Donald Robert Rickgauer Master's Thesis
Donald Robert Rickgauer Master's Thesis
Donald Robert Rickgauer Master's Thesis
A Thesis
Presented
to the faculty of
In Partial Fulfillment
Master of Arts
In
Psychology
by
Spring 2010
A CORRELATIONAL STUDY ON THE RELATIONSHIP
A Thesis
by
Spring 2010
____________________________________
Mark J. Morlock, Ph.D.
_____________________________________
Eddie Vela, Ph.D.
_____________________________________
Michael Ennis, Ph.D.
ACKNOWLEDGEMENTS
The first and foremost of those I’d like to acknowledge is Dr. Eddie Vela,
whose spirited and bountiful encouragement made this thesis and my entire pursuit of the
degree for which this thesis was written possible. From my first pondering of my future
I would also like to thank Dr. Michael Ennis for his support. From the first
incarnations of this thesis, which are now rather distant from the current one, to its final
form, he has shown great patience and eagerness to see me develop as a researcher, even
when the parameters for my study were very ambiguous. This is the mark of a great
educator, and I’m thankful to have had him and his resources at my disposal
I would also like to thank my parents for their financial support through my
undergraduate years, in whatever end of the world I spent them, and their unending
emotional support and encouragement. I would also like to thank my brother, Peter
University of Iowa for allowing me use of his PANAS scale, and for streamlining the
Finally, I would like to thank my research assistants, Nathaniel, Julia and Joel,
without whom I would surely have been lost in a quagmire of data, as well as not
PAGE
CHAPTER
I. Introduction............................................................................................... 1
Participants....................................................................................... 17
Materials .......................................................................................... 18
Procedure ......................................................................................... 19
IV. Results....................................................................................................... 22
V. Discussion ................................................................................................. 30
Limitations ....................................................................................... 34
Suggestions for future research........................................................ 35
PAGE
References ................................................................................................................... 38
Appendices
A. Informed Consent............................................................................................ 45
B. Pre-game demographic inventory ................................................................... 47
C. Hand Placement Sheet .................................................................................... 49
D. Post-game inventory ....................................................................................... 51
E. Debriefing ....................................................................................................... 53
LIST OF TABLES
TABLE PAGE
vi
LIST OF FIGURES
FIGURE PAGE
3. Positive Affect Change Across Right Hand 2D:4D Ratios and Gender ............... 25
vii
ABSTRACT
by
Spring 2010
The ratio of the length of the index finger and the ring finger has been found
testosterone exposure. In the present study, we examined the relationship between this
ratio (2D:4D) and emotional arousal, as measured using the Positive and Negative Affect
Scale (PANAS), in a competitive setting. For this study, 125 participants had their finger
lengths measured and participated in a competitive video game, Soul Caliber 2. Their
state affect was recorded by self-report inventory both before and after playing the game.
Results showed a significant change in positive affect after playing the game. The
valence of this change was found to be statistically correlated with the 2D:4D ratio of the
right hand for both males and females. Those with neutral ratios (the middle third of the
data) exhibited the greatest change, while those with masculine- and feminine- typical
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ratios (the bottom and top thirds of the data, respectively) exhibited less change in
exposure may act as a balancing factor in mood around competitive settings, while those
whose 2D:4D ratio does not indicate this kind of exposure have higher reactivity to
competition.
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CHAPTER I
INTRODUCTION
For years, psychologists have observed human behavior and have sought to
find its roots. Biopsychologists and evolutionary psychologists look for answers on the
chemical and genetic levels, searching for predisposing factors that may lean an
individual towards one type of behavior or another before experience with the outside
world becomes relevant. Developmental and social psychologists look for answers in our
environment and experiences, finding patterns that help predict human behaviors. It is
hardly a topic of discussion whether humans are driven exclusively by nature or nurture.
It is almost unanimously accepted that both play important parts (Dusheck, 2002). Not
only are our genetic and environmental components both important by themselves, but
their interaction throughout life continues to uniquely affect how we develop (Gottlieb,
With that in mind, this study explored the relationship between the ratio of
length of the index finer (2D) to the ring finger (4D) (known as the 2D:4D ratio), and
change in state affect in a competitive setting. It is hoped that this study will reveal more
about the predispositions that humans are subject to as a result of intrauterine factors.
The effects of these early physiological factors can be seen throughout life, but begin to
develop in the womb, before the human has received a gender identity.
1
2
produced in the testes, begin to coordinate the growth of typical male physical attributes,
most notably sexual reproductive organs. The development of these organs is dependent
upon these androgens, one of which, prenatal testosterone (Breedlove, Cooke & Jordan,
1999), will be the hormone of greatest focus in the present study. Several months later,
the brain begins to experience changes as a result of the presence or absence of prenatal
testosterone. During this time, the presence of prenatal testosterone forms another
hormone, called estradiol, which causes the brain to grow more in overall size (Harding,
2004). It is believed that this change in brain mass is where much of the individual’s
later gender identity is decided (Swaab & Garcia-Falgueras, 2009). Also, as a result of
the development of the prenatal male, which results in an increase in the number of
connections between the male brain and the muscles innervated by these motoneurons
interesting sexual dimorphism takes place in the hands. R. George (1930) was among the
first to discover that there is not always a clear pattern among humans whether the index
or ring finger is shorter. His results showed, based on 201 males and 109 females, that
males tended to have a shorter index finger than ring finger, while females tended to have
the opposite. According to George (1930), men typically exhibit lower values in 2D:4D
ratio than women. It was suggested that this relationship may owe most, if not all, of its
(Manning, Scutt, Wilson & Lewis-Jones, 1998). Further studies into the link between
2D:4D ratio and testosterone investigated men with genetic variations in the androgen
receptor genes making them more sensitive to testosterone (Manning, Bundred, Newton
& Flanagan, 2003). These individuals exhibited lower, more masculine 2D:4D ratios.
