.33). All participants completed all tasks in the experiment.
Measurements
For the line bisection task the participants’ deviations from the objective centre of the line
were measured in millimetres (mm) to the nearest 0.5mm on a standard 30cm ruler. When measuring
the directional deviations, if the deviation was to the left of the objective centre it was a negative
value, this indicates the extent of pseudoneglect demonstrated by the participant, and if it was to the
right of the objective centre it was a positive value. For the absolute deviations there were no negative
values.
In the tapping task, the participants’ RTs to press the button and IRIs between each tap were
recorded in milliseconds (ms) by the software E-Studio for both the right and left hand and presented
in an E-DataAid file.
Apparatus/Materials
Participants had to complete a personal details questionnaire and a handedness inventory. The
personal details questionnaire was presented to participants in a paper format and they had to
complete all the questions. As well as asking for demographic details, this questionnaire asked
questions regarding any extra-curricular activities in order to identify any possible confounding
variables which could skew the data obtained by the two tasks. For example, the participants were
asked their gender as Jewell and McCourt (2000) observed that males tended to demonstrate more
10
pseudoneglect than females. A list of the questions used in the questionnaire is presented in Appendix
1.
The handedness inventory, based on the FLANDERS inventory (Nicholls et al., 2013), used
the original 10 questions whilst incorporating 10 new questions in an attempt to create a more in
depth measure of direction of handedness. A copy of the modified inventory is displayed in Appendix
2 with the original questions from the FLANDERS inventory highlighted in yellow. This too was
presented in a paper format and participants had to tick which hand they used to complete the action
in question, the options being the right hand, the left hand or either hand. Upon completion, the
researcher calculated a handedness score by adding one point for a right-handed response, deducting
one point for a left-handed response and leaving the score the same for a mixed-handed response.
This is consistent with the method implemented by Nicholls et al. (2013). There were 20 questions in
the modified inventory in total, therefore to be classed as right-handed participants needed to score
between +10 and +20 and to be classed as left-handed, participants needed to score between -20 and
-10. If a participant received a score between -10 and +10, they were classed as mixed-handed. This
score was used to assign participants to either the right-handed or non-right-handed group (formed
with mixed- and left-handed participants).
During the line bisection task, participants were presented with nine horizontal lines that were
printed in the centre of a landscape orientated piece of plain A4 paper. Of the nine lines, three lines
were 2cm in length, three lines were 10cm long and the remaining three lines were 20cm in length.
The different length lines were presented in a random order for each participant as a counterbalancing
technique to prevent order effects. On each horizontal line, participants marked the line with a pen,
in their dominant hand, where they thought the middle of the line was. They had an unlimited amount
of time to complete this task
The finger tapping task was conducted on the psychological software E-Studio on a Windows
computer. During the task, participants had six ten second periods to tap the space bar on a standard
keyboard as fast as they could, three of these periods were completed with the participant’s dominant
hand and the other three periods were completed with the participant’s non-dominant hand. The order
in which the participants completed the ten second periods (i.e. order they used their dominant and
non-dominant hand) was randomised by the software for each participant to prevent order effects.
Between each period of ten seconds, participants received a thirty second break as timed by the
researcher using a stopwatch. The break was introduced after the pilot study, as without a break to
rest their arms participants became progressively slower as the trials advanced.
11
Procedure
Participants were tested individually and upon arrival they were given an information sheet
(Appendix 3) to read about the experiment. Once the participant understood and consent had been
given, the participant was given the personal details questionnaire and the handedness inventory to
complete.
Each participant was then randomly assigned to either group one or group two using a random
number generator (https://www.random.org/). Group one completed the line bisection task first and
group two completed the tapping task first; this was done in order to counterbalance the tasks.
During the line bisection task, the participant was first presented with the task instructions
(Appendix 4) and given the opportunity to ask any questions. They were then presented with the
booklet of lines to mark with their subjective centres. Once the booklet had been completed, the
researcher later measured the directional and absolute deviations.
To complete the tapping task, the participants first read the instructions (Appendix 5) and
were given the opportunity to ask any questions. They were then shown the standardised hand
position (base of palm flat on the desk with the index finger extended to perform the tapping whilst
the remaining three fingers were folded underneath the palm) and moved the keyboard to wherever
was most comfortable for them. They then proceeded to press any key on the keyboard to begin the
task. Before each period of ten seconds, a screen appeared instructing the participant which hand to
use in the upcoming trial. The participant responded by pressing “s” to start the trial and then received
a three second countdown to start tapping. After each period of ten seconds, the participants received
a thirty second break and the researcher gave the participant a three second count down to press “s”
to begin the next trial. During this task, the computer recorded the IRIs and RTs.
Once both tasks had been completed, the experiment ended and the participant was given a
debrief sheet (Appendix 6) and 0.5 credit points for their participation.
Results
Pre-Analysis
Before the analysis was conducted, it was necessary to randomly select 13 right-handed
participants in order to have equal numbers in both the right-handed and non-right-handed groups.
To do this the right-handed participants were matched for gender with the non-right-handed
participants and randomly selected using a random number generator (https://www.random.org/).
This resulted in having 26 participants included in the ANOVA analyses in total (2 right-handed
males, 11 right-handed females, 2 non-right-handed males and 11 non-right-handed females).
12
Line Bisection Task – Directional Deviations
On the directional deviations, the descriptive statistics of the mean and standard deviation
were calculated for each line length (2cm, 10cm & 20cm) for each group (non-right-handed and right-
handed) and are presented in Table 1.
Table 1. Means (and standard deviations) of directional deviations from the objective centre for the non-right-handed and
right-handed group for lines of varying lengths in the line bisection task
Deviation
Group
Non-right-handed Right-handed
2cm Line Deviation(mm) -0.244 (0.388) -0.140 (0.347)
10cm Line Deviation (mm) -2.076 (1.786) -0.668 (1.714)
20cm Line Deviation (mm) -2.346 (3.155) -1.576 (3.788)
Additionally, the inferential statistical test of a 2x3 split-plot ANOVA was calculated with the
line lengths being the within subject factor and group being the between subject factor. However,
Mauchly’s test of sphericity was significant (p = .003) therefore, the Greenhouse-Geisser correction
was used to interpret the results. Using the correction, a significant main effect of line length was
found, F(1.425, 34.194) = 5.144, MSe = 5.758, p = .019, η²p = .177. However, a significant main
effect of group was not found, F(1, 24) = 1.58, MSe = 7.145, p = .221, η²p = .062, and a significant
interaction was not found, F(1.425, 34.194) = 0.674, MSe = 5.758, p = .47, η²p = .027. As a result of
the significant main effect of line length, a one-sample t test with Bonferroni correction was
conducted to investigate which line lengths had significantly different means. The test revealed that
the means for each line length were all significantly different from each other (2cm deviation: t(25)
= -2.685, p = .013; 10cm deviation: t(25) = -3.762, p = .001; 20cm deviation: t(25) = -2.909, p =
.008).
