Psychophysics Overview

Study Notes

Psychophysics studies the relationship between physical stimuli and psychological responses.
Gustav Fechner is considered the founder of experimental psychology, creating the field of psychophysics.

Absolute threshold: The minimum amount of stimulation necessary to detect a stimulus 50% of the time.
Method of limits: Start at one extreme and make way to the other end to find the threshold.
Method of Adjustment: Adjust stimulus using dial or buttons until it is perceived, 50% of the time.
Method of Constant Stimuli: Multiple stimuli covering a range are presented repeatedly, and the proportion of times each is detected is recorded. This tedious method creates a psychometric function.
Staircase Method: The intensity of the stimulus is increased or decreased based on the previous trial response, finding the 50% detection point.

Psychologists study sensation and perception using scientific methods, including measuring thresholds, scaling, sensory neuroscience, neuroimaging, and patient studies.

Difference Threshold: The smallest change in a stimulus that can be detected 50% of the time (also known as just noticeable difference or JND).

Weber's law states that the JND is a constant proportion of the stimulus level. This means the difference threshold is relative to the intensity of the original stimulus.

Fechner's Law: The perceived intensity of a stimulus increases logarithmically with the physical intensity of the stimulus.
Stevens' Law: The perceived intensity of a stimulus can be described by a power function, where the exponent varies across different sensory modalities.

This theory considers decision-making in perception, accounting for internal biases and sensitivity to the environment. The theory describes four possible outcomes of signal detection:
- Hit: Signal present, observer responds "yes"
- Miss: Signal present, observer responds "no"
- False Alarm: Signal absent, observer responds "yes"
- Correct Rejection: Signal absent, observer responds "no"

The ROC curve plots the hit rate against the false alarm rate, showing how well an observer distinguishes signal from noise.
A good performance is indicated by a curve that "bows out" towards the upper left corner, indicating a high hit rate with few false alarms.

Sensitivity: A measure of how easily an observer can distinguish between the presence and absence of a stimulus.
Criterion: The internal threshold an observer sets for deciding when to report a stimulus.
Bias: An observer's tendency to be liberal or conservative in responding, influenced by the criterion setting.