Lower 2D:4D ratios have also been exhibited in individuals with congenital adrenal
hyperplasia, which exposes the developing fetus to higher levels of testosterone both
male and female, when compared with control groups (Ökten, Kalyoncu & Yariş, 2002;
circulating testosterone in the body later in life (Hampson & Breedlove, 2001). This has
also been shown to correlate with greater readiness for performance and aggression. For
example, studies in the early half of the 20th century have found that manipulations of
testosterone in hens (Allee, Colias & Lutherman, 1939) and mice (Beeman, 1947a & b)
responses, and vice versa. In humans, a positive correlation has been found between
increase being strongest in males (Archer, 2006). Furthermore, physical aggression has
also been shown to be correlated with 2D:4D ratio in men, but not women (Bailey &
Hurd, 2005). The study revealed that men with lower, more masculine 2D:4D ratios
scored significantly higher in trait physical aggression, with the right hand showing much
traits has intrigued scientists for years across numerous fields of study, from
variety of interest in this field, the reason as to why this relationship between these two
measures should exist at all remains a mystery, if there is any reason. It is more likely
that this relationship owes its existence to the hox genes that are responsible for the
development of both fingers and the penis (Dickman, 1997; Jorgenson, Ruman, Doherty
To sum up, research has found numerous relationships between 2D:4D and
observable personality phenotypes: sexual preferences, with higher ratios correlating with
more feminine-typical preferences (Manning, Churchill & Peters, 2007); sexual practices,
with lower ratios correlating with male-typical practices and presentations (Fink, Seydel,
Manning & Kappeler, 2007; Nottebohm, 1980); aggression, with lower finger ratios
correlating with greater aggression (Bailey & Hurd, 2005); competition, with lower
finger ratios correlating with more competitive individuals (Manning & Taylor, 2001). It
is the objective of this study to add to the growing number of studies in 2D:4D research
and further illuminate the relationship between a measurable finger ratio and differences
in behavior. This study should help develop a stronger understanding of the nature-
LITERATURE REVIEW
The scientific findings on finger length ratio date back to a time when ideas of
evolution in humans were still young. The “Darwinist” ideas were still just beginning to
blossom in the scientific world and to be extrapolated into the various models of specific
selective mechanisms, such as predator/prey evolution and the evolution of the eye.
These models are all centered on the idea that certain traits in organisms contributed to
the continuing survival of a species. The earliest observations of index finger (2D) and
ring finger (4D) asymmetry only noted that men had shorter index fingers than women
(Ecker, 1875). Though it was not yet speculated as to why this difference existed, this
observation would come to be of great interest in the next century. It was not until much
later that finger length differences were finally recorded and classified (George, 1930).
This is when a statistically significant difference between men and women in the length
of their index and ring fingers relative to one another was first noted. George noted for
the first time that men tended to have the lower 2D:4D ratios, with a shorter index finger
and longer ring finger, while women tended to have the higher 2D:4D ratios, with the
longer index finger and the shorter ring finger. Since these findings, 2D:4D ratios have
been measured across races and cultures of the world. Manning and colleagues (2007)
surveyed 255,116 participants worldwide, including those from White, Asian, Middle-
5
6
Eastern, Black and Chinese ethnicities. Their data was analyzed for 2D:4D differences
across genders and sexual orientations. The results showed Black and Chinese
participants had significantly lower ratios than White, Asian and Middle-Eastern
nationalities, surveying people of 11 countries (plus the United States) and finding
For decades after the first cataloguing of 2D:4D ratios, it was not yet known
that this relationship between digit lengths was due to differences in prenatal testosterone
regulation. Wilson (1983) was among the first researchers to suggest that this
relationship may exist as a result of genetic differences, wherein sex hormones that affect
bodily growth are delegated differently, with higher levels of the hormones causing the
fourth digit to grow more than the index finger, and lower levels causing less growth in
this finger. He was also the first to begin linking this ratio to personality traits, finding
significance in the relationship between the 2D:4D ratios of women and their
assertiveness.