Line Bisection Task – Absolute Deviations
The absolute deviations were analysed in order to determine if one group of participants
deviated from the objective centre significantly more than the other group, irrespective of direction.
The descriptive statistics of the mean and standard deviation are presented in Table 2.
13
Table 2. Means (and standard deviations) of absolute deviations from the objective centre for the non-right-handed and
right-handed group for lines of varying lengths in the line bisection task
Deviation
Group
Non-right-handed Right-handed
2cm Line Deviation(mm) 0.434 (0.161) 0.511 (0.230)
10cm Line Deviation (mm) 2.307 (1.306) 1.845 (0.973)
20cm Line Deviation (mm) 2.999 (2.099) 3.331 (2.176)
As with the directional deviations, a 2x3 split-plot ANOVA was conducted using the same
within and between subject factors. Mauchly’s test of sphericity was again significant (p = .001) so
the Greenhouse-Geisser correction was applied. The 2x3 ANOVA revealed a significant main effect
of line length, F(1.501, 36.013) = 28.892, MSe = 2.201, p < .001, η²p = .546, but a non-significant
main effect of group, F(1, 24) = 0.002, MSe = 2.634, p = .962, η²p < .001, and a non-significant
interaction between line length and group, F(1.501, 36.013) = 0.648, MSe = 2.201, p = .486, η²p =
.026. A one-sample t test with Bonferroni correction was conducted on the significant main effect of
line length, as in the directional deviation analysis. This again revealed that the means for each line
length were all significantly different from one another (2cm deviation: t(25) = 12.141, p < .001;
10cm deviation: t(25) = 9.182, p < .001; 20cm deviation: t(25) = 7.68, p < .001).
Tapping Task - RTs
For the tapping task, the descriptive statistics of the mean and standard deviation were
calculated for the RTs for each hand that the participants used and each group, and are presented
below as a graph in Figure 1.
14
Figure 1. Mean RTs for each group in the tapping task, for both left and right hand taps, with the standard deviation
presented as error bars
The inferential statistical test of a 2x2 split-plot ANOVA was calculated for the RTs with
hand being the within subject factor (use of either dominant or non-dominant hand) and group being
the between subject factor.
This ANOVA violated the assumption of sphericity, as Mauchly’s test of sphericity was
significant (p < .001), therefore the Greenhouse-Geisser correction was applied. With the correction,
a significant interaction between hand and group was found, F(1, 24) = 51.343, MSe = 65.221, p <
.001, η²p = .681. However, the main effects of hand, F(1, 24) = 0.01, MSe = 65.221, p = .92, η²p <
.001, and group, F(1, 24) < 0.001, MSe = 584.393, p = .987, η²p < .001, were found to be non-
significant. For the significant interaction, the descriptive statistics show a crossed pattern of group
and hand. Therefore, a paired samples t test was run on the non-right-handed group, comparing the
means for the left and right hand, and also run on the right-handed group, comparing the means for
the left and right hand, to assess if each hand was significantly different to the other hand. For the
non-right-handers, there was a significant difference between the use of the left and right hand (t(12)
= -5.002, p < .001) with the left hand being quicker than the right hand. For the right-handers there
was also a significant difference between the use of the right and left hand (t(12) = 5.131, p < .001),
with the right hand having shorter RTs than the left hand.
Tapping Task - IRIs
The descriptive statistics of the mean and standard deviation were also calculated for the IRIs
and are presented in graph form in Figure 2.
0
50
100
150
200
250
Left hand Right hand
Rea
ctio
n T
imes
(m
s)
Hand Used
Non-right-handed
Right-handed
15
Figure 2. Mean IRIs for each group in the tapping task, for both left and right hand taps, with the standard deviation
presented as error bars
A 2x2 split plot ANOVA with the same within and between subject factor was calculated on
the IRI dependent variable and Mauchly’s test of sphericity was found to be significant again (p <
.001), therefore the Greenhouse-Geisser correction was applied. This ANOVA revealed a non-
significant main effect of hand, F(1, 24) = 1.285, MSe = 1051455.772, p = .268, η²p = .051, and a
non-significant main effect of group, F(1, 24) = 0.915, MSe = 329748.633, p = .348, η²p = .037.
Furthermore, a significant interaction between hand and group was not found, F(1, 24) = 0.059, MSe
= 1051455. 772, p = .810, η²p = .002.
Right-Handed Group Correlations
A series of Pearson correlations was conducted on the entire right-handed group (all 37 right-
handed participants) to assess any potential relationships between the tasks themselves, and between
the handedness inventory scores and the tasks. For the line bisection task the mean directional
deviation scores were used and for the tapping task the mean RTs were used. However, the correlation
analyses could not be completed with the non-right-handed group due to the sample size being too
small.
To assess any relationships between the tasks, Pearson correlations were conducted between
left RT mean (tapping task) and mean deviation on 2cm lines, 10cm lines and 20cm lines (line
bisection task); and right RT mean (tapping task) and mean deviation on 2cm lines, 10cm lines and
20cm lines (line bisection task). However, all six of these correlation analyses were found to be non-
significant. All Pearson correlation and p values for the six analyses are presented in Table 3.
