Perception: Perceptual Aspects Of Hearing

Front 1

Loudness...

Back 1

refers to the magnitude of the perception created by the sound of a particular physical intensity

Front 2

Minimum auditory field vs minimum auditory pressure thresholds

Back 2

those obtained through open-ear methods; those obtained through closed- ear (headphones) method. ---The latter allows us to ensure both ears gets equal stimulation
- thresholds obtained with MAF are 6dB lower than MAP

Front 3

What affects absolute detection thresholds with hearing? (3)

Back 3

- hearing sensitivity is related to the frequency of the stimulus - a frequency of about 1500Hz yields the lowest detection threshold, and 50 Hz yields the hightest
- duration of sound
- whether it is binaural or monaural

Front 4

psychophysical function (1); Minimal audibility curve, what does it show (4)

Back 4

portrays how sensory thresholds differ in relation to a particular stimulus parameter (such as frequency); threshold values for hearing perception plotted with respect to the frequencies at which they were obtained.
- It shows that detection ability is best (lowest thresholds) at 2000-4000 Hz
- the lowest frequency that can be heard is about 10-20 hz
- frequencies below or above the optimal range show progressively higher thresholds

Front 5

what factors are responsible for the U-shape of the minimal audibility Curve(in other words, what causes the threshold reduction in the middle frequencies) (3)

Back 5

1) the conductive elements of the outer and middle ear (the middle frequencies are due to sound being enhanced as it travels through outer and middle ear)
2) physiological properties of the auditory nervous system (higher frequencies lead to greater neural activation BUT only up to a certain point)
3) cochlear doesn't affect it because its mechanical response is similar for all frequencies

Front 6

Monaural vs Binaural (definition +3 points)

Back 6

-applied to one ear vs two.
-Monaural stimulation leads to thresholds 6 dB higher than binaural
- sounds heard with both ears are preceived to be twice as loud as those with one ear
- When calculating intensity, your brain is doing a binaural summation

Front 7

Sound duration and thresholds (temporal summation)

Back 7

the NS can integrate neural excitation from successive sound over a period of 200 ms. If the duration is longer, than this, the auditory system can preform integration. if it is below 200 ms, its ability is compromised and thus shorter duration sounds show higher thresholds. Essentially, shorter stimuli need more energy to be detected. The integration ability over time is called temporal summation

Front 8

terminal threshold; dynamic range

Back 8

maximum sound pressure that we can tolerate (130-140 dBspl) (those that produce pain); the range in between the minimal audibility curve and terminal threshold (highly dependent of frequency)

Front 9

Weber constant and sound intensity discrimination (3)

Back 9

- varies from .1 to .4
- A LARGER PROPORTIONAL DIFFERENCE IS NEEDED AT HIGHER INTENSITIES TO PRODUCE A JUST NOTICEABLE DIFFERENCE
- there appears to be no relationship between Weber constant (intensity discrimination) and frequency

Front 10

Characteristic Frequency, neuron firing rate, and Intensity

Back 10

at low intensities, only neurons which respond to that CF will increase discharge, but as intensity increases, the neighbouring neurons with higher intensities will also increase firing. This is called the UPWARD SPREAD OF EXCITATION

Front 11

How does loudness perception relate to physical intensity? a change of what of intensity is needed to double loudness and viceversa? explain this (2) how do we rate perceived intensity? (3)

Back 11

- loudness sensation actually grows at a different rate than intensity (not linear)
- an intensity change of 10 dB is required to double loudness sensation rather than the 6dB it takes to double intensity
- if two people are talking, the perceived loudness versus one person is increased by only 60% not doubled
- method of magnitude estimation (rate it on a scale)
or Method of fractionation (identify pairs of stimulus that generate a certain ratio, such as halved or doubled)
- sone scale

Front 12

Sone Scale

Back 12

- 1 sone= the loudness sensation produced by a 1000Hz tone at 40dB
- an increase of ten scones needed for doubling of loudness

Front 13

What is the intensity-loudness function?

