Experimental Psychology – Lectures
Lecture 2
Research methods in psychology
Behavior can be explained on various levels. Roughly:
- Biological factors: chemical, neural, hormonal, genetic
- Individual factors: learning, psychodynamic and cognitive processes
- Cultural and social factors
Each level has its own research methods. An important distinction is that between descriptive versus
experimental research.
➔ Descriptive research does not provide information about causality, whereas experimental
research does provide information about causality.
Descriptive research:
- Naturalistic observation: behavior is observed within its natural context
- Case studies: a detailed study on one subject or event
- Interview: subjects answer a number of questions about behavior attitudes, believes etc.
- Questionnaires are generally more structured that interviews
- Poll: a sample of subjects that make a small part of the population on which conclusions for
the whole populations are drawn. The sample needs to be ‘representative’
Correlational research: measures association between two variables
Positive correlation: both variables change in the same direction, thus when length increases, weight
increases → (0<x<1)
Negative correlation: variables change in opposite directions, when the number of cigarettes
increases, the lifespan decreases → (-1<x<0)
A correlation of 0 implies that there is no relationship between the two variables.
A correlation is measurable between every random pair of variables. A high correlation does not imply
a causal relationship. The researcher manipulates just one aspect of the situation (A) while the rest
stays the same. The effect of this manipulation on behavior (B) is then measured. The A group is the
experimental group (Manipulation of variable ‘A’) and the B group is the control group (No
manipulation of variable ‘A’).
Timeline of an experimental study:
1. Start with an idea, observations, and read the literature
2. Use theories to formulate a hypothesis (= an expectation that will be tested in the experiment
and that can be proven as wrong/right)
3. Operationalization: You have to become concrete. Many choices need to be made that are
crucial to your study. An experiment succeeds or fails due to these choices.
When results correspond with the hypothesis → theory confirmation
When results conflict with the hypothesis → theory is wrong (falsification)
➔ Or mistakes in operationalization, sample size to small,
wrong subjects, etc.
Different kinds of variables:
1. Independent variable → The variable that is manipulated by the researchers
2. Dependent variable → The variable that is measured
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, 3. Control variables → Aspects of the experiment that are equal for the experimental and
control group
4. Subject variables → Criteria on which the groups are matched
Different kinds of validities:
1. Internal validity → Is the change of the independent variable A the actual cause of the change
in dependent variable B?
2. External validity → To which extent can you generalize results to the real world and the
(intended) population?
Chapter sensation and perception
- Sensation: Peripheral processing by sensory receptors
- Perception: Higher-order interpretation of the stimulus
- There is no sharp demarcation between the two. Usually, sensation and perception are so fast
that ‘seeing’ equals ‘understanding’.
Classification of the senses:
- The traditional 5 senses include: seeing, hearing, taste, smell, and touch
- Additionally: kinesthetic information (limb posture and muscle tension) balance, also touch=
texture, pain, temperature, vibration
- The action of one sense strongly depends on information from other senses.
Psychophysics → Addresses the question of how to measure sensory capacities. Early research
focused on establishing thresholds
- Absolute threshold → The lowest intensity of a stimulus that is detectable for humans.
- Thresholds can be measured with the method of constant stimuli: present stimuli at different
intensities around the threshold in random order. → a typical S-shaped function is then
obtained.
- Tendencies or biases to respond YES or NO may obscure the picture.
- Difference threshold → assess the smallest noticeable difference between two stimuli. The
individual compares the standard-stimulus with another stimulus. The smallest noticeable
variation is called just-noticeable difference (JND).
- JND depends on the ‘size’ of the standard = Weber-Fechner’s Law. JND is a particular constant
proportion of het standard. A small Weber fraction implies good sensitivity.
Signal detection theory (SDT) → Perception is not always an ‘all-or-none’ decision. Thee is often a
transition from not observing a stimulus to observing a stimulus. Moreover, there always is a response
bias (preference for responding ‘yes’ or ‘no’) when testing individuals.
- Assumes that a target stimulus is presented against a background of internal noise. Activity of
the stimulus is added to the constant noise signal. The individual decides whether the
observed activity originates from ‘noise alone’ or from ‘stimulus + noise. The individual uses a
criterium for this.
- The subject decides if there was a signal or not, there are 4 possibilities → hit, miss, false
alarm and correct rejection.
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, Mathematical equation gives 2 measures:
- Sensitivity: correct relative to incorrect answers
- Bias: ‘yes’ relative to ‘no’ answers (left versus right)
SDT is also applied to research that focuses on quality of
decisions (judge, medical field, medical examination etc.)
Vision → Physical aspects: Light is electromagnetic radiation with a
specific frequency that falls within the observable spectrum (visible
to the eye).
The eye
Light first passes through the cornea. This is where most of the refraction takes places. After the
cornea, light passes through the lens of the eye. Ciliary muscles control the accommodation of the
lens, thus allowing light to be focused on the retina. The adjustable lens is responsible for the fine-
tuning of the focusing. The retina is the light-sensitive tissue inside the eye. It comprises light-sensitive
receptors that are responsible for signal transduction.
Cones are mostly packed in the central part of the retina, the fovea. Cones are responsible for
perception of color and fine details. The rods are mostly centered around the fovea and are sensitive
for low-intensity light. Rods are colorblind and responsible for perception of movement, peripheral
vision, and night vision.
1 = retina
2 = optic nerve
3 = optic nerve
4 = blind spot
The blind spot is the sport where the optic nerve leaves the eye. It is a mistake of evolution. The blind
sport is exceedingly difficult to notice because the brain fills in the blind sport with the immediate
surround.
Nearsightedness (myopia), farsightedness (hypermetropia), and astigmatism.
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, - Myopia: the eye is too long. The person is nearsighted and sees distant objects as blurred. A
concave lens (-powered) corrects this
- Farsighted: The eye is too short. Person is farsighted and thus cannot see near objects. A
convex lens (+powered) corrects this.
- Presbyopia: Type of farsightedness as a
consequence of diminished elasticity of the lens
(>40 years). The eye cannot accommodate
enough, and the person thus cannot see nearby
objects. Corrected with reading glasses.
- There is always a dominant eye.
- Astigmatism: Imperfections in the spherical
curvature of the cornea or the lens may result in
a distorted retinal image.
- Cataract: clouding of the lens. (age, diabetes)
- Macular degeneration: Retinal degeneration of
the fovea. The focus is black and distorted.
(smoking)
- Glaucoma: worsening/loss of peripheral vision
(failure of nerve cells due to increased eye
pressure). → Tunnel vision
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