0
500
1000
1500
2000
2500
3000
Left hand Right hand
Inte
rres
pone
Inte
rval
(m
s)
Hand Used
Non-right-handed
Right-handed
16
Table 3. Pearson correlation and p values for each correlation analysis between the tasks in the right-handed group
Correlation Result
Left RT M and M 2cm deviation r = -.12, p = .479
Left RT M and M 10cm deviation r = .08, p = .638
Left RT M and M 20cm deviation r = -.019, p = .912
Right RT M and M 2cm deviation r = .045, p = .791
Right RT M and M 10cm deviation r = .194, p = .251
Right RT M and M 20cm deviation r = -.028, p = .753
In order to explore any potential links between the handedness inventory scores and the tasks,
Pearson correlation tests were conducted between left RT mean (tapping task) and handedness
inventory score, right RT mean (tapping task) and handedness inventory score, mean deviation on
2cm lines (line bisection task) and handedness inventory score, mean deviation on 10cm lines (line
bisection task) and handedness inventory score and finally, mean deviation on 20cm lines (line
bisection task) and handedness inventory score. However, all these Pearson correlations were also
found to be non-significant. The exact Pearson correlation values and p values for each correlation
are presented in Table 4.
Table 4. Pearson correlation and p values for each correlation analysis between the tasks and handedness inventory scores
in the right-handed group
Correlation Result
Left RT M and handedness inventory score r = -.054, p = .753
Right RT M and handedness inventory score r = -.190, p = .261
M 2 cm deviation and handedness inventory score r = -.069, p = .686
M 10 cm deviation and handedness inventory score r = -.105, p = .536
M 20 cm deviation and handedness inventory score r = .034, p = .842
Discussion
Main Findings
This study aimed to investigate any potential differences in the functional asymmetries of
motor planning and spatial functions as a result of handedness. The results indicate that, although
there was a significant effect of line length in the line bisection task which resulted in larger deviations
from the objective centre the longer the line was in length, handedness does not appear to affect
spatial functions as reflected by a line bisection task. Handedness was also found not to affect the
17
IRIs in the tapping task as a significant interaction between handedness and hand used was not found.
However, the tapping task did reveal a significant interaction between handedness and hand used for
RTs. This indicates that handedness did have a significant effect on the RTs on each hand used with
regard to whether it was the dominant or non-dominant hand, with the dominant hand having
significantly shorter RTs in both groups than the non-dominant hand.
Spatial Functional Asymmetry and the Line Bisection Task
The lack of a significant interaction between group and line length in the line bisection task
data contradicted what was expected in this study, as it was predicted that there would be significant
differences between the right- and non-right-handed groups for each line length. However, previous
research has indicated that left-handed individuals are less likely to have a right hemisphere
dominance for spatial functions, unlike right-handed individuals, and instead have no hemispheric
preference for such functions (Vogel et al., 2003). For example, O’Boyle et al. (2005) observed that
left-handed individuals demonstrated no right hemisphere preference during a mental rotation task.
Furthermore, Hécaen and Sauguet (1971) observed that left-handed individuals have a high incidence
of bilateral cerebral dominance in comparison to right-handed individuals. Somers et al. (2015)
suggested that this bilaterality, particularly with regards to spatial functions, in left-handed
individuals could explain why left-handers potentially demonstrate less accurate spatial skills than
right-handers. For example, a link between testosterone and left-handedness has been found (Medland
et al., 2005) and this could potentially influence spatial ability as it could contribute to the bilaterality
of spatial functions in left-handed individuals. Burnett et al.’s (1982) findings also support this theory,
because although their results suggested that an increase in bilateral specialisation is associated with
good spatial functions, the best scores achieved in the spatial task were from participants who had
left-handed relatives and had handedness inventory scores correlating to mixed or slightly right-
handed categories rather than the left-handed category.
This theory could explain why the non-right-handed group in this experiment did not
demonstrate smaller deviations from the objective centre in the line bisection task than the right-
handed group. However, according to this theory it would suggest that in fact the right-handed group
would have significantly smaller deviations in comparison to the non-right-handed group, but this
significant result was also not found in the present study. Perhaps the methodology of this study had
an affect on this, as previous studies which found a difference between left- and right-handed
individuals have used different spatial functional assessments to those used in the present study. For
example, the Burnett et al. (1982) study used the Guildford-Zimmerman Aptitude Survey (Guildford
& Zimmerman, 1953) rather than the line bisection task. However, in the present study in terms of
18
descriptive statistics for the directional deviations, the non-right-handed group demonstrated more
pseudoneglect than the right-handed group, which implies that the right-handed group were more
accurate. It also indicates a strong right hemisphere dominance for spatial functions rather than
bilaterality in the non-right-handed group (Longo & Lourenco, 2007). Furthermore, Zago et al. (In
Press) found that the degree of cerebral lateralisation is correlated with the effect of pseudoneglect
and therefore also indicated, with regard to the present study, a right hemisphere spatial functions
asymmetry rather than bilaterality. But this effect of group in the present study is diminished when
absolute deviations are considered.
The significant main effect of line length found in the line bisection task for both the absolute
and directional deviations supports previous findings by Rotondaro et al. (2015), whose stimuli this
line bisection task stimuli was based on. This demonstrates that both the non-right-handed and right-
handed group made larger deviations from the objective centre of the line as the line increased in
length.
Motor Planning Functional Asymmetry and the Finger Tapping Task
Previous research has indicated mixed findings as to whether a more pronounced motor
functional asymmetry in right-handed individuals (Kim et al., 1993) is a benefit to the group or the
result of a disadvantage. For example, Kilshaw and Annett (1983) found that left-handed individuals
were actually faster than right-handed individuals in hand movement as assessed by a peg moving
task. They suggested this is a result of the right-handed individuals’ superiority of the left hemisphere
in the motor cortex potentially being caused by a fault within the right hemisphere rather than an
advantage in the left hemisphere. This has been demonstrated by Nalçacı, Kalaycıoğlu, Çiçek, and
Genç (2001) who found that when combining the scores of the non-dominant and dominant hand in
a tapping task, it was the non-right-handed group that tended to have greater tapping rates than the
right-handed group, and that the difference between the dominant and the non-dominant hand was
more pronounced in the right-handed group compared to the non-right-handed group. Nalçacı et al.’s
(2001) findings could also be argued to provide further support for the observation that left-handed
individuals are more likely to have bilateral cerebral dominance (Hécaen & Sauguet, 1971) than right-
handed individuals, resulting in the dominant and non-dominant hand being more equally proficient.
This is further supported by an observation that left-handed individuals demonstrate less functional
asymmetry in manual tasks (Buckingham, Main, & Carey, 2011; Goodale, 1990) and therefore, are
more likely to be bilateral in motor planning. However, the data from the present study does not
support this theory as both the right-handed and non-right-handed groups had significant differences
between their dominant and non-dominant hand.
