Detecting the Snake in the Grass
Attention to fear relevant stimuli by
adults and young children
Presented by Aaron Harvey
LoBue, Vanessa DeLoache, Judy S. ;
Psychological Science, Vol 19(3), Mar,
2008. University of Virginia
Abstract
• Snakes are among the common targets of
fears and phobias.
• In Visual Detection Tasks, adults detect their
presence more rapidly than other types of
visual stimuli.
• 3 experiments were performed on adults and
children, both detected snakes more rapidly
than other distractors ( flowers, frogs,
caterpillars.)
ABSTRACT : CONTINUED
It’s not just us!
The fear of snakes extends to non-human primates, who learn to fear snakes from watching
other primate’s fear responses to snakes.
So, what? Snakes are scary, and that’s obvious, right?
This prevalence of the fear of snakes has led researchers to hypothesize that humans possess an
evolved predisposition to fear snakes (and spiders!)
Interesting! How would this carry over?
The idea is that there was differential reproductive success for humans who were able to identify
and avoid snakes, and Ohman (1993; Ohman and Mineka, 2001) proposed the existence of an
evolved fear module- a neural system that is selectively sensitive to evolutionarily relevant threat
stimuli. Those with the system escaped, and repoduced. As a consequence, a mechanism
supporting the rapid detection of this type of dangerous stimuli evolved.
We are talking about hardwired adaptations. Could be very useful to have!
Empirical Support
By Flykt and Esteves, 2001
Detection of Fear Relevant
&
Fear Irrelevant Stimuli
• Visual matrices were provided with both fear relevant and fear
irrelevant stimuli : Snakes and flowers
• Participants had to guess whether or not the target (snake ) was
present in each trial. Reliable detection of target was found, especially
for participants who reported being afraid of snakes.
• Possible Confound: Flowers can be dangerous when ingested and are
evolutionarily relevant
Other Studies Inconsistent:
• Results have been replicated by Lipp, et al; 2004
• Superior detection was found with non threat
relevant animals- eg bears, dogs and kittens.
• There are reports of superior detection of nonthreatening stimuli : guns, knives, syringes
• Results varied with the number of distractors,
contrary to the analysis by Ohman et al.
•
Distractors!
Threat
Irrelevant?
Adults simply won’t work as well!:
• The previous studies performed involved
adults who have had experience with snakes,
cultural predispositions etcetera that would
bias the results.
• If humans evolved these mechanisms, they
would also be present in subjects with no
experience with snakes.
• They use young children instead!
General Method
Modified for Children
• Both Preschool children and
adults with 3.3 matrices of
threat relevant and
irrelevant pictures.
• Instructed to touch the
target as quickly as possible
• Possible confound, would
this work against nature’s
hardwiring of avoidance?
• Only matrices with targets
included.
Participants
• 120, 3-5 year old children and
their accompanying parents.
• Equal number of boys and girls
participated.
• Parents were all female except
5.
• Recruited from birth
announcements,
predominantly caucasian
• Disclosure of participant’s
exposure to snakes recorded.
A preschool child identifying the single flower target among
eight snake distractors by touching the flower image on a touchscreen monitor.
Materials:
•
•
•
•
•
•
24 photographs for each stimulus category
9 Displayed in 3x3 matrix
1 target, 8 distractors
Snakes, flowers, frogs, caterpillars,
All brightly colored
Snakes were coiled in trees, no animals were
threatening
• Scanned from nature books.
Materials, Continued:
• Coder blind was used to establish uniformity
of brightness and the pictures were very
similarly coded for their brightness
eliminating the confound of differential
brightness.
• Pictures were used multiple times
• An outline of a child sized handprint was on
the table.
Procedure: Find the Snake.
• Child was seated in front of monitor.
• Experimenter accompanied them.
• Child’s hands were placed on handprint to
standardize beginning times to record latency.
• Training was given so that the child was able to
learn how to use the touchscreen! Good idea.
• Child saw side by side picture: a distractor and a
target, instructed to touch the target.
• The children readily learned the procedure.
Procedure: Continued
• After the training ended, the children began the experiment
• 24 trials of different picture matrix containing one target and
eight distractors was presented .
• Between each trial, a large smiley face appeared.
• The experimenter pressed the smiley face, beginning the
next trial when he or she gauged that the child was paying
attention and ready for another round.
• Latency was automatically recorded from the onset of the
matrix to when the child touched one of the pictures on the
screen.
• Afterwards, the parents were tested. They were blind to the
hypotheses and not present when the child was tested.
Analyses
• In each experiment ; latency to touch the
target was analyzed in a 2(Target Stimulus:
(snake vs comparison) X 2 ( Age: children vs
adults) X 2 (Child’s Snake Experience: report
of some exp. Vs report of no experience)
analysis of variance: ANOVA. All factors were
between subjects.
We included trials where only the correct
target was selected.
Experiment 1
• 3-5 year old children and adults were asked to
locate either a single snake amidst eight
flowers OR the lone flower among eight
snakes.
• Expected the adults would detect snake
targets more quickly than flower distractors.
• Pivotal Question: Would the Children show
the same pattern of performance?
