1. © 2001 Dr. Laura Snodgrass, Ph.D.1 Psychophysics Mathematical formula for relationship between changes in the physical stimulus and changes in conscious experience of the stimulus Classical methods

2. © 2001 Dr. Laura Snodgrass, Ph.D.2 Method of Constant Stimuli Choose ~ 9 stimuli in equal steps covering a range above and below threshold Present in random order Each stimulus is presented many times and % yes (different) is calculated 50% yes (different) = threshold Problems –choosing, gaps, trials that waste time

3. © 2001 Dr. Laura Snodgrass, Ph.D.3 Method of Limits Similar to constant stimuli, but present in ascending and descending order until response changes Average point of change in response –from yes to no or same to different Problems –errors of habituation and anticipation

4. © 2001 Dr. Laura Snodgrass, Ph.D.4 Method of Adjustment Ascending and descending trials with continuously adjustable stimuli Same calculations and same problems as method of limits, but more precise estimates

5. © 2001 Dr. Laura Snodgrass, Ph.D.5 Magnitude Estimation Assign a value to a standard Let participant assign values to comparison stimuli –if this is 10 then if that is half as intense it is 5, twice as intense would be 20 Produces a ratio scale

6. © 2001 Dr. Laura Snodgrass, Ph.D.6 Signal detection theory Calculate d’ (detectability) Must have trials with a stimulus and trials with no stimulus % hits = say yes when stim is present % false alarms = say yes when stim is absent Use % hits and % false alarms to look up d’ on chart Shows degree of brain response