19
Furthermore, the IRIs results cannot be explained by these theories as no significant results
were found between the right-handed and non-right-handed groups or between the groups’ dominant
and non-dominant hand. This contradicts other studies that have found significant differences in this
measurement (e.g. Peters & Durding, 1979). It is possible however, that the lack of significant results
in the IRIs dependent variable could be a result of this variable measuring a different part of cognitive
processing than RTs. If so, IRIs would arguably be less likely to be influenced by handedness and
functional asymmetries. Théoret, Haque, and Pascual-Leone (2001) observed that IRIs are processed
in the cerebellum, particularly the medial cerebellum, rather than the motor cortex. Therefore based
on this study’s results, the RTs arguably are a part of the motor functional asymmetry in the motor
cortex, but the IRIs are processed in the cerebellum, and perhaps cerebellar processing is not part of
the motor functional asymmetry and is therefore less likely to be influenced by handedness. This
could explain the lack of significant results within the IRIs dependent variable in the finger tapping
task in comparison to the RTs dependent variable.
Limitations and Future Research
Based on this study, future research could investigate the functional asymmetries of motor
planning and spatial functions with a larger sample size in order to have a more representative sample
of left- and mixed-handed individuals in comparison to right-handed individuals. This would prevent
the need to merge the left- and mixed-handed groups. Additionally, if more participants are
incorporated into the sample, the handedness inventory could be used to split the strongly dextral and
sinistral participants into separate groups, as a measure of consistency of handedness as well as
direction. This could be used to investigate whether the functional asymmetries are influenced by
handedness more when the participants themselves are consistently left- or right-handed (strongly
dextral or sinistral). Based on Hicks, Dusek, Larsen, Williams, and Pellegrini’s (1980) theory that
non-right-handedness is caused by a gradual shift away from the dextral norm rather than an abrupt
change from right- to non-right handed, it would suggest that the more strongly a person is left-
handed, the more likely it is to observe any potential differences between the left- and right-handed
group.
Furthermore, this study only used one task to assess the functional asymmetries. Perhaps if
several different tasks were administered to the same participants it would give a more comprehensive
overview of the functional asymmetries and whether handedness affects the entire asymmetry or just
specific aspects of the functional asymmetry. For example, this method could be used to clarify
whether RTs and IRIs are parts of two separate functions. Through further research aimed at gaining
a more comprehensive overview of the functional asymmetries, perhaps neurological measures could
20
reveal differences between the different handedness groups that are not potentially reflected in
behavioural measures, which this study used. For example, previous research has indicated structural
brain differences between left- and right-handed individuals (e.g. Anstey et al., 2004) and perhaps
these structural differences represent differences in functional capabilities also, which could influence
the functional asymmetries.
Conclusion
Overall, this study did not observe an effect of handedness on the spatial functional
asymmetry, as measured by a line bisection task, but did observe an influence of handedness on RTs
in the finger tapping task, therefore inferring an influence of handedness on the motor planning
functional asymmetry. Future research could develop these findings further, to investigate if
handedness has an effect on different functional asymmetries including different aspects of the spatial
and motor planning functional asymmetries. However, based on the data from this study it can be
concluded that handedness does not have an effect on all functional asymmetries, as it did not affect
the spatial functional asymmetry. This implies that overall cerebral lateralisation significantly
influences the speed of movement in the dominant and non-dominant hand, as reflected by the motor
planning functional asymmetry. However, other functional asymmetries such as the spatial functional
asymmetry are efficient, irrespective of direction of handedness and which hemisphere has overall
cerebral dominance.
21
References
Amunts, K., Jancke, L., Mohlberg, H., Steinmetz, H., & Zilles, K. (2000). Interhemispheric
Asymmetry of the Human Motor Cortex Related to Handedness and Gender.
Neuropsychologia, 38, 304-312.
Amunts, K., Schlaug, G., Schleicher, A., Steinmetz, H., Dabringhaus, A., Roland, P.E., & Zilles, K.
(1996). Asymmetry in the Human Motor Cortex and Handedness. Neuroimage, 4, 216-
222.
Annett, M. (1970). A Classification of Hand Preference by Association Analysis. British Journal of
Psychology, 61, 303-321.
Annett, M. (1985). Left, Right, Hand and Brain: The Right Shift Theory. London, UK: Lawrence
Erlbaum Associates.
Annett, M. (1993). Handedness and Educational Success: The Hypothesis of Genetic Balanced
Polymorphism with Heterozygote Advantage for Laterality and Ability. British Journal
of Developmental Psychology, 11, 359-370.
Annett, M. (1997). Schizophrenia and Autism Considered as the Products of an Agnosic Right Shift
Gene. Cognitive Neuropsychiatry, 2, 195-240.
Anstey, K.J., Maller, J.J., Meslin, C., Christensen, H., Jorm, A.F., Wen, W., & Sachdev, P. (2004).
Hippocampal and Amygdalar Volumes in Relation to Handedness in Adults Aged 60-64.
Neuroreport, 15, 2825-2829.
Bailey, L.M., & McKeever, W.F. (2004). A Large-Scale Study of Handedness and Pregnancy/Birth
Risk Events: Implications for Genetic Theories of Handedness. Laterality, 9, 175-188.
Bear, D., Schiff, D., Saver, J., Greenberg, M., & Freeman, R. (1986). Quantitative Analysis of
Cerebral Asymmetries. Fronto-Occipital Correlation, Sexual Dimorphism and
Association with Handedness. Archives of Neurology, 43, 598-603.
Beaton, A.A. (1997). The Relation of Planum Temporale Asymmetry and Morphology of the Corpus
Callosum to Handedness, Gender, and Dyslexia: A Review of the Evidence. Brain
Language, 60, 255-322.
Billiard, S., Faurie, C., & Raymond, M. (2005). Maintenance of Handedness Polymorphism in
Humans: A Frequency-Dependent Selection Model. Journal of Theoretical Biology, 235,
85-93.
22
Bowers, D., & Heilam, K.M. (1980). Pseudoneglect: Effects of Hemispace on a Tactile Line Bisection
Task. Neuropsychologia, 18, 491-498.
Brooks, J.L., Della Sala, S., Darling, S. (2014). Representational Pseudoneglect: A Review.