Back 13

-A power - law function.
-Intensity and loudness are related to each other by a power function because loudness grows at a lower rate than intensity.
-The function rises rapidly until 20 dBspl before taking the form of a straight line L=K*P0.67

Front 14

Intensity coding and loudness perception (4)
(activities of cochlear neruons in response to intensities, what does this mean for our brain?)

Back 14

-as intensity increases, activities of the Cochlear neurons increases
-auditory neurons are only capable of signaling within a range of 40dB (less than the range of human hearing)
-to solve this, the cochlear neurons encode certain intensity regions
-a intensity will only stimulate a group of neurons whose operating range contains that intensity, and thus the brain can convert sound intensity into loudness by assessing which types of nerve fibres are responding to a stimulus and what the firing rate is

Front 15

Equal loudness contours (4)- what are they? when do they change? describe the curves.

Back 15

- give us info on intensities that produce equal loudness perception across a range of frequencies
- as you move towards the higher end of frequency spectrum, you need higher intensities to produce equal loudness
- curves flatten at higher intensities
- the curves that represent this are called Fletch-Munson curves

Front 16

Phon Scale of loudness (2)

Back 16

- phon is the unit of measurement used to indicate loudness level across frequencies
- the number of phons at any frequency =the intensity in dBspl of a 1000hz tone when the two are judged to be of equal loudness

Front 17

Masking (definition, two types, and categories within these two types)

Back 17

- Masking occurs when the detection threshold of a particular sound is raised because of other sounds being present.
- Two types:
- simultaneous when noise and sound occur at same time-
Tonal masking the masking effects of a single tone by another- with tones similar in frequency, it doesn't take something loud to mask, but as you move apart in frequency, the second tone must be louder and louder to mask the test tone
- non-simultaneous:
Backward masking: A sound that occurs a short time after a target sound raises the detection threshold for the target sound. somewhat counterintuitive but it is possible -Forward masking: A sound that occurs a short time before a target sound raises the detection threshold for the target sound.

Front 18

Psychophysical Tuning curve

Back 18

- the process of masking can be thought of as an internal filter showing frequency selectivity, and so is often called a psychophysical tuning curve
- the curves represent hypothetical frequency channels used by the brain
- sharp curves indicate high frequencies and broader ones lower frequencies

Front 19

Describe the inherent asymmetry in the way sounds are processed (masking tones and frequencies)

Back 19

- masking tones whose frequency is higeher than that of the test tone lose their effectiveness much more rapidly
- This is due to how neurons which are tuned to different CFs respond as the travelling wave goes down the basilar membrane from the high-frequency base to the low-frequency apex
- The test tone at 1000 Hz makes neural excitation go steady until it peaks, reaches its CF and then drops. A masking tone with lower frequency will peak further on the membrane than the 1000hz tone and so its level of excitation will still be high when the test tone peaks. A higher frequency tone will peak earlier and then drop, meaning its level of excitation will be low when test tone peaks, making it inefficient at masking

Front 20

Broadband Noise vs Narrow band or bandpass noise

Back 20

A noise which encompasses a large segment of audible frequency range; a noise with a limited range of frequencies
-Narrowband noise is a preferred stimulus for masking experiments because tone maskers can create confounding cues that can be used indirectly for detection when the two are in close frequency

Front 21

Critical band

Back 21

-the narrowband noise bandwidth that can elevate the threshold for detection of a tone.
-The idea of thinking of this as ‘loudness channels’ represents conceptually that your brain is making independent channels and it tries to calculate the intensity of each channel and then for perception it adds them together
-audotory system has adjacent overlapping systems and if we play wider bandwidths of noise, we will find a bandwidth beyond the channel and so anything outside this range will not effect the channel.

