Chapter 5- Temporal Processing

Question 1

How does the auditory system respond to modulated stimuli?

Answer 1

Some IC neurons respond better (synchrony and average firing rate) to AM tomes

Respond to modulation frequencies up to 1000 Hz, although tend to drop after 100-200 Hz

There are neurons that are tuned specifically to different modulations.

Question 2

How does the BM respond to different sized filters?

Answer 2

Wider filters have less ringing

Narrower filters have more ringing (temporal smearing)

Question 3

What is the limit of human temporal resolution?

Answer 3

1-3 ms

Question 4

Why is measuring the temporal resolution a difficult problem?

Answer 4

• Gaps in broadband noise
• Time-reversed broadband signals
• TMTFs

Question 5

Why should researchers use broadband signals?

Answer 5

Broadband signals have consistent long-term spectrum

Question 6

What does TMTF stand for?

Answer 6

Temporal Modulation Transfer Function

Question 7

How does our brain process modulations?

Answer 7

Like a low-pass filter

As frequency increases, performance becomes worse and worse

Question 8

What happens with non-broadband signals?

Answer 8

In theory, temporal resolution should be poorer at low frequencies than high.

Question 9

Why should temporal resolution be poorer at low frequencies than high?

Answer 9

Low frequencies filters have narrower filters resulting in more ringing.

Ringing will fill in the gaps for the temporal characteristics that we want to detect.

Question 10

Does temporal discrimination follow Weber’s Law? Why?

Answer 10

Yes

Fairly linear response for temporal separation.

Question 11

Does temporal resolution vary with center frequency of the auditory filters?

Answer 11

Temporal resolution (TR) should be poorer at low frequencies than at high.

TR is limited by the response time of the auditory filters.

Question 12

List the 2 factors that affect gap detection in bands of noise.

Answer 12

1) BW of the noise

2) CF of noise (dictates the filter you go through)

Question 13

What are single auditory filter predictions?

Answer 13

Gap thresholds should improve with increasing noise BW, but only when the noise BW is less than the BW of the widest auditory filter stimulated by the noise.

Increases in noise BW should not result in improvements in gap threshold.

Question 14

Why is the single filter hypothesis incorrect?

Answer 14

Gap thresholds improve with increasing BW

More than 1 auditory filter is used to detect temporal gaps in broadband noise.

Question 15

What is Moore’s model of temporal resolution?

Answer 15

Stimulus –>
Bandpass filter –> Nonlinear device –>
Temporal integrator –>
Decision device

Question 16

What is the definition of temporal resolution (acuity)?

Answer 16

Ability to detect changes in stimuli over time

Question 17

Should NH or HI listeners have better temporal processing skills?

Answer 17

Theoretically, HI listeners should have better temporal processing skills because they have broader filters.

HI listeners have worse temporal processing than expected.

Question 18

How do you measure a TMTF?

Answer 18

Measure if listener can detect which complex stimulus has a “modulation” in the amplitude.

• Measure the m (modulation depth) at which a person can detect the modulation
• Modulation depth measured by % (none m=0; total m=1)

Question 19

What are gap detection abilities for broadband and narrowband noises?

Answer 19

Noise BW< Filter BW= temporal pattern of noise is not changed by auditory filter
• Gap threshold depends on confusion between the gap and changes in noise
• Narrow bandwidths lead to slower fluctuations, which results in larger gap thresholds
• A little bit of smearing
• Gap threshold is expected to decrease with increasing noise BW

Noise BW> Filter BW= temporal pattern of noise is changed by auditory filter
• Fluctuations are slower in the output than with the input of noise
• Filter BW affects performance (not noise BW)
• Eliminated a lot of energy, filtered down to a 130 Hz and this will result in slower modulations through the auditory filter

Question 20

What were the results from the Eddins et al. paper? Why did these results occur?

Answer 20

Single filter hypothesis is incorrect; gap thresholds improve with increasing BW

Why did these results occur?
• Gap thresholds improve (decrease) w/ increasing noise BW, even when the BW is much greater than the BW of any single auditory filter that is excited by the noise
• Subjects make use of more than 1 auditory filter to detect temporal gaps in broadband noise
• Comparing outputs of many auditory filters reduces the confusion between fluctuations in the noise and the actual temporal gap

Question 21

What were the gap detection thresholds for sine tones in different phases?

Answer 21

Standard phase: sine starts at positive-going zero-crossing (phase continues where it left off before the gap)
• Nonmonotonic function
• Gap was difficult to detect when its duration was an integer multiple of the period of the signal (2.5 and 5 ms)

Reverse phase: sine starts at negative-going zero-crossing
• Nonmontonic function
• Poor performance when gap duration was (n+0.5)P, where n=0 or 1
• Good performance when gap duration was nP

Preserved phase: sine starts at the phase it would have had without interruption
• Performance improved monotonically with increasing gap duration

Question 22

What were the effects of hearing loss on gap detection in tones with different phases?

Answer 22

Effects of Hearing loss
• TMTFs show less non-monotonocities
• More linear
• Performance improves faster

Question 23

What were the results for the Shannon 1989 study? Why did they occur?

Answer 23

Results
• Thresholds were between 1-3 ms (similar to acoustic hearing)

Why did these results occur?
• When electrodes were stimulated at different ends of the arrays, the gap detections become shorter
• No traveling wave with CIs
• Bypass the neural delay caused by acoustic hearing (traveling wave moving down BM to lower frequencies)

Question 24

What are duration discrimination experiments? What are some problems with them?

Answer 24

Change the duration of the 2 tones or keep the duration of the 2 tones the same and vary the time between them

Problems with experiment:
• Possible loudness and spectral confounds
• Spectral confounds result in additional sidebands if the tone duration is short

Question 25

What occurs with aging - temporal processing deficits?

Answer 25

Age and hearing loss affect temporal processing.

Problems with previous studies: didn’t take age into consideration
• Gordon-Salant et al. (2006) found that older people required increased temporal cues for word contrast discrimination than did younger people (OHI did even worse)

Older people perform worse with spectrally-degraded stimuli which force them to attend to temporal cues