Neuropsychology Review, 24, 148-165.
Brown, S.G., Roy, E.A., Rohr, L.E., Snider, B.R., & Bryden, P.J. (2004). Preference and Performance
Measures of Handedness. Brain and Cognition, 55, 283-285.
Bryden, P.J., Pryde, K.M., & Roy, E.A. (2000b). A Developmental Analysis of the Relationship
Between Hand Preference and Performance: II. A Performance-Based Method of
Measuring Hand Preference in Children. Brain and Cognition, 43, 60-64.
Buckingham, G., Main, J.C., & Carey, D.P. (2011). Asymmetries in Motor Attention During A Cued
Bimanual Reaching Task: Left and Right Handers Compared. Cortex, 47, 432-440.
Burnett, S.A., Lane, D.M., & Dratt, I.M. (1982). Spatial Ability and Handedness. Intelligence, 6, 57-
68.
Corballis, M.C. (1997). The Genetic and Evolution of Handedness. Psychological Review, 104, 714-
727.
Corbetta, M., Kincade, J.M., Ollinger, J.M., McAvoy, M.P., & Shulman, G.L. (2000). Voluntary
Orienting is Dissociated from Target Detection in Human Posterior Parietal Cortex.
Nature Neuroscience, 3, 292-297.
Coren, S. (1990). Left-Handedness in Offspring as a Function of Maternal age at Parturition. The New
England Journal of Medicine, 322, 1673-1990.
Coren, S. & Porac, C. (1977). Fifty Centuries of Right-Handedness: The Historical Record. Science,
198, 631-632.
Corey, D.M., Hurley, M.M., & Foundas, A.L. (2001). Right and Left Handedness Defined: A
Multivariate Approach Using Hand Preference and Hand Performance Measures.
Neuropsychiatry, Neuropsychology and Behavioural Neurology, 14, 144-152.
Coull, J.T., Nobre, A.C., & Frith, C.D. (2001). The Noradrenergic α2 Agonist Clonidine Modulates
Behavioural and Neuroanatomical Correlates of Human Attentional Orienting and
Alerting. Cerebral Cortex, 11, 73-84.
23
Dassonville, P., Zhu, X.H., Uğurbil, K., Kim, S.G., & Ashe, J. (1997). Functional Activation in Motor
Cortex Reflects the Direction and the Degree of Handedness. PNAS, 94, 14015-14018.
De Schotten, M. T., Dell’Acque, F., Forkel, S.J., Simmons, A., Vergani, F., Murphy, D.G., & Cantani,
M. (2011). A Lateralised Brain Network for Visuospatial Attention. Nature
Neuroscience, 14, 1245-1246.
Faurie, C. & Raymond, M. (2004). Handedness Frequency Over More than Ten Thousand Years.
Proceedings of the Royal Society B: Biological Sciences, 271 (Suppl.), S43-S45.
Fazio, R., Coenen, C., & Denney, R.L. (2012). The Original Instructions for Edinburgh Handedness
Inventory Are Misunderstood by the Majority of Participants. Laterality, 17, 70-77.
Fink, G.R., Marshall, J.C., Halligan, P.W., Frith, C.D., Driver, J., Frackowiack, R.S.J., & Dolan, R.J.
(1999). The Neural Consequences of Conflict Between Intention and the Senses. Brain,
122, 497-512.
Flöel, A., Buyx, A., Breitenstein, C., Lohmann, H., & Knecht, S. (2005). Hemispheric Lateralisation
of Spatial Attention in Right- and Left-Hemispheric Language Dominance. Behavioural
Brain Research, 158, 269-275.
Francks, C., Maegawa, S., Lauren, J., Abrahams, B.S., Velayos-Baeza, A., Medland, S.E., et al.
(2007). LRRTM1 on Chromosome 2p12 is a Maternally Suppressed Gene that is
Associated Paternally with Handedness and Schizophrenia. Molecular Psychiatry, 12,
1129-1139.
Geschwind, N., & Galaburda. A.M. (1985a). Cerebral Lateralization. Biological Mechanisms,
Associations, and Pathology: I. A Hypothesis and a Program for Research. Archives and
Neurology, 42, 428-459.
Geschwind, N., & Galaburda, A.M. (1985c). Cerebral Lateralisation. Biological Mechanisms,
Associations, and Pathology: III. A hypothesis and a program for research. Archives and
Neurology, 42, 634-654.
Geschwind, D.H., Miller, B.L., DeCarli, C., & Carmelli, D. (2002). Heritability of Lobar Brain
Volumes in Twins Supports Genetic Models of Cerebral Laterality and Handedness.
PNAS, 99, 3176-3181.
Gilbert, A., & Wysocki, C. (1992). Hand Preference and Age in the United States. Neuropsychologia,
30, 601-608.
24
Gilmore, J.H., Zhai, G., Wilber, K., Smith, J.K., Lin, W., & Gerig, G. (2004). 3 Tesla Magnetic
Resonance Imaging of the Brain in Newborns. Psychiatry Research: Neuroimaging, 132,
81-85.
Good, C.D., Johnsrude, I., Ashburner, J., Henson, R.N.A., Friston, K.J., & Frackowiak, R.S.J. (2001).
Cerebral Asymmetry and the Effects of Sex and Handedness on Brain Structure: A Voxel-
Based Morphometric Analysis of 465 Normal Adult Human Brains. Neuroimage, 14,
685-700.
Goodale, M.A. (1990). Brain Asymmetries in the Control of Reaching. In M. A. Goodale (Ed.),
(1990). Vision and Action: The Control of Grasping (pp.14-32). Norwood, NJ: Ablex.
Guildford, J.P., & Zimmerman, W.F. (1953). The Guildford-Zimmerman Aptitude Survey, IV. Spatial
Visualisation Form B. Beverly Hills, CA: Sheridan.
Haaland, K.Y., & Harrington, D.H. (1989). Hemispheric Control of the Initial and Corrective
Components of Aiming Movements. Neuropsychologia, 27, 961-969.
Hardie, S.M., & Wright, L. (2014). Difference Between Left- and Right-Handers in
Approach/Avoidance Motivation: Influence of Consistency of Handedness Measures.
Frontiers in Psychology, 5, 1-10.
Harvey, M., Milner, A.D., & Roberts, R.C. (1995). An Investigation of Hemispatial Neglect Using
the Landmark Test. Brain and Cognition, 27, 59-78.
