Individual differences area core studies (Freud 1909; Baron-Cohen et al. 1997; Van Leeuwen et al. 2008)

Welcome to the Individual Differences Area

Have you ever wondered why people think, feel, and behave so differently from one another? While some psychological approaches look for universal rules that apply to everyone, the Individual Differences Area focuses on what makes each person unique. In this chapter, we explore how psychologists investigate differences in our personalities, mental health, cognitive abilities, and intelligence.

We will examine three core studies in depth:
• Freud (1909): A classic psychodynamic exploration of a young boy's phobia and unconscious conflicts.
• Baron-Cohen et al. (1997): A contemporary cognitive study investigating Theory of Mind in adults with Autism Spectrum Disorder.
• Van Leeuwen et al. (2008): A biological/developmental twin-family study investigating the genetic and environmental influences on intelligence (\(g\)).

Don't worry if these studies seem detailed or complex at first! We will break down each study into clear, bite-sized sections: aims, methods, findings, conclusions, and evaluations.

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1. Classic Study: Freud (1909) — Analysis of a Phobia of a Five-Year-Old Boy

The Big Picture: What Was Freud Trying to Understand?

Sigmund Freud believed that our adult personality and psychological difficulties stem from unresolved childhood conflicts tucked away in our unconscious mind. Freud proposed that children pass through psychosexual stages of development. During the phallic stage (around ages 3 to 5), boys experience the Oedipus complex: an unconscious sexual desire for their mother and subconscious jealousy or hostility toward their father, accompanied by a terrifying fear of punishment from the father known as castration anxiety.

Aim of the Study

• To provide empirical support for the existence of the phallic stage and the Oedipus complex.
• To demonstrate how a childhood phobia could develop through unconscious defence mechanisms: repression (pushing disturbing thoughts into the unconscious) and displacement (shifting anxiety from its true source onto a neutral substitute object).

Method and Sample

• Research Design: Longitudinal clinical case study.
• Participant: A single male child referred to as "Little Hans" (real name Herbert Graf), observed between the ages of 3 and 5 years.
• Data Collection Method: Almost all observations, conversations, and dream diaries were recorded and transcribed by Hans's father (a devoted supporter of Freud). The father posted these written accounts to Freud. Freud met Hans in person only on a very limited number of occasions to provide guidance.

Key Events, Dreams, and Freud's Interpretations

• The Horse Phobia: Hans developed an intense fear of going out into the street because he feared being bitten by a horse. He was particularly terrified of white horses with black blinkers and black muzzles, as well as large carts or horses falling down. Freud interpreted the black muzzles and blinkers as symbolic representations of Hans's father's dark moustache and eyeglasses. The fear of being bitten was analyzed as displaced castration anxiety (fear of his father castrating him as punishment for his desire for his mother).
• The Giraffe Fantasy: Hans described a fantasy featuring a big giraffe and a crumpled giraffe in his bedroom. Hans took the crumpled giraffe away and sat on it, causing the big giraffe to shout out in protest. Freud interpreted the big giraffe as the father, the crumpled giraffe as the mother (possessing female genitalia), and Hans sitting on it as taking possession of his mother.
• The Plumber Fantasies: Hans envisioned a plumber coming to the house, removing his bottom and "widdler" (penis) with a pair of pliers, and replacing them with a much bigger bottom and a larger widdler. Freud interpreted this fantasy as the resolution of the Oedipus complex: Hans overcame his castration anxiety by identifying with his father and accepting his role as a growing male.

Conclusions

• Phobias can develop when unresolved unconscious psychosexual conflicts are displaced onto neutral external objects (such as horses).
• Hans's case provided qualitative evidence supporting the existence of the phallic stage, the Oedipus complex, and the role of castration anxiety in emotional development.

