Hearing Science - Psychoacoustics

What is psychoacoustics?

A branch of psychophysics; the study of the relationship between the physical stimuli of sound and the human perception of them.

What is the difference between sensation and perception?

Sensation is an awareness of change in the environment but not identifying or making any judgement the sound (INTERNAL SENSATION).

Perception is how we interpreted the change in environment, where we start to identify what is different.

Define Sensation:

Sensation is an awareness of change in the environment but not identifying or making any judgement the sound (INTERNAL SENSATION).

Define Perception: 

Perception is how we interpreted the change in environment, where we start to identify what is different.

What are some examples of auditory sensation?

Hearing a song or hearing a voice.

What are some examples of auditory perception?

Identifying the song and singing along, and knowing who the voice belongs to.

What is the difference between hearing and listening? 

Hearing: A sound/noise comes into your ear without you making an effort. Knowing that a sound is present.

Listening: When you pay attention and try to listen to sounds. Paying attention and making an effort to comprehend the sound.

What range of frequencies is the human ear able to detect?

20 Hz to 20,000 Hz 

Across what frequency range is human hearing most sensitive?

300 Hz to 10,000 Hz

(because the sound that occurs most in this range is human speech)

Across what frequency range is human hearing tested during an audiological evaluation?

250 Hz to 8,000 Hz

(narrowed for what’s important for human communication) 

What does frequency often refer to?

The change in pitch

What does duration often refer to?

how long or short the stimulus is

The perception of duration is known as what?

Timing perception, as long versus short.

Why does sensitivity improve as suration of a stimulus is lengthened?

There are longer opportunties for you to be able to hear and understand the sound.

What does intensity often refer to?

The volume or power behind the sound.

The perception of intensity is known as what?

Loudness.

What does the range of usable intensity mean?

Dynamic Range including the softest sound I can hear, all the way to the loudest sound I can tolerate without being in pain. Individual for every person.

How are sounds of very low intensity usable and useful for only relatively short periods of time?

Listening to low intensity sounds for long periods of time causes fatigue or can be a sign of early-onset dementia.  

What is the measurement of sensation?

A perceptual scale

What is the physical stimuli (i.e. acoustic event) termed?

Your signal.

What are the human responses to these physical stimuli termed?

A threshold.

Define Threshold:

The ability to detect at the softest intensity 50% of the time.

Define Absolute Threshold:

The ability to detect that a sound is present 50% of the time.

What are the two subclassifications of Absolute Threshold?

Detection Threshold and Recognition Threshold.

What is the difference between detection and recognition threshold?

Being able to identify and correctly label a sound.

Define Detection Threshold: 

Simply telling the instructor whether you heard or detected a sound—point blank-- (“did you hear that”; non-linguistic)

Define Recognition Threshold: 

The listener telling the instructor WHAT they heard, not if they’ve heard it. (“repeat the word after me”)

Define Difference Threshold:

The ability to determine a difference between two sounds, based off a 75% accuracy.

What is difference threshold also known as?

Difference Limens or just noticeable differences.

How is a difference threshold is determined?

You are given two stimuli that are initially very different and asked if they are different. As you go through saying yes, it begins to get harder to tell the difference between the two stimuli, as one is changed to get closer to the other every time. This keeps going until you cannot tell the difference anymore.

Define Hearing Area:

Also referrred to as a Audiogram, this is the range of perceived intensities across frequency from very low (125 Hz) to high (8,000 Hz) to only assess the range of sound needed for communication. 

Why is there a certain amount of uncertainty in the human perception of sound?

Human response to sound is imperfect.

What does the signal detection theory examine?

The probability that the listener will respond to a sound.

What is the probability associated with human response to acoustic simuli reliant upon? 

Based off when the specific intensities of the stimulus and the noise are known.

What are the three classical psychophysical methods of psychoacoustics?

Method of Limits, Method of Adjustment, Method of Constant Stimuli

Define Method of Limits: 

- Used in audiological evaluations.

- Presented with a loud tone that the subject will hear.

- Each time the subject correctly hears the beep, the next tone will be softer.

- This repeats until they stop hearing the sound.

Define Method of Adjustment:

- Done for research purposes.

- Subject is given a tone to listen to the intensity or pitch very carefully.

- Subject will then be given a second, slightly adjusted tone to see if the subject can determine the difference.

- Does not tell you anything clinically.

Define Method of Constant Stimuli:

- Randomly presents the subject with different tones of different intensities.