Hécaen, H., & Sauguet, J. (1971). Cerebral Dominance in Left-Handed Subjects. Cortex, 7, 19-48.
Hicks, R.A., Dusek, C., Larsen, F., Williams, S., & Pellegrini, R.J. (1980). Birth Complications and
the Distribution of Handedness. Cortex, 16, 483-486.
Hubel, K.A., Reed, B., Yund, E.W., Herron, T.J., & Woods, D.L. (2013). Computerised Measures of
Finger Tapping: Effects of Hand Dominance, Age, and Sex. Perceptual and Motor Skills,
116, 929-952.
Jewell, G., & McCourt, M.E. (2000). Pseudoneglect: A Review and Meta-Analysis of Performance
Factors in Line Bisection Tasks. Neuropsychologia, 38, 93-110.
Kertesz, A., Polk, M., Black, S.E., & Howell, J. (1990). Sex, Handedness, and the Morphometry of
the Cerebral Asymmetries on Magnetic Resonance Imaging. Brain Research, 530, 40-48.
25
Kilshaw, D., & Annett, M. (1983). Right- and Left-Hand Skill 1: Effects of Age, Sex and Hand
Preference Showing Superior Skill in Left-Handers. British Journal of Psychology, 74,
253-268.
Kim, S.K., Ashe, J., Hendrich, K., Ellermann, J.M., Merkle, H., Uğurbil, K., & Georgopoulos, A.P.
(1993) Functional Magnetic Resonance Imaging of Motor Cortex: Hemispheric
Asymmetry and Handedness. Science, 261, 615-617.
Kimura, D. (1973). The Asymmetry of the Human Brain. Scientific American, 228, 70-78.
Kimura, D. (1977). Acquisition of a Motor Skill After Left-Hemisphere Damage. Brain, 100, 527-
542.
Knecht, S., Dräger, B., Deppe, M., Bobe, L., Lohmann, H., Flöel, A., Ringelstein, E.B., &
Henningsen, H. (2000). Handedness and Hemispheric Language Dominance in Healthy
Humans. Brain, 123, 2512-2518.
Knecht, S., Dräger, B., Flöel, A., Lohmann, H., Breitenstein, C, Deppe, M., Henningsen, H., &
Ringelstein, E.B. (2001). Behavioural Relevance of Atypical Language Lateralisation in
Healthy Subjects. Brain, 124, 1657-1665.
Lai, C.S.L., Fisher, S.E., Hurst, J.A., Vargha-Khadem, F., & Monaco, A.P. (2001). A Forkhead-
Domain Gene is Mutated in a Severe Speech and Language Disorder. Nature, 413, 519-
523.
Liu, H., Stufflebeam, S.M., Sepulcre, J., Hadden, T., & Buckner, R.L. (2009). Evidence from Intrinsic
Activity that Asymmetry of the Human Brain is Controlled by Multiple Factors. PNAS,
106, 20499-20503.
Longo, M.R., & Lourenco, S.F. (2007). Spatial Attention and the Mental Number Line: Evidence for
Characteristic Biases and Compression. Neuropsychologia, 45, 1400-1407.
Manning, L., Halligan, P.W., & Marshall, J.C. (1990). Individual Variation in Line Bisection: A
Study of Normal Subjects with Application to the Interpretation of Visual Neglect.
Neuropsychologia, 28, 647-655.
Marshall, R.S., Lazar, R.M., Van Heertum, R.L., Esser, P.D., Perera, G.M., & Mohr, J.P. (1997).
Changes in Regional Cerebral Blood Flow Related to Line Bisection Discrimination and
Visual Attention Using HMPAO-SPECT. Neuroimage, 6, 139-144.
26
McManus, I.C. (1981). Handedness and Birth Stress. Psychological Medicine, 11, 485-496.
McManus, I.C. (1985). Handedness, Language Dominance and Aphasia: A Genetic Model.
Psychological Medicine Monograph Supplement, 15, Whole No. 8.
McManus, I.C. (2002). Right Hand, Left Hand: The Origins of Asymmetry in Brains, Bodies, Atoms
and Cultures. London/Cambridge, MA: Weidenfeld & Nicolson/Harvard University
Press.
McManus, I.C., Davison, A., & Armour, J.A.L. (2013). Multi-Locus Genetic Models of Handedness
Closely Resemble Single-Locus Models in Explaining Family Data and are Compatible
with Genome-Wide Association Studies. Annals of the New York Academy of Sciences,
1288, 48-58.
Medland, S.E., Duffy, D.L., Spurdle, A.B., Wright, M.J., Geffen, G.M., Montgomery, G.W., &
Martin, N.G. (2005). Opposite Effects of Androgen Receptor CAG Repeat Length on
Increased Risk of Left-Handedness in Males and Females. Behaviour Genetics, 35, 735-
744.
Moffat, S.D., Hampson, E., & Lee, D.H. (1998). Morphology of the Planum Temporale and Corpus
Callosum in Left Handers with Evidence of Left and Right Hemisphere Speech
Representation. Brain, 121, 2369-2379.
Nalçacı, E., Kalaycıoğlu, C., Çiçek, M., & Genç, Y. (2001). The Relationship Between Handedness
and Fine Motor Performance. Cortex, 37, 493-500.
Nicholls, M.E.R., Thomas, N.A., Loetscher, T., & Grimshaw, G.M. (2013). The Flinders Handedness
Survey (FLANDERS): A Brief Measure of Skilled Hand Preference. Cortex, 49, 2914-
2926.
O’Boyle, M.W., Cunnington, R., Silk, T.J., Vaughan, D., Jackson, G., Syngeniotis, A., & Egan, G.F.
(2005). Mathematically Gifted Male Adolescents Activate a Unique Brain Network
During Mental Rotation. Cognitive Brain Research, 25, 583-587.
Oldfield, R.C. (1971). The Assessment and Analysis of Handedness: The Edinburgh Inventory.
Neuropsychologia, 9, 97-133.
Perelle, I.B., & Ehrman, L. (1994). An International Study of Human Handedness: The Data.
Behaviour Genetics, 24, 217-227.
27
Peters, M. (1995). Handedness and Its Relation to Other Indices of Cerebral Lateralisation. In R.J.
