Lecture 4: Signal detection theory

Question 1

What is signal detection theory

Answer 1

Separate sensitivity - capacity to percieve the stimulus, from decision of saying you perceived it or not

Question 2

Describe signal

Answer 2

True sensory info coming from external world

Question 3

Describe noise

Answer 3

Various physiological or psychological processes influencing our perception of that external stimulus in an unpredictable manner
Not perfect, noise in system

Question 4

Name physiological noises

Answer 4

Caused by spontaneous activity in our sensory nerves = spontaneous baseline firing

Question 5

Name psychological sources of noise

Answer 5

Spontaneous fluctuations in attention that alter perception of sensory stimulus in unpredictable manner, expectations too

Question 6

What are signal and noise

Answer 6

Statistical concepts
Noise is whatever is not measured and that contributes variability to participants responses = boost or decrease perception of stimuli
Need to know difference betwene noise and signal when finding detection threshold

Question 7

Describe conservative ppl - response bias

Answer 7

Tend to withold correct identifications
Until completely clear that they have perceived something
Cause them to have higher thresholds = could be erroneously interepretd as having lower sensitivity

Question 8

Describe liberal ppl - response bias

Answer 8

Quick to say have percieve something
Cause them to Have lower thresholds
Does not mean they are more sensitive
Liberal criterion may sometimes cause them to wrongfully detect presence of sensory stimulus when there is none

Question 9

What is sdt designed for

Answer 9

Getting rid of response bias

Question 10

Describe sensitivity

Answer 10

Individuals ability to distinguish between signal and noise
Reflect how well can detect target stimulus
Higher sensitivity indicates better discrimination

Question 11

Describe criterion

Answer 11

Decision threshold set by individual in sdt - determining whether they report presence of signal
Reflects their response bias
Influenced by factors like expectations or consequences of false alarms and misses (could be conscious or unconscious, can consciously change it though)
Conservative ppl = higher criterion
Internally set criterion for saying yes

Question 12

Describe sdt ex

Answer 12

Perceive phone vibrating??

Question 13

Signal present Yes response

Answer 13

Hit

Question 14

Signal absent Yes response

Answer 14

False alarm

Question 15

Signal present NO response

Answer 15

Miss

Question 16

Signal absent NO response

Answer 16

Correct rejection

Question 17

What do blue and green curves stand for

Answer 17

Strength of felt sensations as a function of vibrations or not

Question 18

What is criterion on sdt graph

Answer 18

Internal trheshold = how something feels

Question 19

What is probability on sdt graph

Answer 19

Of getting sensation at the exact level
Most of time will feel this way

Question 20

Describe proportion of hits and misses

Answer 20

Inversely proportional

Question 21

Describe whole of blue curve = left to right

Answer 21

Few trails where do feel anything at all
Correct rejections
Say no since below threshold
Then say yes and get false alarms bc signal not there

Question 22

Describe whole of green curve = left to right

Answer 22

Faint sensation - but say no = miss
Then get hits = yes when stimulus
Few exs wehre will feel v strong clear vibrations

Question 23

What marks sensitivity

Answer 23

Differnce bewteen blue and green peak

Question 24

Describe sdt graph directly at criterion and middle of blue and green curve

Answer 24

Range of sensations with major overlap = hard to say if feel stimulus or not

Question 25

What would happen to criterion if experimenter threatened to kill you for saying stimulus present when no stimulus

Answer 25

Become more careful = consciously change criterion

Question 26

What would happen to criterion if experimented threatened to kill you for saying stimulus present when no stimulus = CRITERION

Answer 26

Move criterion to right = less inclined to say yes Wait to feel v strong sensation Say no all teh time = less hits and false alarms

Question 27

Describe sdt graph when always yes

Answer 27

100% hits and 100% false alarms

Question 28

Describe sdt graph when always no

Answer 28

0% hit 0% false alarm

Question 29

Describe receiver operating characteristics (ROC) curves

Answer 29

Probability of hit over probability of false alarm As a fucntion of where you place criterion Perfect discriminability = no false alarms, 100% hits Performance suboptimal unless at specific points Chance level = linear line, always yes yes or no, same # hits and false alarms, cannot go under this

Question 30

What happens to roc curve as sensitivity increases

Answer 30

Goes more out Becomes like square

Question 31

What does sdt allow

Answer 31

Estimate participants sensitivity = d’ and criterion = c As a fucntion of their specific ratio of hits and false alarms

Question 32

What happens if someone detects vibration of cell phone with 40% hits and 20% false alarms

Answer 32

Coordinate falls on roc curve of d’=0.5 = belongs to specific roc curve + criterion Reflects bias towards saying no Point falls to left of roc curve = know it was generated by a stricter criterion, participant more likely to say didn’t percieve stimulus

Question 33

What is tinnitus & phantom limb pain

Answer 33

Cns lowering threshold for us to perceive something or not

Question 34

Describe stimulus intensity during sdt trials - variation

Answer 34

Kept constant But may vary form trial to trial = green distribution Random or unexplained variation due to noise

Question 35

Describe stimulus intensity during sdt trials - when no stimulus

Answer 35

May feel like there is one = due to noise (blue distribution)

Question 36

Why is green distribution to right of blue on sdt graph

Answer 36

Indicates that strength of subjectively felt sensation is higher when there is really a stimulus present

Question 37

Why is there overlap between teh 2 distributions

Answer 37

Sometimes the presence or absence of a stimulus feels exactly teh same

Question 38

Low probability that subjective sensation is medium to low

Answer 38

Green low Misses

Question 39

High probability that a given trial when a stimulus is present will be associated with medium to high subjective sensation

Answer 39

Green high Hits

Question 40

Low probability that subjective sensation high

Answer 40

Green low but high sensation Still hit

Question 41

Low probability that subjective sensation low

Answer 41

Low blue Correct rejections

Question 42

High probability that a given trial when stimulus absent will be associated with medium to low subjective sensation

Answer 42

Very high blue Correct rejections

Question 43

Low probability that subjective sensation is medium to high

Answer 43

Low False alarms

Question 44

What does sdt do

Answer 44

Describes sensitivity of test

Question 45

Which test is most sensitive - sdt graphs

Answer 45

Ones with blue and green peaks hella far away

Question 46

Which test is most sensitive - ROC curve

Answer 46

One that looks most square

Question 47

Where to put criterion for maximal accuracy

Answer 47

Put at point closest to top left corner = perfect discrimination So closest to that = greatest accuracy

Question 48

Where to put criterion for maximal hits

Answer 48

When closest to highest probability of hit = more false alarms tho too, bc higher chance

Question 49

What does sdt graph do

Answer 49

How it works = assum it’s working this way

Question 50

Is stimulus always felt the same - sdt curve

Answer 50

NOOO Bc noise