research to be uncovered with these findings. The presence of prenatal testosterone not
only accounts for developmental differences between men and women throughout their
bodies, but also for developmental differences in their brains (Harding, 2004; Swaab &
Garcia Falgueras, 2009; Breedlove et al., 1999). Certain structures in the brains of
humans have shown differences in mass between genders. Males have significantly
and females have significantly greater volume in the hippocampus, which encodes short-
term memory, and the striatum, which plays a role in reward motivation and executive
function (Caviness, Kennedy, Richelme, Rademacher & Filipek, 1996; Giedd et al. 1997;
Lange, Giedd, Castellanos, Vaituzis & Rapoport, 1997). The male typical difference was
et al., 2009). Differences in brain structures most likely are related to levels of prenatal
hormones. However, we can also find differentiation in behavior within each gender,
utero. Given that prenatal hormones (not circulating hormones) are responsible for the
dichotomy in digit ratios, as well as tend to affect our sensitivity to circulating hormones
later in life (Archer, 2006), it has become reasonable to suppose that some correlations
may exist between personality and digit ratio, as Glenn (1983) has found. His findings
have revealed numerous possibilities for many different dependent variables associated
Theories on why 2D:4D ratio should have any correlation with any displayed
traits are rooted in this endocrinology of the developing fetus. It has been shown that
higher levels of prenatal testosterone are also related to higher levels of prenatal estradiol,
which plays a significant role in neural development (Harding, 2004). The increased
presence of estradiol causes the brain to increase in mass, which may be linked to certain
sexually dimorphic traits (Breedlove et al., 1999). There is still no clear understanding of
8
what happens specifically in the brain during this period of development that may
account for all of the sexual dimorphisms. It is believed that high levels of testosterone
in utero promote development of the right hemisphere of the brain (Geschwind &
Galaburda, 1985). Breedlove et al. (1999) has cited the existence of more motoneuron
connections in the “masculinized” brain. These two factors may have a connection to
greater development of spatial skills in males. Still, while the deeper understanding of
this relationship has yet to be discovered, most results still indicate that exposure to
causes structural changes in the brain and, thus, behavioral changes involved exposing
female guinea pigs to androgens during fetal development (Phoenix, Hoy, Gerall &
Young, 1959). The results of this experiment showed that the female guinea pigs did not
display the typical sexually receptive behaviors toward male guinea pigs. This exposure
Inversely, male zebra finches have been shown to have a larger robustus archistriatum
(RA) nucleus than females. This is a crucial structure in the zebra finch mating practice,
as it assists the male in the production of songs that attract the female of the species.
That is, females will recognize this more masculine pattern of singing and will be
structure induced the females to sing in more masculine patterns (Nottebohm, 1980). The
implications of these studies on animals are interestingly reflected in the sexual practices
9
heterosexual, homosexual and bisexual males and females has yielded typically
masculine ratios for homosexual women and feminine ratios in homosexual men
(McFadden & Shubel, 2002; Manning et al., 2007), though not always consistently or
Loehlin, Breedlove, Lippa, Manning & Rahman, 2005). Another study showed a
significant negative correlation between male 2D:4D ratio and ratings by women on how
well they thought the men danced (Fink et al., 2007), which was implied to be related to
how women perceived symmetry in a male’s dancing patterns (Brown, Cronk, Grochow,
Jacobson, Liu & Popovic, 2005). This relationship between 2D:4D ratio and perceived
dancing ability is reflective of the studies on the zebra finch’s mating ritual of singing to
attract the female. Higher levels of testosterone promote behaviors which are intended to
convince the female to choose a particular mating partner over other possible mating
partners. These competitive mating rituals are seen across numerous species (Darwin,
1871).
abnormalities increased the belief that exposure to prenatal androgens in utero affects not
only the finger length ratio, but also certain hormonally-balanced traits. Individuals, both
male and female, with congenital adrenal hyperplasia (CAH), a disorder known to be
associated with abnormally high levels of prenatal and circulating testosterone, exhibited
a much lower 2D:4D ratio than control groups (Ökten, Kalyoncu & Yariş, 2002; Brown
10
amniocentesis samples, measuring the ratio of fetal testosterone to fetal estradiol and
finding a negative correlation between this ratio and 2D:4D ratios at the age of 2 years
In addition to CAH, other disorders have also been found to have significant
relationships with 2D:4D ratio, vis-à-vis endocrine system and hormone abnormalities.
Perhaps the most prominent of hormone-linked disorders to have been found correlated
with 2D:4D ratio is autism (Manning et al., 2001; Voracek, 2008). While it was already
1978), Manning and colleagues sought to discover if low 2D:4D ratio could be a potential
marker of autism. Their results showed that children with autism had significantly lower
ratios on both hands than children with Asperger’s Syndrome (AS) and control children,
and that their siblings and parents who were not afflicted with autism or AS also had
lower ratios than control populations. These findings suggested that exposure to high
levels of prenatal androgen may make the fetus more susceptible to autism. Also
associated with low 2D:4D ratio is ADHD in boys (Martel, 2008). The study found
2D:4D ratio has also been studied for correlations with disorders in
individuals with female-typical ratios. Anxiety, for example, was found to have some
correlation with 2D:4D ratios. Evardone and Alexander (2009) found that males who had
higher digit ratios reported more trait anxiety than men with lower digit ratios, suggesting
11
that men with less exposure to prenatal androgens may be more susceptible to anxiety.
However, this differentiation in trait anxiety across digit ratios was not found in women
in this particular study. Another disorder to have a correlation with female-typical 2D:4D
related to an imbalance of hormones because of its typical onset during the reproductive
age, and almost never before or after. This also signals a disruption in the lateralization
of the left, language-oriented hemisphere of the brain, which is typically more dominant
2D:4D ratio than control females, though males were found to have a lower 2D:4D ratio.
