Psychophysics Flashcards
Psychophysics
Relation between subjective sensory experience and objective physical stimuli that give rise to them?
- how is perceived magnitude related to stimulus intensity?
- what is the smallest difference between two stimuli we can detect?
- what are the absolute limits of perception?
Psychometrics
Are people’s responses reliable?
Are they consistent?
Are they true reports?
Psychophysical function
Mathematical relationship comparing strength of a stimulus and strength of experience to its presentation
Perceived magnitude and stimulus intensity
Threshold finding methods
Method of limits
Pick several stimuli intensities
Threshold falls somewhere in middle
Start with weakest —> highest
Where ppt can feel, threshold will be
Some conditions start with highest —> lowest
Final threshold= average of thresholds found
Threshold finding methods
Method of adjustment
Adjust stimulus intensity themselves
Aiming for perceptual threshold
Repeated with different starting intensities
Sliding monitor or knob
Value of setting ppt can feel= perceptual threshold
Final threshold= average of thresholds found
Threshold finding method
Method of constant stimuli
Stimuli pre-selected by experimenter, run in random order
Psychometric curve fit to results
Ppts receive same conditions, complete full experiment
Final threshold= average of thresholds found
Magnitude estimation
Present standard stimuli, assign perceptual value
Present another stimuli, ask ppt to rate magnitude with respect to standard
Perceptual threshold
contextual effects determine whether we can feel stimuli at the threshold
50% value and corresponding stimulus intensity
Just noticeable difference JND
Smallest detectable difference
Present two stimuli on each trial, ask whether same or different
One baseline stimulus, one different
Relative thresholds
75%
Weber’s law
Difference= JND
Need to increase / decrease stimulus by 20% to become noticeable
JND is constant proportion of stimulus intensity
Percentage needed is specific for each sense
Signal detection theory
Perceptual thresholds
How confident the perceptual threshold is correct?
All bias, no sensitivity= straight line
Different strategies to participating
Signal detection theory
Sensitivity and bias
Perceivers sensitivity can be distinguished from their bias
All perceivers have bias, influenced by costs and benefits
Signal detection theory
To measure sensitivity independent of bias-
- ask whether stimulus detected when present
- ask whether stimulus detected when not present
Good at detecting when present, good at detecting when not present= high sensitivity
Good at detecting when present, bad at detecting when not present= high bias
Stimulus present
Detected = HIT
Not detected = miss
Stimulus absent
Detected = false alarm
Not detected = correct rejection
