week 4: psychophysics

Question 1

what is sensation

Answer 1

how our sensory organs (eyes, ears, etc) convert physical/chemical info into signals that our NS can understand

Question 2

what is perception

Answer 2

how we acquire info from the environment
how we process that info to form internal representation of the environment

Question 3

what is cognition

Answer 3

how we use the internal representation to do more complex things

Question 4

examples of sensation

Answer 4

psychophysics
vision
hearing

Question 5

examples of perception

Answer 5

pattern recognition
mental imagery
attention and performance

Question 6

examples of cognition

Answer 6

memory
problem solving
reasoning and decision making
navigation
language

Question 7

what is difference threshold

Answer 7

the smallest change in a stimulus that can be detected

Question 8

what is absolute threshold

Answer 8

the minimum intensity of a stimulus that can be detected

Question 9

what is webers law

Answer 9

weber found that the size of the JND (just noticeable difference) is a function of the magnitude of a reference stimulus

Question 10

what was fechners idea

Answer 10

if a weber fraction is constant for a given stimulus dimension, then the mind might use the weber fraction as a unit for perceiving that stimulus dimension

Question 11

implication of fechners law

Answer 11

fechners law relates to internal experience (psyche) and physical environment (physics)

(psyche+physics=psychophysics)

Question 12

what is fechners law about

Answer 12

the absolute. not relative, intensity of a stimulus

Question 13

fechners law asserts that our:

Answer 13

psychological experience of the intensity of a stimulus tends to change less quickly than the actual change in stimulus intensity

Question 14

what does fechners law relate to

Answer 14

fechners law relates internal experience (psyche) and physical environment (physics)

Question 15

what is fechners law about

Answer 15

fechners law is about the absolute, not relative, intensity of a stimulus

Question 16

fechners law asserts that:

Answer 16

our physical experience of the intesity of a stimulus tends to change less quickly than the actual change in stimulus

Question 17

why is it hard to measure thresholds

Answer 17

because humans are very good at perceiving

Question 18

methods to measure thresholds

Answer 18

methods of constant stimuli
methods of limits
staircase procedures

Question 19

method of constant stimuli

Answer 19

construct a set of stimuli with magnitudes ranging from above to below the presumed threshold value
present these stimuli a number of times in a random order
participants respond whether or not they detect the stimulus on each trial
plot the proportion of detections occurring at each stimulus magntitude
the threshold is taken as a magnitude at which the stimulus is detected a criterion proportion of the time (eg. 50%)

Question 20

advantages to the method of constant stimuli

Answer 20

allows the shape of the psychometric function to be established
provides an accurate estimate of threshold

Question 21

disadvantages to the method of constant stimuli

Answer 21

requires pre-testing to roughly estimate the threshold
wastes alot of trials which lie far from the threshold
it is difficult to measure changes in threshold over brief time periodss

Question 22

methods of limits

Answer 22

measures the threshold without determining the shape of the psychometric function

Question 23

types of series in method of limits

Answer 23

ascending and descending series in trials

Question 24

what is descending series in method of limits

Answer 24

present the stimulus at a suprathreshold level
decrease stimulus intensity in small steps until participants can no longer detect the stimulus

Question 25

what is ascending series in method of limits

Answer 25

present the stimulus at subthreshold level
increase stimulus intensity in small steps until participants can detect the stimulus

Question 26

advantages to method of limits

Answer 26

more efficient than method of constant stimuli
still reasonably accurate in determining the threshold

Question 27

disadvantages for method of limits

Answer 27

many trials are wasted as they are presented at intensities away from the threshold
participant may habituate (get used to giving a yes or no answer) and thus overshoot the true threshold
the overall shape of the psychometric function cannot be derived

Question 28

staircase procedures

Answer 28

they involve linked series of ascending and descending runs with each successive run being based on the outcomes of the preceding run
the stimulus is presented either above or below threshold and the intensity is changed in small steps until a reversal (change response) occurs
the procedure is terminated after a criterion number of reversals
the threshold is taken as the average of these reversal intensities

Question 29

why was staircase procedure designed

Answer 29

to overcome the problems surrounding the other methods

Question 30

advantages to staircase procedure

Answer 30

even more efficient than the method of limits
can be modified in a number of different ways to overcome other limitations

Question 31

disadvantages to staircase procedure

Answer 31

estimation of the threshold tends to require more complex calculations (especially when the procedure is modified), making it less intuitive

Question 32

why can we never perceive stimuli under perfect conditions

Answer 32

because there is always noise and we never know whether we are perceiving the true stimuli (signal) or the noise

Question 33

correct signal trials in signal detection

Answer 33

the level of activity will be above the criterion and lead to a correct yes response (hit)

Question 34

signal trials for signal detection that are incorrect

Answer 34

will have activity below the criterion leading to an incorrect no response (miss)

Question 35

what leads to a false alarm in signal detection

Answer 35

on some catch trials the level of activity may be above the criterion, leading to an incorrect yes response (false alarm)

Question 36

what leads to correct rejection in signal detection

Answer 36

on the other catch trials the level of activity will be below the criterion, leading to a correct no response (correct rejection)

Question 37

the separation between the signal+noise and noise distribution tells us:

Answer 37

how sensitive an observe is to that stimulus

Question 38

what is the measure of sensitivity called

Answer 38

d-prime (d’)

Question 39

how do we estimate d prime

Answer 39

the proportion of hits (or misses) tells us the location of the criterion relative to the signal+noise distribution
the proportion of flase alarms (or crrect rejections) tells us the location of the criterion relative to the noise distribution
convert these proportions to z scores
d’ is then the sum of these distances
d’=Z(FA)-Z(HIT) (=Z(FA)+{-Z(HIT)})