1. Signal detection
Psychophysics

2. Psychophysics
The study of the relationship between physical stimulation and subjective sensations.
Signal-Detection Theory
The theory that detecting a stimulus is jointly determined by the signal and the subject’s response criterion.

3. Psychophysics
The formal study of the relationship between the properties of stimuli as measured by a physical scale and the psychological impressions of those stimuli.
Lawful relationships were uncovered between stimulus differences, measured on a physical scale, and experienced differences.
Measurable stimulus values were observed below and above the threshold of awareness

4. Psychophysics Relationship between physical stimuli and percepts
Objective measurement of stimuli
Eg varying light intensity, frequency of tones
What can you hear see taste smell etc???

5. Psychophysics Method of limits – descending and ascending
Method of constant stimuli – random level
Method of adjustment - control
2AFC (2 alternative choice or 3..)
Go–no go
2IFC (2 interval choice or 3..)
demos

6. The Method of Limits
A psychophysical method where a standard stimulus is compared with various values of comparison stimuli presented in both ascending and descending series. The task of the subject is to specify when the standard and the variable appear to be the same.

7. The Method of Constant Stimuli
A psychophysical method where a standard stimulus is judged against comparison stimuli. Various values of the comparison stimuli above and below the standard stimulus are presented on a random basis. The task of the subject is to specify whether the comparison is =, <, > standard.

8. Absolute Threshold
The smallest amount of stimulation that can be detected
Just Noticeable Difference
The smallest amount of change in a stimulus that can be detected

9. Typically small n experiments
Regardless of the sensory domain, there are three main topics in the psychophysical classification scheme:
absolute thresholds
discrimination thresholds
scaling
Typically small n experiments

10. Signal Detection Theory
Find the signal in the noise

11. Gives all possible choices and we can determine the sensitivity and response bias
Stimulus
present
Noise
Responds
stimulus
Hits
False alarm
noise
Miss
Correct rejection

12. Criterion of decision

14. d’ or how much separation? d' = separation / spread
d' = ZFA - ZHit

15. Signal detection applet