Hassett Et Al.
(Monkey Toy Preferences)
Aim:
To test if sex differences in children's toy preferences result from biological factors - for
example, from prenatal hormone exposure rather than through socialization.
To investigate if male and female rhesus monkeys have similar toy preferences to human
infants, despite no socialization experience with human toys.
Background:
Introducing Kim Wallen and Janice Hassett-Vick:
Professor Wallen has worked with monkeys for over 50 years, at Emory University and the
Yerkes National Primate Research Centre (YNPRC).
Drs Melissa Hines and Gerianne Alexander found that male vervet monkeys played more
with stereotypical male than female toys. Wallen investigated whether monkeys showed a
preference for sex-typed toys when given a choice between stereotypical male and female
toys. He found that the behavior of monkeys paralleled that of children using a toy-
preference task, suggesting that toy preferences are not primarily a result of socialization,
but rather are due to biological differences.
Professor Wallen, researcher at the Yerkes National Primate Research Center, says:
“I have been working with monkeys for over 50 years, first as an undergraduate, then a
graduate student, and for the last 43 years as a professor of psychology and behavioral
neuroendocrinology at Emory University and the Yerkes National Primate Research Centre.
Drs Melissa Hines and Gerianne Alexander had found that male vervet monkeys interacted
longer with male-stereotyped toys and spent less time with female-stereotyped toys. I was
interested whether monkeys would show a preference for sex-stereotyped toys if they had a
choice between male and female-stereotyped toys.
Janice Hassett had joined my lab for a summer internship and was somewhat surprised when
I suggested we look at monkeys' preferences for human sex-typed toys. We were both quite
surprised when the monkeys' behavior almost completely paralleled what had been found in
children using a human toy-preference task.”
The Psychology Being Investigated:
Play Socialization And The Role Of Nurture
All animals play, including humans, but the In humans, gender refers to the individual's
concept is hard to define due to the many personal sense of their own masculinity and/or
different types of play seen at different femininity. Children learn about gender and
developmental levels. Seashore (1913) defined societal expectations of how males and females
play as 'pleasure gained in self-expression. behave through interactions with parents and
This definition may apply to some forms of other children. For example, a little boy who
human play, but it does not describe non- bangs two trucks together may be praised for
human animal play very well as animals do not creating an exciting game, whereas a little girl
really have a sense of self to express! Bergen may be discouraged and offered a more
(2015) emphasizes that play is always traditionally feminine toy, such as a doll or tea
voluntary, explaining that we play because we set. Daily interactions like this gradually lead
choose to, not because we have to. We also boys and girls to conform to stereotypical
choose what we wish to play with, how and gender roles and seek out specific toys. The
with whom. Many psychologists agree that fact that boys play less with stereotypically
play allows the individual to practice the skills feminine toys than girls play with
required ni adulthood and this is true of both stereotypically masculine toys suggests boys
humans and animals. So, play may be adaptive may be more actively discouraged from
- that is, it helps us to survive. opposite-sex behavior, whereas opposite-sex
behavior in girls may be ignored rather than
rejected. Psychologists who accept these ideas
believe that sex differences in children's play
result from socialization.
Sex Differences And The Role Of Nature Hormones And Toy Preferences
In mammals, biological sex is determined by Hassett rejects the socialization explanation for
our sex chromosomes, typically XX for toy preferences. They believe male and female
females and XY for males, although many children prefer toys that can be used for
differences can occur. Typically, these activities that suit their specific cognitive
chromosomes determine levels of hormones abilities. These abilities, as stated above,
such as testosterone and oestrogen, which depend upon the children's differing sex
cause differences in the development of male hormone levels. This means that toys are
and female brains. For example, the sex selected according to the different play
hormones affect neural development, activities they promote rather than society's
including neurogenesis (cell birth) and attitudes regarding 'gender-appropriate' toys.