Literature suggests that men are prone to a different, more degenerative type of
schizophrenia, as compared to women (Castle & Murray, 1991), which may account for
the difference in 2D:4D ratio. In addition, studies correlating 2D:4D ratio and the eating
disorders bulimia nervosa and anorexia nervosa, two more female-typical disorder,
showed that females with lower, more masculine ratios were less susceptible to these
Due to the fact that this study implies the effects of prenatal exposure to
mention one of the more widely known and misunderstood incarnations of a testosterone-
as a variant to testosterone for patients who may suffer from hormone deficiency.
Research on anabolic steroid users and abusers has shown that psychiatric symptoms of
12
steroid misuse may include aggression (Pope, Kouri & Hudson, 2000), mood swings with
violent, manic episodes (Pope & Katz, 1988) paranoid jealousy, extreme irritability,
delusions and impaired judgment (NIDA, 2009). While it is assumed that none of the
participants in this study are anabolic steroid abusers, these findings are relevant to the
present study because of its implications for higher levels of circulating testosterone.
Since it is the male hormone testosterone that, when taken in excess levels, can cause
greater negative affect symptoms, it may stand to indicate the direction of the relationship
potential relationship is only considered in light of evidence from steroid abusers who
have 10 to 100 times the therapeutic amount of this hormone. The implications of affect
humans, it may indicate the direction of the affect in those with higher exposure to
intrauterine testosterone.
Many studies have already shown significant differences between men and
women in many different traits and task performances. Fink and colleagues (2002)
measured the correlation between 2D:4D ratios and personality traits, as determined by
the NEO Five Factor Inventory (NEO-FFI). The NEO-FFI included the “Big Five”
neuroticism. It was found that neuroticism was positively correlated with finger ratio on
the right hand for both genders. Males did not correlate significantly with any of the
13
personality traits. It was concluded that the association between personality and 2D:4D
ratio was “weak,” but still indicated “gender related behaviour is affected by the amount
of steroid hormones present during critical periods of prenatal development” (pg 1).
Men have also been known to score higher in physical and verbal aggression
than women (Archer, 2006), and individuals with lower 2D:4D ratios have shown similar
results (Bailey & Hurd, 2005). In addition to aggression, males display more sensation-
seeking and risk-taking than women (Zuckerman, Eysenck & Eysenck 1978; Apicella,
Dreber, Campbell, Gray, Hoffman, & Little, 2008), with similar results being reflected in
2D:4D ratios (Austin, Manning, McInroy & Mathews, 2002). One study by Resnick and
colleagues (1993) found that female members of opposite-sex twins displayed higher
consistent with the view that sharing a womb with a male exposed them to higher levels
in the United Kingdom. The results of these studies showed that professional male
soccer players had lower, more masculine 2D:4D ratios than a control group of men, and
males with a lower 2D:4D ratio reported higher achievement in sports than males with
more neutral or female-typical 2D:4D ratios. Similar results have been discovered in
other sports, such as rugby, basketball (Tester, 2007), and general sporting ability in
females (Paul, Kato, Hunkin, Vivekanandan & Spector, 2006). These studies are of great
Competition is recognized in Darwin’s The Origin of the Species (1871) in terms of the
14
male’s attempt to find a mate and attain the resources necessary to do so before another
male can do this first. This idea about competition is further reflected in a study by
Coates and colleagues (2009) in which 2D:4D ratios were used as a predictor of the level
of success of financial traders in the United Kingdom. The results revealed a negative
correlation between 2D:4D ratios and level of success. These two studies show us that
individuals who are exposed to higher levels of prenatal androgens are more disposed to
put themselves into competitive situations. In addition, these individuals are more likely
to succeed in those situations than individuals who have not been exposed to higher
levels of prenatal androgens. Consider these findings in light of the findings of van Honk
and colleagues (2004), Booth and colleagues (1999) and other studies that correlated
testosterone levels and 2D:4D ratio with sensation-seeking and risk-taking (e.g.,
Zuckerman et al., 1978; Apicella et al., 2008). The implication is that an individual
the animal kingdom are known to compete for a female’s favor and the right to breed
with that female, as well as for contested resources. Birds sing songs and may put on
dances, wolves will fight each other, and humans may do any and all of the above. These
are all practices that have evolved because they help in leaving more genes behind. It is
considered to be in the “best interest” of the genes to beat out others to spread themselves
possible (Dawkins, 1976). Therefore, these competitive practices have evolved through
15
In order to further prove this point in humans, consider that 2D:4D ratios in
males has been shown to correlate with a woman’s approval of the respective male’s
dancing patterns, which tend to be more symmetrical with lower ratios (Fink et al., 2007).
In the end, it could be suggested that much of what is competition in modern society is
hardly anything more than an extension of what was once just a primal dance of
seduction. In any case, a correlation has been found between prenatal testosterone
correlation between 2D:4D ratio and, among other things, competitiveness, particularly in
competitiveness and 2D:4D ratio is similar for both males and females, or if it is sexually
dichotomous, since Manning et al.’s sample of athletes only included males. Still, it
would be reasonable to search for a correlation between 2D:4D ratio and arousal from
competition in both genders, since it is theoretically higher levels of testosterone that are
It is with this in mind that we seek to bring out this competitive spirit in both
male and female participants and determine whether the competition evoked in a video
game will cause differential changes in affect. We believe that a 15-minute session of
as video games have been used in numerous laboratory settings to bring about changes in
testosterone and cortisol levels (Mazur, Susman and Edelbrock, 1997; Hébert, Béland,
16
Dionne, Fournelle, Crête & Lupien, 2004) and feelings of aggression and hostility
Hypothesis
The research question that motivated the study was the degree to which
2D:4D ratio is correlated with changes in reported state affect as assessed in a pre-test
and post-test paradigm. Based on the current literature, it is hypothesized that the
intervention should produce a negative correlation between 2D:4D ratio and affect
change, with masculine-typical ratios exhibiting the greatest change in affect and
METHODS
Participants
University, Chico. Sign-up sheets were posted in Modoc Hall, offering extra credit to
building, so it can be assumed that most students who signed up for this study had been
volunteer sign-up, with the exception of the pilot study. This consisted of four
participants were required to give any contact information, as their participation was only
needed in one instance. All participants were given the e-mail address of the primary
researcher and the thesis chair if they required any information after they had completed
their participation.
