Visual and Auditory Localization of the Barn Owl
1. Localization is the process by which living organism perceive the location of objects or activities. Vision and hearing are very important sense for bird and mammals when it comes to localization processes. Although this process occur independently the perception that arise from them are integrated and we perceive what we see and what we hear as one (Huo, Murray, Smith and Yang, 2008). Localization in the barn owl is mainly dependent on visual and auditory senses. Auditory localization is whereby the organism locates by tracing sounds emitted by the object while in visual localization the organism utilizes visual perceptions to locate an object. It has been noted that the process of localization of objects by the barn owl is heavily dependent on the interaction.
In the brain of most mammals the computational map is dependent on different sensory process. These maps translate the input signals from the different senses into localized activities in the map (Haessly, Sirosh & Miikkulainen, 1995). The sensory inputs usually work independently from each other. However, in the ban owl the auditory map has been found to be under the strong influence of the visual senses. Existence of this influence has been support by the tendency of the barn owl to adopt the auditory map even when only the visual senses have been disrupted. The visual /auditory localization in barn owls works by the auditory map in the external nucleus in the inferior colliculus projecting signals to the optic tectum. The auditory information in the optic tectum is then combined with visual signals to form a bimodal topographical map of space (Haessly, Sirosh & Miikkulainen, 1995). This mode of localization enable the barn owl to locate it’s pray with the topographical map using both visual and auditory senses.
2. In order to support this bimodal system a calibration signal based on visual sense must be involved and the auditory map must be appropriately structured (Haessly, Sirosh & Miikkulainen, 1995). Since the owl operates during the night, it is mostly dependent on sound to locate it prey. In order to give it the necessary accuracy of spotting prey, the auditory map is located in the inferior colliculus. The Inferior Colliculus is divided into superficial nucleus, external nucleus and central nucleus. While the neurons in external nucleus are broadly tuned to frequency and spatiotopically organized, the neurons in the central nucleus are sharply tuned and tonotopically organized (Haessly, Sirosh & Miikkulainen, 1995). The location of auditory response is also very close to the corresponding visual response location. For accuracy of location of prey, the visual attention and the sound source must coincide. When these two senses coincide the learning signal is turned on and allows the auditory map to adapt (Knudsen & Knudsen, 1989). The barn owl tends to direct more attention to the center of the field rather the peripheries and therefore the visual attention is generated using a Gaussian distribution originating from the center of the field (Haessly, Sirosh & Miikkulainen, 1995).
3. The owl may receive sound signals from different location within the auditory map (Knudsen, 2002). These signals may become ambiguous to the owl. In order to bring about clarity in the auditory perception, the sound frequencies must be integrated across all cues. This process is performed concurrently in the midbrain and forebrain (Knudsen, 2002). In the middle brain the external and central nucleus of the inferior colliculus play a significant role in integrating the sounds. The sound collect from the external nucleus, which is adapted for broad and spatiotopically organized sound frequencies, is channeled towards the central nucleus, which is adapted to collect high turned and tonotopically organized sound frequencies, where the two different frequencies of sounds are combined to create a map a space. This is then sent to the optic tectum. The forebrain on the hand is responsible for combining channels that are beyond the primary auditory field to create a clustered space (Knudsen, 2002) \
4. One of the most recent research studies on visual and auditory localization in the barn owl is Adapation of Barn Owl Localization System with Spike Timing Dependent Plasticity by Huo, Murray, Smith and Yang (2008). This study was based on the concept that the barn owl localize objects by integrating the visual maps to the auditory maps and therefore when the one of these senses in impaired the localization of the barn owl is distorted. Huo, Murray, Smith and Yang (2008) objective was to investigate whether the spike time dependent plasticity has any role in the visual and auditory localization of the barn owl. In order to achieve this objective, these researchers investigated the process through which the auditory and visual maps are integrated by building a computational model of the auditory and visual integration with map adjustment in the deep superior colliculus. Huo, Murray, Smith and Yang (2008) introduced an anomaly in both the visual and auditory processes at different times and observed that the localization precision of the owl was diminished. This study found out that the spike time dependent plasticity is involved in the alignment of visual and auditory senses.
References
Huo J. Murray L. Smith A. and Yang Z. (2008). Adapation of Barn Owl Localization System with Spike Timing Dependent Plasticity. International Joint Conference on Neural Networks. April 28, 2011. Retrieved from http://www.cs.stir.ac.uk/~lss/recentpapers/IJCNN_NN0081.pdf
Haessly A. Sirosh S. & Miikkulainen R. (1995). A Model of Visually Guided Plasticity of the Auditory Spatial Map in the Barn Owl. April 28, 2011. http://nn.cs.utexas.edu/web-pubs/haessly.cogsci95/paper-rev-form.html
Knudsen E. (2002). Instructed Learning in the Auditory Localization Pathway of the Barn Owl. Stanford University.
Knudsen E. & Knudsen P. (1989). Visual Calibrates Sound Localization in Developing Barn Owls. The Journal of Neuroscience. 9(9), 3306- 3313
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