measuring people Flashcards
Defining reaction time
What can reaction times tell us?
• Provide an indirect measure of mental processes
• Specifically, measuring reaction times can tell us about:
• The nature of mental processes
• The effect different stimuli has on mental processes
Example 1 of reaction time: Shepard and Metzler (1971)
- mental rotation of 3D objects
- Participants had to determine whether the two pictures were of the same object or not
- Reaction time increased with the angular difference between the two objects
• Results suggest that participants imagined rotating the object in order to solve the task
Example 2 of reaction time: Stroop effect (1935)
- Participants are asked to state the ink colour of the word (i.e., ignore what the word says)
- Reaction times are shorter for congruent than incongruent trials
- Manipulation demonstrates cognitive inference
types of reaction time experiments
- simple choice time
- choice reaction time
- discrimination reaction time
- simple choice time
1 type of stimulus; one type of response
- choice reaction time
more than 1 stimulus; each has its own specific choice
- discriminant reaction time
more than 1 stimulus; but ppt only needs to respond to 1
Measuring Brain Activity
Positron Emission Tomography (PET)
• Utilises the fact that the uptake of glucose is greater in active brain areas
• Some preparation is required
– a radioactive substance that mimics glucose is injected into the bloodstream
• Active cells take up this radioactive substance more readily
Subtraction method (PET)
- Typically, participants will be asked to perform a control task in addition to the experimental one whilst they are inside the scanner
- The control task provides a baseline measure of brain activation
- To understand what brain areas are activated during the cognitive task- baseline activity is subtracted out
eval of PET
• Creates relatively high spatial resolution images of the brain
- BUT
• Poor temporal resolution
• Individuals are also exposed to radioactive substances, which limits the number of scans that can be carried out
Functional Magnetic Resonance Imaging (fMRI)
- Utilises the fact that active brain regions require more oxygen- thus, blood flow increases to these areas
- Crucially, oxygenated blood produces a different signal to deoxygenated blood
• Signals are used to create high spatial resolution images of the brain
Evaluation of FMRI
• In comparison to PET: • Nothing needs to be injected into the participants • Offers better spatial resolution o BUT • Poor temporal resolution
Transcranial Magnetic Stimulation (TMS)
- Used to establish causal effects
- Magnetic field is applied to the scalp inhibiting the neurons directly below
- By temporarily ‘turning off’ brain areas we can understand their involvement in tasks
Electroencephalography (EEG)
- Measures the brain’s electrical activity
- Electrodes are attached to the scalp
- Serve to detect small changes in voltage
- Different waveforms produced reflect different functional states of the brain
Event related potentials
• Researchers are typically interested in EEG waves produced in response to psychological events (e.g., presentation of a stimulus) - Event related potentials (ERPs)
• ERP components - peaks observed in the ERP
e.g., P300 and N400
• Named after their polarity and latency
• Researchers are typically interested in EEG waves produced in response to psychological events (e.g., presentation of a stimulus) - Event related potentials (ERPs)
• Typically, researchers are interested in how task conditions affect the amplitude and latency of specific ERP components