synaptogenesis (creation of connections This view is supported by the fact that children
between neurons), and have been associated tend to explain their toy preferences in terms of
with differences in cognitive processes 'what can be done with' a specific toy in
(Overman et al., 1996). contrast to its gender-appropriateness
Anyone visiting a kindergarten or nursery (Eisenberg et al., 1982) - for example, teddies
might see boys playing with cars and girls can be cuddled whereas trucks can be moved
playing with dolls, but psychological research by pushing them along.
has demonstrated that girls are more likely to
play with trucks than boys are to play with
dolls. These behavioral sex differences are
strong, and Hassett explores the idea that these
differences may be hormonal in origin.
Research Method And Design:
Research Method ➜ Field experiment involving a controlled observation, and a
correlational study using a behavioral checklist.
Research Design ➜ Independent measures design.
Independent Variable ➜ The sex of the monkey (male or female).
Dependent Variable ➜ Whether the monkeys interacted more with the plush toys or the
wheeled toys.
Sample:
The sample was a troop of 135 monkeys at the Yerkes National Primate Research Center
Field Station. The troop included both infant (juvenile) and adult monkeys. Fourteen of the
monkeys had previously participated in research on prenatal hormones, so they were not
included in the current study. Thirty-nine babies (3 months and younger) were not included
as it was very hard to tell them apart, making it difficult to know which sex they were. Of
the remaining monkeys (61 females and 21 males), 34 interacted with the toys on more than
five occasions (23 females and 1 males) and were included in the analysis.
Design and Variables:
The design was independent measures as two groups of monkeys were compared: males and
females. Sex is a naturally occurring independent variable, determined by the appearance of
the external sex organs. The dependent variable was whether the monkeys intera cted more
with the plush toys or the wheeled toys. Seven trials were completed, each with a different
pair of toys. When the monkeys interacted with the toys, their social rank and age were
recorded. Social rank had already been determined by observing gro oming behavior; the
monkey doing the grooming is always subordinate (has less social status) than the monkey
being groomed.
Procedure:
Seven 25-minute observations were completed in the outdoor area of the monkey enclosure
at the research centre. Before each observation, the observers positioned a pair of toys (one
wheeled, one plush) in the outdoor area while the monkeys waited indoors. Toys were
always placed ten metres apart and the positions were counterbalanced – wheeled toys were
on the right and plush on the left in half of the trials and the other way around on the
remaining trials. This ruled out the possibility that the monkeys preferred a certain area of
the enclosure rather than genuinely preferring the properties of the toy that they found there.
The toys varied in size, shape and colour and were selected according to what you could do
with them rather than simply choosing traditionally male or 'female toys. There were six
wheeled toys: wagon, truck, car, construction vehicle, shopping cart and dump truck, ranging
from 16 to 46 cm, and seven plush toys: Winnie-the-Pooh, Raggedy-Ann, Scooby-Doo and
four soft toy animals, including a koala, armadillo, teddy and turtle, ranging from 14 cm to
73cm.
A video camera was focused on each toy so that all interactions could be recorded for later
analysis. Two observers watched the videos and used a behavioral checklist to
code/categorize every interaction between the monkeys and the toys. Using an app called
Handobs, the observers recorded their data using palm pilots (digital devices like modern
mobile phones). They recorded the start and finish times of each interaction and calculated
the duration (in seconds).
The checklist included: extended touching, holding, sitting on, dragging, carrying and
manipulating the toys, as well as briefly touching, sniffing, mouthing, destroying, jumping
away from and throwing them. Ambiguous (unclear) behaviors were discussed until the
observers agreed on how to code the interaction. For each interaction, the observers also
recorded the monkey's age, rank and sex.
Results:
Most monkeys didn’t interact with the toys. Only very few interacted frequently and for
long. Data of 17 monkeys who showed less than 5 behaviors were excluded.
− Male monkeys played with wheeled toys for a longer time than female monkeys.
However, the standard deviation was high, meaning that some males played for
longer than others.
