Experimental Psychology:
Experimental Psychology or cognitive psychology
- core discipline that studies cognitive functions
- Perception
- Memory
- thinking & decision making
- motor skills
- attention & consciousness
- language
- learning
- emotion
- functions are the building blocks of which all complex behaviour (bake a cake) is made
- cognitive psychology
- is photographic memory real?
- is unconscious (subliminal) perception real?
- perception is sometimes inaccurate, why?
- can animals think etc?
closely linked to:
- cognitive neuropsychology: patients with specific disorders (local brain damage) allow more
specific & reliable inferences about brain functioning
- dyslexia, neglect, aphasia, prosopagnosia
-physiological psychology: investigates relationship between mental processes & their biological
foundations in the Central Nervous System (CNS). Certain types of behaviour are traceable in
brain activity.
- Dualism: Descartes proposed that there is an interaction between mind & body. Free will not
involved in reflexes
- Hermann von Helmholtz: first experimenter: conduction velocity of the nerve impulse
- Gustav Fechner: discovered math. relationship between physical & perceptual world
- JND used in psychophysics
- Darwins Evolution Theory—> comparative psychology: discipline that allows scientists to
compare behaviours in different species
- Donders: Mental chronometry: additive factor logic still used
- Wundt: Structuralism: psych is immediate experience
- sensation, images (memories), feelings—> combination of these rise conscious experience
- analytical introspection
- Behaviourism: Watson: observable behaviour —> mental (covert) behaviour can’t be studied
- part of the logical positivism movement —> introduced: operational definition:
hunger=duration of food deprivation measured in hours
- precise measurements could be made (replicateable)
- Classic Conditioning: Pavlov
- Operant Conditioning: Skinner: learning occurs through reward & punishment
- Gestalt psychology: the whole is more than the sum of its parts // rejected Wundt &
behaviourism
- used phenomenon of apparent motion as proof for their argument
- perception is a construct, not a reflection of the sensation
,- methods in cognitive neuroscience
- experiment. research with behavioural measures (RT) traditional
- non-invasive brain imaging techniques —> EEG, MEG, fMRI
- blocking normal brain function through medication or Transcranial Magnetic Stimulation
(TMS)
- patients with (in best case) focal lesions
- comp. stimulations
- methods in psychology
- biological factors: chemical, neural, hormonal, genetic
- individual factors: learning, psychodynamic & cognitive processes
- cultural & social factors
- each level has its own research method: important distinction between descriptive vs
experimental research
- descriptive: does not provide info about causality (whether A causes B)
- experimental: does provide info about causality
- descriptive research
- naturalistic observation: behaviour observed within its natural habitat/context
- case studies: detailed study based on one subject/event. (cogn. neuropsych)
- interview: subjects answer a number of q’s about behaviour, attitudes, beliefs etc
(questionnaires are more structured than interviews)
- poll: sample of subjects that make up a small part of the population on which conclusions for
the whole populations are drawn. Sample needs to be representative
- correlational research: measures association between two variables. E.g. large people are
heavy
- correlation varies between -1 and +1
- positive correlation: (0<x<1): both variables in the same direction height & weight increase
- negative correlation: (-1<x<0): variables change in opposite direction
- correlation of 0 implies no relationship between the two variables
- when the correlation between the variables approaches +1 or -1 you can predict it better
- correlation cannot be interpreted causally!
- correlation is measurable between every random pair of variables. High correlation does not
imply a causal relationship
- experimental research
- researcher manipulates just one aspect of the situation (A) while the rest stays the same.
Then measures the effect of the manipulation on behaviour. This does allow interferences
about causality
- timeline of an experimental study
- idea, observations, read the literature
- use theories to formulate a hypothesis (expectation that will be tested in the experiment)
- operationalisation: become concrete. —> which subjects (age, gender, background) and
how many and so on
- collect data & run statistical analyses
- evaluate hypothesis & theory
- independent variable: variable the researcher manipulates
- dependent variable: variable that is measured
- control variable: aspects of the experiment that are equal for the experimental & control
group (e.g. length of the film, room, test leader etc.)
- subject variable: criteria on which groups are matched (age, sex)
,- limitations in experimental research
- internal validity: Is the change of the independent variable A the actual cause of the change
in dependent variable B?
- external validity: To what extent can you generalise results to the real world & the (intended)
population?
- sensation & perception
- sensation: peripheral processing by sensory receptors
- perception: higher-order interpretation of the stimulus
- usually ‘seeing’ equals ‘understanding’ since it happens so fast. However the time between
the two can be separated
- classification of the senses:
- traditional 5 senses: seeing, hearing, taste, smell, touch
- additionally: kinesthetic info (limb posture & muscle tension), balance, touch (texture, pain,
temp., vibration)
- psychophysics: question how to measure sensory capacities
- absolute threshold: lowest intensity of a stimulus that is detectable for humans
- can be measured with the method of constant stimuli: present stimuli at different intensities
around the threshold in random order. usually S-shaped function
- tendencies or biases can obscure the picture
- difference threshold: smallest noticeable difference between two stimuli. just noticeable
difference (JND)—> depends on the ‘size’ of the standard
- —> Weber’s law: ∆l/l = Constant // small Weber fraction = good sensitivity
- signal detection theory (SDT)
- perception is not always an ‘all-or-none’ decision
- often: transition from not observing a stimulus to observing it
- there’s always a response bias
- hit, miss, false alarm, correct rejection—> sensitivity: correct relative to incorrect // bias:
‘yes’ relative to ‘no’ answers
- SDT also applied to research the quality of decisions
- vision
- light is electromagnetic radiation with a specific frequency that falls within the observable
spectrum (visible to the eye)
- the eye
- light first passes the cornea —> most refraction takes place there
- then light passes through the lens of the eye
- ciliary muscles control the accommodation of the lens
- thus allowing to be focused on the retina
- retina is the light-sensitive tissue inside the eye. with cones & rods
, - cones are mostly packed in the central part of the retina, the fovea
- cones are responsible for perception of colour & fine details
- rods are mostly centered around the fovea and are sensitive to low-intensity light
- rods are colourblind and responsible for the perception of movement, peripheral vision,
night vision
- blind spot is where the optic nerve leaves the eye —> difficult to notice because the brain fills
in the blind spot with the immediate surroundings
- nearsightedness (myopia), farsightedness (hypermetropia), and astigmatism
- myopia: eye is too long. distant objects are blurry. concave lens corrects this
- hypermetropia: eye is too short. cannot see near objects. convex lens corrects this
- presbyopia: Alterssehschwäche. consequence of diminished elasticity of the lens. Eye
cannot accommodate enough. Reading glasses. near point increases with age
- astigmatism: imperfections in the spherical curvature of the cornea or the lens —> distorted
retinal image. Blurry vision at all distances, corrected with a cylinder
- cataract: clouding of the lens (age, diabetes)
- macular degeneration: retinal degeneration of the fovea. Focus is black and distorted
(smoke)
- glaucoma: worsening/loss of peripheral vision (failure of nerve cells due to increased eye
pressure) (tunnel vision)
- info from the 130 mill. receptors (rods & cones) is compressed via bipolar cells & ganglion
cells and then sent to the 1 mill. fibres of the optic nerve (nervus opticus)
- compression factor is highest in the periphery &
with a factor of 1
- compression factor is lowest in the macula (fovea
& surrounding area)
- Note: light has to pass through the bipolar cells &
ganglion cells before reaching the receptors
- ganglion cells (cells of the optic nerve) have a
donut-like receptive field that is either centerON/
surroundOFF or centerOFF/surroundON
