Perception exam 1

Fechner's Law

S = k*logI S: sensation, the psychological experience, the JND k: Weber fraction for that task (AI/I) I: physical intensity

Ogive curve

S shaped curve Cumulative form of the normal distribution We add or accumulate % going left to right

Magnitude estimation

a psychophysical method in which the participant assigns values according to perceived magnitudes of the stimuli

Conservative

tendency to say no that stimulus is present cost/benefit ratio is the question

Liberal

tendency to say yes that stimulus is present

difference threshold

the minimum difference between two stimuli required for detection 50 percent of the time (JND)

Absolute Threshold

the minimum stimulation needed to detect a particular stimulus 50 percent of the time

Method of limits

A psychophysical method in which the particular dimension of a stimulus, or the difference between two stimuli, is varied incrementally until the participant responds differently.

Webers Law

A/I = K where AI (delta I) represents the difference threshold, I represents the initial stimulus intensity and k signifies that the proportion on the left side of the equation remains constant despite variations in the I term

Point of subjective equality (PSE)

"most similar" to standard

Gustav Fechner

Believed that medicine didn't know what it was doing, and whatever happens happens- why he didn't practice medicine after med school Wrote parodies about medical situations Convex → C ← concave October 22nd, 1850- he woke up and had a solution: Study the relationships rather than the details Led to the development of psychophysics (SI)

Lower difference limen (LDL)

Difference threshold for less intense than PSE

Upper difference limen (UDL)

Difference threshold for more intense than PSE

How do you calculate Interval of uncertainty (IoU)?

IoU = UDL - LDL

How do you calculate Just noticeable difference (JND)?

JND = IoU/2

Method of Adjustment

Observer makes adjustment to stimulus source until threshold is achieved

Steven's power law

S = a*I^n S: intensity or magnitude of the experience A: scaling constant (don't worry about this value) I: physical intensity of stimulus N: exponent that controls size of transformation

What do visual illusions tell us?

We can only experience the world through our senses However, illusions show us that our senses can be fooled

"Senses can be fooled" means

We cannot know the real world- only the world reported by the senses

S. S. Stevens

We don't want to create a scale of differences, we want to create a scale of magnitudes Magnitude of experience is important, not whether you can tell the difference

The psychophysical function is created in the following fashion

X-axis contains the information about the physical dimension (x-axis = intensity) Y-axis contains the information about the observer's judgment of the experience (y-axis = sensation)

Clueless conservative detector

hit rate of 0, false alarm of 0

Perfect detector

hit rate of 1.0, false alarm of 0

Clueless liberal detector

hit rate of 1.0, false alarm of 1.0