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Showing papers by "Hermann Wagner published in 2007"


Proceedings ArticleDOI
15 Apr 2007
TL;DR: The gammatone features presented here lead to competitive results on the EPPS English task, and considerable improvements were obtained by subsequent combination to a number of standard acoustic features, i.e. MFCC, PLP, MF-PLP, and VTLN plus voicedness.
Abstract: In this work, an acoustic feature set based on a gammatone filterbank is introduced for large vocabulary speech recognition. The gammatone features presented here lead to competitive results on the EPPS English task, and considerable improvements were obtained by subsequent combination to a number of standard acoustic features, i.e. MFCC, PLP, MF-PLP, and VTLN plus voicedness. Best results were obtained when combining gammatone features to all other features using weighted ROVER, resulting in a relative improvement of about 12% in word error rate compared to the best single feature system. We also found that ROVER gives better results for feature combination than both log-linear model combination and LDA.

187 citations


Journal ArticleDOI
TL;DR: The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.
Abstract: Owls are known for their silent flight. Even though there is some information available on the mechanisms that lead to a reduction of noise emission, neither the morphological basis, nor the biological mechanisms of the owl's silent flight are known. Therefore, we have initiated a systematic analysis of wing morphology in both a specialist, the barn owl, and a generalist, the pigeon. This report presents a comparison between the feathers of the barn owl and the pigeon and emphasise the specific characteristics of the owl's feathers on macroscopic and microscopic level. An understanding of the features and mechanisms underlying this silent flight might eventually be employed for aerodynamic purposes and lead to a new wing design in modern aircrafts. A variety of different feathers (six remiges and six coverts), taken from several specimen in either species, were investigated. Quantitative analysis of digital images and scanning electron microscopy were used for a morphometric characterisation. Although both species have comparable body weights, barn owl feathers were in general larger than pigeon feathers. For both species, the depth and the area of the outer vanes of the remiges were typically smaller than those of the inner vanes. This difference was more pronounced in the barn owl than in the pigeon. Owl feathers also had lesser radiates, longer pennula, and were more translucent than pigeon feathers. The two species achieved smooth edges and regular surfaces of the vanes by different construction principles: while the angles of attachment to the rachis and the length of the barbs was nearly constant for the barn owl, these parameters varied in the pigeon. We also present a quantitative description of several characteristic features of barn owl feathers, e.g., the serrations at the leading edge of the wing, the fringes at the edges of each feather, and the velvet-like dorsal surface. The quantitative description of the feathers and the specific structures of owl feathers can be used as a model for the construction of a biomimetic airplane wing or, in general, as a source for noise-reducing applications on any surfaces subjected to flow fields.

124 citations


Journal ArticleDOI
TL;DR: Recordings from the time-sensitive subnuclei of the barn owl's inferior colliculus show that the deviation of the representation of interaural time difference from optimal-coding models in the low-frequency range is attributable to the diminished importance of low frequencies for catching prey in this species.
Abstract: Interaural time differences are an important cue for azimuthal sound localization. It is still unclear whether the same neuronal mechanisms underlie the representation in the brain of interaural time difference in different vertebrates and whether these mechanisms are driven by common constraints, such as optimal coding. Current sound localization models may be discriminated by studying the spectral distribution of response peaks in tuning curves that measure the sensitivity to interaural time difference. The sound localization system of the barn owl has been studied intensively, but data that would allow discrimination between currently discussed models are missing from this animal. We have therefore obtained extracellular recordings from the time-sensitive subnuclei of the barn owl's inferior colliculus. Response peaks were broadly scattered over the physiological range of interaural time differences. A change in the representation of the interaural phase differences with frequency was not observed. In some neurons, response peaks fell outside the physiological range of interaural time differences. For a considerable number of neurons, the peak closest to zero interaural time difference was not the behaviorally relevant peak. The data are in best accordance with models suggesting that a place code underlies the representation of interaural time difference. The data from the high-frequency range, but not from the low-frequency range, are consistent with predictions of optimal coding. We speculate that the deviation of the representation of interaural time difference from optimal-coding models in the low-frequency range is attributable to the diminished importance of low frequencies for catching prey in this species.

55 citations


Journal ArticleDOI
TL;DR: Optical quality in barn owl eyes is presented in terms of measuring the ocular wavefront aberrations with a standard Tscherning-type wavefront aberrometer under natural viewing conditions and the results suggest that image quality is excellent.

28 citations


Journal ArticleDOI
TL;DR: An algorithm for localizing a sound source with two microphones is introduced and used in real-time situations and showed that localization accuracy decreases with decreasing direct-to-reverberant ratio.
Abstract: An algorithm for localizing a sound source with two microphones is introduced and used in real-time situations This algorithm is inspired by biological computation of interaural time difference as occurring in the barn owl and is a modification of the algorithm proposed by Liu et al [J Acoust Soc Am 110, 3218-3231 (2001)] in that it creates a three-dimensional map of coincidence location This eliminates localization artifacts found during tests with the original algorithm The source direction is found by determining the azimuth at which the minimum of the response in an azimuth-frequency matrix occurs The system was tested with a pan-tilt unit in real-time in an office environment with signal types ranging from broadband noise to pure tones Both open loop (pan-tilt unit stationary) and closed loop experiments (pan-tilt unit moving) were conducted In real world situations, the algorithm performed well for all signal types except pure tones Subsequent room simulations showed that localization accuracy decreases with decreasing direct-to-reverberant ratio

26 citations


Journal ArticleDOI
TL;DR: The findings reported here indicate that vernier acuity is hyperacute in the barn owl, with grating acuity being about 3.75 arcmin in this species.