- Unsure what tone you’ll get next.

Define Aural:

Ears.

Define Binaural:

Hearing with both ears.

How is binaural hearing superior to monaural hearing?

Improved localization, improved speech intelligibility in noise (understanding speech while noise is present), increased sound intensity, and enhanced sound quality. 

What is the improvement experienced in auditory perception when listening with both ears is called?

Binaural advantage (most people experience this)

Define Localization:

The process of determining the location of a sound source within an environment

What is localization dependent upon?

How your ears in the auditory system resolves information coming from both ears (information doesn’t have to be the same)

What are the three localization cues used to aid in localization of a sound?

1. Azimuth

2. Elevation

3. Distance

Define the localization cue Azimuth: 

Looking at where on the horizontal plane that the sound is coming from

Define the localization cue Elevation:

Looking at where on the vertical plane that the sound is coming from

Define the localization cue Distance:

Looking at how close [harder sound pressure] or how far [softer sound pressure] the sound is coming from around me

Define Interaural Timing Difference (ITD):

The difference in time for when the ears received the sound.

Define Interaural Intensity Difference (IID):

The differences in intensity for when the ears received the sound.

Associated with the head-shadow-effect. 

What does the introduction of masking noise preclude the listener from hearing?

The target, the signal they want to hear. 

T/F: There are no universal acoustic properties of a masker. 

True

Provide real-life examples of masking situation:

The environment of a basketball game: hearing the buzzer, the bounce of the basketball, the people shouting, etc.

Cleaning the dishes while someone is talking to me.

Reverberation in the classroom.

What are the two basic elements of the basic masking paradigm:

Signal and masker

Define this basic element of the basic masking paradigm; Signal:

What I want to hear.

Define this basic element of the basic masking paradigm; Masker:

Any unwanted noise that detracts from understanding the signal 

When is masking used clinically?

When the need arises when presented with asymmetrical hearing loss and possibly cross-over effect. Putting masking noise in the “good” ear to distract it, and continue to test the “bad” ear.

Why is masking used clinically?

My good ear can potentially help my bad hear (this is the cross-over effect, which we are trying to avoid) and doesn’t result in a true threshold. 

What is the audiologist trying to avoid when masking clinically?

Cross-over effect

What are the two types of noise typically used during masking paradigm?

Narrowband and Wideband Noise.

Define Narrowband Noise:

• Noise is restriced to a specific frequency

• Created by using filters

The frequency pass points of the narrowband noise are called what? 

Low pass (high frequency) and high pass (low frequency) filters.

Define Critical Band:

The range where the sound occur in frequency.

Define Cut-Off Frequency:

Cutting off anything I don’t want to pass through.

How is wideband noise different from narrowband noise?

It’s not filtered and it covers a wide range of frequencies.

For what is Wideband Noise most effective in masking and why?

In masking speech because speech is a dynamic signal (each sound has its unique pitch and intensity, words vary a lot in terms of pitches and intensity)  

Please explain how the frequency of the stimulus influences which localization cues are used during binaural hearing.

Low frequency sounds are localized by interaural time differences (ITDs), also known as the difference in time each ear receives the sound.

High frequency sounds are localized by interaural intensity differences (IIDs), also known as the difference in intensity between the ears.

Lower frequencies bend around someone’s head easier than higher frequencies, making the time difference more apparent.

IID happens when higher frequencies are blocked by someone’s head, creating a shadow and clear intensity difference. 

Please explain the signal detection theory. What does it examine? What are the four responses we may obtain when a stimulus is presented? Be sure to describe each response.

Human responses to sound are imperfect.

The signal detection theory examines the probability that the listener will respond to a sound based off when the specific intensities of the stimulus and the noise are known.

• If the response to hearing a sound is yes and the signal is present, this is a hit.

• If the response to hearing a sound is yes and the signal is not present, this is a false alarm.

• If the response to hearing a sound is no and the signal is present, this is a miss.

• If the response to hearing a sound is no and the signal is not present, this is a correct rejection.

Please explain why masking (while not ideal for everyday listening) has an important function in a diagnostic audiological evaluation. Be sure to identify the situation under which masking is most utilized. In addition, be sure to mention the goal of clinical masking and what we might see as a result of utilizing masking.

Clinical masking is used when a subject has asymmetrical hearing loss. A subject’s good ear can potentially help their bad ear; this is known as the cross-over effect and thus doesn’t create a true threshold. Audiologists try to use clinical masking to avoid the cross-over effect.