Mathias Dietz
Research interests
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InterestsAuditory System, Psychoacoustics, Animal Physiology, Human Physiology
Publications
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1.52Impact points
Lateralization based on interaural differences in the second-order amplitude modulator.
The Journal of the Acoustical Society of America. 01/2012; 131(1):398-408.
Second-order amplitude modulation is a relatively slow variation of the modulation depth of a first-order amplitude modulation with higher frequency. In contrast to first-order modulation, which appears as a physical component in the stimulus spectrum after half-wave rectification, second-order modu... [more] Second-order amplitude modulation is a relatively slow variation of the modulation depth of a first-order amplitude modulation with higher frequency. In contrast to first-order modulation, which appears as a physical component in the stimulus spectrum after half-wave rectification, second-order modulation is not necessarily demodulated by the auditory periphery. For binaural processing of second-order amplitude modulated stimuli it is unknown whether interaural time differences (ITDs) in the second-order modulation result in a lateralized percept. Thus, second-order modulation can serve as a tool to investigate whether demodulation of interaurally delayed components is a prerequisite for lateralization. In most of the psychoacoustic experiments presented here, a 25 Hz sinusoidally amplitude-modulated (SAM) 160 Hz tone was either transposed to 4 kHz by half-wave rectifying this SAM waveform before multiplication with a 4 kHz tone (TSAM), or by adding an offset before multiplication (SAMAM). The experiments revealed an inability to lateralize the SAMAM based on ITDs in the 25 Hz component, whereas subjects could lateralize the TSAM. Given that only the TSAM results in a demodulated 25 Hz component after peripheral auditory processing, this result supports the hypothesis that demodulation is a prerequisite for lateralization, which has consequences for temporal modulation processing in models of binaural interaction.
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1.52Impact points
The influence of different segments of the ongoing envelope on sensitivity to interaural time delays.
The Journal of the Acoustical Society of America. 06/2011; 129(6):3856-72.
The auditory system is sensitive to interaural timing disparities in the fine structure and the envelope of sounds, each contributing important cues for lateralization. In this study, psychophysical measurements were conducted with customized envelope waveforms in order to investigate the isolated e... [more] The auditory system is sensitive to interaural timing disparities in the fine structure and the envelope of sounds, each contributing important cues for lateralization. In this study, psychophysical measurements were conducted with customized envelope waveforms in order to investigate the isolated effect of different segments of a periodic, ongoing envelope on lateralization. One envelope cycle was composed of the four segments attack flank, hold duration, decay flank, and pause duration, which were independently varied to customize the envelope waveform. The envelope waveforms were applied to a 4-kHz sinusoidal carrier, and just noticeable envelope interaural time differences were measured in six normal hearing subjects. The results indicate that attack durations and pause durations prior to the attack are the most important stimulus characteristics for processing envelope timing disparities. The results were compared to predictions of three binaural lateralization models based on the normalized cross correlation coefficient. Two of the models included an additional stage to mimic neural adaptation prior to binaural interaction, involving either a single short time constant (5 ms) or a combination of five time constants up to 500 ms. It was shown that the model with the single short time constant accounted best for the data.
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Auditory model based direction estimation of concurrent speakers from binaural signals.
Speech Communication. 01/2011; 53:592-605.
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1.52Impact points
Model-based direction estimation of concurrent speakers in the horizontal plane.
The Journal of the Acoustical Society of America. 05/2009; 125(4):2527.
A computational auditory model for the direction estimation of concurrent speakers in the horizontal plane is presented. The auditory signal processing is motivated by mammalian physiology and human psychoacoustic data, extending the binaural model by Dietz et al. [Brain Res., 1220, 234-245 (2008)].... [more] A computational auditory model for the direction estimation of concurrent speakers in the horizontal plane is presented. The auditory signal processing is motivated by mammalian physiology and human psychoacoustic data, extending the binaural model by Dietz et al. [Brain Res., 1220, 234-245 (2008)]. The model exploits a wide range of interaural parameters, namely, the interaural level difference, the interaural phase difference of the fine structure, and the interaural coherence. The parameters are determined at the output of auditory filters allowing for a simultaneous estimation of several sound source directions in a multidimensional internal representation. By focusing on time segments with high interaural coherence [Faller and Merimaa, J. Acoust. Soc. Am. 116, 3075-3089 (2004)] in the auditory bands, which likely stem from a localized sound source, the robustness of the direction estimation of the model was considerably improved: for two well-separated speakers in quiet, the estimation error is generally less than or equal to 10 deg. In noisy environments, the direction of a single speaker can be estimated for signal-to-noise ratios below 0 dB. Further improvements of the model by concurrent pitch estimation to reduce permutation errors between nearby speakers are investigated and discussed.
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1.52Impact points
Lateralization of stimuli with independent fine-structure and envelope-based temporal disparities.
The Journal of the Acoustical Society of America. 04/2009; 125(3):1622-35.
Psychoacoustic experiments were conducted to investigate the role and interaction of fine-structure and envelope-based interaural temporal disparities. A computational model for the lateralization of binaural stimuli, motivated by recent physiological findings, is suggested and evaluated against the... [more] Psychoacoustic experiments were conducted to investigate the role and interaction of fine-structure and envelope-based interaural temporal disparities. A computational model for the lateralization of binaural stimuli, motivated by recent physiological findings, is suggested and evaluated against the psychoacoustic data. The model is based on the independent extraction of the interaural phase difference (IPD) from the stimulus fine-structure and envelope. Sinusoidally amplitude-modulated 1-kHz tones were used in the experiments. The lateralization from either carrier (fine-structure) or modulator (envelope) IPD was matched with an interaural level difference, revealing a nearly linear dependence for both IPD types up to 135 degrees , independent of the modulation frequency. However, if a carrier IPD was traded with an opposed modulator IPD to produce a centered sound image, a carrier IPD of 45 degrees required the largest opposed modulator IPD. The data could be modeled assuming a population of binaural neurons with a physiological distribution of the best IPDs clustered around 45 degrees -50 degrees . The model was also used to predict the perceived lateralization of previously published data. Subject-dependent differences in the perceptual salience of fine-structure and envelope cues, also reported previously, could be modeled by individual weighting coefficients for the two cues.
