2009/5/16 HST.723J Theme 7 Presentation
2009/5/16 HST.723J Theme 7 Presentation
Introduction• Accurate neural coding of the pitch of complex
sounds is an essential part of auditory scene analysis
• Differences in pitch help segregate concurrent sounds, while similarities in pitch can help group sounds from a common source.
• In quiet, nonreverberant backgrounds, pitch can be derived from timing information in broadband high-frequency auditory channels and/or from frequency and timing information carried in narrowband low-frequency auditory channels.
2009/5/16 HST.723J Theme 7 Presentation
f0
Repetition rate=f0
Courtesy of Dr. Bendor
How does the auditory system compute pitch?
2009/5/16 HST.723J Theme 7 Presentation
Cochlear Filtering, Temporal Fine Structure, & Temporal-Envelope Modulation
Resolved: low number of harmonics will each pass through a different filter
Unresolved: in high frequency area each filter pass several harmonics
Temporal mechanism: rely on “phase-locking”
Spectral mechanism:rely on resolved harmonics in orderto determine the frequency composition of the sound.
Harmonic-related
2009/5/16 HST.723J Theme 7 Presentation
Natural pitch-evoking sounds vs artificial ones
1. Dynamic pitch
2. Usually heard in reverberant environments: (eg. when listening to an actor on stage in a theater)
2009/5/16 HST.723J Theme 7 Presentation
Materials and methods
Recording the responses of VCN neurons of anesthetized guinea pigs
To harmonic complex tones With time-varying F0s (F0-swept harmonic
complexes) Under a range of real-room reverberation
conditions With varying reverberation strength
2009/5/16 HST.723J Theme 7 Presentation
Complex Stimuli
200–400 Hz F0-swept harmoniccomplex tones
2009/5/16 HST.723J Theme 7 Presentation
Outline
1. Neuronal Responses to Dynamic PitchStimuli with Added Reverberation
2. The Effect of Harmonic Resolution3. The Effect of Phase-Locking Ability4. Pitch-Related Temporal-Envelope Cues
Are More Degraded than Fine-Structure Cues in Reverberant Spaces
5. Influence of F0 Sweep Rate
2009/5/16 HST.723J Theme 7 Presentation
1. Neuronal Responses to Dynamic Pitch Stimuli with Added Reverberation
2. The Effect of Harmonic Resolution3. The Effect of Phase-Locking Ability4. Pitch-Related Temporal-Envelope Cues
Are More Degraded than Fine-Structure Cues in Reverberant Spaces
5. Influence of F0 Sweep Rate
2009/5/16 HST.723J Theme 7 Presentation
Responses to F0-Swept Harmonic Complex from Pri-like Unit & Low-Freq. Unit
autocorrelogram
2009/5/16 HST.723J Theme 7 Presentation
Short Summary
• Both units can reliably represent the dynamic pitch in the absence of reverberation.
• Adding strong reverberation results in a dramatic reduction in the pitch-related response of the high-BF primary-like unit
• The effects of reverberation on single unit pitch-related responses seems to depend mainly on unit’s BF
2009/5/16 HST.723J Theme 7 Presentation
1. Neuronal Responses to Dynamic Pitch Stimuli with Added Reverberation
2. The Effect of Harmonic Resolution3. The Effect of Phase-Locking Ability4. Pitch-Related Temporal-Envelope Cues
Are More Degraded than Fine-Structure Cues in Reverberant Spaces
5. Influence of F0 Sweep Rate
2009/5/16 HST.723J Theme 7 Presentation
Temporal Representations of Responses: Unresolved vs Resolved
Short Summary:Harmonic resolution is at least one important factor in determining the effect of reverb on the ability to represent the pitch of harmonic complex sounds in the temporal pattern of AP discharge.
