01. Psychophysics & research methods Flashcards
What is single-cell recording?
- electrode measures activity of one cell in response to different stimuli
- stimuli = light bars at different angles
- each cell responds to only one specific angle
Types of brain imaging?
- PET scans
-fMRIs
-Diffuse optical tomography (DOT)
PET scans?
- one of the first types of brain imaging
- measures bloodflow to see brain activity during different actions
Problems: - same action/stimuli for a long time to be accurate
- involves radiation
fMRI?
- more modern
- oxygen level in blood
- more activity = more oxygen
- better spatial resolution
DOT?
- diffuse optical tomography
- oxygen in brain by detecting light reflected by brain
- temporal resolution = fMRI, spatial resolution is a little worse
- Portable equipment!!
Psychophysics def
study of relationship between physical energy in a stimulus and the perceptual experience it produces
helps make inferences without directly observing brain activity
Absolute threshold def
- minimum intensity of a stimulus required to produce a sensation
- defined as stimulus detected 50% of the time
Difference threshold def
minimum difference in intensity that can be detected
–> Just noticeable difference (JND)
Method of limits?
- present series of stimulus intensities IN ORDER
- ask if they detect it at each presentation
- Threshold = midpoint between where the response changed
2 potential problems of method of limits (and solutions)?
- they keep reporting that they heard it –> error of habituation (present ascending and descending series)
- they remember how many stimuli they detect (start the series at a different point each trial)
Method of adjustment
- same as limits
- except the subject (or experimenter) CONTINUOUSLY adjusts the stimulus until they can’t detect it
Method of constant stimuli
- more accurate than limits, but more trials needed
- fixed set of stimulus intensities, including extremes
- presented in RANDOM order
- each intensity is presented several times
- graph is an elongated S curve
compare “classical threshold theory” graph to actual “psychophysical function”
Staircase method
- begin at an extreme (far above/below) threshold
- increase 1 step if not detected, decrease 1 step if detected
- stop after a predetermined number of response reversals
- threshold = average intensity at response reversal
- more efficient than constant stimuli (don’t waste trials on stimuli we know they will/won’t detect)
Method of constant stimuli for difference threshold
- use pre-selected stimulus intensities presented RANDOMLY
- on each trial, present TWO stimuli
–> one standard (reference stimuli)
–> one comparison (varies each trial) - possible responses:
–> C is bigger/brighter/heavier than S
–> C is smaller/dimmer/lighter than S
Key terms:
- point of subjective equality: stimulus intensity judged greater/less than standard 50% of the time
- point of objective equality: actual value of standard
- constant error: diff. btw PSE & POE
- Diff threshold –> 1/2(75%-25%)
Look at powerpoint 01.methods for ex
Size-weight illusion
- the larger of 2 equal-weight objects feels lighter
- context influencing perception
ex –> envelopes with coins