Biological Foundations of Psychology: Genes, Brains, and Perception

Posted on Dec 11, 2025 in Psychology and Sociology

Behavioral Genetics and Heredity

Core Concepts in Behavioral Genetics

  • Behavioral Genetics: The study of gene-environment interaction influencing behavior, traits, and brain function.
    • Example: How genes and environment contribute to anxiety.
  • Epigenetics: Changes in gene expression without altering the DNA sequence, often due to environmental factors.
    • Example: How childhood trauma alters gene expression.
  • Behavioral Genomics: The relationship between DNA, specific genes, and behavior (e.g., identifying genes linked to addiction).

The Nature vs. Nurture Debate

This debate focuses on genetic versus environmental influence on behavior. It involves complex interaction, making random assignment difficult in research.

Research Methods in Genetics

  • Twin Studies: Compare identical (monozygotic) and fraternal (dizygotic) twins. Greater similarity in identical twins suggests genetic influence.
  • Adoption Studies: Assess the relative influence of genetic versus environmental factors.

Fundamentals of Heredity

  • Chromosomes: 23 pairs in humans.
  • Genes: Units of heredity.
  • Alleles: Different versions of a gene.
  • Heredity: 50% genetic material from each parent; siblings share approximately 50% of genes.
  • Genotype: An organism’s genetic makeup.
  • Phenotype: The observable expression of genes.

Mechanisms of Gene Expression Change (Epigenetics)

Changes in gene expression without altering the DNA sequence. Example: Identical twins differing with age.

  • DNA Methylation: Reduces gene expression.
  • Histone Modification: Can increase or decrease gene expression.
  • Influences: Early childhood experiences, nutrition, and psychological disorders.

Measuring Genetic Influence

  • Heritability: The proportion of trait variation due to genetic variation.
  • Heritability Coefficient: A value from 0.0 (none) to 1.0 (all).
  • Reaction Range: The range of potential phenotypes for a given genotype.
  • Environmental Factors:
    • Familial Environment (Shared): Shared environmental influences.
    • Unique Environment (Non-shared): Non-shared environmental influences.

Evolutionary Psychology Concepts

  • Natural Selection: Traits increasing survival and reproduction are preserved. Reproductive success is key.
  • Adaptation: Traits that increase survival and reproduction.
  • Types of Adaptations:
    • Physiological: Broad adaptations for the environment.
    • Psychological: Specific adaptations for problems.
  • Interactionist Perspective: Behavior is influenced by genetics, epigenetics, environment, culture, and other factors.

Theories of Altruism

  • Kin Selection: Increasing the survival of relatives.
  • Reciprocal Altruism: Helping others with the expectation of reciprocation.

The Nervous System and Neural Communication

Synaptic Transmission

This process involves communication between neurons:

  1. Neurotransmitters are released into the synaptic cleft.
  2. They bind to receptors on the postsynaptic neuron.
  3. This generates Postsynaptic Potentials (which can be excitatory or inhibitory).

Organization of the Nervous System

  • Central Nervous System (CNS): Brain and spinal cord.
  • Peripheral Nervous System (PNS): Nerves outside the CNS.
    • Somatic Nervous System: Controls sensation and voluntary movement.
    • Autonomic Nervous System: Controls involuntary movement.
      • Sympathetic Nervous System: Responsible for the “fight or flight” response.
      • Parasympathetic Nervous System: Responsible for “rest and digest” functions.

Brain Structure, Function, and Measurement

Key Brain Regions and Functions

  • Basal Ganglia: Associative learning.
  • Amygdala: Emotional learning.
  • Hippocampus: Formation of new memories.

Memory and Amnesia

  • Long-Term Potentiation (LTP): The strengthening of synapses based on recent patterns of activity.
  • Types of Amnesia:
    • Anterograde Amnesia: Inability to form new memories.
    • Retrograde Amnesia: Inability to recall past memories.

Structural Brain Imaging Techniques

  • Postmortem Examination: Brain examination after death.
  • CT (Computed Tomography): Uses X-rays to create cross-sectional brain slices.
  • MRI (Magnetic Resonance Imaging): Measures blood flow using magnetic fields to create detailed images.

Measuring Brain Function

  • EEG (Electroencephalography): Measures electrical activity in the brain.
  • PET (Positron Emission Tomography): Uses a radioactive tracer to measure blood flow and metabolic activity.
  • fMRI (Functional Magnetic Resonance Imaging): Measures blood flow changes associated with neural activity.

Manipulating Brain Activity

  • Disrupting Activity (Virtual Lesions):
    • Lesion: Destroying a specific part of the brain.
    • TMS (Transcranial Magnetic Stimulation): Creates temporary “virtual lesions” to study function.
  • Directly Stimulating Activity:
    • Electrical Stimulation: Applying current directly to brain regions.

Sensation and Perception

Vision and Visual Processing

Photoreceptors

  • Rods: Responsible for light/dark perception (low light).
  • Cones: Responsible for color perception (high light).

Visual Information Pathway

Light → Photoreceptors → Bipolar Cells → Ganglion Cells → Optic Nerve → Brain

Color Theories

  • Trichromatic Theory: Proposes three cone types sensitive to red, green, and blue wavelengths.
  • Opponent Process Theory: Receptors make antagonistic responses (red-green, blue-yellow, black-white).
  • Color Blindness: Reduced ability to perceive colors.

Depth Perception Cues

  • Binocular Cues: Retinal disparity, convergence.
  • Monocular Cues: Linear perspective, texture gradients, interposition, relative size, height in plane, light and shadow, motion parallax.

Perceptual Processes and Errors

  • Perceptual Set: A predisposition to perceive things in a certain way.
  • Inattentional Blindness: Failure to notice a visible object when attention is focused elsewhere.
  • Processing Types:
    • Bottom-Up Processing: Analysis starting from sensory receptors and moving up to the brain.
    • Top-Down Processing: Guided by higher-level mental processes, expectations, and experience.
  • Prosopagnosia: The inability to recognize faces (face blindness).
  • Perceptual Constancies: Perceiving objects as unchanging despite changes in sensory input.
  • Visual Illusions: Incorrect assumptions about the world. Examples: Müller-Lyer Illusion, Ponzo Illusion.

Audition (Hearing)

Sound Waves

Defined by:

  • Amplitude: Loudness.
  • Wavelength: Pitch.
  • Purity: Timbre (quality).

Theories of Pitch Perception

  • Place Theory: Specific frequencies vibrate specific places on the basilar membrane (explains high pitches).
  • Frequency Theory: Pitch corresponds to the rate of vibration of the basilar membrane (explains low pitches).

Auditory Localization

Determining sound source location using interaural time/level differences and monaural cues.

Body Senses (Somatosensation)

  • Proprioception (Kinesthesia): Sense of body part position and movement.
  • Vestibular Sense: Sense of balance and spatial orientation.
    • Semi-Circular Ducts: Detect rotational movements.
    • Otoliths: Detect linear acceleration and head position.