2009/5/16 HST.723J Theme 7 Presentation
Fine-Structure vsEnvelope-Modulation Spectra
2009/5/16 HST.723J Theme 7 Presentation
Spectral Representations of Responses: Unresolved vs Resolved
the only cue to pitch is the noisy fine structurearound BF
No modulation band
Pitch of the unresolved stimulus relies more on AP locked to the fine structure & less on AP locked to the temporal-envelope modulation
the effect of increasing reverberation strength isto smear the frequency-domain representation over time
2009/5/16 HST.723J Theme 7 Presentation
Effects of F0• peak reduced in amplitude
(due to the reduced envelope-modulation) & shifted to a longer period reflecting the smeared temporal fine structure arising from the addition of indirect sound components.
• the effect of increasing reverb strength is to smear the frequency-domain representation over time
F0 significant effects of harmonic resolvability and reverberation strength on the position of peak, which reflects the smearing of the fine structure through time
2009/5/16 HST.723J Theme 7 Presentation
1. Neuronal Responses to Dynamic Pitch Stimuli with Added Reverberation
2. The Effect of Harmonic Resolution3. The Effect of Phase-Locking Ability4. Pitch-Related Temporal-Envelope Cues
Are More Degraded than Fine-Structure Cues in Reverberant Spaces
5. Influence of F0 Sweep Rate
2009/5/16 HST.723J Theme 7 Presentation
Population Data in Response to200–400 Hz F0-Swept Harmonic Complexes
Summary: under reverb listening condition the temporal representation of pitch in the central auditory system relies on the responses of neuronstuned within the range phase-locking
Phase lock at 3.5k Hz Phase lock 1.5 K Hz
Correlation index decreases with increasing reverberation, not significantly greater than 1 at 3.5k & 1.5k respectively
2009/5/16 HST.723J Theme 7 Presentation
1. Neuronal Responses to Dynamic Pitch Stimuli with Added Reverberation
2. The Effect of Harmonic Resolution3. The Effect of Phase-Locking Ability4. Pitch-Related Temporal-Envelope Cues
Are More Degraded than Fine-Structure Cues in Reverberant Spaces
5. Influence of F0 Sweep Rate
2009/5/16 HST.723J Theme 7 Presentation
Fine-Structure vsEnvelope-Modulation Spectra
2009/5/16 HST.723J Theme 7 Presentation
Fine-Structure vsEnvelope-Modulation Spectra
Phase lock at 3.5K Hz
Phase lock at 1.5K Hz
Temporal band
Fine structure band (preserved at early stage)
N= 56
N=72
2009/5/16 HST.723J Theme 7 Presentation
Short Summary
• Temporal cues degraded more • Fine structure preserved in the responses
of neurons at this early stage of central auditory processing likely contributes to the increase in errors
when attempting to track a sound’s pitch over time in a reverberant environment against a complex background of other pitch-evoking sounds
2009/5/16 HST.723J Theme 7 Presentation
1. Neuronal Responses to Dynamic Pitch Stimuli with Added Reverberation
2. The Effect of Harmonic Resolution3. The Effect of Phase-Locking Ability4. Pitch-Related Temporal-Envelope Cues
Are More Degraded than Fine-Structure Cues in Reverberant Spaces
5. Influence of F0 Sweep Rate
2009/5/16 HST.723J Theme 7 Presentation
The effect of F0 Sweep rate
Summary: rapidly varying F0 and reverbsignificantly diminish the magnitude and increase the smearing of the temporal representation of pitch
BF 1.35K Hz
Lose of env-mod rx
Fine structure blurred
2009/5/16 HST.723J Theme 7 Presentation
Summary• Recording from VCN of anesthetized guinea pigs showed
that neural representation of pitch based on temporal information is severely degraded in the presence of reverb, and degradation increases with increasing reverb strength.
• In a parallel human psychophysical study, when restricted to using envelope-modulation cues in high-frequency channels under reverb. conditions, human listeners demonstrated a dramatically reduced ability to discriminate pitch-evoking sounds from noise.(supplement)
• Together, these findings explain the origin of perceptual difficulties experienced by both normal-hearing and hearing-impaired listeners in reverberant spaces.