20 citations


Journal Article
TL;DR: It is suggested that interaural time difference is an important determinant of azimuthal tuning in all neurons of the core and lateral shell of the central nucleus of the inferior colliculus, and is the only determinant in many of the neurons from the core.
Abstract: Standard electrophysiology and virtual auditory stimuli were used to investigate the influence of interaural time difference on the azimuthal tuning of neurons in the core and the lateral shell of the central nucleus of the inferior colliculus of the barn owl. The responses of the neurons to virtual azimuthal stimuli depended in a periodic way on azimuth. Fixation of the interaural time difference, while leaving all other spatial cues unchanged, caused a loss of periodicity and a broadening of azimuthal tuning. This effect was studied in more detail in neurons of the core. The azimuthal range tested and the frequency selectivity of the neurons were additional parameters influencing the changes induced by fixating the interaural time difference. The addition of an interaural time difference to the virtual stimuli resulted in a shift of the tuning curves that correlated with the interaural time difference added. In this condition, tuning strength did not change. These results suggest that interaural time difference is an important determinant of azimuthal tuning in all neurons of the core and lateral shell of the central nucleus of the inferior colliculus, and is the only determinant in many of the neurons from the core.

13 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigate the influence of interaural time difference on the azimuthal tuning of neurons in the core and the lateral shell of the central nucleus of the inferior colliculus of the barn owl.
Abstract: Standard electrophysiology and virtual auditory stimuli were used to investigate the influence of interaural time difference on the azimuthal tuning of neurons in the core and the lateral shell of the central nucleus of the inferior colliculus of the barn owl. The responses of the neurons to virtual azimuthal stimuli depended in a periodic way on azimuth. Fixation of the interaural time difference, while leaving all other spatial cues unchanged, caused a loss of periodicity and a broadening of azimuthal tuning. This effect was studied in more detail in neurons of the core. The azimuthal range tested and the frequency selectivity of the neurons were additional parameters influencing the changes induced by fixating the interaural time difference. The addition of an interaural time difference to the virtual stimuli resulted in a shift of the tuning curves that correlated with the interaural time difference added. In this condition, tuning strength did not change. These results suggest that interaural time difference is an important determinant of azimuthal tuning in all neurons of the core and lateral shell of the central nucleus of the inferior colliculus, and is the only determinant in many of the neurons from the core.

11 citations


Journal ArticleDOI
TL;DR: In older cultures, isolated neurons from the auditory region of the avian brainstem differentiate to specific neuronal subtypes and autonomously develop synaptic connections in vitro by recording postsynaptic activity elicited by extracellular stimulation and styryl dye loading of vesicles.
Abstract: Neurons in the auditory hindbrain pathway of the chicken are physiologically and morphologically highly specialized. It remains unclear to what extent independent differentiation vs. activity-dependent mechanisms determines the development of this system. To address this question we established a primary culture system of the early auditory hindbrain neurons. Primary cultures of neurons from nucleus magnocellularis and nucleus laminaris were prepared from embryonic day 6.5 chicken. These cells developed in culture under serum-free conditions for up to 15 days. Immunocytochemical staining and whole-cell patch recordings were used to characterize the development of the neurons. A stable expression of the calcium-binding protein calretinin, which serves as a characteristic marker of the auditory pathway, was found at all stages. A voltage-gated potassium channel (Kv3.1b) with a specific function in the auditory system was also expressed after about 1 week in culture. Electrophysiological recordings showed a general maturation of the neuronal phenotype as reflected by an increase in the mean resting membrane potential, a decrease in the mean input resistance as well as a maturation of action potential parameters. Four groups of neurons that generate action potentials could be distinguished. One of these showed the phasic firing pattern of auditory brainstem neurons known from slice preparations. In older cultures we demonstrated functional synaptogenesis in vitro by recording postsynaptic activity elicited by extracellular stimulation and styryl dye loading of vesicles. Thus, isolated neurons from the auditory region of the avian brainstem differentiate to specific neuronal subtypes and autonomously develop synaptic connections in vitro.

11 citations


Proceedings Article
01 Jan 2007
TL;DR: This paper investigates and discusses the combination of sound source localization and laser-based object recognition on a mobile robot and suggests spatial filtering can be used to improve the signal-to-noise ratio of speech signals emanating from a given direction in order to enhance speech recognition abilities.
Abstract: Mobile robots, in general, and service robots in human environments, in particular, need to have versatile abilities to perceive and interact with their environment. Biologically inspired sound source localization is an interesting ability for such a robot. When combined with other sensory input both the sound localization and the general interaction abilities can be improved. In particular, spatial filtering can be used to improve the signal-to-noise ratio of speech signals emanating from a given direction in order to enhance speech recognition abilities. In this paper we investigate and discuss the combination of sound source localization and laser-based object recognition on a mobile robot.

11 citations