Psychophysical Methods II

Question 1

The threshold determined in an experiment or clinical procedure may be influenced by a number of factors such as

Answer 1

Decision criteria
Attention
Motivation
Internal neural noise

Question 2

What is signal detection theory good for

Answer 2

Provides a useful model to predict the effects of certain of these factors (decision criteria, attention, motivation, and internal neural noise)

Question 3

A stimulus produces a nearual visual that is ________ on this neural noise

Answer 3

Superimposed

Question 4

What is the observers task in signal detection theory

Answer 4

Differentiate the signal and noise combination from the background noise alone

Question 5

Noise or activation present in the absence of a stimulus, randomly distributed over time, randomly fluctuating over time

Answer 5

Neural noise

Question 6

A stimulus causes a constant level of neural activation-a signal-to be added to the noise

Answer 6

Noise + signal

Question 7

Noise + signal

Answer 7

• if the stimulus is presented many times at various noise levels, the distribution of noise is shifted to the right by a constant amount to produce a noise plus signal distribution (N+S)
• keep in mind that neural noise is present in the absence of the signal, and the signal is superimposed on this noise
• the oberservers task is to determine if what he or she is seeing (or hearing) is noise or signal plus noise

Question 8

As the signal becomes larger, the distributions of N and N+S become _______, and the detectability (d’) of the stimulus ______

Answer 8

Further apart

Increases

Question 9

What happens to the detectibility when the signal becomes larger

Answer 9

Increased

Question 10

What does detectability (d’) refer to

Answer 10

The difference between the means of the N and N+S distributions

Question 11

What do the distributions look like with a very larger detectability (d’)

Answer 11

No overlap of the distributions, therefore, there is no uncertainty regarding whether a stimulus is present

Question 12

The _____ the signal, the easier to os for the observer to determine that noise plus signal, rather than noise alone, is being experienced

Answer 12

Larger

Question 13

Weak stimulus in signal theory detection

Answer 13

Results in substantial overlap of the N and N+S distributions

Question 14

If the stimulus is delivered when the noise is low, the resulting level of neural activation is

Answer 14

Ambiguous
-there is no way for the observer to be certain where the stimulus os absent or present because this level of neural activation can be produced by either the signal plus noise or noise alone

Question 15

If the stimulus is delivered at a point in time when the noise is very high, the resulting level of neural activation is

Answer 15

Unambiguous

-this level of neural noise occurs only when the stimulus is present

Question 16

Yes-no method modeled using signal detection theory

Answer 16

• when the level of neural activation is above the criterion line, the subject will report seeing the stimulus
• when the level is below the criterion line the subject will report not seeing the stimulus

Question 17

The subjects response in yes no method of using signal detection theory is determined by what

Answer 17

The level of neural activation and not by whether the stimulus is present of absent

Question 18

A ____ occurs when the stimulus results in neural activity that exceeds the threshold criterion

Answer 18

Hit

Question 19

A ____ when the activity does not exceed the criterion

Answer 19

Miss

Question 20

A _____ occurs when the neural activity exceeds the threshold criterion in the absence of a stimulus (blank trial)

Answer 20

False positive

Question 21

A _____ when the activity is below the criterion during a blank trial

Answer 21

Correct reject

Question 22

Lax threshold criterion and stimulus detection theory

Answer 22

Results in many hits and few misses, but a large number of false positives

Question 23

Strict threshold criterion and the stimulus detection theory

Answer 23

The strict criterion results in fewer hits and more misses than does a lax criterion, but has the low number of false positives

Question 24

ROS (receiver operating characteristic) curve

Answer 24

Shows the probability of a hit as a function of the probability of a false positive for different threshold cireteria

Question 25

L on the ROC curve

Answer 25

Lax criterion

Question 26

S on the ROC curve

Answer 26

Strict criterion

Question 27

M on the ROC curve

Answer 27

Moderate criterion

Question 28

For a lax criterion, the probability of what two things is high?

Answer 28

A hit and false positive

Question 29

For a strict criterion, what two things are low?

Answer 29

Hits and false positives

Question 30

The task is to discriminate between the combination of stimulus and background and background alone

Answer 30

Webers law

Question 31

How can Weber’s law be understood

Answer 31

Considering an increment threshold experiment

Question 32

How is an increment threshold experiment for Weber’s law run?

Answer 32

• observers task is to detect the increment stimulus which is flashes on the background
• the threshold increment is sometimes referred to as JND (just noticeable difference) or difference limen (DL)
• another way of thinking of this task is that the observe must discriminate the combined stimulus and background from the background itself

Question 33

As the background intensity increases, what happens to JND

Answer 33

Also increases such that the ratio of the JND to the background intensity remains constant

Question 34

What is Weber’s law

Answer 34

As the background intensity increases, the JND also increases such that the ratio of the JND to the background intensity remains constant

Question 35

Mathematical expression of Weber’s law

Answer 35

Delta I=KIb

Delta I=increment threshold (JND)
Ib= background illumination
K=Weber’s constant or fraction

Question 36

The optotypes E reflects ____ of the light incident pin it, and the gray background reflects _____.

Answer 36

10%

10.40%

Question 37

Ratio of the optotype to the background illuminance in photopic vs scotopic illumination

Answer 37

Remains the same

Question 38

Since the visual system detects constraint, rather than absolute luminance, the appearance of the E is the same under both dim and bright lighting conditions, this phenomenon is referred to as

Answer 38

Lightness constancy

Question 39

Brightness depends on the background, a phenomenon called

Answer 39

Simultaneous contrast

-contrast of the stimulus, not its luminance, is the key in predicting its appearance

Question 40

Why is it that one square looks dark and one looks light when they are really the same color?

Answer 40

Due to the visual systems tendency to analyze brightness in the context of surrounding elements. In this case, the surrounding squares and shadow case by the cylinder contribute to the effect