Mental Abilities 2

Developmental Psychology of Mental Abilities

When examining changes in mental abilities across a typical person's lifespan, the focus is on individual absolute levels, not relative comparisons to peers.

  • On average, mental abilities increase over a lifespan, with rapid growth in childhood and adolescence, stability in middle age, and decline in old age.

  • Verbal abilities often peak in the 40s, 50s, and 60s, while spatial ability and perceptual speed are typically highest in younger adults.

  • Cohort effects, such as differences in education levels between age groups, can influence test scores.

  • Longitudinal research, which follows the same individuals over time, helps address cohort effects.

Stability of Mental Abilities

  • High levels of stability exist in relative levels of mental ability across a lifespan.

  • The graph in the video shows data from Deary's study, which tracked 500 elderly Scottish adults. Their intelligence was tested at age 11 and again at age 80, revealing a correlation of r = 0.66.

Biological Basis of Intelligence

  • Researchers explore cognitive tasks to find indicators of a biological basis for intelligence.

Brain Size

  • Early studies measured external head size, finding a weak positive correlation with mental ability.

  • Modern techniques using MRI scans show a more reliable correlation of approximately r = 0.33 between brain volume and intelligence test scores.

  • Specific brain regions may be more crucial for cognitive abilities.

Processing Speed

  • Processing speed as a measure of how fast someone can process information is thought to be correlated with intelligence.

Reaction Time Tasks:

  • Simple Reaction Time: Measures the speed of reaction to a flashlight stimulus by measuring the time it takes to lift a hand off a home button.

  • Choice Reaction Time: Measures reaction time when one of several light bulbs flashes.

  • 'Odd Man Out' Reaction Time: Three lights flash, and the participant must react to the one not adjacent to another lit light.

  • Studies show a correlation of approximately r = -0.13, indicating faster reaction times correlate with higher intelligence test scores.

Inspection Time

  • Inspection time involves:

    • A fixation cross.

    • Followed by a brief presentation of two lines of different lengths.

    • Immediately masked to make it unclear which line is longer.

  • Participants identify the longer line, and the exposure time is reduced until they perform at chance level.

  • Shorter inspection times correlate with higher IQ scores (approximately r = -0.30).

  • Again, this shows something about information processing speed that says something about your general capacity to perform well on intelligence tests.

Modern Brain Scanning Techniques

  • Techniques, such as EEG and PET scans, are used to find indicators that predict intelligence test scores.

    • Nerve conduction velocity (transmission speed of electrical impulses).

    • Analysis of brain waves using electroencephalography.

    • Brain glucose metabolism with positron emission tomography.

  • Faster transmission speed may correlate with higher intelligence.

  • Complex or shorter brain waves may correlate with higher test scores.

  • More efficient brains may use less glucose.

  • Findings have been somewhat inconsistent, needing further research.

Genetic and Environmental Influences on Mental Abilities

  • Twin studies are used to estimate the heritability of mental abilities.

    • Monozygotic (identical) twins share 100% of their genes.

    • Dizygotic (fraternal) twins share about 50% of their genes.

Heritability Estimates

  • If monozygotic twins are raised separately, their correlation directly estimates heritability.

  • Comparing correlations between monozygotic and dizygotic twins raised together helps estimate heritability: H = 2 * (r{MZ} - r{DZ}) where r{MZ} is the correlation for monozygotic twins and r{DZ} is the correlation for dizygotic twins.

  • Typical heritability estimates for IQ are around 0.5.

  • Children have a heritability estimate of approximately 0.4 with a shared environment influence of 0.35, that moves to being 0.65 in adulthood with the shared environment estimate dropping to 0.2.

  • Heritability estimates tend to be lower in childhood (around 0.4) and higher in adulthood (around 0.65).

  • Shared environment influence decreases as individuals grow up and leave home.

Environmental Influences

  • Factors such as nutrition and exposure to harmful substances (e.g., alcohol poisoning, lead poisoning, severe malnutrition) can negatively impact cognitive abilities.

Breastfeeding

  • Some studies suggest that breastfed children have higher IQs (about 6 points higher).

  • However, smarter mothers are more likely to breastfeed, creating a causality problem & confounding results.

  • When studies control for the mother's IQ, the difference in IQ points between breastfed and non-breastfed children becomes very small (less than 1 point).

Being a Twin

  • Some theories posit that being a twin could lead to cognitive costs due to shared nutrition in the womb.

  • Findings are inconsistent, with some studies showing IQ differences (e.g., 5 points) but more recent findings showing no significant differences.