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quiz #1 Flashcards

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1
Q

what is sensation?

A

the ability to detect a stimulus, and perhaps to turn that detection into a private experience.

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2
Q

what is perception?

A

giving meaning or purpose to a detected sensation.

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3
Q

what are the three steps in the sensory process?

A

physical stimulus –> physiological response –> sensory experience.

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4
Q

what is a physical stimulus?

A

a physical stimulus has to interact with at least one of the sensory systems. For example, a light, sound, or odor.

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5
Q

what is the physiological response?

A

the physical stimulus interacts with our sensory system in order to create a pattern of electrical activity in sensory receptors, nerves, and the brain.

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6
Q

what is the sensory experience?

A

the electrical activity then leads to a sensory experience (also known as a sensation). For example: we see something, hear, or smell something.

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7
Q

how do we study the physical stimulus –> physiological response step?

A

single-unit animal recording studies

human brain imaging (MEG, EEG, PET, fMRI).

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8
Q

how do we study the physiological response –> sensory experience step?

A

animal lesion studies, human clinical studies or human brain imaging.

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9
Q

why do researchers often study the physical stimulus –> sensory experience stage instead?

A

studying physiological response is expensive, requires a highly specialized group of people, and requires fancy equipment. It is much easier to study the effect of the physical stimulus on the sensory experience.

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10
Q

what is the easiest way to study an individual’s sensory experience?

A

to ask them what they are experiencing.

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11
Q

why is this method flawed?

A

everyone experiences things differently, and we cannot verify what they are experiencing.

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12
Q

what quantitative method is used when studying sensory experience?

A

psychophysics.

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13
Q

who invented psychophysics?

A

Fechner.

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14
Q

how can psychophysics be defined?

A

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

a behavioural technique.

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15
Q

what is psychophysics concerned with?

A

what the brain is doing, not HOW the brain is doing it, which essentially bypasses the physiological response stage.

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16
Q

what is the absolute threshold?

A

detection: the minimal amount of stimulation necessary to just detect the presence of a stimulus.

alternative definition: the minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time.

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17
Q

what is a psychometric function?

A

a graph of stimulus value (i.e., intensity) on the horizontal axis versus the subject’s responses (i.e., proportion “yes”) on the vertical axis.

used in the method of constant stimuli.

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18
Q

where do we see the absolute threshold on a psychometric function?

A

in ideal cases: the point where it goes from never to detecting to always detecting.

realistic experiments: since thresholds vary from moment to moment, we use the 50% point.

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19
Q

what is the “S” shaped curve on a psychometric function referred to as?

A

an ogive.

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20
Q

when a threshold is ______ it means your sensitivity is ______?

A

low, high.

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21
Q

what are the three methods used for detection?

A

method of constant stimuli, method of limits, and method of adjustments.

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22
Q

what is the method of constant stimuli?

A

select stimulus intensities above and below the expected threshold; present many trials of each intensity in random order to the same individual; plot psychometric function; read 0.5 or (50%) detected point from the psychometric function graph.

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23
Q

what is the method of limits?

A

using a descending series: stimulus intensity decreases in equal steps until response changes to “no”. Then an ascending series is attempted. Stimulus intensity is increased in equal steps until response changes to “yes.”
To do this experiment, alternative between ascending and descending trials, and vary starting points.

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24
Q

how to calculate the absolute threshold in the method of limits experiment for discrimination?

A

calculate the crossover points for each trial and take the average of them all.

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25
Q

what is the method of adjustments?

A

observer adjusts the stimulus intensity, using a potentiometer until it is just detectable. The experimenter randomly adjusts the starting position of the potentiometer during each trial.

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26
Q

how do we calculate the absolute threshold in the method of adjustments experiment for discrimination?

A

take the average of the threshold adjustments that the observer makes.

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27
Q

when do we use discrimination experiments?

A

once we get into the range where we can always detect the stimulus, we can look at how much we have to change a stimulus in order to notice that it has been changed.

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28
Q

what is a suprathreshold?

A

above the absolute threshold, always detectable.

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29
Q

what is the different threshold?

A

the smallest difference between stimuli or change in a stimulus that the observer notices 50% of the time. This is also referred to as a just noticeable difference (JND).

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30
Q

what techniques are used to measure discrimination?

A

method of constant stimuli, method of limits, and method of adjustments.

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31
Q

how do we use the method of constant stimuli for discrimination?

A
  • presenting two stimuli at the same time, one is standard (fixed value) and the other is a comparison (value changes).
  • the magnitude of comparison (values are above and below threshold) is varied in random order with many trials of each value.
  • then plot % “stronger” responses versus comparison magnitude.
32
Q

how do we calculate the JND?

A

subtract the upper limit (0.75) from the lower limit (0.25) and divide by 2.

33
Q

what does the 0.50 point on the graph represent?