− Female monkeys played with plush toys for a longer time than male monkeys. There
wasn’t a significant difference in time spent playing with wheeled or plush toys.
− Social Rank – A significant positive correlation between social rank (dominance of
monkeys) and frequency of interaction was found.
o Higher-ranking monkeys interacted more with the toys.
o Female monkeys who preferred plush toys had a higher rank than those who
had no preference.
Results – Male Monkeys
− Male monkeys preferred wheeled toys (mean = 9.77), compared to plush toys (mean
= 2.06). Males played with plush toys less than females.
− 73% of males preferred wheeled toys and only 9% preferred plush toys. 18% showed
no significant preference. These preferences were not affected by age or rank.
Results – Female Monkeys
− Female monkeys showed no preference, other than an insignificant preference for
plush toys. Mean plush toys preference = 7.97. Mean wheeled toys preference = 6.96.
− Only 30% of females preferred plush toys, whereas 39% preferred wheeled toys, and
30% showed no significant preference.
Conclusions:
1. Sex-typed preferences in humans may be due to biological differences because even
without differences in socialization, monkeys showed preferences similar to human
infants.
− Male monkeys similar to boys, have a strong preference for masculine-type toys.
− Whereas female monkeys are more variable in their toy preferences.
2. Toy preferences reflect behavioral and cognitive biases which have been influenced
by hormones.
Strengths:
Ethical guidelines on treating lab animals were followed by researchers when caring for the
monkeys. They had constant access to water, they were fed monkey chow twice a day, and
fruits and vegetables every day.
Using the operationalized behavioral checklist increased the validity and reliability of
results, as it guided researchers on how to record observations in the same way. For example,
the behavior ‘sit on’ was described as sitting on or part of a toy.
Different pairs of toys were used on each trial, and this increased the validity as we can
determine that males were drawn to wheeled toys in general, and not just a specific wheeled
toy.
Using video cameras increased the validity of the data recorded because the monkeys were
used to the cameras. If a researcher recorded data in person instead, the monkeys might show
demand characteristics by playing with the toys.
Quantitative data collected on toy interaction duration allowed for the objective calculations
of the average time the monkeys spent with the toys. This removes room for subjective
interpretations.
Weaknesses:
The standardized procedure was abandoned for a trial because a monkey tore a plush toy
causing the trial to be stopped 7 minutes early. This reduces the reliability of results.
There is a chance observer bias may have increased subjectivity. The researchers who
analyzed the tapes were familiar with the monkeys and their gender and this could have led
them to unintentionally code the behavior of the monkeys differently to their ac tual behavior.
There was a lack of adult males in the sample, hence reducing the generalizability of results.
The only one high-ranking male didn’t interact with any toys, hence, findings can only be
generalized to lower-ranking, non-adult male monkeys.
Ecological validity is low because the sample consisted of monkeys in captivity, and they
might be more likely to show interest in new objects in their environment. Therefore, we
can’t entirely generalize results to explain if wild monkeys behave in the sa me way.
Validity is low because, in each trial, a group of monkeys were sent out. So if one monkey
occupied the wheeled toy, another monkey wanting to play with a toy would go to the plush
toy regardless of their personal preference.
Nature vs Nurture:
Hassett believed that toy preferences in humans are due to nature because male monkeys
prefer wheeled toys over plush toys, whereas females show no clear preference.
Findings supported the nurture debate that interactions were affected by social rank. Female
monkeys' social rank was positively correlated with the time spent interacting with both toys.
However, female dominance is influenced by testosterones which is a biological effect.
Application To Everyday Life:
Findings are helpful when choosing toys for children. Results suggest that boys like moving
toys, so if a parent wants to develop their empathy, toy vehicles with expressive faces can
be bought.
As girls like plush toys with faces, their visuospatial skills can be improved by using toys
with moving parts but in a context where dolls are included. For example, playing a scene
with toy school buses and dolls.
