Measuring Perception Slides

Question 1

Psychologists typically study:

Answer 1

Sensation and perception

Question 2

Sensation and perception, aside from being studied by psychologists, is studied by:

Answer 2

biologists, computer scientists, linguists, neuroscientists and many other fields

Question 3

The study of sensation and perception is a scientific pursuit and requires:

Answer 3

scientific methods

Question 4

What are some of the scientific methods used in the study of sensation and perception (6):

Answer 4

(1) Thresholds: Finding the limits of what can be perceived
(2) Scaling: Measuring experience
(3) Sensory neuroscience: The biology of sensation and perception
(4) Patient Studies: Individuals with brain damage
(5) Neuroimaging: An image of the mind (e.g. PET, fMRI)
(6) Brain stimulation: Transcranial Magnetic Stimulation (TMS), transcranial direct current stimulation (tDCS)

Question 5

Gustave Fechner invented __

Answer 5

psychophysics

Question 6

Gustave Fechner invented psychophysics and is often considered to be the true founder of:

Answer 6

Experimental psychology

Question 7

Define psychophysics:

Answer 7

The science of defining quantitative relationships between physical and psychological (subjective) events

Question 8

What are some new concepts psychophysics adopted for understanding sensation and perception (2):

Answer 8

(1) Absolute threshold
(2) Method of adjustment
(3) Method of constant stimuli
(4) Staircase method
(5) Difference threshold
(6) Weber’s law
(7) Fechner’s law
(8) Steven’s law

Question 9

Define absolute threshold:

Answer 9

Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time

Question 10

Method of Adjustment:

Answer 10

“quick and dirty”. Adjust using a
dial / buttons until stimulus is perceived.

Question 11

Method of Constant Stimuli:

Answer 11

Select number of stimuli
that cover a range likely to include absolute threshold.

Two forms:
a) simple yes/know response on one block of trials.
b) Psychometric function from many blocks.

Question 12

Staircase Method

Answer 12

intensity of stimulus one up or down
from previous trial.

Question 13

Difference threshold

Answer 13

same or different? (also called just
noticeable difference, or JND).

Question 14

Difference threshold can be measured using method of

Answer 14

Adjustment and constant stimuli.

Question 15

Ernst Weber (1795–1878) discovered

Answer 15

that the smallest change in a stimulus
(e.g., the weight of an object) that can
be detected is a constant proportion of the stimulus level
E.g., for 100g, JND is 2g (or 2%).
For 1000g, JND is 20g (or 2%).

Question 16

Weber’s law JND = kl

Answer 16

The principle describing the relationship between
stimulus and resulting sensation
intensity (l) that says the JND is a
constant fraction (k) of the comparison
stimulus.

Question 17

Psychophysical Scaling

Answer 17

Measuring how changes in stimulus intensity relate to changes in
perceived intensity

Question 18

Fechner’s law, S = k ln I/Io

Answer 18

Variant of Weber’s law

A principle describing the
relationship between the perceived intensity (S) of a stimulus as it changes in comparison to the natural log ratio between the physical intensity (I) and the intensity at absolute threshold (Io).

Question 19

Weber’s law is good for __ but not for other sensations, like __

Answer 19

Weber’s law is good for BRIGHTNESS and LOUDNESS, but not for other sensations, like electric shock

Question 20

Stevens law, S = cln:

Answer 20

relationship between the peceived intensity of a stimulus (S),
its physical instensity (I), the exponent n is different for each perceptual dimension,
and c is the constant that depends on which units are being used for S and I.

Question 21

Signal detection theory

Answer 21

A psychophysical theory that quantifies the response of an
observer to the presentation of a signal in the presence of noisy perceptual evidence.

Question 22

There are __ possible stimulus/response situations in signal detection theory

Answer 22

four

Question 23

Receiver operating characteristic
(ROC):

Answer 23

In studies of signal
detection, the graphical plot of the
hit rate as a function of the false
alarm rate

Question 24

In Receiver operating characteristic
(ROC), chance performance will fall:

Answer 24

Along the diagonal

Question 25

In Receiver operating characteristic
(ROC), good performance (high
sensitivity):

Answer 25

“bows out” towards
the upper left corner

Question 26

Plotting the ROC curve allows one
to:

Answer 26

Predict the proportion of hits for a
given proportion of false alarms,
and vice-versa

Question 27

Signal detection theory makes a distinction between:

Answer 27

An observers’ ability to perceive a signal, and their willingness to report it. These are three separate
concepts

Question 28

What are the three separate concepts in regards to signal detection theory?

Answer 28

(1) Sensitivity
(2) Criterion
(3) Bias

Question 29

Define sensitivity:

Answer 29

A value that defines the ease with which an observer can tell the difference between the presence
and absence of a stimulus or the difference between
stimulus 1 and stimulus 2

Question 30

Define criterion:

Answer 30

An internal threshold that is set by the
observer. If the internal response is above criterion, the
observer gives one response (e.g., “yes, I hear that”).
Below criterion, the observer gives another response
(e.g., “no, I hear nothing”).

Question 31

Define bias:

Answer 31

Observer tendency to be liberal or conservative in
response, indicated by value of criterion.