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Is overshoot caused by an efferent reduction in cochlear gain?
Mark Fletcher1, Jessica de Boer, Katrin Krumbholz
1Institute of Hearing Research, MRC, University Park, NG7 2RD, Nottingham, UK. markf@ihr.mrc.ac.uk
Advances in Experimental Medicine and Biology
|May 30, 2013
Summary
Temporal effects, or overshoot, improve tone detection with a precursor sound. This study found that overshoot requires suppressive masking and is not mediated by the medial olivocochlear bundle, challenging the gain reduction model.
Area of Science:
- Auditory Neuroscience
- Psychoacoustics
- Sensory Physiology
Background:
- Auditory masking involves the elevation of a tone's detection threshold by a masker.
- Temporal effects, such as overshoot, describe improved tone detection due to a preceding sound.
- The gain reduction model, involving the medial olivocochlear (MOC) bundle, is a leading explanation for overshoot.
Purpose of the Study:
- To investigate the masking types (suppressive vs. excitatory) contributing to overshoot.
- To test the gain reduction model's predictions regarding MOC-mediated gain reduction.
- To directly assess the effect of precursors on cochlear suppression.
Main Methods:
- Two experiments were conducted using a 4-kHz tone pip signal.
- Experiment 1: Masking and precursor energy was either on-frequency or off-frequency to isolate suppressive vs. excitatory masking.
- Experiment 2: Forward-masking measured suppression of a 4-kHz tone by a 4.75-kHz suppressor, with and without a precursor.
Main Results:
- Significant overshoot was observed only with off-frequency masking, suggesting a requirement for suppressive masking.
- No reduction in cochlear suppression was found when a precursor was present, despite large suppression and overshoot.
- These findings contradict the gain reduction model's predictions.
Conclusions:
- Measurable overshoot necessitates off-frequency masking.
- Off-frequency overshoot is likely mediated by a mechanism distinct from MOC-mediated gain reduction.
- The gain reduction model does not fully explain the observed temporal effects in auditory masking.
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