For this study, 125 participants were used, with 87 females (69.6%) and 38
Participants were also asked about their video game playing habits. A total of 81.6% of
males and 32.2% of females said that they sometimes play video games. Of those
participants, males reported playing an average of 5.97 hours per week (SD = 5.35) and
females reported playing an average of 2.85 hours per week (SD = 3.23). When asked if
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they had played a fighting game before, 88.8% of all participants said that they had,
implying some level of general familiarity with the genre of game used for this study.
Materials
It was important to find a video game that would place two players against
each other in one-on-one competition. Toward this end, Soul Caliber 2 for the Microsoft
Xbox was determined to be the most appropriate choice. This game allows players to
choose their own characters, who then engage each other in a three-dimensional
rounds, usually finishing within 15-20 seconds each. It was determined that the fast
competition with each other in this game) and rapid progression of game-play (latency
between moments of player action, such as loading screens, was minimal) would help
control for any confounding factors related to frustration in adapting to the game or loss
of stimulation between matches. Participants used the Xbox controllers that came with
camera were used to photograph the hands of the participants. The second and fourth
digits from each hand in each photo were measured, starting from the basal crease of each
finger and ending at the tip of the respective finger, on a computer using the freeware
version of Iconico Screen Calipers. When this measuring tool was not available,
Mathworks MatLabs, programmed with an algorithm to measure the pixels between two
State affect was evaluated using the Positive Affect Negative Affect Scale
(PANAS), developed by Watson, Clark & Tellegen. (1988). This measure, used to
quantify both state and trait affect, consists of 10 positive affect items (attentive,
interested, alert, excited, enthusiastic, inspired, proud, determined, strong and active) and
10 negative affect items (distressed, upset, hostile, irritable, angry, scared, afraid, fearful,
ashamed, guilty, nervous and jittery) compiled by factor analysis, and is considered to
cover a broad range of the affective lexicon. A normative study on the PANAS has
assured the validity of this study across multiple demographics (Crawford & Henry,
2004). Permission was obtained from both co-author David Watson of the University of
Procedure
when they signed up. Participants were scheduled two at a time for each 30-minute slot.
This was to ensure that the participant has someone with which to compete. If only one
participant was available for the 30-minute slot, the researcher present filled in the open
spot and competed against the participant. Researchers were instructed to keep their
Upon arriving at the laboratory, students were given an informed consent form
(Appendix B) to inform them of their rights as a participant in this study. When both
participants had arrived, or when it was determined that only one participant would be in
this session, they were given the pre-game demographic inventory (Appendix C). Upon
completion, the participant was then brought to a station in the lab set up for hand photos.
They were instructed to place their hands flat and palms up on a sheet of paper with two
designated spaces, one for each hand (Appendix D). A photo was then taken with the
camera set on a tripod and positioned directly above and facing the paper. The exact
position of the camera was maintained throughout the study. These photos were saved on
Participants were then given the PANAS to complete (Appendix E). The
researcher instructed the participants to rate how each question on the PANAS with
respect to how they feel at that specific moment, so as to gather data on state affect. In
addition, participants were asked to take their time in responding honestly to the items.
After both participants completed the PANAS, they were set up to play Soul Caliber 2 for
15 minutes. The game was ready and waiting at the character select screen before
participants arrived with the volume on mute, to decrease distractions. When both
participants were ready, the mute was taken off and the volume was kept at an audible,
yet reasonable, level. Participants were allowed to choose any character they wished and
could change characters after each match if they chose to do so. Brief instructions on
specific controls for this game were given at the outset of the game-playing. After fifteen
minutes of playing, participants were instructed to put down their controllers and
21
complete the post-game inventory (Appendix F). The game was again muted to avoid
distractions. After this, they completed the PANAS a second time, again being instructed
to rate each item as it pertains to how they felt at that particular moment. Upon
completing the PANAS for the second time, participants were debriefed (Appendix G).
CHAPTER VI
RESULTS
The 2D:4D ratios for each participant were determined by having three
separate researchers independently measure the finger lengths for each participant hand
photo. Left and right hand 2D:4D ratios were computed for each of the three research
assistants. Cronbach alphas were then computed to determine consistency among the
three raters. A high inter-rater reliability was found for this method for both the left
hand, α = 95.2%, and the right hand, α = 95.2%. These three ratios for each hand, as
determined by the three raters, were then averaged into a new variable, representing one
ratio for each hand for each participant. Collapsing across all participants the ratio for the
right hand (M = .953, SD = .031) and the left hand (M = .961, SD = .031) showed that on
average the second finger (2D) was shorter than the fourth finger (4D).