A

the point of subjective equality, which is a measure of accuracy.
- 50% tells us how good we are at matching the weights.

34
Q

how do we use the method of limits for discrimination?

A

the standard and comparison are presented together.

  • descending series: comparison decreases in equal steps until response changes from “stronger” to “equal” to “weaker.”
  • ascending series: comparison increases in equal steps until response changes from “weaker” to “equal” to “stronger.”
  • alternate between descending & ascending series; vary starting point
35
Q

how do we calculate the JND and PSE for the method of limits for discrimination?

A

The upper limit is the crossover point between “stronger” & “equal” on each series
The lower limit is the crossover point between “equal” & “weaker” on each series
JND = (average upper limit -average lower limit) / 2
PSE = (average upper limit + average lower limit) / 2

36
Q

how do we do the method of adjustment for discrimination?

A

observer adjusts the comparison stimulus until it matches the standard stimulus.
- the experimenter will randomly vary the starting point.

37
Q

how do we calculate the JND and PSE for the method of adjustment for discrimination?

A 
JND = SD of the matches*0.6745
PSE = the averages of all the matches.
38
Q

what are the advantages of the method of constant stimuli?

A

accurate and repeatable threshold values.

39
Q

what are the disadvantages of the method of constant stimuli?

A

time-consuming, not good for tracking thresholds that change over time, not good for children or clinical patients, not efficient because too much unnecessary data is collected.

40
Q

why is the method of constant stimuli not good for children or patients?

A

it requires too much time and attention that patients and children may not have.

41
Q

what are the advantages to the methods of limits?

A

efficient, no psychometric function necessary.

42
Q

what are the disadvantages of the method of limits?

A

error of habituation, and error of habituation.

- to solve this we add more series and change the starting point, however, this decreases efficiency.

43
Q

what are the advantages to methods of adjustment?

A

quick, participants like it.

44
Q

what are the disadvantages to the method of adjustments?

A

not very accurate or repeatable threshold values.

45
Q

what are the modern improvements used in these techniques?

A

the staircase method, and the 2-alternative forced-choice paradigm.

46
Q

what is the staircase method?

A

starts out similar to the method of limits. Stimulus intensity decreases (or increases) in equal steps until stimulus can’t be detected. Then, stimulus intensity increases (or decreases) until stimulus can be detected, etc. So essentially, we do not start a new series, we just change it from ascending to descending when the participant changes their response.

adaptive method - stimuli kept hovering around threshold by adapting test sequence to participant’s responses. So the experimenter is adapting the stimulus based on the response from the participant.

47
Q

when the series is switched from increasing to decreasing as a result of the participants’ response, what do we call it?

A

response reversal.

48
Q

when does the experiment end?

A

after a fixed # of trials or a fixed # of reversals.

49
Q

how do we determine the absolute threshold with the staircase method?

A

absolute threshold is the average of the cross-over points at response reversals.

50
Q

what are the advantages of the staircase method?

A

efficient (most data is collected around the threshold).

can be used to track threshold changes over time.

51
Q

what are the disadvantages to the staircase method?

A

Errors of anticipation and habituation.
To avoid anticipation and habituation errors, randomly interleaved descending and ascending staircases can be used. This is difficult to do unless we have a computer.

52
Q

why is the 2-alternative forced-choice paradigm used?

A

The normal “yes/no” paradigm involves the participant reporting presence or absence of a stimulus (detection) or stimulus difference (discrimination).
However, this is very subjective and the experimenter cannot verify or dispute the participants’ response.

This modern method is more objective since the participant must prove they can detect or discriminate the stimulus.

53
Q

how do mathematics change with this paradigm?

A

In this method, the 50% interval is the guess rate, and 75% becomes the absolute threshold.

the psychometric function will start at the 50% mark.

Percent correct is plotted rather than just yes responses.

54
Q

what are some advantages to the 2-alternative forced-choice paradigm?

A

Lower thresholds. People’s performances come out better because people are not allowed to guess. They are forced to choose an option.
Reduces non-sensory differences between participants (bias or criterion differences).

55
Q

with which of the psychophysical methods can a 2-alternative forced-choice paradigm be used?

A

Method of constant stimuli, method of limits, and the staircase method.

56
Q

what is webers law?

A

Ernst Weber discovered that difference thresholds are larger for larger stimuli.
Weber’s Law: △I = k*I
△I - the difference threshold
k - is a constant that depends on the sensory system
I - the physical magnitude of the stimulus
Weber fraction (k) = △I/I
Weber’s Law states that the difference threshold is a constant proportion of the physical magnitude of the stimulus.

From Weber’s discrimination experiments, he determined that the JND is larger for larger standard stimuli (I), with a linear relationship.

57
Q

what did Fechner want to do with this information?

