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  Chapter 4 of Moore (1997)

Temporal Processing (II)

Scope

• Introduction to Modeling : A Generic Model of Early Auditory Processing
• Some Examples: What Can and Cannot be Learned from Modeling Results
• Modulation Filter Bank: Parallels Bee's Study on Second-order Edge Detectors
• Duration Discrimination
• Across-channel Analysis

A Generic Model of Early Auditory Processing

• Bandpass Filter: Simulating auditory filters.
• Nonlinear Device: Taking out the negative signs.
• Temporal Integrator: Smoothing out bumpy variations while keeping the slow-changing signals.
• Decision Device: Mapping the (neural) outputs to an overt response (such as Yes/No).

Examples

• Implementation I: Nonlinear device = a half-wave rectifier; Temporal integrator = a lowpass filter. Mostly found in the context of studying TMTF.
• Implementation II: Nonlinear device = Squaring nonlinearity; Temporal integrator = a sliding time window.
• Decision Device: thresholding; Variance; Max/min ratio in an observation window; Dip detection (Fig.4.9)

Can's & Can'ts

• One can learn what are usually being taken care of at the auditory periphery and what should be left as a job for the central system.
• It can be said with some confidence that the temporal integration part is the most critical stage in determining temporal resolution.
• It has been shown that the TI has tapering tails. Its width increases at low temporal frequencies and low sound levels.
• A second nonlinearity for mapping neural activities and the response might be needed to account for "excess masking".
• One cannot easily tell what is THE way of implementing a given stage.

Evidence for Modulation Filter Bank

• Masking in the modulation domain: Fig. 4.10.
• Band-widening experiment: Fig. 4.11.
• Narrow-band carrier data: Modulation detection is worse when the modulation fequency falls within the spectral range of the carrier's inherent fluctuations.
• Modulation with a missing-fundamental profile: It is the energy in the modulation spectrum that counts, not the periodicity of modulation.
• Modulation detection interference (MDI): An AM can be masked by another AM or FM, but will not be affected by an unmodulated carrier. MDI is quite independent of the carrier freq, which remains at odds with physiological data.

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