A new variable was then created for the average of each hand, separating the
measured values by thirds into three categories: masculine-typical hand ratio (Left hand
N = 42, right hand N = 45), neutral hand ratio (Left hand N = 39, right hand N = 46) and
feminine-typical hand ratio (Left hand N = 44, right hand N = 34). This variable was
defined for each hand by finding the lower, middle and upper thirds of the 2D:4D ratios
relationship between 2D:4D ratio for each hand and changes in affect from before to after
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23
playing the competitive video game. The grouping variable for each ANOVA was ratio
category, determined separately for each hand (masculine-typical lower third ratio,
feminine-typical upper third ratio, and gender-neutral middle third ratio) and the
dependent variable was the difference in the pre- and post-test PANAS scores calculated
separately for positive and negative affect changes. Hence, a total of four separate
ANOVAs were computed; for the left hand two ANOVAs were computed, with one
using the difference score for positive affect and the other using the difference score for
negative affect as the dependent variable. Two more ANOVAs using the same grouping
variable and dependent variables were computed for the right hand. A significant main
effect was found for 2D:4D ratio on the right hand with change in positive affect, F (2,
A marginally significant main effect was found for 2D:4D ratio on the left hand on
overall change in positive affect, F (2, 121) = 3.022, p = .052. No significant main effect
was found at the .05 level for the right hand, F (2, 122) = .316, or the left hand, F (2, 122)
grouping variable and either change in positive affect or change in negative affect as the
change in positive affect, t (122) = -2.89, p < .01, but not on overall change in negative
significant relationships of right and left hand 2D:4D ratios and gender with overall
change in positive affect. This ANOVA was performed to examine the relationship of
overall change of positive affect with 2D:4D ratio for the right hand and gender, as well
as with the 2D:4D ratio for the left hand and gender. The main effect for the right hand
on overall change in positive affect remained significant, F (2, 118) = 6.46, p < .05, and
was also significant for gender, F (1, 118) = 7.455, p < .05, with no significant interaction
between right hand 2D:4D ratio and gender (See Figure 3).
26
positive affect between masculine and neutral hand ratios, but not between masculine and
feminine hand ratios. The main effect for the left hand on overall change in positive
affect was found to no longer be significant at the .05 level when including gender in the
factorial design, F (2, 118) = 1.923. These findings are in accordance with the relevant
research in that the strongest differences were found in the right hand (Fink et al., 2004;
Bailey & Hurd, 2005). Table 1 shows the means for all these conditions.
The hypothesis that changes in affect were linearly related to changes in digit
ratio, however, was not confirmed. Those with neutral ratios (between male-typical and
female-typical ratios) exhibited the strongest change in positive affect for both males (M
= 3.83, SD = 3.51) and females (M = 6.72, SD = 6.35), while those with masculine-
typical hand ratios, both male (M = -1.40, SD = 5.47) and female (M = 2.17, SD = 6.21),
and feminine-typical hand ratios, both male (M = 1.18, SD = 5.94) and female (M = 4.21,
SD = 5.96) had weaker changes, significantly so for masculine ratios compared to neutral.
Follow-up Analyses
These were found to be non-significant and did not affect the results mentioned in the
previous subsection. Their corresponding analyses are included here in this subsection.
affect. In this questionnaire (available in the appendices), the participants were asked, in
addition to the factor of gender, their age, if they play video games (yes/no), how many
Table 1
Means & Standard Deviations of Positive & Negative Affect, Pre- & Post-Test
Note: Digit ratio categories were created by dividing participants according to upper, middle and lower digit ratio cut-off points.
28
hours per week they play video games (continuous), if they have ever played fighting
games before (yes/no), and how much of their game-playing time was spent playing
fighting games (1-7 Likert scale). Researchers were also instructed on this questionnaire
to privately mark if the participant’s opponent was male or female. In coding this, males
were entered as ‘1’ and females as ‘2.’ This was paired with the participant’s gender
(coded similarly) to create a variable stating whether the match was male/male (2),
between all of these variables, (except for gender pairing, for which one-way ANOVA
was conducted) and overall change in positive affect (overall change in negative affect is
being omitted at this point because it never approached significance with either hand),
and no significant correlation (or main effect) was found with any of these variables.
.073.
participants filled out asked them how well they enjoyed their game (1-7 Likert scale),
how well they enjoyed playing with the other participant / present researcher (1-7 Likert
scale), if they would play the game again with this partner (yes/no), and then a 1-7 Likert
scale of their perceived in-game performance in the first five minutes, followed by their
perceived in-game performance towards the end of the session. These last two variables
were combined, with the early-game performance being subtracted from the end-game
participant’s enjoyment of the game, r = .459, p < .001, and enjoyment of playing with
this particular partner, r = .379, p < .001. All other variables showed no significant main
effect.