Davidson, & K. Hugdahl (Eds.), (1996). Brain Asymmetry (pp. 183-214). Massachusetts,
MA: MIT Press.
Peters, M., & Durding, B. (1979). Left-Handers and Right-Handers Compared on a Motor Task.
Journal of Motor Behaviour, 11, 103-111.
Prichard, E., Propper, R.E., & Christman, S.D. (2013). Degree of Handedness, but not Direction, is a
Systematic Predictor of Cognitive Performance. Frontiers in Psychology, 4, 1-6.
Provins, K.A., & Cunliffe, P. (1972). The Reliability of Some Motor Performance Tests of
Handedness. Neuropsychologia, 10, 199-206.
Pujol, J., Deus, J., Losilla, J., & Capdevila, A. (1999). Cerebral Lateralisation of Language in Normal
Left-Handed People Studies by Functional MRI. Neurology, 52, 1038-1043.
Rotondaro, F., Merola, S., Aiello, M., Pinto, M., & Doricchi, F. (2015). Dissociation Between Line
Bisection and Mental-Number-Line Bisection in Healthy Adults. Neuropsychologia, 75,
565-576.
Searleman, A., Porac, C., & Coren, S. (1989). Relationship Between Birth Order, Birth Stress, and
Lateral Preferences: A Critical Review. Psychological Bulletin, 105, 397-408.
Serrien, D.J. (2009). Functional Connectivity Patterns during Motor Behaviour: The Impact of Past
on Present Activity. Human Brain Mapping, 30, 525-531.
Somers, M., Shields, L.S., Boks, M.P., Kahn, R.S., & Sommer, I.E. (2015). Cognitive Benefits of
Right-Handedness: A Meta-Analysis. Neuroscience and Behavioural Reviews, 51, 48-63.
Steinhuis, R.E., & Bryden, M.P. (1989). Different Dimensions of Hand Preference that Relate to
Skilled and Unskilled Activities. Cortex, 25, 289-304.
Sun, T., Patoine, C., Abu-Khalil, A., Visvader, J., Sum, E., Cherry, T.J., Orkin, S.H., Geschwind,
D.H., & Walsh, C.A. (2005). Early Asymmetry of gene Transcription in Embryonic
Human Left and Right Cerebral Cortex. Science, 308, 1794-1798.
Sun, T., & Walsh, C.A. (2006). Molecular Approaches to Brain Asymmetry and Handedness. Nature
Reviews Neuroscience, 7,655-662.
Szaflarski, J.P., Holland, S.K., Schmithorst, V.J., & Byars, A.W. (2006). fMRI Study of Language
Lateralisation in Children and Adults. Human Brain Mapping ,27, 202-212.
28
Théoret, H., Haque, J., & Pascual-Leone, A. (2001). Increased Variability of Paced Finger Tapping
Accuracy Following Repetitive Magnetic Stimulation of the Cerebellum in Humans.
Neuroscience Letters, 306, 29-32.
Vogel, J.J., Bowers, C.A., & Vogel, D.S. (2003). Cerebral Lateralisation of Spatial Abilities. A Meta-
Analysis. Brain and Cognition, 52, 197-204.
Volkmann, J., Schnitzler, A., Witte, O.W., & Freund, H.J. (1998). Handedness and Asymmetry of
Hand Representation in Human Motor Cortex. Journal of Neurophysiology, 79, 2149-
2154.
Weinberger, D.R., Luchins, D.J., Morihisa, J., & Wyatt, R.J. (1982). Asymmetrical Volumes of the
Right and Left Frontal and Occipital Regions of the Human Brain. Annals of Neurology,
11, 97-100.
Weintraub, S., & Mesulam, M.M. (1987). Right Cerebral Dominance in Spatial Attention. Further
Evidence Based on Ipsilateral Neglect. Archives of Neurology, 44, 621-625.
White, L.E., Andrews, T.J., Hulette, C., Richards, A., Groelle, A., Paydarfar, J., & Purves, D. (1997).
Structure of the Human Sensorimotor System II: Lateral Symmetry. Cerebral Cortex, 7,
31-47.
Witelson, S.F., & Pallie, W. (1973). Left Hemisphere Specialisation for Language in the Newborn:
Neuroanatomical Evidence of Asymmetry. Brain, 96, 641-646.
Wycke, M. (1966). The Effect of Brain Lesions in the Performance of an Arm-Hand Precision Task.
Neuropsychologia, 6, 125-134.
Zacks, J.M. (2008). Neuroimaging Studies of Mental Rotation: A Meta-Analysis and Review.
Journal of Cognitive Neuroscience, 20, 1-19.
Zago, L., Petit, L., Mellet, E., Jobard, G., Crivello, F., Joliot, M., Mazoyer, B., & Tzourio-Mazoyer,
N. (In Press). The Association between Hemispheric Specialisation for Language
Production and for Spatial Attention Depends on Left-Hand Preference Strength.
Neuropsychologia.
Ziemann, U. & Hallett, M. (2001). Hemispheric Asymmetry of Ipsilateral Motor Cortex Activation
During Unimanual motor Tasks: Further Evidence for Motor Dominance. Clinical
Neurophysiology, 112, 107-113.
29
Zilles, K., Dabringhaus, A., Geyer, S., Amunts, K., Qu, M., Schleicher, A., Gilissen, E., Schlaug, G.,
& Steinmetz, H. (1996). Structural Asymmetries in the Human Forebrain and the
Forebrain of Non-Human Primates and Rats. Neuroscience & Biobehavioural Reviews,
20, 593-605.
30
Appendices
Appendix 1: Personal details and extra-curricular activity questionnaire
1) Please circle the correct sex:
a) Male b) Female
2) Please state your nationality: ……………….
3) Please state your age: ……………….
4) Please circle the correct handedness status:
a) Left b) Right c) Mixed
5) Has your hand preference changed throughout the course of your life? (For example due to a
medical reason or an accident)
a) Yes b) No
6) Are you currently studying at university?
a) Yes b) No
If yes, what course do you study? ……………….
7) Do you play a musical instrument?
a) Yes b) No
If yes, which one(s) do you play? ……………….
How long have you played for? ……………….
8) Do you play a sport?
a) Yes b) No
If yes, which sport do you play? ……………….
How long have you played for? ……………….
9) Do you play video/computer games?
a) Yes b) No
If yes, how many hours a week do you spend playing (roughly)? ……………….
