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Survey of the Senses > Midterm 1 - Topic 2 > Flashcards

Midterm 1 - Topic 2 Flashcards

1
Q

Psychophysics

A

Study of the relation between physical stimuli and sensation

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2
Q

How do we access sensation to measure it?

A

Indirectly, we have to rely on people’s responses to physical stimuli (source of bias)

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3
Q

4 topics of psychophysics

A

Detection
Identification
Discrimination
Scaling

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4
Q

Detection basis question

A

Is there anything there?

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5
Q

Identification basis question

A

What is it?

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6
Q

Discrimination basis question

A

Is “A” different from “B”?

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7
Q

Scaling

A

Direct relation between sensation and perception

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8
Q

Application of detection

A

Person in charge of radar in England during WWII
You have to decide whether there is actually flying over the Channel so that you can send a squad to prevent them from reaching your country

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9
Q

Detection threshold
AKA?

A

Minimal amount of energy
How much of a stimulus is necessary for detection
Absolute threshold

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10
Q

Method of limits purpose

A

Methods to assess the absolute threshold

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11
Q

2 different procedures to assess the absolute threshold

A

Ascending trial
Descending trial

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12
Q

Method of limits - ascending trial

A

Present a very faint, undetectable stimulus
Intensity is increased in small steps, until the observer detects it

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13
Q

Method of limits - descending trial

A

Present a stimulus that can easily be detected
Intensity decrease until the observer cannot detect the stimulus

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14
Q

Disadvantage of method of limits

A

Creates expectations –> anticipation errors

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15
Q

Method of limits, AT =

A

mean intensity across ascending and descending trials
A dozen of each type of trials typically sufficient (no clear rule except, more trials is better)

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16
Q

Method of constant stimuli procedure

A

Present a set of stimuli that judge are around the threshold from your subjective experience in a random order
The observer indicates whether they can detect (hear, see, smell, taste, feel) anything on each trial

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17
Q

Method of constant stimuli scoring

A

Proportion of “yes” responses

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18
Q

Disadvantage of method of constant stimuli

A

Requires a very large # of trials to obtain reliable estimates
20-25 trials per stimulus, minimum

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19
Q

Method of constant stimuli AT =

A

Point at which there is a 50% chance of responding “yes”
Proportion of “yes” responses = .5

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20
Q

Topics covered under signal detection theory

A

What is the problem? Logic of SDT
Response bias measurement
Sensitivity measurement

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21
Q

4 factors that can affect threshold measurement in signal detection theory

A

Response bias (the listener’s tendency to say “Yes, I heard that”)
Attention
Memory
Motivation

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22
Q

Basic rationale of SDT

A

Even when no stimulus is present, an observer’s sensory system generates sensory noise
These fluctuations can be represented in the form of a probability distribution

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23
Q

In SDT, in deciding whether a signal has been presented, what info is available?

A

The only info available is the level of sensory activity

24
Q

In SDT, what needs to be set for sensory activity level? What does it represent?

A

A criterion
Represents the level of sensory activity you are willing to accept as indicating that a signal is present

25
4 possible outcomes of a signal detection trial - explain each
Hit: Signal present and "yes" False alarm: Signal absent and "yes" Mistake: Signal present and "no" Correct rejection: Signal absent and "no"
26
How is response bias usually symbolized? Explain
By Greek letter beta Large beta: Stringent/strict criterion (no more than yes) Small beta: Lax criterion (yes more than no)
27
What affects the placement of response bias?
Variations in observer's expectations
28
Sensitivity in the context of signal detection theory
Represents the amount of shift elicited by the presence of the signal in the noise distribution
29
Trends in proportions of sensitivity
Large proportion of hits and a small proportion of false alarms typically product a large d' Small proportion of hits and a large proportion of false alarms typically produce a small d'
30
Why should we care about detection?
If you set a very high criterion to decide that a car coming your way as you are about to cross the street, your life expectancy could be greatly reduced
31
Discrimination basic question
By how much must two stimuli differ in order to be discriminated as not the same?
32
Discrimination topics
Measurement Weber's law
33
Discrimination - measurement how to Give examples
Involves variations of stimuli along one dimension Sound: intensity, frequency, loudness Light: intensity, brightness, size Smell, taste, touch: intensity
34
In practice, how does discrimination measurement occur?
Present a stimulus designated as the standard Observer must distinguish this standard from a series of graded comparison stimuli
35
What specific methods are used in discrimination measurement? Expand
Method of limits or constant stimuli Choice does not include "same" Plot the proportion of (e.g.,) "heavier" responses
36
Discrimination measurement - 50% point
Point of subjective equality
37
In discrimination measurement, what is the interval of uncertainty?
Interval between 75% and 25%
38
In discrimination measurement, how do we obtain the just noticeable difference (JND)? AKA?
By dividing the difference between the 25% and 75% points by 2 Difference threshold
39
What is Weber's law concerned with? What does it state?
Relation between the size of the JND and the size of the standard JND increases with the size of the standard (proportional)
40
Weber's law equation
Delta(I) = jnd = KI I = intensity of stimulus K = fraction equal to JND/I, which is Weber's fraction
41
Is Weber's fraction constant?
Yes
42
With Weber fractions, what do smaller values indicate?
Better discrimination
43
Why should we care about discrimination?
The high difference threshold for the taste of salt should remind us not to over-salt our food. It could save your life!
44
Scaling basic question
How much of X is there? Relation between physical stimulus and perception
45
Scaling topics
Indirect scaling and Fechner's Law Direct scaling: category judgment, magnitude estimation and Stevens' Law, cross-modality matching
46
Indirect scaling and Fechner - premises
Weber's Law is true Subjective impression of two stimuli separated by 1 jnd is the same regardless of the magnitude of the stimuli Sensation differences can be represented by adding or subtracting jnd's
47
Fechner's law equation
S = W log(I) S = intensity of sensation I = intensity of stimulus W = constant based on Weber's fraction
48
Direct scaling and Stevens
Argued that it was actually possible to implement direct scaling All you need to do is give people a task that makes it feasible (e.g., category judgment)
49
Category judgment Example
Observers are asked to put stimuli of similar intensity in an arbitrary number of categories E.g., lines of different length put in seven categories
50
Magnitude estimation
We give observers full freedom in quantifying stimuli E.g., frequency discrimination Standard = 100 Task: rate other sensations based on this standard
51
Magnitude estimation equation AKA?
S = aI^n S = sensation a = constant I = intensity of stimulus n = exponent Stevens' power law
52
Magnitude estimation exponent size
Large exponents indicate that our sensation overestimates the physical stimulus Small exponents indicate underestimation Exponents of 1 indicate a close correspondence between sensation and physical stimulus
53
Magnitude estimation and electric shocks
We tend to overestimate electric shocks (exponent = 3.5)
54
Cross-modality matching
Stevens developed this technique to counter criticisms that magnitude estimation tells us more about how humans use numbers than about sensations Observers presented with a series of stimuli Indicate the magnitude of the stimulus b adjusting the intensity of another stimulus
55
Examples of cross-modality matching
Hand grip strength and liquor mixture strength
56
Why should we care about scaling?
Setting your sound system to the correct intensity could make the difference between a romantic evening or the police banging at your door!

Survey of the Senses (13 decks)

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