A one-way ANCOVA was performed on the relationship that gender and right
hand 2D:4D ratio have with change in positive affect, with gender pairing of participants,
enjoyment of the game and enjoyment of the partner as covariates. These three were
effects were found for enjoyment of the game, F (1, 110) = 10.85, p = .001, as a
covariate. Right hand ratio was discovered to still have a significant main effect with all
covariates accounted for, F (2, 110) = 4.85, p < .05, and a marginally significant main
effect was found for gender, F (1, 110) = 3.86, p = .052. This further confirms the
hypothesis that there would be a significant main effect for the right hand. While the
main effect for gender was not significant at the .05 level, its proximity to significance
helps support the hypothesis that there would be a significant difference between males
2D:4D ratio and gender, with all ten of the dimensions of positive affect as dependent
variables, and enjoyment of the game as a covariate. No significant main effect was
DISCUSSION
The hypothesis for the present study was not confirmed. It was expected that
2D:4D ratio and affect change would be negatively correlated. This was not found to be
true for positive affect or negative affect. However, the research question posed is
justified by the findings in the present study. It was asked to what degree 2D:4D ratio
mediates changes in reported state affect. While the hypothesis did not predict the
correct relationship, several significant main effects were still found that should be
First, a significant main effect was found for 2D:4D ratio on positive affect
change, but not negative affect change. The relationship found was different from the
hypothesis, not only in direction, but also in the shape. Whereas it was hypothesized that
low 2D:4D ratios would exhibit greater change in affect than high 2D:4D ratios, the
results indicated that both high 2D:4D ratios (e.g., feminine-typical) and low 2D:4D
ratios (e.g. masculine-typical) exhibited relatively little change in positive affect from
pre-test to post-test. Interestingly, it was the neutral hand ratios that exhibited the
greatest change from pre-test to post-test. For all groups except for one (male-typical
2D:4D ratio in males), positive affect increased. For male-typical 2D:4D ratio in males,
the change in positive affect was negative (see Figure 1). Furthermore, the relationship
30
31
between right hand 2D:4D ratio and change in positive affect was found to be virtually
identical across genders. However, females showed greater overall change in positive
affect than males in all three 2D:4D categories (see Figure 3). Therefore, we can
conclude that both high and low levels of exposure to intrauterine testosterone are
correlated with less change in positive affect in competitive situations in adulthood, while
the neutral exposure to intrauterine testosterone is correlated with the greatest change in
It was expected that the mediating effect of 2D:4D ratio on state affect would
reveal a linear, negative and unidirectional relationship between prenatal testosterone and
state affect. However, the curvilinear nature of the findings suggests that relatively high
stable state positive affect responses during adulthood. While only speculative, it may be
the case that there is some intermediate range of testosterone exposure that creates a
tendency for adult affect lability. In any event, the results of the current study show that
testosterone.
It was mentioned earlier that the results indicated a negative change in overall
positive affect for males with masculine 2D:4D ratios, though only minimally. This
subgroup was the only group to experience a negative change in overall positive affect of
the six subgroups. While the research in question only looked for change, the direction
should be considered. However, it is not known at this point what the implications are of
these findings. It is possible that, since this subgroup was theoretically exposed to the
32
most prenatal testosterone in utero, their response to the competitive situation may have
been one of aggression, which is not associated with positive affect, and would make the
As has been noted in the literature (Manning et al., 2003; Lutchmaya et al.,
2001), 2D:4D ratio is negatively correlated with prenatal testosterone, which appears in
much higher levels than estrogen in the developing fetus when a ‘Y’ chromosome is
(Manning et al., 1998), which appears in much higher levels than testosterone in the
developing fetus when that ‘Y’ chromosome is not present. This is why those
participants with 2D:4D ratios in the bottom third of the data were designated as
“masculine” and those participants in the top third of the data were designated as
“feminine.” It was because testosterone has often been linked to aggressive behaviors
and unstable behavioral patterns, especially in males (Lee & Coccaro, 2001; Giammanco
et al., 2001; Melloni et al., 1997) that the current study hypothesized a negative linear
anabolic steroids is consistent with the theoretical prediction that fetal exposure to
However, the patterns exhibited in studies (Pope & Katz, 1988) were exhibiting trait
aggression, and this study was designed to study state affect. Therefore, it may be that
exposure to prenatal testosterone can affect one’s lifetime tendencies to behave more or
less aggressively, as well as have less variability in state fluctuations. It should be noted
33
that the term “stability,” refers to relatively low levels of state affect fluctuation. So
whether or not the individual is more or less aggressive, their state affect may actually be
not being exposed to relatively higher amounts of either testosterone & estrogen, and thus
estrogen and 2D:4D ratio is not sufficient to draw a conclusion about the effect of
intrauterine estrogen as a mediating factor in positive affect change. 2D:4D research has
largely concerned itself up to this point with the relationship between intrauterine
testosterone and various phenotypes, but not intrauterine estrogen. At this point, it can
only be speculated upon that, based on the data in the present study, estrogen has a
competition. Prenatal testosterone has often been an encouraging factor for competitive
individuals (Manning et al., 2001; Coates et al., 2009) and sensation-seekers (Zuckerman
et al., 1978; Apicella et al., 2008; van Honk et al., 2004). While circulating testosterone
has been shown to increase during competition, it is still unclear how this circulating
testosterone changes state affect. The present research suggests that exposure to
The last item to speculate on is why the change was only found to be
significant for positive affect and not negative affect. Pertinent to the study, competition
34
may actually be very enjoyable, especially given the neutral atmosphere of the research
and the typical lack of acquaintanceship between two subjects, who were often strangers
to one another. There was little need to prove one’s superiority to a stranger, and no
emphasis was placed on performance for the subjects. Therefore, the potentially