Methodological Evaluation of Freud (1909)

• Sampling Bias: Studying a single, middle-class Austrian boy means the findings lack generalisability to wider populations, other cultures, or females (ethnocentric and androcentric).
• Validity and Researcher Bias: Hans's father was an ardent follower of Freud who asked leading questions when speaking with his son. Freud's interpretations were subjective and unfalsifiable, significantly lowering the internal validity of the findings.
• Data Richness: The longitudinal case study design provided exceptionally rich, detailed qualitative data regarding childhood emotional development in a natural home setting.
• Ethics: While Hans's father gave parental consent, Hans was too young to provide fully informed consent or understand his right to withdraw.

Key Takeaway for Freud: Freud used the case of Little Hans to argue that phobias are not learned fears of external objects, but rather internal, unconscious anxieties (like the Oedipus complex) displaced onto symbolic targets.

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2. Contemporary Study: Baron-Cohen et al. (1997) — Advanced Test of Theory of Mind

The Big Picture: What is Theory of Mind (ToM)?

Theory of Mind (ToM) is the ability to attribute mental states (such as beliefs, intents, desires, emotions, and knowledge) to oneself and others, and to understand that others have beliefs and desires different from one's own. Earlier developmental tests (like the Sally-Anne test) worked well for young children, but high-functioning adults with Autism Spectrum Disorder (ASD) could easily pass them because of their normal intelligence. Baron-Cohen and colleagues wanted to create a more sensitive, advanced test.

Aim of the Study

• To develop an advanced test of Theory of Mind suitable for high-functioning adults with Autism Spectrum Disorder (ASD) or Asperger Syndrome (AS).
• To assess whether high-functioning adults with ASD/AS show specific deficits in mentalising compared to neurotypical adults and adults with Tourette syndrome (TS).

Method, Design, and Sample

• Research Design: Quasi-experiment / matched-group design.
• Sample (3 Groups):
1. Group 1 (Autism / AS): 16 individuals (13 males, 3 females) of normal intelligence (\(\text{IQ} > 85\)).
2. Group 2 (Normal / Neurotypical Adults): 50 adults (25 males, 25 females) with no psychiatric history.
3. Group 3 (Tourette Syndrome): 10 adults (8 males, 2 females) of normal intelligence. Why include Tourette syndrome? Tourette syndrome is a childhood-onset neuropsychiatric disorder. Including this group controlled for whether having a developmental disorder in general impairs social cognition, ensuring any deficit was specific to autism.

Procedure and Tasks

• The Eyes Task (Experimental Task): Participants viewed 25 black-and-white photographs of the eye region of human faces (male and female) displayed for 3 seconds each. Participants completed a forced-choice between two mental state words (one target mental state and one foil, e.g., "concerned" vs "unconcerned").
• Gender Recognition Task (Control Task): Participants identified the biological sex of the same 25 eye photographs to check whether face perception cues were intact.
• Basic Emotion Recognition Task (Control Task): Participants identified 6 basic emotions from whole faces (Ekman faces) to confirm that any poor score was not due to basic visual or emotional recognition problems.
• Happé's Strange Stories: A complex story-based comprehension task used to assess concurrent validity with the Eyes Task.

Key Findings

• Eyes Task Performance (Mean score out of 25):
• ASD / AS Group: Mean = \(16.3\)
• Normal Adult Group: Mean = \(20.3\) (Normal females scored higher than normal males: \(21.8\) vs \(18.8\))
• Tourette Syndrome Group: Mean = \(20.4\)
• The ASD group performed significantly worse on the Eyes Task than both the normal adult and Tourette syndrome groups (\(p < 0.0001\)).
• The ASD group performed normally on both the Gender Recognition Task and Basic Emotion Recognition Task, showing their basic visual processing was intact.

Conclusions

• High-functioning adults with ASD/AS possess a subtle, specific deficit in Theory of Mind (mentalising) that persists into adulthood.
• This impairment is not caused by general intellectual disability or general neuropsychiatric illness (as proven by the Tourette control group).
• The Eyes Task is a valid, sensitive psychometric measure of advanced Theory of Mind.