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3.06Impact points
Overloaded phase-code multiplexing for volume holographic storage.
Optics letters. 07/2008; 33(11):1252-4.
Overloaded phase codes for volume holographic data storage are introduced. In contrast to any previous phase-code design, overloaded phase codes enable multiplexing of a number of data pages that exceeds the number of utilized reference beams. In this way the achievable data capacity can be augmente... [more] Overloaded phase codes for volume holographic data storage are introduced. In contrast to any previous phase-code design, overloaded phase codes enable multiplexing of a number of data pages that exceeds the number of utilized reference beams. In this way the achievable data capacity can be augmented. Overloaded codes are generated by extending multilevel phase codes based on the discrete Fourier transform. We demonstrate multiplexing of 70 analog pages by means of 64 reference beams. The analysis of reconstructed digital data pages suggests that a capacity gain of up to 15% is reasonable.
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1.52Impact points
Lateralization of binaural stimuli with independent fine-structure and envelope-based temporal disparities.
The Journal of the Acoustical Society of America. 06/2008; 123(5):3296.
A computational model for the lateralization of binaural stimuli, motivated by recent physiological findings in the literature and psychoacoustic data is presented. The model is based on the evaluation of the interaural phase difference (IPD). In the model, IPDs are separately assessed for the stimu... [more] A computational model for the lateralization of binaural stimuli, motivated by recent physiological findings in the literature and psychoacoustic data is presented. The model is based on the evaluation of the interaural phase difference (IPD). In the model, IPDs are separately assessed for the stimulus' fine-structure and envelope. Psychoacoustic measurements were conducted and compared to model predictions. Sinusoidally amplitude modulated 1-kHz tones with a modulation frequency of 25, 50, and 100 Hz were employed. The IPD of the fine-structure and the envelope IPD were independently matched with an interaural level difference or were traded against each other. Lateralization increased for increasing IPDs up to 135 degrees of either the fine-structure or envelope independent of the modulation frequency. However, trading a fine-structure IPD with an opposing envelope IPD revealed a most persistent fine-structure IPD at 45 degrees . The data could be modeled assuming a physiological distribution of the best IPDs of binaural neurons clustered around 45 degrees . The model was also utilized to correctly predict the perceived lateralization of critical stimuli from literature. Individual differences in the perceptual salience of envelope and fine-structure cues, also known from the literature, could be modeled by a personal weighting coefficient for the fine-structure cue.
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2.46Impact points
Coding of temporally fluctuating interaural timing disparities in a binaural processing model based on phase differences.
Brain research. 10/2007;
A model of the effective processing of interaural timing disparities in the human auditory system is presented which provides modifications and extensions to existing models motivated by recent physiological findings. In particular, an established model of excitatory-inhibitory (EI) neuronal connect... [more] A model of the effective processing of interaural timing disparities in the human auditory system is presented which provides modifications and extensions to existing models motivated by recent physiological findings. In particular, an established model of excitatory-inhibitory (EI) neuronal connectivity is complemented by a model that is based on a rate code derived from the interaural phase difference (IPD). The IPD model is shown to successfully simulate literature data on fine structure and envelope-based binaural detection and lateralization experiments. In order to investigate the processing of temporal fluctuations of interaural timing disparities, detection thresholds of broadband binaural-beat stimuli were measured in six normal-hearing listeners and were compared with model simulations. In a first experiment, the highest detectable beat frequency was found to be 96 Hz for a noise bandwidth of 550 Hz and 219 Hz for a bandwidth of 1100 Hz. Both models predicted lower thresholds, but performed increasingly better when the integration time constants of the binaural processors were reduced. In a second experiment, the signal-to-noise ratio at the detection threshold of binaural-beat stimuli mixed with interaurally uncorrelated noise was measured as a function of the beat frequency. The threshold increased about 1.7 dB per octave which was simulated similarly by both models. The results indicate that the primary temporal resolution of the binaural system for detecting interaural timing disparities is much higher than the temporal resolution found in higher auditory processes as supposedly involved in, e.g., masking.
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3.06Impact points
Unitary matrices for phase-coded holographic memories.
Optics letters. 05/2006; 31(8):1047-9.
We propose a novel type of unitary matrix for phase-code multiplexed holographic memories, which could be quickly generated from geometric sequences. Our analysis shows that the phase-code matrices are unitary rather than orthogonal. The new matrices have complex elements. The order of unitary matri... [more] We propose a novel type of unitary matrix for phase-code multiplexed holographic memories, which could be quickly generated from geometric sequences. Our analysis shows that the phase-code matrices are unitary rather than orthogonal. The new matrices have complex elements. The order of unitary matrices can be any positive integer, so that we can accommodate the available spatial light modulators to obtain the maximum possible storage capacity. The cross-talk noises in phase-encoded memories with unitary matrices and with Hadamard matrices are of the same order of magnitude, which are much lower than those in holographic memories with wavelength multiplexing or angle multiplexing.
Following (2)
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Bastian Epp
Carl von Ossietzky Universität Oldenburg
