Cognitive and precognitive visual mechanisms

Barn owls have frontally oriented eyes that allow them to extract binocular disparities. Behavioral experiments in our lab have demonstrated that barn owls possess global stereopsis (Willigen et al. 1998). Moreover, these birds judge depth as created by motion parallax equivalent to depth as generated by disparity (van der Willigen et al. 2002)

Owls have neurons in the forbrain, the so-called Visual Wulst, that are sensitive to binouclar disparities. Wagner and Frost (1993, 1994) have found that these neurons have characteristic disparities. Using telemetry (Nieder 2000), Nieder has recorded from these neurons in awake, behaving animals and could show that they share many characteristics with disparity-sensitive neurons in monkeys (Nieder and Wagner 2000, 2001). Moreover our research demonstrated a hierarchy of processing leading to neural responses that may be the correlate of the owl's behavior (Nieder and Wagner 2001). Our theoretical work has shown that encoding by characteristic phase and characteristic disparity provides a robust representation of depth (Fleet et al. 1996; Lippert et al. 2001) Recently, Lippert and Wagner (2002) could show that populations of stereo-energy neurons could represent depth unambigiously.

Moreover, owls are also able to detect illusory contours and neurons in the visual wulst may form the neuronal substrate for this accomplishement (Nieder and Wagner 1999)

1. German Science Foundation (DFG) since1994

2. Stipend of German "Studienstiftung" for Joerg Lippert

Publications in refereed journals

1. Lippert J and Wagner H (2002) Visual depth encoding in populations of neurons with localized receptive fields. Biol. Cybernetics (in press)

2. v.d. Willigen RF, Frost B and Wagner H (2002) Depth generalization from stereo to motion parallax in the owl. J. comp. Physiol. 187: 997-1007

3. Nieder A and Wagner H (2001) Hierarchical processing of horizontal-disparity information in the visual forebrain of behaving owls. J. Neuroscience 21: 4514-4522

4. Nieder A and Wagner H (2001) Encoding of both vertical and horizontal disparity in random-dot stereograms by Wulst neurons of awake barn owls. Vis. Neuroscience 18: 541-547

5. Nieder A (2000) Miniature stereo radio transmitter for simultaneous recording of multiple single-neuron signals from behaving owls. J Neurosci Methods 101: 157-164

6. Nieder A and Wagner H (2000) Horizontal-disparity tuning of neurons in the visual forebrain of the behaving barn owl. J. Neurophysiol. 83: 2967-2979

7. Lippert J, Fleet D and Wagner H (2000): Disparity tuning as simulated by a neural net. Biological Cybernetics 83: 61-72

8. Nieder A and Wagner H (1999) Perception and neural coding of subjective contours in the owl. Nature Neuroscience 2: 660-663.

9. v.d.Willigen R, Frost BJ and Wagner H (1998) Stereoscopic depth perception in the owl. Neuroreport 9: 3-7.

10. Fleet DJ, Wagner H and Heeger DJ (1996) Neural Encoding of Binocular Disparity: Energy Models, Position Shifts and Phase Shifts. Vision Res. Vol 36: 1839-1857

11. Wagner H and Frost B (1994) Binocular responses of neurons in the barn owl's visual wulst. J. Comp Physiol A174: 661-670

12. Wagner H and Frost B (1993) Disparity-sensitive cells in the owl have a characteristic disparity. Nature 364: 796-798

PhD-Theses

• Andreas Nieder, Diplombiologe (1999) Mechanisms of depth perception in the visual forebrain of the behaving barn owl.

• Rob van der Willigen, Drs., Biologe (2000) On the perceptual identity of depth vision in the owl.

• Joerg Lippert (2002) Representation of Depth in Neural Population Responses

Diplomtheses

• Joerg Lippert (1997) Untersuchung der Disparitätskodierung im visuellen Wulst der Schleiereule durch Computersimulation neuronaler Netze

• Monika Schaefer (2000) Neuronale Mechanismen der Repräsentation von Querdisparation im visuellen Vorderhirn der Schleiereule (Tyto alba)

• Sabine Vossen (2000) Untersuchung des Einflusses räumlicher Frequenzmodulationen auf das Stereosehen bei Schleiereulen (Tyto alba)