Lecture 10 Flashcards
What is the relationship between auditory sensitivity and dynamic range as a function of hearing?
Finding out the lowest sound level that humans can hear and the highest sound levels at which human hearing can still function.
Lowest level - determined by absolute thresholds at various frequencies.
Sensitivity is frequency dependent. Sensitivity declines as frequency decreases.
Higher sensitivity = smaller thresholds.
What is a threshold?
Smallest physical change that can be detected by a listener -inversely related to sensitivity;
The more sensitive listener is to an acoustic change in stimuli, the lower the threshold.
The physical change is 50% or correct responses.
What is the difference between measuring thresholds in the auditory field vs. headphones?
Headphones: calibrate with specific couples - stimulate volume that is occurring for the average ear between transducer in headphones.
Auditory Field: (loudspeakers); calibrate level of signal to where listener is supposed to be, then increase signals.
-> Shouldn’t be a difference between the two different measurement setups, even though there appears to be
What are psychophysical procedures?
Methods for estimating thresholds or differences between stimuli, or identification accuracy, or amounts of subjective qualities.
Studying relationship between physical properties and perceptual attributes of sounds.
What are the two main approaches to psychophysical procedures?
- Ask listeners to discriminate two or more stimuli, or to identify (classify) a stimulus, given two or more choices
- Ask listeners to estimate directly what they hear - based on rating scales or matching a perceived ratio (2x as loud)
What does an upward spread of masking mean?
For a masker of a given frequency the masker will produce more masking above its frequency compared to below.
What is the method of constant stimuli?
Present each of a number of stimuli a bunch of times whether there is a signal or not. Use different levels in dB.
Present single trial - signal is present/not present.
Threshold chosen as level corresponds to 50% of the possible range of Yes/No responses (signal level will decrease, people won’t be able to hear as well, fewer Yes)
In the method of constant stimuli, what does the Yes/No task measure?
What is the 2 Alternative Forced Choice Task?
Measures absolute thresholds - participants asked if tone is present/not present in single interval.
- Psychometric function (50% correct)
2AFC: Each trial has 2 interval and participants asked to select interval that contains tone.
- tone present and noise
- only noise present
How does the two-down one-up procedure work?
Adaptive track procedure
Change physical magnitude of stimuli depending on the response of listener on particular trial.
Level of stimulus relatively high to start with; lowered if participants make correct response in 2 consecutive trials.
Several trials presented so direction of change in stimulus level switches a specified number of time.
The threshold is measured as the average of level at reversals - specific number of turn points of reversal - direction of change in level switches up/down
How would one reduce the bias in the measuring of absolute thresholds?
(If person says yes all the time)
Include catch trials - trials in which the signal is absent.
- Correct rejection - Present: Yes; Absent - NO
- False Alarm - Present: No; Absent Yes
Remove the response bias from calculation of the threshold by including false alarms and hits (sensitivity and specificity)
How do you measure the sensitivity and specificity of response biases?
Compare the listeners % correct (hits and correct rejections)
The more sensitive person will say Yes more often overall
What does the signal detection theory claim?
Listeners respond in a certain way with certain probability. Theory represents probability of responding as normal distribution of frequency. Shall expect that magnitude of stimulus should be higher when there is not stimulus and only noise.
Probability that you will respond in a certain way - what you are measuring that is above/below is a distribution of probabilities.
How do you represent sensitivity in signal detection theory?
What does d’=1, d’=2 mean?
Difference between means of frequency distributions.
Not just subtracting the hits and false alarms proportions - transforming them into z scores. Number you end up with is estimated difference between 2 distributions = sensitivity.
d’=1 ->moderate sensitivity for a specific difference between stimuli
d’=2->higher sensitivity
How does “c” change in discrimination figures of signal detection theory?
Takes into account the sensitivity and specificity. Want to remove measure of sensitivity from criterion that person adopts.
Yes/No and 2FC task possible - responses to conditions with noise/signal.
Criterion (c) can move. As it moves up, more liberal - criterion moves left (say yes more often). This can change depending on how often you say Yes or No.
Everything above criterion suggests a yes response.
