Psychophysics -- Basics, Laws, and Methods

Question 1

definitions of psychophysics

Answer 1

science underlying nearly all clinical optometric test procedures
science of measurement of sensory and mental phenomena
involves mathematical relationships between perception and physical reality

Question 2

Gustave Fechner

Answer 2

founder of classical psychophysics

Question 3

classical phychophysical issues

Answer 3

detection
recognition
discrimination
scaling

Question 4

discrimination of sensory stimuli

Answer 4

involves difference thresholds

two things are detected–are they different?

Question 5

detection of sensory stimuli

Answer 5

involves absolute thresholds
“is something there?”
Ex: humphrey visual field (is a light there?)

Question 6

scaling

Answer 6

internal vs external scales (or psychological vs physical)
answers question: how does physical stimulus intensity relate to subjective perception of stimulus intensity? (i.e. if i double physical stimulus intensity, will subjective perception of stimulus intensity double?)

Question 7

recognition of sensory stimuli

Answer 7

something is there–what is it?

Question 8

threshold

Answer 8

boundary between two different responses to a stimulus (such as perception/no perception)

Question 9

how sensory thresholds must be measured and why

Answer 9

repeated and averaged

humans are not perfect observers and exact thresholds vary depending on motivation, focus, etc

Question 10

examples of sensory thresholds

Answer 10

phorias, accomodative lag, vergence ranges, VA, VF measurement, auditory acuity tests

Question 11

absolute threshold, and what is another term for it

Answer 11

minimum physical stimulus required to evoke a sensation

other term: absolute limen (subliminal means below the threshold)

Question 12

difference threshold, and two other terms for it

Answer 12

least change in physical stimulus intensity to evoke a sensation of difference
other term 1: difference limen
other term 2: JND (just noticeable difference)

Question 13

clinical significance of DT/JND

Answer 13

small DT/JND: can be diff to examine (too precise in noticing differences)
large DT/JND: sometimes can’t provide useful response during subjective procedures (large changes in stimulus intensity may not be perceived as different)

Question 14

signal detection theory

Answer 14

there is no consistent sensory threshold

Question 15

psychophysical laws and what issue they address

Answer 15

Weber’s law
Fechner’s law
Stevens’s law
they address the classical issue of scaling

Question 16

Weber’s law

Answer 16

CONSTANT PERCENTAGE
stimulus must be changed by constant percentage of its value to be JND (ex: two hands holding weights. whatever weight is in one hand, the weight in other hand must be changed by constant percentage (such as by 5%) to perceive difference between hands)

Question 17

Fechner’s law

Answer 17

LOGARITHMIC

to double sensation, stimulus intensity must be squared

Question 18

Stevens’s law

Answer 18

EXPONENTIAL

intensity raised to some exponential power

Question 19

Classical Psychophysical Methods

Answer 19

Method of limits
method of constant stimuli
method of adjustment
adaptive psychophysical methods (modern psychophysics)

Question 20

Method of limits (how, terminal judgment, errors)

Answer 20

how: present stimulus intensities in ascending and descending trials, slightly above and below approximate threshold. take mean of test trials to get absolute threshold.
terminal judgment: one of difference
errors: expectation (saying yes before suprathreshold intensity), habituation (continuing to say yes when intensity is subthreshold)

Question 21

method of constant stimuli (how, what it controls for)

Answer 21

how: similar to method of limits, but 4-8 preset stimulus values within interval of uncertainty are presented in random order
controls for: expectation (same level of expectation for each stimulus)