Biomedical subjects

Hermann Wagner

Publications and source records attributed to Hermann Wagner.

93 records · Page 6Linked to original sources

PubMed2002

Precognitive and cognitive elements in sound localization.

Sound localization behavior is of great importance for an animal's survival. To localize a sound, animals have to detect a sound source and assign a location to it. In this review we discuss recent results on the underlying mechanisms and on modulatory influences in the barn owl, an auditory specialist with very well developed capabilities to localize sound. Information processing in the barn owl auditory pathway underlying the computations of detection and localization is well understood. This analysis of the sensory information primarily determines the following orienting behavior towards the sound source. However, orienting behavior may be modulated by cognitive (top-down) influences such as attention. We show how advanced stimulation techniques can be used to determine the importance of different cues for sound localization in quasi-realistic stimulation situations, how attentional influences can improve the response to behaviorally relevant stimuli, and how attention can modulate related neural responses. Taken together, these data indicate how sound localization might function in the usually complex natural environment.

Journal Article↗

PubMed1990

Receptive Fields of Neurons in the Owl's Auditory Brainstem Change Dynamically.

Binaural neurons in the barn owl's auditory brainstem have spatial receptive fields. It is shown here that both the frequency tuning of these neurons and their tuning to interaural time difference (ITD), the prime cue for azimuthal sound localization, improves with time after stimulus onset, a process I shall term 'dynamic sharpening'. Thus, the receptive fields of these neurons also have a temporal dimension. Data were collected in four hierachically ordered nuclei concerned with the computation of ITD: the nucleus ventralis lemnisci lateralis, pars anterior (VLVa), and three subnuclei in the inferior colliculus. Dynamic sharpening in the frequency tuning curves is evident from a dynamic reduction of tuning width. When stimulated with a tone, the response of all neurons varies in a cyclic manner with ITD. The ITDs at the response peaks differ by one period of the stimulus tone. The responses with noise stimulation are similar to the responses with tonal stimulation in all but the hierarchically highest nucleus, the external nucleus of the inferior colliculus. In this nucleus are found neurons that, if stimulated with noise, respond maximally only to one ITD while the responses at the other peaks are suppressed. This sidepeak suppression is a dynamic process. Dynamic sharpening of ITD tuning is also evident from a dynamic reduction of the tuning width around each of the response peaks. The proportion of neurons showing dynamic sharpening of ITD tuning is the same in all collicular subnuclei, but is lower in VLVa. Therefore, a major component of dynamic sharpening of ITD tuning occurs at the first station of the inferior colliculus. Lateral inhibition is one of the mechanisms underlying dynamic sharpening. Part of the inhibition may be mediated by GABA (Fujita and Konishi, 1988). The function of dynamic sharpening of ITD tuning may be to increase the fine representation of auditory space in single neurons.

Journal Article↗

PubMedDate not supplied

A comparison of neural computations underlying stereo vision and sound localization.

Stereo vision and sound localization are behaviors that help organisms to orient in space. Stereo vision provides information about the distance of an object. In sound localization mainly directional signals are analyzed. Two specific cues, binocular disparities underlying stereo vision, and the interaural time difference, suited to represent azimuth in sound localization, have many computational problems in common, although they are generated in two different modalities. The extraction of both cues requires a comparison of signals that arise from two independent sensors, called two-sensor comparison here. This two-sensor comparison is achieved by algorithms similar to summation, half-wave rectification and multiplication. Since the underlying neurons are band-pass filters, the two-sensor comparison results in ambiguities. These are removed in a hierarchical way in several computational steps, involving squaring, inhibition and across-frequency integration.

Animals↗