Showing papers by "Hermann Wagner published in 2003"

Anatomical markers for the subdivisions of the barn Owl's inferior-collicular complex and adjacent peri- and subventricular structures

Abstract: The anatomy of the inferior-collicular complex of the barn owl, situated below the fourth ventricle in the tectal lobe, was studied by determining the distribution of antigens with antibodies directed against tyrosine hydroxylase, -aminobutyric acid (GABA)A, dopamineand cyclic AMP-regulated phosphoprotein (DARPP-32), calretinin, and calbindin. Additionally, the somata were stained with cresyl violet, and fibers were marked according to the Gallyas procedure. These markers were chosen to allow for an easy delineation of the boundaries between the subnuclei of the inferior colliculus. We could discriminate eight structures that belong to the three subnuclei of the inferior colliculus [the central nucleus (ICC), the superficial nucleus (ICS), the external nucleus (ICX)] and to the optic tectum. Periventricular tectal layers 15a and 15b stained well with all the antibodies used. The ICS, embedded in tectal layer 15a, may be divided into a dorsal and a ventral lamina. It does not have direct contact with the other nuclei of the inferior colliculus. The border between tectal layer 15a and ICX was well marked by all antibodies, but less so in Gallyas and cresyl violet stains. The ICC consists of a core and a medial and lateral shell. The core was clearly demarcated with antibodies against calretinin and calbindin. The border between the lateral shell and the ICX was marked less well than the borders between ICX and 15a, but the somata were much more darkly labeled with the DARPP-32 antibody in ICX than in the lateral shell of ICC. None of the markers delineated the border between the medial and lateral shell of ICC. J. Comp. Neurol. 465:145–159, 2003. © 2003 Wiley-Liss, Inc. Indexing terms: space map; superior colliculus; auditory system; external nucleus

How owls structure visual information

Abstract: Recent studies on perceptual organization in humans claim that the ability to represent a visual scene as a set of coherent surfaces is of central importance for visual cognition. We examined whether this surface representation hypothesis generalizes to a non-mammalian species, the barn owl (Tyto alba). Discrimination transfer combined with random-dot stimuli provided the appropriate means for a series of two behavioural experiments with the specific aims of (1) obtaining psychophysical measurements of figure–ground segmentation in the owl, and (2) determining the nature of the information involved. In experiment 1, two owls were trained to indicate the presence or absence of a central planar surface (figure) among a larger region of random dots (ground) based on differences in texture. Without additional training, the owls could make the same discrimination when figure and ground had reversed luminance, or were camouflaged by the use of uniformly textured random-dot stereograms. In the latter case, the figure stands out in depth from the ground when positional differences of the figure in two retinal images are combined (binocular disparity). In experiment 2, two new owls were trained to distinguish three-dimensional objects from holes using random-dot kinematograms. These birds could make the same discrimination when information on surface segmentation was unexpectedly switched from relative motion to half-occlusion. In the latter case, stereograms were used that provide the impression of stratified surfaces to humans by giving unpairable image features to the eyes. The ability to use image features such as texture, binocular disparity, relative motion, and half-occlusion interchangeably to determine figure–ground relationships suggests that in owls, as in humans, the structuring of the visual scene critically depends on how indirect image information (depth order, occlusion contours) is allocated between different surfaces.

Development of output connections from the inferior colliculus to the optic tectum in barn owls

Abstract: We studied the development of the projection from the external nucleus of the inferior colliculus (ICX) to the optic tectum (OT) in the barn owl. The projection was labeled by tracer application in vitro to either the OT or the ICX, or by staining ICX cells intracellularly with biocytin. The axons of ICX neurons bifurcated into an ascending branch that projected toward the OT and a descending branch that coursed caudally to an unknown target in the brainstem. Axons of the ICX were observed to grow into the OT from embryonic day 16 (E16) on. From E22 on, side branches of the axonal projections could be found within the OT. At the day of hatching (E32), the projection displayed a dorsoventral topography comparable to the adult owl; however, atopically projecting cells remained. The complexity of the axonal arborization in the adult barn owl was found to be slightly increased compared with the hatchling. The terminal area of individual ICX cells in the OT of the adult barn owl was still broad, a finding that had not been expected from the sharply defined physiological response properties of the bimodal neurons in the space map of the OT. However, the width of the termination zone was in accordance with the large dendritic tree of the adult ICX cells, because both spanned comparable angles in their respective maps. Our data suggest that a coarse projection from the ICX to the OT can develop without coherent sensory input and may, therefore, be innately determined.

Aspects of sound localization and spatial attention in barn owls and rats

Abstract: Diese Dissertation ist auf den Internetseiten der Hochschulbibliothek online verfügbar.