91 lines
4.2 KiB
TeX
91 lines
4.2 KiB
TeX
\documentclass[a4paper, 12pt]{article}
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\usepackage{parskip}
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\title{Physiologically inspired model of the grasshopper auditory system}
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\author{Jona Hartling, Jan Benda}
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\date{}
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\begin{document}
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\maketitle{}
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\section{The sensory world of a grasshopper}
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Strong dependence on acoustic signals for ranged communication\\
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- Diverse species-specific sound repertoires and production mechanisms\\
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- Different contexts/ranges: Stridulatory, mandibular, wings, walking sounds\\
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- Mate attraction/evaluation, rival deterrence, loss-of-signal predator alarm\\
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$\rightarrow$ Elaborate acoustic behaviors co-depend on reliable auditory perception
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Songs = Amplitude-modulated (AM) broad-band acoustic signals\\
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- Generated by stridulatory movement of hindlegs against forewings\\
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- Shorter time scales: Characteristic temporal waveform pattern\\
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- Longer time scales: High degree of periodicity (pattern repetition)\\
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- Sound propagation: Signal intensity varies strongly with distance to sender\\
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- Ectothermy: Temporal structure warps with temperature\\
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$\rightarrow$ Sensory constraints imposed by properties of the acoustic signal itself
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Multi-species, multi-individual communally inhabited environments\\
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- Temporal overlap: Simultaneous singing across individuals/species common\\
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- Frequency overlap: No/hardly any niche speciation into frequency bands\\
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- "Biotic noise": Hetero-/conspecifics ("Another one's songs are my noise")\\
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- "Abiotic noise": Wind, water, vegetation, anthropogenic\\
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- Effects of habitat structure on sound propagation (landscape - soundscape)\\
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$\rightarrow$ Sensory constraints imposed by the (acoustic) environment
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Cluster of auditory challenges (interlocking constraints $\rightarrow$ tight coupling):\\
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From continuous acoustic input, generate neuronal representations that...\\
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1)...allow for the separation of relevant (song) events from ambient noise floor\\
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2)...compensate for behaviorally non-informative song variability (invariances)\\
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3)...carry sufficient information to characterize different song patterns,
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recognize the ones produced by conspecifics, and make appropriate behavioral
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decisions based on context (sender identity, song type, mate/rival quality)
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How can the auditory system of grasshoppers meet these challenges?\\
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- What are the minimum functional processing steps required?\\
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- Which known neuronal mechanisms can implement these steps?\\
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- Which and how many stages along the auditory pathway contribute?\\
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$\rightarrow$ What are the limitations of the system as a whole?
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How can a human observer conceive a grasshopper's auditory percepts?\\
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- How to investigate the workings of the auditory pathway as a whole?\\
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- How to systematically test effects and interactions of processing parameters?\\
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- How to integrate the available knowledge on anatomy, physiology, ethology?\\
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$\rightarrow$ Abstract, simplify, formalize $\rightarrow$ Functional model framework
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\section{Pre-split pathway: Population pre-processing}
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Filtering of behaviorally relevant frequencies by tympanal membrane\\
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- Bandpass 5-30 kHz
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Extraction of signal envelope (AM encoding) by receptor population\\
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- Full-wave rectification + lowpass 500 Hz
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Logarithmically compressed intensity tuning curve of receptors\\
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- Decibel transformation
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Spike-frequency adaptation in receptor and interneuron populations\\
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- Highpass 10 Hz
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\section{Post-split pathway: Feature extraction}
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Template matching by individual ascending neurons\\
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- Separate convolution with each of a set of Gabor kernels\\
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- Pathway splitting: Single population response into several separate branches
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- Expansion into a higher-dimensional sound representation
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Thresholding nonlinearity in ascending neurons (or further downstream)\\
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- Step-function (or sigmoid) threshold\\
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- Binarization of response values into "relevant" vs. "irrelevant"
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Temporal averaging by neurons of the central brain\\
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- Lowpass 1 Hz\\
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- Finalized set of slowly changing kernel-specific features\\
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- Different (species-specific) songs are characterized by a distinct combination of feature values
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\section{Pre-split intensity invariance:\\Logarithm-highpass mechanism}
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\section{Post-split intensity invariance:\\Threshold-lowpass mechanism}
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\section{Conclusion and outlook}
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\end{document} |