A

Fechner wanted to quantify sensation. He suggested using JNDs to describe the perceived intensity. For example, A is 3 JNDs above your absolute threshold for detection; B is 2 JNDs brighter than A.

Fechner then used Weber’s findings to describe the sensation. If we assume that JNDs produce equal steps in sensation (△S), then sensory steps at the upper end of scale require larger increases in stimulus intensity (logarithmic relationship).

58
Q

what is Fechner’s law?

A

Fechner’s Law: a principle describing the relationship between stimulus magnitude and resulting sensation magnitude (scaling).
S = k log R
k - Weber fraction
R - stimulus level (same as I in Weber’s law)

Essentially, as stimulus intensity increases, sensation intensity increases rapidly at first, but then more slowly.
Sensation magnitude has a logarithmic relationship since sensory steps at the upper end of the scale require larger increases in stimulus relationships.

59
Q

What is the difference between Fechner and Weber’s Law?

A

Fechner Laws - describes stimulus magnitude, and the resulting sensation magnitude.
Weber was trying to see what had to be done for an individual to notice a difference whereas Fechner wanted to know what people were experiencing with these changes (as in brightness, loudness, etc.).

60
Q

what is magnitude estimation?

A

participant assigns a number to describe stimulus intensity. This is a very simple way to do psychophysical scaling.

Magnitude estimation experiments showed that once detected, the sensory magnitude of a stimulus increases with its physical magnitude, within limits.
The rate of increase varies with different sensations.

61
Q

what is Steven’s power law?

A

a principle describing the relationship between stimulus magnitude and resulting sensation magnitude, such that the magnitude of subjective sensation is proportional to the stimulus magnitude raised to an exponent (or power).
S = a*I^b
S = sensation
I = stimulus intensity
a = constant that corrects for units.
b = exponent (will determine the shape of the curve).
Stevens Law and Fechner’s law predict the same scaling result for sensory modalities in which b < 1, but not for other sensory modalities.

62
Q

what are some possible rationales that explain the discrepancies between Fechner and Steven?

A

Fechner’s law assumes that all JNDs are perceptually equal, but this law is violated for some sensory modalities.
magnitude estimation is more subjective than determining JNDs.

63
Q

what is cross-modality matching?

A

a scaling method in which the intensities of sensations that come from different sensory modalities are matched. This is used to sensory differences across individuals.

This method has shown us that the relationship between visual experience and auditory experience appears to be similar across individuals.
However, being able to match intensities of sensations from different sensory experiences does not hold for all sensory experiences.

for example: taste.

64
Q

what does the signal-detection method recognize?

A

Recognizes that perceptual measurements are influenced by the motivational state and sensory capacities of the perceiver.

It also understands that all decisions are made in the presence of noise.

65
Q

what is a catch trial?

A

trials in a signal detection experiment on which the stimulus/signal is absent.

66
Q

what does sensitivity refer to?

A

the ease with which a perceiver can tell the difference between the presence and absence of a stimulus.

  • If a participant has perfect sensitivity they would have a hit rate of 1.0.
  • However, if the participant is completely insensitive, they will have equal hit and false alarm rates.
67
Q

which responses provide the sensitivity measures?

A

hits and false alarm.

68
Q

what does d’ tell you?

A

the statistic that reflects a perceiver’s sensitivity. If the two distributions have less overlap, d’ is larger.

reducing stimulus intensity decreases sensitivity (d’). Refer to the dot example from class.

69
Q

why do people make false alarms?

A

sensory and non-sensory distractions.
sensory: reducing stimulus intensity decreases sensitivity (d’). Refer to the dot example from class.

non-sensory: criterion.

70
Q

what does the criterion tell us?

A

response bias within a perceiver; depends on expectations & motivation.

71
Q

changing the probability of the stimulus changes the ______?

A

response pattern.

72
Q

how does changing the criterion manipulate the response pattern?

A

High stimulus probability → high hits and false alarms. SMALL β VALUE.
Low stimulus probability → low hits and false alarms. LARGE β VALUE.
Here we change the response pattern by varying the stimulus probability, but NOT the sensitivity.
d’ stays the same, but β CHANGES.
Higher β = stricter criterion.

73
Q

what does sensitivity depend on?

A

Sensitivity (d’) depends on the overlap of signal absent and signal present distributions.
If you are completely insensitive d’ is zero.
If there is more distance, sensitivity is higher because the two distributions are distinctly different.
d’ = distance between the means of N and S+N distributions.

74
Q

a liberal criterion produces? a strict criterion produces?

A

A liberal/lax criterion (small β) produces high hits and high false alarms.
A conservative/strict (large β) produces low hits and low false alarms.

75
Q

what is a ROC curve?

A

If you plot false alarms on the x-axis of a graph against hits on the y-axis for different criterion values, you get a curve known as a receiver operating characteristic (ROC) curve.

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