Notes on Threats to Internal Validity and Intro to Neuroscience (Transcript)

Threats to internal validity

  • Concept: Internal validity is the extent to which a study demonstrates that the observed effect is due to the manipulated variable, not other confounding factors. Poor control introduces confounds that threaten the truth of the relationship.
  • Social desirability bias (subject-related threat): participants may answer in a way that makes them look good rather than provide truthful responses.
    • Typical context: self-report measures where participants want to be liked or viewed favorably by the researcher.
    • Examples from transcript:
    • Participants may guess what the study is about and answer in a way that supports the hypothesis to please the experimenter.
    • In a cheating honesty question (scale 1–5), a participant might report a lower likelihood of cheating to appear more honest, even if their true behavior would indicate higher likelihood.
    • Consequences: false data leads to useless results; data do not reflect true behavior or attitudes.
    • Mitigation strategies discussed:
    • Avoid relying solely on self-report measures when possible.
    • Use alternative measures that assess social desirability or implement methods to adjust for this bias.
    • Be mindful that the bias can originate from both subjects and experimenters.
  • Experimenter bias (unintentional): researcher’s expectations or interactions unintentionally influence the outcome.
    • Distinction: not malfeasance (not lying or faking data), but subtle, unintentional effects.
    • Example from transcript: in a dissertation study, the experimenter’s tone or interaction style with participants in different conditions (competitive vs. individual tasks) could unintentionally affect responses and create a confound.
    • Mitigation: use a double-blind procedure where the experimenter does not know which subjects are in which condition, reducing potential influence.
  • Sampling bias (threat to external validity): how the sample is selected affects generalizability to other populations.
    • In the transcript, SONA studies often use students as subjects (typically 18–23 years old).
    • Question raised: would results generalized from students extend to non-students or older individuals?
  • External validity (generalizability): the extent to which findings generalize to other people, places, or situations.
    • Emphasis that internal validity (the rigor of the study itself) comes first; external validity is an additional objective that can be expanded later.

Foundations: psychology as a biological science

  • Core claim: Humans are biological systems; understanding neuroscience and brain function is essential to understanding psychology.
  • Structure of today’s content: focus on biology in this class, with more in subsequent sessions.
  • Context for the coming topics: connecting brain function to behavior, cognition, and emotion.

Quick diagnostic: 10 true/false questions (brain & neuroscience themes)

  • Note: These items were used to gauge prior knowledge and stimulate interest in topics to be covered.

  • The instructor stated some answers during the session; here are the statements with the presented truth values and brief notes.

  • Statement 1: A small amount of brain tissue from a person cannot be distinguished from that of a monkey.

    • Answer: True
    • Explanation: The microscopic tissue looks similar between species; species differences are more evident at the whole-brain level.

  • Statement 2: The brain produces its own natural opiates that elevate mood and ease pain.

    • Answer: True
    • Discussion: These are endogenous opioids; commonly discussed are endorphins and enkephalins. The instructor initially queried the exact name and noted endorphins as a likely example, with enkephalins as another endogenous opioid.

  • Statement 3: The brain mass accounts for a larger percentage of body weight in humans than in any other species.

    • Answer: False
    • Explanation: Humans have a large brain relative to body size, but the claim that no other species has a larger percentage is false.

  • Statement 4: Both animals and humans seem to have pleasure centers located in their brains.

    • Answer: True
    • Context: This relates to reward circuitry, particularly in the limbic system.

  • Statement 5: We ordinarily use only 10% of our brains.

    • Answer: False
    • Note: This is a common myth; the class indicated it would be addressed later.

  • Statement 6: Electronically stimulating a cat's brain at a certain point can cause the animal to cower in the presence of a small mouse.

    • Answer: True
    • Location: Involves the limbic system, particularly the amygdala, which is tied to fear and aggression responses.

  • Statement 7: How many people would say true to the claim that we use only 10% of our brains?

    • Answer: (Context from transcript) The class discussion explored this question; the instructor later notes this is a topic to be addressed in depth. The takeaway presented is that the claim is generally considered false, with more nuance to be discussed.

  • Statement 8: Some people can write but are unable to read.

    • Answer: True
    • Explanation: This indicates dissociation between writing and reading abilities; related to how brain regions for reading and writing are distributed and lateralized.

  • Statement 9: The two hemispheres of the brain are connected by a thick band of tissue called the corpus callosum. If that connection were severed, would you necessarily notice a difference in daily life?

    • Answer: Yes, but with caveats
    • Explanation: In some cases, people show no apparent daily-life deficits, yet specialized testing can reveal differences. The severing can disrupt communication between hemispheres, leading to unusual coordination challenges in some tasks.
    • Additional notes: Motor control is contralateral (left hemisphere -> right side; right hemisphere -> left side).

  • Statement 10: Neural impulses travel through the body at the same speed as electricity passes through a wire.

    • Answer: False
    • Rationale: Neural transmission is much slower than electrical conduction in wires; precise speeds vary with myelination and fiber type.

  • Statement 11: If a blind person uses one finger to read braille, the brain area dedicated to that finger expands.

    • Answer: True
    • Concept connection: This is an example of neuroplasticity, where practice and use cause cortical areas to reorganize and expand.

Key brain concepts introduced in the session

  • Two cerebral hemispheres
    • Structure: The hemispheres are connected by the corpus callosum, a thick band of neural tissue.
    • Function: Interhemispheric communication enables integrated processing of information.
  • Lateralization of function
    • Left hemisphere generally controls the right side of the body; right hemisphere controls the left.
    • Some tasks become specialized to one hemisphere; severing the corpus callosum does not always produce dramatic daily-life deficits, but can produce distinctive cognitive effects detectable via specific tests.
  • Limbic system and reward/punishment processing
    • Reward centers are located in the limbic system and associated with pleasure and motivation.
    • The amygdala, a key structure within the limbic system, can be stimulated to evoke fear or aggression responses.
  • Neuroplasticity
    • The brain is not fixed; use and practice can expand or repurpose brain regions.
    • Example: Braille reading can lead to expansion of the brain area dedicated to the sensory finger because of heightened fine motor and tactile processing demands.
  • Brain tissue indistinguishability at micro level
    • At the level of small tissue samples, human brain tissue is not easily distinguishable from non-human primate tissue; species differences are more apparent when examining larger-scale brain organization.
  • Misconceptions addressed during the session
    • The 10% myth is false; the premise that we only use a small fraction of the brain is not supported by evidence.
    • The brain-to-body weight ratio is not absolute across species; while humans have a relatively large brain, other species can have different proportions.

Summary implications for research methods and real-world relevance

  • Internal validity requires controlling biases (social desirability, experimenter bias) to ensure observed effects reflect true relationships.
  • Sampling bias affects external validity and generalizability; relying solely on student samples may limit applicability to broader populations.
  • Ethical considerations: minimizing bias is part of responsible research practice; double-blind designs and multiple measurement approaches can reduce bias.
  • Neuroscience concepts provide foundational context for interpreting psychological phenomena, emphasizing the brain-behavior link and the potential for neural adaptation with experience.
  • The discussion foreshadows the interplay between methodological rigor and biological explanation in psychology, underscoring why both domains are essential for a comprehensive understanding of behavior.