The Bifurcating Neuron (BN), a chaotic integrate-and-fire neuron, is a model of a neuron augmented by coherent modulation from its environment. The BN is mathematically equivalent to the sine-circle map. and this equi...
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The Bifurcating Neuron (BN), a chaotic integrate-and-fire neuron, is a model of a neuron augmented by coherent modulation from its environment. The BN is mathematically equivalent to the sine-circle map. and this equivalence relationship allowed us to apply the mathematics of one-dimensional maps to the design of a BN network. The study of the bifurcating diagram of the BN revealed that the BN, under a suitable condition, can function as an amplitude-to-phase converter. Also. being an integrate-and-fire neuron, it has an inherent capability to function as a coincidence detector. These two observations led us to the design of the BN Network 2 (BNN-2), a pulse-coupled neural network that exhibits associative memory of multiple analog patterns. In addition to the usual dynamical proper-ties as an associative memory, the BNN-2 was shown to exhibit volume-holographic memory: it switches to different pages of its memory space as the frequency of the coherent modulation changes, meaning context-sensitive memory. (C) 2002 Elsevier Science Ltd. All rights reserved.
The Bifurcating Neuron (BN), a chaotic integrate-and-fire neuron, is a model of a neuron augmented by coherent modulation from its environment. The BN is mathematically equivalent to the sine-circle map, and this equi...
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The Bifurcating Neuron (BN), a chaotic integrate-and-fire neuron, is a model of a neuron augmented by coherent modulation from its environment. The BN is mathematically equivalent to the sine-circle map, and this equivalence relationship allowed us to apply the mathematics of one-dimensional maps to the design of BN networks. The study of symmetry in the BN revealed that the BN can be configured to exhibit bistability that is controlled by attractor-merging crisis. Also, the symmetry of the bistability can be controlled by the introduction of a sinusoidal fluctuation to the threshold level of the BN. These two observations led us to the design of the BN Network 1 (BNN-1), a chaotic pulse-coupled neural network exhibiting associative memory. In numerical simulations, the BNN-1 showed a better performance than the continuous-time Hopfield network, as far as the spurious-minima problem is concerned and exhibited many biologically plausible characteristics. (C) 2001 Elsevier Science Ltd. All rights reserved.
Weakly electric fish can detect nearby objects and analyse their electric properties during active electrolocation. Four individuals of the South American gymnotiform fish Eigenmannia sp., which emits a continuous wav...
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Weakly electric fish can detect nearby objects and analyse their electric properties during active electrolocation. Four individuals of the South American gymnotiform fish Eigenmannia sp., which emits a continuous wave-type electric signal, were tested for their ability to detect capacitive properties of objects and discriminate them from resistive properties. For individual fish, capacitive values of objects had to be greater than 0.22-1.7 nF ('lower threshold') and smaller than 120-680 nF ('upper threshold') in order to be detected. The capacitive values of natural objects fall well within this detection range. All fish trained could discriminate unequivocally between capacitive and resistive object properties. Thus, fish perceive capacitive properties as a separate object quality. The effects of different types of objects on the locally occurring electric signals which stimulate electroreceptors during electrolocation were examined. Purely resistive objects altered mainly local electric organ discharge (EOD) amplitude, but capacitive objects with values between about 0.5 and 600 nF changed the timing of certain EOD parameters (phase-shift) and EOD waveform. A mechanism for capacitance detection in wave-type electric fish based on time measurements is proposed and compared with the capacitance detection mechanism in mormyrid pulse-type fish, which is based on waveform measurements.
Electroreceptive afferents from A- and B-electroreceptor cells of mormyromasts and Knollenorgans were tested for their sensitivity to different stimulus waveforms in the weakly electric fish Gnathonemus petersii . Bot...
