Elemente der psychophysik, Threshold and threshold measurement, Webers law

Question 1

Elemente der pschophysik

Answer 1

Two volumes
Outer psychophysics: Relation between the intensity of the physical stimuli (R for Reiz) and the intensity of the sensation (S)
“inner psychophysics”: the relation between
the intensity of the neural excitation (E) and
the intensity of the sensation (S)

Question 2

Threshold

Answer 2

Limit between stimuli that evoke one kind of responses and stimuli that evoke another kind of responses

Question 3

Absolute threshold (RL)

Answer 3

Limit that indicates the transition between absence and presence of a sensation

Question 4

Differential threshold (DL)

Answer 4

The smallest added stimulus intensity that allows perceiving a difference

Question 5

Lowest threshold (floor)

Answer 5

Minimal stimulus intensity that is required to be perceived

Question 6

How to measure floor

Answer 6

Mostly a straighforward detection task
ideal situation discrete step function
In reality often no abrupt transition

Question 7

Examine DL or JND

Answer 7

Serveral tasks can be used
Mostly discrimination tasks
IU = interval of uncertainty
JND = IU/2

Question 8

Weber’s Law

Answer 8

Measure DL or JND at different locations along the physical scale
DL no fixed value but a value in proportion to the stimulus intensity of a standard stimulus
Stimulus intensity must be increased by a constant fraction of its value in order to obtain a just noticeable difference
Fraction usually presented as k = ΔI / I

Question 9

Upper Threshold

Answer 9

Might be usefull the limit above which the subject is no longer able to precieve the differences

Question 10

Graphic ways to represent Weber’s law

Answer 10

Plot ΔI vs I
-Rising line with k= slope
-High sens: minor increase
-low sens: large k
Plot k(ΔI/I) against I
-straight line all I-values at the same value k, parallel with the abscissa

Question 11

Weber’s law: modifications

Answer 11

• ΔI = k ( I + Ir ) with Ir a small added value

- ΔI = k.In with n not necessarily equal to 1

Question 12

Big differences in sensitivity based on the stimulus

Answer 12

k=  .016 luminace
k= .33 for sound volume

Question 13

Weber-Fechner law

Answer 13

Fechner realized that the absolute threshold (RL) could be used to determine the starting point and JND to determine a measurement unit
to increase the strength of the sensation (S) as an arithmetic sequence (summed with a constant) one has to increase the stimulus intensity (R) according to a geometric sequence
(multiplied by a constant)

S= k log R

Question 14

Stevens’ Power Law

Answer 14

Weber-Fechner law based on indirect scaling method
Ψ = k log Φ
Stevens’ Power law based on direct method maginitude estimation
Ψ = k Φn