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Psychology being Investigated
● The Hassett et al. study looks at why boys and girls prefer different
types of toys.
● Boys usually like toys that are considered more “boyish,” while girls
prefer toys that are seen as more “girlish.”
● Some people think this happens because society tells boys and girls
what toys they should like.
● But, there’s another idea that says maybe boys and girls just naturally
like different activities, and that’s why they choose certain toys.
● The Hassett et.al. study investigated whether this second idea is true
by looking at a particular species of animals, rhesus monkeys, in which
there is no influence ofrom society, but still, differences are seen in
behavior between males and females.
● If they would find similarities in toy preferences between these
animals and human children, it would support the second idea that
natural activity preferences play a role in toy choices.
Background to the Study
● Studies have shown that the hormones a baby is exposed to in
the womb can affect their toy preferences later in life.
● Girls with the condition called congenital adrenal hyperplasia
(CAH) are exposed to high levels of androgens in the womb, and they
tend to prefer boy-typical toys.
● This preference is still seen in CAH girls even when they are raised
as girls and encouraged to play with female-typical toys.
●This suggests that toy preferences are influenced by hormones, not
just by what parents teach their children.
● The Hassett et al. study examined toy preferences in rhesus
monkeys to see if the results would be similar to those seen in humans.
● Monkeys are not raised to play with certain toys, so any differences
in how male and female monkeys play must be due to their biology, not
their environment.
Aims of the Study
● Investigate whether sex differences in toy preferences in humans are
also present in rhesus monkeys.
● Determine whether these sex differences are due to socialization or
to biological factors.
● Explore the relationship between toy preferences and activity
preferences in monkeys.
Sample
Sample Characteristics
● Initially, 82 rhesus monkeys (macaca mulatta) were made part of the
study.
●There were 61 female and 21 male rhesus monkeys.
● The monkeys were members of a multi-male, multi-female social
group of 135 animals that had lived together for more than 25 years at
the Yerkes National Primate Research Center Field Station.
●The social group had a species-typical multiple matriline social
structure with a full age-range of group members from infants to
adults.
●14 monkeys were not included from the group of 135 in analyses
because they had been exposed to varying hormonal treatments
prenatally.
●39 baby monkeys from the group of 135, of 3 months or younger age
were excluded from the study because it was difficult to determine
their sex.
● Of the remaining 82 monkeys, 34 interacted with the toys on more
than five occasions and were included in the analysis.
● So, the final sample consisted of 34 rhesus monkeys, 23 females
and 11 males.
Sampling Technique
● The Hassett et.al. (2008) monkey toy preference study
used convenience(opportunity) sampling.
● They only tested a small number of monkeys from the Yerkes
National Primate Research Center in Atlanta, Georgia.
● This means that the authors did not randomly select the monkeys, but
instead chose them based on availability at the center.
Controls
●Matching the toy categories to stereotypical gender assignments –
The researchers used two categories of toys, “wheeled” and “plush,”
which they believed were comparable to stereotypical gender
assignments of “masculine” and “feminine.”
● Balancing the placement of the toys – The toys were placed in the
outdoor area in a counterbalanced fashion, meaning that they
were equally likely to be placed on the left or right side.
● Using a variety of behavioral measures – The researchers used a
variety of behavioral measures, such as frequency of occurrence and
duration of interaction, in order to understand the monkeys’
preferences.
●Using nonparametric tests when necessary – The researchers used
nonparametric tests when the data were not normally distributed.
● Controlling for social rank and age – The researchers controlled for
social rank and age of the rhesus monkeys.
Research Technique for Data Collection
● The research technique for data collection in the Hassett et.al. 2008
study is observational study.
● In this study, the researchers observed the rhesus monkeys as they
interacted with two types of toys: wheeled toys and plush toys.
● The researchers recorded the frequency and duration of each type of
behavior that the monkeys displayed towards the toys.
Measured(dependent) Variables
● Toy type – wheeled or plush;
● Behavior – frequency and duration of specific behaviors directed
towards the toys, such as approaching, touching, holding, carrying,
manipulating, and destroying, measured in terms of1. Total frequency – the total number of times a specific behavior
was performed by a subject;
2. Total duration – the total amount of time a subject spent
performing a specific behavior
● Subject – gender, age, and social rank
Ethics
All research was conducted in accordance with the NIH Guide for the
Care and Use of Laboratory Animals and under an environmental
enrichment/management protocol of the Yerkes National Primate
Research Center approved by Emory’s Institutional Animal Care and
Use Committee.