Methodological Evaluation of Baron-Cohen et al. (1997)

• High Internal Validity: The use of matched control groups (Tourette syndrome and neurotypical adults) and control tasks (gender and basic emotion tests) successfully isolated Theory of Mind from general perceptual ability.
• Ecological Validity Issues: Static, 2D black-and-white photographs shown for 3 seconds do not capture the dynamic, multi-sensory nature of real-life social interactions, which include vocal tone, body language, and motion cues.
• Quantitative Data: Objective numerical scores out of 25 allowed direct statistical comparisons (\(p < 0.0001\)) and high test-retest reliability.
• Sample Size: The ASD sample was relatively small (\(N = 16\)) with an uneven gender split (\(13\) males, \(3\) females), though this reflects the diagnostic prevalence of ASD in the wider population.

Key Takeaway for Baron-Cohen et al.: Even when individuals with autism have normal or high general intelligence, they show a specific, measurable difficulty in reading subtle emotional and mental states purely from the eye region.

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3. Contemporary Study: Van Leeuwen et al. (2008) — A Twin-Family Study of General IQ

The Big Picture: Where Does Intelligence Come From?

Is general intelligence (\(g\)) inherited from our biological parents through our DNA (nature), or is it shaped by our upbringing, schooling, and life experiences (nurture)? Traditional twin studies compare identical (monozygotic / MZ) twins to fraternal (dizygotic / DZ) twins. Van Leeuwen and colleagues used an extended twin-family design to look not just at twins, but also at their biological siblings and parents, providing a much clearer picture of genetic vs environmental influences.

Aim of the Study

• To determine whether variation in intelligence (\(g\)) in children is primarily influenced by genetic or environmental factors.
• To investigate whether assortative mating (people choosing partners with similar cognitive ability) occurs for intelligence.
• To examine whether genotype-environment interactions influence cognitive ability.

Method, Design, and Sample

• Research Design: Extended twin-family design (cross-sectional, correlational/psychometric).
• Sample: 112 Dutch families recruited from the Netherlands Twin Register (NTR).
• Included \(42\) monozygotic (MZ) twin pairs, \(70\) dizygotic (DZ) twin pairs, an extra singleton sibling aged 9 to 14 per family, and both biological parents (totaling \(214\) offspring pairs and their parents).

Procedure and Measurements

• Offspring Cognitive Testing: Children and siblings completed the Raven's Standard Progressive Matrices (SPM) to measure general intelligence (\(g\)) and fluid cognitive ability.
• Parent Cognitive Testing: Biological parents completed the Raven's Advanced Progressive Matrices (APM).
• Statistical Modelling: Phenotypic correlation matrices and structural equation modelling were applied to partition variance into:
• \(A\) = Additive genetic effects
• \(D\) = Dominance genetic effects
• \(C\) = Shared / common environmental effects (e.g., shared home, family wealth)
• \(E\) = Unique / non-shared environmental effects (e.g., individual peer groups, accidents, personal life events)

Key Findings

• High Heritability: Additive genetic factors (\(A\)) accounted for approximately \(67\%\) of the total variance in general intelligence (\(h^2 = 0.67\)).
• Unique Environment: Non-shared environmental factors (\(E\)) accounted for the remaining \(33\%\) of the variance in intelligence.
• No Shared Environmental Effect: Shared family environment (\(C\)) did not account for a significant portion of individual differences in general intelligence in this cohort.
• Assortative Mating: A statistically significant positive correlation was found between spouses for IQ scores (\(r \approx 0.33\)), demonstrating that people tend to choose romantic partners with similar cognitive ability.

Conclusions

• Individual differences in general intelligence (\(g\)) are predominantly determined by genetic variation (nature), with individual-specific environmental experiences (nurture) contributing the rest.
• The cognitive resemblance observed between parents and their children is primarily due to shared genetics rather than a shared home environment.
• Spousal similarity in intelligence is driven by assortative mating.

