Psychology 7

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Psychology 7 Experimental Psychology
Experimental Design
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Basic Experimental Designs

• Posttest Only Design
• Pretest-Posttest Design
• Repeated Measures Design
• Matched Pairs Design

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BEHAVIORAL ENDOCRINOLOGY

• The study of how hormones affect behavior and
  vice-versa
• A dozen millennia years ago or so, an
  adventurous soul managed to lop off a surly
  bulls testicles and thus invented behavioral
  endocrinology. It is unclear from historical
  records whether this individual received either a
  grant or tenure as a result of this experiment,
  but it certainly generated an influential finding
  something or other comes out of the testes that
  helps make males such aggressive pains in the
  ass. That something or other is testosterone.
  Sapolsky (1997)

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• Arnold Berthold in 1849 removed testes of a
  rooster stopped crowing, no more aggressive
  behavior, no more sexual behavior
• Reimplanted one testis in body cavity and
  restored normal crowing, sexual behavior, and
  aggression
• The reimplanted testis had no nerve connections
  must have been a chemical released into the
  circulatory system that changed behavior
• Castration in humans long known to have similar
  effects e.g., the castrati

Alessandro Moreschi
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• Castrated males (experimental animals) showed
  absence of sexual responses to females
• Injection of testosterone into castrated males
  restored sexual behavior to normal levels
• Was there a reverse direction of causality, as
  well would sexual behavior or mere exposure to
  females increase testosterone?

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Can Exposure to Females Increase Males
Testosterone?

• The first studies to investigate this used
  posttest only designs
• Purvis Haynes (1974)
• Cages with 2 compartments separated by wire mesh
  barrier
• Males randomly assigned to one of 2 conditions
  (1) female on other side of barrier for period of
  time, or (2) other side of cage was empty for
  same period of time
• Males were sacrificed at end of exposure period
  and blood testosterone levels were determined

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Post-Test Only Design
Purvis Haynes (1974)
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Posttest Only Design
Empty Cage
Testosterone
Random
Participants (male rats)
Female in Cage
Testosterone
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• Randomly assign 1000 people to have monthly
  bloodlettings for 6 months vs. no bloodlettings
• At end of 6 months, doctor blind to condition
  rates each person for general health
• Post-test only design

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Limitations of Posttest Only Design

• Posttest only for measuring testosterone
  responses was limited in sample size since rats
  had to be sacrificed
• Some studies failed to find significant effects
  of exposure to females using between-subject
  (posttest only) designs
• Many sources of variability in testosterone may
  have been masking the effect

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• Pulsatility of testosterone
• Circadian rhythms
• Individual differences

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Pretest-Posttest Designs

• Improved hormone assays made it possible to draw
  blood multiple times from the same animals
  without sacrificing them
• This allowed pretest measures of testosterone
  that could be compared to posttest measures

Testosterone (posttest)
Female
Testosterone (pre-test)
Random
Testosterone (posttest)
No Female
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Pretest-Posttest
Amstislavskaya Popova, 2004 mice
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Pretest-Posttest vs. Posttest Only

• Advantages of Pre-tests
• For small sample sizes, can ensure groups are
• Can measure changes within an individual instead
  of only across group as a whole
• Experimental manipulation may have different
  effects depending on baseline values
• Can assess effect of a manipulation in spite of
  mortality effects

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Mortality/Unequal Groups Revealed by
Pretest-Posttest
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Pretest-Posttest vs. Posttest Only

• Advantages of Pre-tests
• For small sample sizes, can ensure groups are
• Can measure changes within an individual instead
  of only across group as a whole
• Experimental manipulation may have different
  effects on different individuals
• Can assess effect of a manipulation in spite of
  mortality effects
• Disadvantages of Pre-Tests
• Expensive
• May affect the posttest results

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Solomon 4-Group Design

• Tests for effects of pretest. Groups
• Posttest only control group
• Posttest only experimental group
• Pretest control group posttest
• Pretest experimental group posttest

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Example of Solomon Design
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Example of Solomon Design
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Repeated Measures Design

• Each participant takes part in each experimental
  condition

Participants
Control condition
Experimental condition
Participants
Control condition
Experimental condition
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Repeated Measures and Bloodletting

• All individuals undergo 6 months of monthly
  bloodletting and 6 months of no bloodletting
• Dependent measure Doctor health ratings at end
  of each 6 month period
• Half subjects bleed first, half no bleed first

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What Brain Mechanisms Control Responses to
Females?
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Everitt,1990
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Different Effects of Lesions to Amygdala vs. POA
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Does the POA Control Testosterone Responses to
Females?
Testos
POA lesion
Testos
Participants (rats)
(Random)
Testos
Sham surgery
Testos
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Medial Preoptic Lesions Disrupt Testosterone
Responses
Kamel Frankel, 1978
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Summary of Endocrinology Experiments

• Exposure to females increases male testosterone
  (posttest only, pretest-posttest, repeated
  measures)
• Lesions to POA disrupt copulation (posttest only)
• Lesions to POA disrupt male testosterone response
  to females (complex design pretest-posttest with
  2 factors (1) lesion or sham, (2) exposure to
  female or not

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Matched Pairs Design

• Subjects are matched on a characteristic related
  to the dependent variable and then randomly
  assigned to conditions
• Technique to ensure that experimental groups are
  equal before being subject to the experimental
  manipulation
• Usually used with small sample sizes

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Example of Matched Pairs

• Researchers want to test hypothesis that
  computerized tutorials will improve math
  performance more than written workbooks
• Students 1 hour study period in one or other
  condition each day for 1 month dependent
  variable is score on math test at end of month
• Researchers have previous evidence that IQ scores
  relate to performance on math test IQ scores
  available at school for each student
• 16 students with low math grades chosen for
  study, with 8 males and 8 females
• Researchers first obtain students IQ scores and
  gender info

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102 F (A) 78 F (B) 93 F (C) 86 F (D) 84 F
(E) 94 F (F) 96 M (G) 89 F (H) 94 M (I) 109 M
(J) 105 M (K) 80 M (L) 104 F (M) 84 M (N) 89 M
(O) 95 M (P)
Match for Gender and IQ
Set 1 104 F (M) and 102 F (A) Set 5 109 M (J)
and 105 M (K) Set 2 94 F (F) and 93 F (C) Set
6 96 M (G) and 95 M (P) Set 3 89 F (H) and 86 F
(D) Set 7 94 M (I) and 89 M (O) Set 4 84 F (E)
and 78 F (B) Set 8 84 M (N) and 80 M (L)
Randomly assign 1 from each set to each condition
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Costs and Benefits of Different Designs

• Repeated Measures
• Advantage Since compare each individual to
  themselves, decrease effects of subject
  variability and make effects of independent
  variable easier to detect
• Disadvantage Order effects
• Matched Pairs
• Advantage Similar to repeated measures without
  having problem of order effects (decrease subject
  variability)
• Disadvantage Cost of identifying and measuring
  matching variable
• Procedure is worthless if matching variable not
  related to dependent measure
• May be unnecessary with large enough sample size