CORE STUDY: HASSETT ET AL. (2008)
AICE PSYCHOLOGY 9990- AS LEVEL
CREATED BY: SETH M. ALPER, PH.D.
Background to the study
• Sex differences in toy preference based on the nature/nurture debate
• Is it one’s upbringing with societal pressures of gender stereotypes?
• Is it the features of the toy itself?
• Is it biological pre-programming that affect toy choice and play?
Background to the study
• Research findings among boys and girls has shown:
• Boys tend to interact with masculine-type toys (e.g. wheeled trucks) as girls tend to favor femininetype toys (e.g. stuffed animals)
• Boys tend to stick to stereotypical masculine toys as girls will play with a range of masculine &
feminine toys
• Studies looking at bio differences among boys & girls point to the notion that girls with CAH
(congenital adrenal hyperplasia) producing more androgen favor masculine toys even with
stereotypical upbringings
Background to the study
• Previous study with Vervet monkeys (Alexander & Hines, 2002) looked into sex differences in
nonhuman primates with human toys available
• *The study used a single masculine or feminine toy and recorded how long the monkey would play with it
• Contradicting human boy & girl play trends, the male monkeys spent similar time with both masculine &
feminine toys, whereas the female monkeys spent more time with the feminine toys
• Hassett et al. argues that this did not display toy preference itself among nonhuman primates, but rather
simply the amount of time playing with a type of toy
• This is the basis for the current study in using rhesus monkeys is a methodological weakness as the Vervet
monkeys were not given a masculine or feminine toy choice
• Purpose
Setup of the study
• Overall, to investigate potential sex differences among rhesus monkeys for toy preference
• To investigate if toy preference is related to biological factors rather than socialization
• To compare the toy preference of male and female rhesus monkeys to previous research findings for
human children
• Hypothesis
• Toy preference among sexes is due to biological causes (that influence behavioral and cognitive biases) rather
than learned differences
Setup of the study
• Type of study
• Can be considered a natural field experiment
• Variables of the study
• IV= (a) sex of monkey (natural IV)
(b) category of toy- wheeled (masculine) or plush (feminine)
(c) rank & age of monkey (natural IV)
• DV= (a) frequency of playing with toy
(b) duration of playing with toy
(c) magnitude of preference score
• Design of the study
• Independent groups
• (a) gender of monkey
• (b) one exposure to each available toy (one truck was repeated)
Setup of the study
• Sample
• Opportunity sample (troop of rhesus monkeys)
• From Yerkes National Primate Research Center (Emory University in ATL)
• N= 82… 61 females & 21 males met the criteria for the study
• Sample chosen from a large social group of 135 rhesus monkeys that have lived there for 25+ years
• 14 excluded b/c of participating in other prenatal hormone study & 39 babies excluded as it was too
difficult to tell them apart in observations
Setup of the study
• Sample
• Monkeys were pre-coded for social rank & age (used for later data analysis)
• Social rank was previously determined by behavioral observations of grooming, dominance, and
submissive behavior
• E.g.- monkey being groomed has higher social status in the troop compared to the groomer
Social Rank & Age chart
Setup of the study
• Apparatuses
• Available toys were categorized by object properties rather than traditional gender assignments
• The colors and shapes of the items varied
‘Plush’ toys
‘Wheeled’ toys
Winnie-the-Pooh
Wagon
Raggedy-Ann
Truck
Scooby-Doo
Car
Koala hand puppet
Construction vehicle
Armadillo
Shopping cart
Teddy bear
Dump truck
Turtle
(a truck was repeated)
• Summary
Procedure of the study
• Subjects were housed in 25m x 25m outdoor compound that had a temperature-controlled inside
area also
• Subjects were kept in the enclosed area while researchers placed one wheeled and one plush toy in
the outside area, 10m apart
• For each trial (7 in total), the placement of the wheeled and plush toy was counterbalanced
• Helps to reduce the possible issue of the monkeys preferring one side of the enclosure and then
playing with the toy that is already there
• Summary
Procedure of the study
• Each trial was to last 25 minutes (one was only 18 mins as a plush toy was ripped apart)
• For each trial, a video camera was focused on each toy for review by 2 observers
• Each observer noted the identity of each animal (w/age & sex) & the behavior displayed
• A consensus for each monkey was made b/w the raters
• The time of interacting with each toy was calculated
• Observers used a behavioral checklist with the following:
• Extended touch
Hold
Sit on
• Carry in hand
Carry in arm
Carry in mouth
• Drag
Manipulate part
Turn entire toy
• Touch (like poke)
Sniff
Mouth (put to)
• Destroy
Jump away from
Throw