Methodological Evaluation of Van Leeuwen et al. (2008)

• Reliability & Standardisation: Raven's Progressive Matrices (SPM and APM) are well-validated, highly standardised psychometric tests with high internal reliability.
• Ethnocentrism & Sampling: The sample consisted entirely of Dutch families registered with the Netherlands Twin Register. These families likely shared relatively homogeneous, middle-class socioeconomic environments, which may minimise the observable effects of shared environment.
• Construct Validity of IQ: Raven's Matrices measure fluid, abstract non-verbal reasoning. They do not assess multiple intelligences, such as emotional intelligence, creativity, or practical problem-solving.
• Complex Family Design: Including siblings and parents alongside MZ and DZ twins controlled for generational effects and provided a more accurate heritability estimate than classic twin designs.

Key Takeaway for Van Leeuwen et al.: Around two-thirds (\(67\%\)) of the differences in general intelligence among children can be explained by inherited genetic factors, while the remaining one-third (\(33\%\)) is shaped by non-shared, unique life experiences.

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4. Comparing the Core Studies Across Psychological Debates

To score top marks in OCR Component 02, you must be able to evaluate these studies through core psychological debates:

Debate 1: Nature vs Nurture

• Freud (1909): Combines both. Nature provides innate psychosexual drives (Oedipus complex, biological instincts), while Nurture shapes how parents handle these conflicts (Hans's relationship with his mother and father).
• Baron-Cohen et al. (1997): Primarily Nature. Suggests Theory of Mind deficits are rooted in underlying biological/neurodevelopmental differences in autism.
• Van Leeuwen et al. (2008): Strongly supports Nature (\(67\%\) heritability) while acknowledging Nurture via non-shared environmental factors (\(33\%\)).

Debate 2: Psychology as a Science

• Freud (1909): Unscientific. Unfalsifiable theories, highly subjective interpretations, researcher bias, no standardised controls.
• Baron-Cohen et al. (1997): Scientific. Controlled quasi-experiment, matched control groups, standardised 3-second stimuli, objective quantitative data (\(p < 0.0001\)).
• Van Leeuwen et al. (2008): Scientific. Standardised psychometric testing (Raven's Matrices), large twin-family sample, advanced structural equation statistical modelling.

Debate 3: Reductionism vs Holism

• Freud (1909): Holistic. Examined Hans's complete family context, daily interactions, dreams, and emotional life over several years.
• Baron-Cohen et al. (1997): Reductionist. Reduces complex social communication and Theory of Mind to a 25-item 2D photograph matching task.
• Van Leeuwen et al. (2008): Reductionist. Reduces general human intelligence to a single numerical score (\(g\)) derived from abstract pattern completion tasks.

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5. Common Pitfalls & Examiner Tips

Avoid these frequent exam mistakes highlighted in OCR examiner reports:
• Don't say Freud directly observed Hans every day: Freud only met Hans a couple of times. Hans's father collected the data, asked the questions, and posted the letters.
• Don't confuse the 1997 Eyes Task with later versions: The 1997 study used 25 pairs of eyes with 2 forced choices (target vs 1 foil). (Do not describe the 2001 revised version, which has 36 items and 4 choices).
• Remember why Tourette syndrome was included: It was a critical control group to prove that mentalising impairments were unique to autism, not just a general byproduct of having any neurological or developmental condition.
• Don't claim intelligence is 100% genetic in Van Leeuwen: Always cite the \(67\%\) additive genetic estimate alongside the \(33\%\) unique environmental influence and mention assortative mating (\(r \approx 0.33\)).

Quick Memory Mnemonic for the Core Studies:
• Freud = Fear of horses & Father's letters (Psychodynamic / Oedipus)
• Baron-Cohen = Blind to mental states / Black-and-white eyes (Theory of Mind in ASD)
• Van Leeuwen = Variation in IQ / Value of twin-families (\(67\%\) Nature, \(33\%\) Nurture)