Front 22

Infrasonic vs ultrasonic

Back 22

Sounds that have a frequency below 20Hz- often found in nature- like thunder, waves; sound frequencies above 2000Hz

Front 23

Difference threshold for frequencies

Back 23

under 3hz for frequencies less than 1000 and then after this the threshold rises progressively

Front 24

Mel scale of pitch

Back 24

- Stevens arbitrarily gave 1000Hz tone a pitch of 1,000 mels, and a pitch half of this 500 mels etc. He then corresponded the pitches with the frequencies that produced them.
We find that there is a non-equivalent relationship, in order words, a dissociation. For example a pitch of 500 mels is produced by 400 hz, and a pitch of 2000 mels is produced by 3000 hz

Front 25

What is pitch? (4)

Back 25

-a perceptual quality associated with how high or low a sound is
-For pure tones, frequency and pitch are the same.
- For complex harmonic tones and noise, we can determine what pitch percept they evoke by having people match the frequency of a pure tone to the perceived pitch of a sound.
- pitch is metathetic (difficult to quantify)

Front 26

Pure tone pitch and intensity relationship

Back 26

Above 2500 Hz, increasing the intensity of a tone produces an increase in pitch: The intensity effect on pitch becomes progressively greater for higher frequencies.
Below 2500 Hz, increasing the intensity of a tone produces a decrease in pitch.

Front 27

fundamental; harmonic; complex harmonic

Back 27

the first tone in the series of tones in the spectrum of harmonics; each successive component; a signal made up of an orderly set of harmonic components that have a precise relationship to each other

Front 28

What two ways can harmonic tones be heard?

Back 28

Holistically- as a single tone with a pitch equal to the spacing between components, or Analytically- as a collection of individual tones

Front 29

The missing Fundamental

Back 29

-removing the fundamental by masking it with a cough for example, doesnt change the pitch
-if cochlear neurons phase lock to the pressure changes in the waveform, then it appears that frequency coding is used to determine pitch

Front 30

Sound localization uses...

Back 30

- both time and intensity difference cues are used

Front 31

HRTF

Back 31

head related transfer function- a 3d dataset that contains all the info about how sound intensity at dif frequencies changes in the ear canal, depending on the angle it comes from

Front 32

Azimuth; elevation

Back 32

horizontal angle around head, vertical angle with respect to head. a sound source with 0 azimuth is straight ahead

Front 33

Diotic vs Dichotic stimulation

Back 33

Diotic stimulation: when the sound is identical at the two ears, such as when the source is directly in front or behind the head (midsagittal location) .
Diotic stimulation has identical sound cues at the two ears because of the OVERALL APPROXIMATE BILATERAL SYMMETRY of our heads.

Dichotic stimulation: at all other locations, the sounds the two ears get will not be identical.

Front 34

Interaural Intensity Differences (IID); head shadow effect

Back 34

sound reaching the farther ear has slightly less intensity than sound reaching the nearer ear, occurs because pressure decreases with distance; the head reflects incoming sounds in a frequency-dependent way. The difference between the two ears is: Much greater with higher frequency sounds. High frequency sounds are reflected more when they interact with head, while low frequency sounds can bend (diffract) around head and continue.

Front 35

Interaural Time Differences (ITDs)

Back 35

-Sounds require extra time to travel to farther ear.
-The path difference of sound transmission to the two ears will depend on the azimuth angle
-ITDs do not change as much with frequency as IIDs.

Front 36

Rotating the head ...

Back 36

will result in increasing the binaural differences if the head is rotated away from the sound source, and decreasing the binaural differences if the head is rotated toward the sound source.

Front 37

Cross-correlation

Back 37

- based on network of binaural neuronsthat need to be activated binaurally at the same time to fire (coincidence detection).
-Therefore, only those neurons with binaural input delay values that match ITD will be stimulated

Front 38

MSO - medial superior olive

Back 38

first place where binaural sound differences are represented in the brain

Front 39

Binaural Masking Level Difference

Back 39

how much less intense a sound can be in the dichotic conditions than in the diotic condition

Front 40

Auditory scene analysis; primitive grouping; schema-driven grouping

Back 40

This is the manner by which auditory processing achieves an effortless segregation of concurrent sounds; a process where similarity in basic acoustic parameters like frequency spectrum similarity, intensity and location are used to segregate the aspects of the sounds that produced by separate sound-producing objects BOTTOM-UP processing; dependent on prior experience with the environment TOP - DOWN processing