Chapter 5- Temporal Processing Flashcards
How does the auditory system respond to modulated stimuli?
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.
How does the BM respond to different sized filters?
Wider filters have less ringing
Narrower filters have more ringing (temporal smearing)
What is the limit of human temporal resolution?
1-3 ms
Why is measuring the temporal resolution a difficult problem?
- Gaps in broadband noise
- Time-reversed broadband signals
- TMTFs
Why should researchers use broadband signals?
Broadband signals have consistent long-term spectrum
What does TMTF stand for?
Temporal Modulation Transfer Function
How does our brain process modulations?
Like a low-pass filter
As frequency increases, performance becomes worse and worse
What happens with non-broadband signals?
In theory, temporal resolution should be poorer at low frequencies than high.
Why should temporal resolution be poorer at low frequencies than high?
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.
Does temporal discrimination follow Weber’s Law? Why?
Yes
Fairly linear response for temporal separation.
Does temporal resolution vary with center frequency of the auditory filters?
Temporal resolution (TR) should be poorer at low frequencies than at high.
TR is limited by the response time of the auditory filters.
List the 2 factors that affect gap detection in bands of noise.
1) BW of the noise
2) CF of noise (dictates the filter you go through)
What are single auditory filter predictions?
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.
Why is the single filter hypothesis incorrect?
Gap thresholds improve with increasing BW
More than 1 auditory filter is used to detect temporal gaps in broadband noise.
What is Moore’s model of temporal resolution?
Stimulus –>
Bandpass filter –> Nonlinear device –>
Temporal integrator –>
Decision device
What is the definition of temporal resolution (acuity)?
Ability to detect changes in stimuli over time
Should NH or HI listeners have better temporal processing skills?
Theoretically, HI listeners should have better temporal processing skills because they have broader filters.
HI listeners have worse temporal processing than expected.
How do you measure a TMTF?
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)
What are gap detection abilities for broadband and narrowband noises?
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
What were the results from the Eddins et al. paper? Why did these results occur?
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
What were the gap detection thresholds for sine tones in different phases?
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
What were the effects of hearing loss on gap detection in tones with different phases?
Effects of Hearing loss
• TMTFs show less non-monotonocities
• More linear
• Performance improves faster
What were the results for the Shannon 1989 study? Why did they occur?
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)
What are duration discrimination experiments? What are some problems with them?
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
What occurs with aging - temporal processing deficits?
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
