PSYCHOACOUSTICS: Psychophysical methods

Question 1

what do psychophysicists measure?

Answer 1

Psychophysicists measure the relationship between physical stimulus features (e.g., velocity, duration, brightness, weight) and forced-choice responses of test subjects using a psychometric function. This function models the percentage of correct responses (or a similar value) on the y-axis against the physical parameter on the x-axis. It helps determine the threshold of perception and discrimination abilities.

Question 2

how do we determine a threshold from a psychometric function?

Answer 2

-there’s too much info in a psychometric function so we want to summarise it into 1 number

-we randomly take a particular performance level (e.g. 75%0 and consider the stimulus level that produces this performance level. This stimulus level is called a threshold.

Question 3

how do we read a psychophysicists graph?

Answer 3

• When the stimulus parameter is at one extreme, the person always responds correctly.
• At the other extreme, they never perceive the stimulus properly, so responses are just guesses.
• In between, there’s a transition range where they’re more likely to respond correctly.

Question 4

how do we classify the psychophysical experimental paradigsm?

Answer 4

• Simple forced choice (yes-no task)
• Two-alternative forced choice (2AFC)
• n-alternative forced choice (more than 2)

Question 5

how does the number of alternative options effect the lower section of the graphs curve (lower asymptote)?

Answer 5

When there are more alternatives, it becomes relatively easier for participants to guess randomly and still achieve a correct response by chance. As a result, the lower asymptote of the function, which represents the lowest level of performance, tends to be higher when there are fewer alternatives.

Question 6

what are the different classes of psychophysical methods?

Answer 6

1- method of adjustment
2- method of constant stimuli
3- method of limits

Question 7

what is the method of adjustment and how is used in perceptualized research?

Answer 7

-the method of adjustment is a versatile tool for studying perceptual thresholds and subjective perception, offering a straightforward and relatable approach for participants to engage with stimuli.

-Controls Stimulus Level: In this method, the person conducting the experiment, called the observer, is responsible for adjusting the intensity or level of the stimulus being presented to the participant.

• Adjustment to Perceptual Threshold: The participant, under the guidance of the observer, manipulates the stimulus level until it’s just at the point where they can detect it. This is known as the perceptual threshold, the point at which the stimulus becomes noticeable to the participant.

Question 8

how is the method adjustment intuitive?

Answer 8

This method is intuitive for participants because it resembles everyday activities like adjusting the volume on a radio or the brightness using a dimmer switch on a light. It’s a familiar concept that most people can easily grasp.

Question 9

what makes the method of adjustment an intuitive method?

Answer 9

This method is intuitive for participants because it resembles everyday activities like adjusting the volume on a radio or the brightness using a dimmer switch on a light. It’s a familiar concept that most people can easily grasp.

Question 10

what is meant by the Point of Subjective Equality (PSE)?

Answer 10

where two stimuli are perceived as identical by the observer

Question 11

what is the Point of Subjective Equality (PSE)?

Answer 11

This is the setting at which the participant perceives two stimuli as being the same. For instance, in vision research, if one stimulus is presented at a certain brightness, the participant adjusts another stimulus until it appears equally bright.

Question 11

how does the method of adjustment help compare or match one stimulus to another?

Answer 11

The method of adjustment is particularly useful for comparing or matching one stimulus to another. It helps determine the Point of Subjective Equality (PSE), where two stimuli are perceived as identical by the observer.

Question 12

what is the easiest method of finding a stimulus threshold?

Answer 12

-the method adjustment

Question 13

how is the method of adjustment used to determine an absolute threshold?

Answer 13

The method of adjustment involves asking a participant to adjust the sound level using a dial until they can just detect the presence of the stimulus. This approach is commonly used to determine absolute hearing threshold, where the faintest sound a person can hear is identified.

Question 14

how should you choose the starting threshold when using the method of adjustment?

Answer 14

• The starting value should be well above or well below the expected threshold to ensure accurate adjustments.
• Additionally, the final “threshold” value may vary depending on whether the threshold is approached from above or below, impacting the outcome.
• Overall, this method tends to yield better average values compared to other techniques.

Question 15

how do we use the method of adjustment to measure relative thressholds?

Answer 15

• The method of adjustment involves participants adjusting a parameter value until it matches a reference stimulus.
• For instance, in sound experiments, participants may adjust until a sound matches the pitch or loudness of a reference sound.
• Similarly, this method can be used to match light intensity by adjusting until it matches a reference brightness.

Question 16

what is the method limits and how does it determine thresholds?

Answer 16

1) On some trials the intensity ascends from low to high intensity

• When the stimulus or a difference between stimuli is noticed the trial stops

2) On other trials the intensity descends from high to low intensity

• When the stimulus or a difference between stimuli is not noticed any more the trial stops

3)Averaging the stopping values across several trials yields thresholds

Question 17

what are the pros and cons of the method of adjustment?

Answer 17

*Advantages:
- Very quick.
- Easy to understand.

*Disadvantages:
- We don’t always know the criterion used by participant = great potential for bias.

• No direct evidence that participant actually perceives a nominally supra-threshold stimulus.
• Stimulus duration is not controlled (in context of testing audiometric threshold)

Question 18

how does the method of limits work?

Answer 18

• With the method of limits, the tester controls the intensity.
• The intensity is changed from trial to trial by a fixed amount. Usually automated.
• At each intensity the participant presses a button if they can the perceive stimulus.

Question 19

what are the pros and cons of the method of limits?

Answer 19

*Advantages:

• Relatively quick – measurement stops as soon as the detection threshold is reached.
• Stimulus presentation paradigm can be varied (e.g. combined with 2AFC or 2AFI paradigm)
• Stimulus duration is under control of the tester (in context of audiometric testing)

*Disadvantages:

• Initial trials are wasted in that they don’t contribute to the threshold estimate.
• Not enough runs
• threshold can fluctuate from moment to moment: Adaptation & habituation

Question 20

what is the method of constant stimuli?

Answer 20

• A psychophysical procedure for determining the sensory threshold by randomly presenting several stimuli known to be close to the threshold.
• You can plot an entire psychometric function using this method, which is very informative
• And you can find set an arbitrary probability of response as the threshold

Question 21

what are the pros and cons of method of constant stimuli?

Answer 21

*Advantages:

• Can get the whole psychometric function -> very informative
• Can be combined with 2AFC or 2AFI.
• Stimulus duration under control of the tester (or pre-programmed if automated).

*Disadvantages:

• Time consuming if we just want threshold
• Needs a pilot experiment to get a suitable range of stimulus levels.

Question 22

what is an adaptive procedure in psycoacouctics?

Answer 22

An adaptive procedure is a technique where stimuli are dynamically adjusted based on the participant’s responses, aiming to efficiently determine thresholds or psychophysical parameters.

Question 23

what is the difference between the 1-down-1-up method and the 2-down-1-up method?

Answer 23

-In the 1-down-1-up method, the intensity or parameter of the stimulus decreases (goes “down”) after each incorrect response from the participant.
Conversely, the intensity increases (goes “up”) after each correct response.

-however, with the 2-down-1-up method, the intensity decreases after two consecutive correct responses and increases after one incorrect response.

Question 24

How to interpret a psychometric function: threshold, slope?

Answer 24

*Threshold:

• Represents the stimulus level where the participant achieves a predefined criterion level of performance, often 50% correct responses.
• Lower threshold indicates higher sensitivity.

*Slope:
- Describes how steeply performance changes with variations in stimulus intensity.

• Steeper slope indicates higher sensitivity; shallower slope indicates lower sensitivity.