Experiment 1: Participants
-Twenty Four :Three Year Olds
-Twenty Four: Four Year Olds
-Twenty Four : Five Year Olds
-Also included in the study was their 72 parents.
-3 additional three year olds were excluded for
failure for following directions!
-Parental Report: 55 of the Children ( 81% of the
68 children whose parents responded) had
some experience with snakes.
Results:
• Because the pattern for responding was the
same for children in all three age groups, they
were combined for the analyses.
• The ANOVA on latency to touch the target
yielded significant main effects on the target
stimulus, F(1,140) = 9.66, p < .01, Prep= 1.0
and age, F(1,140) = 109.04, p<.01, Prep= 1.0.2
• There was no effect of the child’s experience
with snakes F(1,140) = 1.18, p < .28, Prep= .66
Average latency to detect target stimuli (snakes
vs. nonsnakes) among adult and child
participants in Experiments 1 through 3.
Not Surprisingly…Adults were faster.
However:
•
•
•
•
•
•
The adults generally located the targets significantly faster than the
children did, in keeping with prior research
The pattern of performance was the same as that of adults: the children
located the snakes more rapidly than the flowers.
This data is highly relevant to the hypotheses that humans evolved
special sensitivity to certain categories of evolutionarily significant
threatening stimuli because children were tested.
It is very significant that the children had relatively little cultural
exposure to snakes or to facts and cultural lore about snakes that would
bias the study : Disney Effect.
The children that had been exposed to snakes was unrelated to how
quickly they located the snake target.
Flowers and snakes look nothing alike! ♪♬ “One of these things is not like
the other, one of these things just doesn’t belong…” ♬
Experiment 2
Taking This One Step Further:
• Snakes are animate, flowers are not.
• In this study, a much stronger test for bias was
used: other animals were included, including
frogs! Frogs have similar textures, color and
animacy.
Experiment 2 Participants:
• Only Three Year Olds were included in
Experiment 2.
• Frame of Reference, does anyone remember
what it was like being three years old?
• 2 additional Three year olds were excluded for
failure to follow directions.
• Fifteen of the children (63%) were reported to
have had an experience with snakes.
Experiment 2 Results:
• The ANOVA on latency to touch the target , there
were significant main effects on the target stimulus,
F(1,44) = 7.27, p < .01, Prep= .95, and age, F(1,44) =
102.95, p<.01, Prep= 1.0.
• There was no effect of the child’s experience with
snakes F(1,44) = 0.17, p < .68, Prep= .37
Experiment 3
• The Most Stringent of all of the tests
• Caterpillars were used, they are animate,
brightly coloured, and their most salient
characteristic: their elongated shape!
• As Previously Discussed, Caterpillars are at
times significant threats to your survival.
Participants
• Twenty Four 3-Year-olds were tested, along with
their 24 parents
• Three additional 3-year-olds (1 for whom snakes
were targets and 2 for whom snakes were
targets) were excluded for failure to follow
instructions
• 17 Children (77% of the 22 Children whose
parents responded) had experience with snakes
Results & Discussion
• The ANOVA on latency to touch the target yielded
significant main effects on the target stimulus,
F(1,140) = 13.42, p < .01, Prep= .96
-and age, F(1,44) = 29.05, p<.01, P = 1.0.
rep
-as well as an age-by-target interaction, F(1,44)=
5.12 p <.05 Prep= .91.
• There was no effect of the child’s experience with
snakes F(1,44) = .16, p < .69, Prep= .36
• Latency increased, but only for children:
Caterpillars were included in this experiment
Discussion Continued
• Experiment 3 provides further evidence that
even young children detect threat relevant
targets more quickly than threat irrelevant
ones, even though there was a high degree of
similarity between the two: suggests that this
is because of the snake’s unique constellation
of features- supporting the hypothesis.
General Discussion
• First evidence of advanced detection of
evolutionarily relevant threat stimuli in children
• Remarkable similarity in the pattern of responses
of the children and their parents
• Supports hypothesis of advanced fear module- a
neural system developed that is selectively
sensitive to evolutionarily relevant threat stimuli
• But that’s not all!
Control Experiment
• Compared detection of two categories of nonthreat relevant stimuli- frogs versus flowers
• The results revealed no difference for either
children or adults in the detection of a single
frog amongst flowers versus a single flower
amongst frogs.
• This predicted null is relevant in the context of
the main hypothesis
General Discussion
• In all three studies, the children detected the
threat relevant stimuli significantly faster than
the non-threat stimuli.
• The adults detected the threat relevant stimuli
significantly faster than the non-threat stimuli
in two of the three studies
• The difference was in the expected direction
of the third- the experiment involving the
caterpillar.
Final Points
• Other studies done with children and adults
being able to detect angry facial expressions
more quickly than happy ones.
• WHY Are the children able to detect the snakes
more quickly?!
• Three physical attributes of snakes- they slither
idiosyncratically- but these images were static.
Snakes Coil, and are elongated.
• Study where infants orient more preferentially to
snakes on a screen vs another exotic animals
Works Cited
• Article:
LoBue, V., & DeLoache, J. S. (2008). Detecting the
snake in the grass: Attention to fear-relevant stimuli
by adults and young children. Psychological
Science, 19(3), 284-289. doi:10.1111/j.14679280.2008.02081.x