Detecting the Snake in the Grass Attention to fear relevant stimuli by adults and young children Presented by Aaron Harvey

Transcription

1 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, University of Virginia

2 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.)

3 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!

4 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

5 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. Threat Irrelevant? Distractors!

6 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!

7 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.

8 A preschool child identifying the single flower target among eight snake distractors by touching the flower image on a touchscreen monitor.

9 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.

10 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.

11 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.

12 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.

13 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.

14 Experiment 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?

15 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.

16 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, P rep = 1.0 and age, F(1,140) = , p<.01, P rep = There was no effect of the child s experience with snakes F(1,140) = 1.18, p <.28, P rep =.66

17 Average latency to detect target stimuli (snakes vs. nonsnakes) among adult and child participants in Experiments 1 through 3.

18 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

19 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.

20 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.

21 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, P rep =.95, and age, F(1,44) = , p<.01, P rep = 1.0. There was no effect of the child s experience with snakes F(1,44) = 0.17, p <.68, P rep =.37

22 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.

23 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

24 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, P rep =.96 - and age, F(1,44) = 29.05, p<.01, P rep = as well as an age-by-target interaction, F(1,44)= 5.12 p <.05 P rep =.91. There was no effect of the child s experience with snakes F(1,44) =.16, p <.69, P rep =.36 Latency increased, but only for children: Caterpillars were included in this experiment

25 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.

26 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!

27 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

28 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.

29 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

30 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), doi: /j x

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