humiliating effects of defeat were not implicated and may have made the competition of
the present study seem less costly in the event of a loss. In addition, video games have
been designed to be enjoyable by those who play them, and this may be reflected in the
Data was not collected on ethnicity for this study. Manning and colleagues
their study. However, we did not believe that we would recruit enough participants of the
ethnicities listed as significantly different in the previous study (African, Asian, Middle
Limitations
The current study did not utilize a control group or a sham group who
completed a noncompetitive orienting task. As such a control group would better ensure
the change in affect was not a result of maturation effects, and perhaps differentially so
for those who varied according the upper, lower, and middle digit ratio categories. While
it is possible that there may have been a change in affect in the 20 minutes between the
completion of the pre-game PANAS and the starting of the post-game PANAS that was
irrelevant to the intervention condition, there is no obvious reason why any such change
35
should differentially occur for the three digit ratio groups. Still it would be advisable for
Another possible limitation stems from the deviation of our mean 2D:4D
ratios from those of other studies, especially Manning and colleagues (2001). Manning’s
study gathered ratios from an immense sample size (255,116 participants), and the mean
2D:4D ratios for men and women were .984 (SD = .049) on the right hand and .985
(.047) on the left hand. The mean ratios in the present study were .953 (SD = .031) for
the right hand and .961 (SD = .031) for the left hand. However, there is no reason to
believe that the participants demographics of CSU, Chico are notably different from the
cross-section of participants for Manning’s study. Also, the interrater reliability was high
One very important limitation of the study is that all participants were exposed
to the same condition. More specifically, every participant played Soul Caliber 2, and no
other video games were used in this study. It would be advisable in future research of
similar goals to use video games of different genres and functioning. Soul Caliber 2 was
assumed to bring out competitive feelings in the individuals present. However, it may be
that the video game itself caused a physiological change due to characteristics specific to
that game. Therefore, more prosocial games wherein the participants are not in direct
competition or are forced to cooperate to achieve a common goal would serve as good
alternate conditions to compare with the first game. Given the relatively small number of
36
male participants, however, it would be advised to gather more than 125 participants to
Those with lower 2D:4D ratios have been prone to greater aggression (Bailey & Hurd,
2005) and higher neuroticism (Manning et al., 2004), which might be expected to
increase emotional lability. Still, the results go against the hypothesized direction and
shape of the relationship. Given the significance of these findings, it is suggested that
further research be done on the relationship between state affect and exposure to prenatal
state affect, it may be of interest to conduct a study using changes in salivary testosterone
as another fixed factor in the experimental design. This would help in establishing how
competition.
settings may do well to use a more naturalistic competitive setting for the subjects. For
example, participants in a track meet are being exposed to real competition that may
affect their status on their respective track teams or in the overall rankings for their
league. Another example is the financial traders, as utilized by Coates et al. (2009).
These individuals were in a real-life competitive setting that determined how much
money they would be taking home. The potential cost of their performance was much
37
more relevant to the subjects than was the potential cost from video game players. In any
case, the use of a realistic reward or punishment system may result in a significant change
in negative affect as well, which was absent from the present study.
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APPENDIX A
INFORMED CONSENT FORM
AGREEMENT TO PARTICIPATE
This study investigates the relationship between finger length, reaction to stress, and
emotional arousal. Your hands will be photographed so that we can accurately measure
the length of your second and fourth finger. You will also be asked to complete a series
of questionnaires that include your gender, age, video game habits and your current
emotional state.
Your answers are strictly confidential. No one will be able to associate your data with
you personally. You will be identified only by an ID code, and that code will not be
linked to your name. However, if at any time you choose to not complete the study you
are free to do so without penalty. We have taken steps to ensure your confidentiality so
we appreciate your honest responses.
The total time necessary to complete the study will vary from 30 to 45 minutes.
The study is supervised by Dr. Edward Vela and will be conducted by students with
specific training in this area.
I certify that I have read the foregoing and understand that I am free to discontinue
participation in the project at any time. I hereby give my consent to participate in this
project.
___________________________
Name (please print)
___________________________ __________________________
Signature Date
NOTE: This informed consent form will not be linked with the ID code that
is associated with the data we collect from you.
46
APPENDIX B
Pregame Inventory ID#:_______________
Age: ________
Have you played fighting games before? (This includes such games as Street Fighter, Mortal
Kombat, Smash Bros., Virtua Fighter) (Circle one): YES / NO
How would you rate your stress level right now? (Circle one):
1--------2---------3--------4--------5--------6--------7
Very Low Very High
48
APPENDIX C
APPENDIX D
Post-game inventory ID#:_______________
How much did you enjoy playing this game today? 1------2-------3-------4-------5-------6-------7
(Circle one): Not at all Very much
How much did you enjoy playing with your partner? 1------2-------3-------4-------5-------6-------7
(Circle one): Not at all Very much
Would you play this game, or any game, with them again? (Circle one) YES / NO
52
APPENDIX E
Debriefing
Recent research has shown that the length of your index and
ring fingers is related to the amount of testosterone a fetus is
exposed to in the womb. This also correlates with testosterone
levels later in life, which have been found to have an influence
on such traits as aggression and sexual preferences.
The ratio between your index and ring fingers may also be an
indicator of how one responds to stress, competition, and
threat. We hope to determine whether there exists a correlation
between your finger length ratio and emotional arousal in
competitive settings, as measured by your responses on the
questionnaires.
54