|M.Sc Student||Yarin Inna|
|Subject||Tracking of Pupil Size for the Study of Auditory-Visual|
Integration in Barn Owls
|Department||Department of Medicine||Supervisor||Professor Yoram Gutfreund|
|Full Thesis text|
Many species of animals integrate auditory and visual information for the control of behavior. A challenge is to understand where and how in the brain such integration occurs. In recent years, the barn owl (Tyto alba) is emerging as a model system for studying auditory-visual integration (AVI) at the neuronal level. However, little is known about AVI in barn owls at the behavioral level.
Barn owls are nocturnal predators with high
auditory and visual capabilities. They are adapted to detect small prey in dim
and noisy environments.
In this study we searched for an indication of AVI in barn owls at the behavioral level, using their pupil responses. Previous studies showed that pupil diameter increases immediately following a stimulus, in proportion to the saliency of the stimulus. Thus, the magnitude of the pupil response can provide an estimation of the perceived saliency of the stimulus.
We measured pupillary responses of the right eye using a custom made algorithm for tracking the pupil size. Infra-red light was shone on the eye, and an infra-red sensitive video camera captured the reflected light from the retina. We presented long sequences of randomly alternating auditory and visual stimuli, with a small probability for the auditory and visual stimuli to occur simultaneously (bimodal stimulation). Stimuli were presented either in front of the owl or to the left, i.e. outside the binocular zone, but within the field of view of the left eye. Because the bimodal stimulation was rarely presented, we expected that if AVI took place between both stimuli, a larger pupil dilation response would be recorded.
We report that auditory stimuli induced dilation responses regardless of their spetial position. The visual stimulus induced a constriction when placed in the front and only a slight constriction or no response when placed on the left of the barn owl. When the visual stimulus was located on the left side, and the auditory stimulus was either on the left (congruent) or in the front (incongruent), the bimodal responses were mostly not significantly larger than the responses to the auditory stimulus alone. However, congruent bimodal stimulation, where both stimuli were located in the front, induced, in several cases, significantly larger constriction responses than the responses to the visual stimulus alone. Thus, AVI is reflected in the pupillary responses. Surprisingly, however, AVI is not manifested in the dilation responses but rather in the constriction responses.