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Electroreceptive afferents from A- and B-electroreceptor cells of mormyromasts and Knollenorgans were tested for their sensitivity to different stimulus waveforms in the weakly electric fish Gnathonemus petersii . Both A- and B-mormyromast cells had their lowest sensitivity to a waveform similar to the self-generated electric organ discharge (EOD) (around 0 degrees phase-shift). Highest sensitivities, i.e. lowest response thresholds, in both A- and B-cells were measured at phase shifts of + 135 degrees. Thus, both cell types were inversely waveform tuned. The sensitivity of B-cells increased sharply with increasing waveform distortions. Their tuning curves had a sharp minimum of sensitivity at + 7 degrees phase shift. A-cells had a much broader waveform tuning with a plateau level of low sensitivity from + 24 degrees to -15 degrees. Across a 360 degrees cycle of phase-shifts, the range of thresholds was 16 dB for individual B-cells and 4.5 dB for individual A-cells. Knollenorgan afferents were tuned to 0 degrees phase-shifted EODs and had a dynamic range of 12 dB. Lowest sensitivities were measured at a phase shift of + 165 degrees. Experiments with computer-generated stimuli revealed that the strong sensitivity of mormyromast B-cells of EOD waveform distortions cannot be attributed to any of the seven waveform parameters tested. In addition, EOD stimuli must have the correct duration for B-cells to respond to waveform distortions. Thus, waveform tuning appears to be based on the specific combination of several waveform parameters that occur only with natural EODs.
coding of amplitude modulated acoustic stimuli was studied within isofrequency planes of the tonotopically organized field L, the avian analogue of the mammalian auditory cortex. The synchronization of unit responses ...
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coding of amplitude modulated acoustic stimuli was studied within isofrequency planes of the tonotopically organized field L, the avian analogue of the mammalian auditory cortex. The synchronization of unit responses to envelopes of sinusoidally amplitude modulated tones (AM) and repetitive noise bursts (RN) were determined as a function of envelope frequency (EF). From 249 synchronizing units, 66% were tuned to a best envelope frequency (BEF) using a synchronization criterion. BEFs varied from 0.3 to 380 Hz and showed an orderly representation within isofrequency planes orthogonal to the lamination of field L. The majority (68%) of these units had BEFs below 20 Hz down to 0.3 Hz. Thus, they were tuned to rhythms typical for animal communication sounds, speech, and music. Thirty-two % had BEFs between 20 Hz and 380 Hz and covered at least 4 of 5 octaves of the range of periodicity pitch sensation.
Evidence for and against classical theories of ‘place’ and ‘period’ mechanisms for the coding of frequency, and the modifications of the theories invoked to account for the pitch of ‘residue’ and other types of ...
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Evidence for and against classical theories of ‘place’ and ‘period’ mechanisms for the coding of frequency, and the modifications of the theories invoked to account for the pitch of ‘residue’ and other types of stimuli, are examined in the light of physiological data. These include new data on the temporal discharge patterns of cochlear nerve fibres under stimulation with two-tone complexes, harmonic and inharmonic three-tone complexes, and five-tone complexes of differing relative phase. They show, in particular, that certain arguments against ‘period’ coding of ‘residue’ pitch are invalid. The interspike intervals in the discharge patterns of cochlear fibres under these conditions are consistent with the pitches heard. On the other hand, the classical ‘period’ theory needs to be modified to take into account the normally relatively sharp frequency selectivity of cochlear fibres, and requires certain inefficiencies on the part of the central processor for *** of measures of cochlear fibre frequency selectivity with analogous psychophysical data in man, including those on the ‘existence region’ of ‘residue’ pitch, suggests that ‘residue’-type stimuli judged to be tonal in quality could both: (a) be sufficiently resolved spectrally at the cochlear fibre level to serve as input to any of the current spectral ‘pattern recognition’ mechanisms proposed for the pitch extraction of complex signals, and also, (b) could generate patterns of temporal discharge reflecting enough waveform interaction between the harmonics to convey the pitch heard, because of the shape of the cochlear filters. (This conclusion might have to be qualified in the light of further physiological experiments on the ‘second effect’ of pitch shift.)The present evidence, both psychophysical and physiological, suggests the following synthesis: musical interval recognition and relatively crude frequency discrimination can be accomplished by trained observers on signals where the frequency app
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