10) Do you draw at all in your free time?
a) Yes b) No
If yes, how many hours a week do you spend drawing? ……………….
31
And how would you rate your drawing ability out of 10 (1 being poor and 10 being excellent)?
……………….
Appendix 2: Handedness inventory
The twenty questions below ask which hand you prefer to use in a number of different situations.
Please tick one box for each question, indicating whether you prefer to use the left-hand, either-hand,
or the right-hand for that task. Only tick the ‘either’ box if one hand is truly no better than the other.
Please answer all questions, and even if you have had little experience in a particular task, try
imagining doing that task and select a response.
Question Preferred Hand
Left Either Right
With which hand do you write?
In which hand do you prefer to use a spoon when
eating?
In which hand do you prefer to hold a toothbrush
when cleaning your teeth?
In which hand do you hold a match when you
strike it?
In which hand do you prefer to hold the rubber
when erasing a pencil mark?
In which hand do you hold the needle when you
are sewing?
When buttering bread, which hand holds the
knife?
In which hand do you hold a hammer?
In which hand do you hold the peeler when
peeling an apple?
Which hand do you use to draw?
Which hand do you place at the top of a broom to
sweep?
With which hand do you hold a key to open a
door?
With which hand do you operate a computer
mouse?
When holding a large bat (requires two hands)
which hand is nearest the base of the bat?
With which hand do you throw a ball?
With which hand do you turn the page of a book?
32
Handedness Score (experimenter fills this out): …………….
Responses of left, either and right are given scores of -1, 0, +1 respectively. These scores are then
summed to give a test score of -20 to +20. Individuals with scores ranging between -20 and -10 are
deemed to be left handed whereas individuals with scores ranging between +10 and +20 are deemed
to be right handed. Individuals with scores in between these ranges are deemed to be mixed handed.
*Highlighted questions were the original 10 questions in the FLANDERS inventory (Nicholls et al.,
2013)
Appendix 3: Information sheet
This is an invitation to take part in a research study on effects that influence hemisphere specific
tasks.
Before you decide if you wish to take part, it is important for you to understand why the research is
being done and what it will involve. Please take time to read the following information carefully.
If you participate, you will complete two questionnaires. One of which is a handedness inventory to
establish which is your preferred hand and the other is a personal details questionnaire (e.g. gender,
age etc.). After completing the questionnaires, you will complete two separate tasks. One task is a
speed finger tapping task which will use your dominant and non-dominant hand. The other task is a
line bisection task where participants must mark a line where the middle should be.
The whole procedure will last no more than 30 minutes.
Participation in this study is totally voluntary and you are under no obligation to take part. You are
free to withdraw at any point before or during the study. All data collected will be kept confidential
and used for research purposes only. It will be stored in compliance with the Data Protection Act.
If you have any questions or concerns, please don’t hesitate to ask now. I can also be contacted after
your participation at the above address.
If you have any complaints about the study, please contact:
Stephen Jackson (Chair of Ethics Committee)
With which hand do you hold a phone?
With which hand do you open a jar?
With which hand do you hold a TV remote
control?
When playing snooker/pool which hand is nearest
the base of the cue?
33
Appendix 4: Line bisection task instructions
You will be presented with a series of nine drawings of horizontal lines drawn in the centre of a plain
piece of landscape A4 paper. These lines will be of varying lengths. Please will you mark the line
with a pen, with your dominant hand, where you think the centre should be so that the line is dissected
into two equal parts. The distance between the mark you make and the true centre of the line will be
measured in millimetres and recorded.
Appendix 5: Tapping task instructions
During this task, you will have to tap the spacebar as fast as you can for 10-second intervals. Please
be sure to tap with your hand flat on the table using only your index finger to tap the spacebar. You
will complete three 10-second intervals with your dominant hand and three 10-second intervals with
your non-dominant hand. Therefore, you will complete six trials in total, with dominant and non-
dominant trials in a random order. At the start of this task, the computer will ask for your details
before then showing you more instructions on the screen. Once you have read and understood the
instructions you can press any button on the keyboard to begin, however once you have pressed a
button you will have a three second count in before you need to start tapping. Please do not start
tapping before “go” appears. After each period of 10 seconds a screen will appear telling you to stop
and to provide a break which will last 30 seconds, you then press the “s” button again to begin the
next trial. The interval between your taps and your reaction times will be measured in milliseconds
for both your dominant and non-dominant hand and recorded.
Appendix 6: Debrief sheet
Background/Hypothesis:
It has been found that motor tasks have strong links with the left hemisphere and that spatial functions
tasks have strong links with the right hemisphere. Therefore, this experiment predicted that left-
handers would show an advantage in spatial functions tasks and that right-handers would show an
advantage in motor tasks due to the natural lateralisation process of the hemispheres associated with
handedness.
Design and Dependent Measures:
A repeated measures design was used whereby all participants completed two tasks. One was a
tapping task to assess motor function and therefore targeted the left hemisphere of the brain. The other
was the line bisection task in order to assess spatial functions and therefore targeted the right
hemisphere. For the tapping task, the interval between taps and reaction times was measured in
34
milliseconds for both the dominant and non-dominant hand. For the line bisection task, the distance
from the true centre of the line was measured in millimetres and recorded.
Intended Analysis:
For the results generated from the line bisection task a 2x3 repeated measures ANOVA will be
conducted; using the independent variable (IV) of group (left and right) and the IV of length of line
(2cm, 10cm and 20cm). For the results generated by the tapping task a 2x2 repeated measures
ANOVA will be conducted, using the IV of group (left and right) and the IV of hand (dominant and
non-dominant).
Useful Reading:
Fink, G.R., Marshall, J.C., Halligan, P.W., Frith, C.D., Driver, J., Frackowiack, R.S.J. & Dolan, R.J.
(1999). The Neural Consequences of Conflict Between Intention and the Senses. Brain, 122,
497–512.
Nicholls, M.E.R., Thomas, N.A., Loetscher, T. & Grimshaw, G.M. (2013). The Flinders Handedness
Survey (FLANDERS): A Brief Measure of Skilled Hand Preference. Cortex, 49, 2914-2926.
Taylor, H.G. & Heilam, K.M. (1980). Left-Hemisphere Motor Dominance in Righthanders. Cortex,
16, 587-603.