● Minimizing harm and maximizing benefit – The researchers did
minimize harm to the monkeys by using a non-invasive
procedure. Additionally, the monkeys were not physically harmed,
and they were not deprived of food or water. Water was continuously
available, and the animals were fed monkey chow twice daily,
supplemented once per day with fruits and vegetables.
●Replacement – The researchers did not replace the use of animals in
this study. However, they did use a relatively small number of
monkeys, which is in line with the recommendations of the British
Psychological Society.
● Species: The researchers used a species of animal (rhesus monkeys)
that is both scientifically and ethically suitable for the research. Rhesus
monkeys are a well-studied species, and they are known to be capable
of experiencing pain and suffering. However, they are also social
animals that are capable of forming strong bonds with each other.
The researchers took steps to minimize the stress and discomfort of the
monkeys, such as providing them with a comfortable environment and
allowing them to interact with each other.
● Numbers: The researchers used the smallest number of animals
possible to meet the research aims. They also used statistical
significance tests to ensure that the results were reliable.
● Procedures:
■Pain, suffering, and distress – The researchers avoided causing pain
or distress to the monkeys. They did not use any surgical
procedures, and they did not deprive the monkeys of food or water. The
monkeys were able to move freely within their enclosures, and they
were allowed to interact with each other.
■Housing – The researchers considered the social and natural behavior
of the monkeys when housing them. The monkeys were housed in
groups of 3-4, which is the typical social grouping for rhesus monkeys.
The enclosures were spacious and well-equipped, and the monkeys
had access to a variety of toys and enrichment materials. Subjects
were housed with their natal group in a 25 m×25 m outdoor
compound with
attached temperature-controlled
indoor
quarters. Water was continuously available, and the animals were
fed monkey chow twice daily, supplemented once per day with fruits
and vegetables.
■Reward, deprivation, and aversive stimuli – The researchers did
not use food deprivation or aversive stimuli in this study. They used a
variety of positive reinforcers, such as food and social interaction (as
noted above), to motivate the monkeys to participate in the study
Results (Quantitative Findings only)
Male monkeys:
● Preferred wheeled toys (mean = 9.77) over plush toys (mean = 2.06).
● 73% of males preferred wheeled toys, 9% preferred plush toys,
and 18% showed no significant preference.
● Males who preferred wheeled toys played with them for significantly
longer periods of time (mean = 4.76 minutes) than males who
preferred plush toys (mean = 0.53 minutes).
Female monkeys:
● There was no significant difference in the duration of time spent
playing with either plush (mean = 1.49 minutes) or wheeled toys (mean
= 1.27 minutes) for female monkeys.
●Females who preferred plush toys ranked significantly higher in the
social hierarchy than females who preferred wheeled toys or had no
preference.
● Showed some preference for plush toys (mean = 7.97) over wheeled
toys (mean = 6.96), but the difference was not significant.
●30% of females preferred plush toys, 39% preferred wheeled toys,
and 30% showed no significant preference.
Social rank and toy preference:
●There was a significant positive correlation between social rank and
frequency of interaction for both types of toys.
● Higher-ranking monkeys interacted more with the toys.
●When the data from females was examined more closely, the
researchers found that the higher the rank, the more time females spent
interacting with plush toys. This was not true for wheeled toys.
● Following is a summary of the results presented aboveToy Type
Plush
Wheeled
Gender
Mean Frequency
Mean Duration (minutes)
Preference (%)
Male
2.06
0.53
9%
Female
7.97
1.49
30%
Male
9.77
4.76
73%
Female
6.96
1.27
39%
Table 1: Results of Interactions with Plush and Wheeled Toys for Male and Female
Monkeys
Conclusions
● Male rhesus monkeys show a consistent and strong preference for
wheeled toys, while female rhesus monkeys show greater variability in
preferences.
●The magnitude of preference for wheeled over plush toys differs
significantly between males and females.
●These findings parallel those seen in human children, suggesting
that such preferences may have a biological basis.