Auditory 3

Audibility

Range of sound frequencies that are detectable

What is 2AFC

2 Alternative forced choice: A way of testing audibility with a threshold of 75% correct. If someone is guessing they would be at about 50%. Can be used to plot psychometric functions of audibility.

Minimal audible field threshold (MAF)

The gold standard for determining audibility. The tone is presented from a single loud speaker in a sound proofed room, the subject faces the loudspeaker and is one meter away. The subject can listen with both ears.

Minimal audible pressure Threshold (MAP)

Taken under headphones and is a commonly used hearing test because it is much easier to administer than a MAF test.

Why are MAF thresholds about 6dB lower than MAP thresholds?

MAF has a binauaral advantage and MAP has interference from Physiological noise due to ears being covered by headphones.

Human sensitivity curve

Sensitivity falls of below 1000Hz by 6dB per octave and above 4000 Hz by about 24dB per octave. This shape is explained by bandpass filter.

Lower envelope principle

Behavioral thresholds for detecting tones in quiet match thresholds of most sensitive ANFs.

Why are high intensity low frequency sounds more painful than high intensity high frequency sounds

This is because more of the Basilar membrane is activated by lower frequencies than is activated by higher frequencies.

What is the range of normal hearing on an Audiogram

Will be a flat audiogram with 0-20dB of hearing loss.

How does Duration affect audibility

If duration is over 300ms then the detection threshold is dependent solely on level. If duration is below 300 ms then it is dependent on both duration and level with lower durations needing higher level.

Discrimination

Whether or not you can tell the difference between 2 stimuli. Minimal detectable change is called the just noticible difference (JND)

Weber’s law

States that the JND increases in direct proportion to the intensity of a stimulus.

Intensity Discrimination

Is close to Weber’s law, independent of sound pressure, better for broadband noise than tones.

Weber’s law near miss explanations

Range fractionation: High intensities are handled by low SR fibers and low intensity is handled by High SR fibers even though there are many more High SR fibers.

Excitation pattern: As sound gets louder a greater number of whisper neurons are activated giving them the ability to discriminate between high and low levels equally well. Is the preferred explanation.

Frequency JND

1 Hz at low frequencies but grows with frequencies above 2KHz. Does not follow Webers law and is explained by temporal theory.

Loudness

Describes the perceived volume of a sound.

Matching

A way of studying loudness by adjusting loudness of test signal to equal a standard/reference signal.

Scaling

A way of studying loudness by having someone estimate loudness on a numerical scale relative to a reference signal.

Loudness curve

Shows that sensation of loudness is not equal for all frequencies even when sound pressure is constant.

Sone

Subjective unit of loudness equal to 1 standard kHz tone. Loudness will roughly double for each 10 dB increase.

Loudness recruitment

Marker of cochlear impairment is the perceptual phenomena of sounds becoming rapidly louder with increasing sound level.

How does duration affect loudness

If the duration is greater than 300 ms then loudness depends solely on stimulus level. If duration is less than 300 ms then loudness depends on duration and level, as duration decreases level must increase to have same loudness.

Pitch

Perception of frequency that lets sounds be ordered on a musical scale.

Mel scale

perceptual scale of pitches judged by listeners to be equal in distance, relationship between pitch and frequency is non-linear

Pitch chroma

The cyclic quality of pitch: sounds that are separated by an octave have a similar pitch quality.

Pitch of Periodic sounds

Sound will have a very strong sense of pitch, if it is a complex sound it will be made up of harmonics.

Resolved vs Unresolved harmonics

Low number harmonics fitting within one auditory filter are considered resolved while high number harmonics are often unresolved. Pitch is stronger for tones with resolved harmonics, this suggests place theory, unresolved still creating pitch suggests temporal.

Repetition on pitch

Perception of pitch can be yielded with repeating broadband sounds in a click train.

Effect of duration on pitch

Pitch quality increases with stimulus duration.

Effect of intensity on pitch

Pitch quality changes slightly with intensity, as intensity increases the pitch decreases if the tone is below 2000 Hz but increases if it is greater than 2000 Hz.

Simultaneous vs non-simultaneous masking

Simultaneous is when masking occurs at the same time as the signal and non-simultaneous is either forward or backward where it occurs just in front of or just after the signal.

What determines masker strength

Determined by the masker threshold, a high masker threshold means it’s a weak masker and a low masker threshold means its a strong masker.

Why aren’t psychophysical tuning curves believed?

Maskers cannot mask frequencies below very well so the high frequency side isn’t believed, The tuning curve shouldn’t come to a nice point is should be a w shape due to off frequency listening, these tuning curves also don’t show the distortion effects caused by harmonics and sub harmonics.

Upward spread of masking

Maskers can always work above but doesn’t work well at frequencies below.

Off frequency listening

Auditory syste will choose a filter just above or below the signal frequency if it is being masked to that it can still be heard. Creates the w shape at the bottom of a curve.

What masker is the best for tests

Notched noise, the wider the notch the weaker the masker. You can find the width of the tuning curve with the notch.

When is masking the strongest

At the on and offset due to the initial large amount of NT released in response to the masker and less NT being available at the end.

STrength of masking time

Simultaneous is the strongest, followed by forward with backwards being the weakest.

When can forward masking be good?

When timed correctly it can cause the yield of a sharper tuning curve.

What do tuning curves allow you to infer?

Phase locking.