Research Methods in Psychology

Case Studies

• Case study method is used to get a detailed picture of one participant or a small group of participants
• Clinical psychologists use case studies to present information about a person suffering from a particular disorder
• However, the findings cannot be applied to a larger population due to the focus on a small group of participants

Descriptive Statistics

• Descriptive statistics describe a set of data
• Frequency distribution is a set of data represented as numbers
• Frequency polygon is a line graph, while histogram is a bar graph
• Central tendency marks the center of distribution using mean, median, and mode
• A distribution can be bimodal, meaning two scores appear equally frequently and more frequent than any other score
• Extreme scores or outliers can distort the mean, making the median a better measure of central tendency in such cases
• Positively skewed distributions occur when the skew is caused by a particularly high score, while negatively skewed distributions occur when the skew is caused by a particularly low score
• Measures of variability include range, variance, and standard deviation, which attempt to depict the diversity of the distribution
• Range is the distance between the highest and lowest score in a distribution
• Variance and standard deviation are closely related, with standard deviation being the square root of the variance
• The higher the variance and standard deviation, the more spread out the distribution
• Z scores measure the distance of a score from the mean in units of standard deviation, with scores below the mean being negative and scores above being positive
• Percentile indicates the distance of a score from 0

How a Neuron "Fires"

• In its resting state, a neuron has an over-negative charge
• The cell membrane is selectively permeable and prevents ions from mixing
• The reaction begins when the terminal buttons of the first neuron are stimulated and release neurotransmitters into the synapse
• These neurotransmitters fit into receptor sites on the dendrites of the second neuron
• If enough neurotransmitters are received, positive ions rush into the cell and travel down the neuron like a bullet from a gun
• This firing is called the action potential
• A neuron needs to receive enough neurotransmitters to pass its threshold to make it fire
• A neuron cannot fire a little or a lot, it's the same every time, which is called the all-or-none principle

Neurotransmitters

• Some neurotransmitters are excitatory, meaning they excite the next cell into firing
• Others are inhibitory, meaning they inhibit the next cell into firing
• Each synaptic gap may contain different kinds of neurotransmitters
• The amount and types of neurotransmitters received on the receptor sites determine whether or not it will pass the threshold and fire
• Acetylcholine is involved in motor movement and its lack is associated with Alzheimer's disease
• Dopamine is involved in motor movement and alertness, and its lack is associated with Parkinson's disease, while its excess is associated with schizophrenia

Endocrine System

• Adrenal glands produce adrenaline, which signals the rest of the body to prepare for fight or flight
• Ovaries and testes produce sex hormones, estrogen for women and testosterone for men
• Levels of these hormones in men and women may partially explain gender differences

Genetics

• Most human traits result from the combined effects of nature (our genetic code) and nurture (the environment where we grow up and live)
• Every human cell contains 46 chromosomes in 23 pairs
• Chromosomes are made up of DNA (deoxyribonucleic acid)
• Segments of DNA produce specific proteins that control some human traits
• These are called genes, which can be dominant or recessive
• Identical twins share the same genetic material, and researchers study their traits to determine how much of an impact genes have on these traits
• Effective psychological environment refers to when a pair of twins grows up in similar environments, causing them to have alike traits
• Chromosomal abnormalities can occur, resulting in mental retardation, with Down syndrome being the most common type

Sensation and Perception

• Transduction is the process of a signal being transformed into neural impulses
• Sensory adaptation refers to decreasing responsiveness to stimuli due to constant stimulation
• Sensory habituation refers to the fact that our perception of sensation is partially due to how focused we are on them
• Deafness can be caused by conduction deafness or nerve deafness, with nerve deafness being more difficult to treat
• The gate-control theory explains that pain messages have a higher priority than others
• Endorphins can also affect the gate, releasing it when they are released into the body

Chemical Senses

• Taste (gustation) involves the absorption of chemicals by taste buds, which are located on the papillae
• Humans sense five types of tastes: sweet, salty, sour, bitter, and umami (savory)
• Smell (olfaction) depends on the chemicals emitted by substances
• Researchers estimate that 100 different types of smell receptors may exist
• These receptors are linked to the olfactory bulb, which sends this information to the brain

Body Position Senses

• The vestibular sense tells us how our body is oriented in space using the semicircular canals in the inner ear
• The kinesthetic sense tells us the position and orientation of specific body parts using receptors in muscles and joints

Perceptual Theories

• Signal detection theory investigates the effect of distractions and interference on perception
• Response criteria refer to how motivated we are to detect certain stimuli and what we expect to perceive
• False positives occur when we think we perceive a stimulus that is not there, while false negatives occur when we do not perceive a stimulus that is present
• Top-down processing involves using background knowledge to fill in gaps in perception
• Bottom-up processing is the opposite, using features of an object to build a complete perception
• Feature detectors allow our mind to build a picture using basic characteristics
• Principles of visual perception include the figure-ground relationship, which determines what part of the image is the figure and what part is the background
• Gestalt rules state that we normally perceive images as groups, not as isolated elements, and are influenced by factors such as proximity, similarity, continuity, and closure
• Constancy refers to our ability to maintain a constant perception of an object despite changes