• Data was recorded only by category of toy, not by individual toy
Results of the study
• Summary
• Each monkey received their own ‘data set’ for frequency and duration of behavior(s) with the toys
• Not all individuals interacted with a toy (no data for them)
• Those with less then 5 recorded behaviors were excluded in the data analysis (14 males & 3 females)
• Frequency data showed the following:
• Within the sexes:
• *Males showed a statistical preference for wheeled toys over plush toys (9.77:2.06)
• Females did not show a statistical preference between the two categories of toys (6.96:7.97)
• Comparing the sexes:
• Females interacted with the plush toys more, but no statistical difference in preference for wheeled
toys
Type of Toy Sex of Monkey Frequency
Wheeled
Plush
Male
9.77
Female
6.96
Male
2.06
Female
7.97
Results of the study
• Summary
• Duration data showed the following:
• Within the sexes:
• *Males showed a statistical time spent playing with wheeled toys over plush toys (5mins: 30secs)
• Females did not show a statistical difference among the toys (1 ½ each minutes on average)
• Comparing the sexes:
• *No overall statistical difference was found b/w the sexes for the time spent playing with the
wheeled and plush toys
Type of
Toy
Sex of Monkey
Duration (minutes)
Wheeled
Male
4.76
Female
1.27
Male
0.53
Female
1.49
Plush
Results of the study
• Summary
• ‘Magnitude of preference’ score was calculated for all Ps
• For males= total frequency/total duration w/wheeled toys – total
frequency/duration w/plush toys
• For females= opposite (plush-wheeled toys as above)
Males
Females
Wheeled
preference
73%
39%
Plush
preference
9%
30%
No
preference
18%
30%
• Results:
• *Males had a significantly higher preference for wheeled toys whereas females
showed no strong preference
• Rank data
• Males did not show a correlation with rank (neither frequency or duration)
• Females showed (a) a positive correlation with rank for frequency of play
for wheeled & plush toys and (b) positive correlation with duration only for
plush toys
• Age data
• No differences were found
• Summary
Results of the study
• Comparison of rhesus monkeys to human children study (Berenbaum & Hines, 1992)
• Human study looked at 3-8-year-old girls w/CAH compared to boys and found that the girls exposed to
higher levels of prenatal androgen preferred ‘boy toys’ over ‘girl toys’ (concluded hormonal cause)
• Both rhesus monkeys and human children showed gender differences
• Males strongly preferred the masculine toys as females slightly preferred the feminine toys
• This preferences was greater among males in both studies
Conclusions of the study
• Summary
• Hassett et al. note that their findings support a biological basis for differences in toy preference
• In both this study and the Berenbaum & Hines (1992) one, biological hormones influenced the preference
for masculine toys
• These hormones “influence behavioral & cognitive biases” which in turn are influenced by learning
experiences and social pressures
• Not found in monkeys due to absence of socialization influences (such as mass media)
• Found in humans, such as if boys were to choose to play with ‘girl toys,’ they would likely receive
negative feedback from society than if girls were to choose to play with ‘boy toys’
• May explain why boys are much more likely to choose masculine toys whereas girls are more
likely to have variation in toy choices
Ethics of the study
• Study met ethical guidelines while working with animals
• Study conducted in accordance with NIH Guide for the Care & Use of Laboratory Animals
• Took place at the Yerkes National Primate Research Center
• Approved by the Emory University Ethical committee on animal care and use
• Proper housing
• Lived in social/family groups (as in the wild) in large, safe enclosures with access to indoor temperaturecontrolled areas and outside areas
• Fed ‘monkey chow’ 2x daily & fruits/veggies 1x daily
• Water was always available
• Unlikely distress
• Were bred/raised in captivity, familiar with keepers who entered the facility & cared for them
• Toy choices did not pose potential harm
• Use of video cameras reduced researcher involvement
Strengths & Weaknesses of the study
• Notable Strengths
• Standardized procedure with counterbalancing of toy placement
• Use of video cameras to be able to review data (and not disrupt Ps)
• Use of inter-rater reliability
• Use of a set behavioral checklist
• Consideration & data analysis of potential confounding variables of social rank & age
• Pre-rating of the rank helped as well
• Notable Weaknesses
• Data from those not interacting with the toys was not included (potential researcher bias)
• Comparing the monkey to human child data was not identical as the monkey toys were
based on category (wheeled or plush) and the human data was on gender stereotypes
• Quan data only, no descriptive qual data included
• Lower generalisability (based on captivity, setting)