Discussion

Aims: To demonstrate the viability of a novel mobile eye tracker device for noninvasive recording of eye movements and the visual scene and to demonstrate the potential for characterising fundamental relationships between eye movement and motor action. Methods: An array of cameras was mounted on a custom designed framework such that synchronised recordings of the scene visible to a horse, and the eye movements made by the horse could be obtained. A tripod-mounted high definition video camera and a 3D optical motion capture system both synchronised to the eye tracker video streams were used to record the motor actions of the horse. All video streams were combined into a montage and proprietary image analysis software used to obtain quantitative measurements. Results: The direction of auditory attention determined by ear movement and visual attention determined by eye movement are mostly independent. Although the ears are frequently moved independently the eyes are usually moved together and in the same direction. Eye movements during normal walking compensate for head movements and stabilise the visual scene. Visual attention directed towards a target moving at constant angular speed is achieved using a synchronised combination of head and eye movement. Conclusions: We have demonstrated a technique to obtain time-synchronised measurements of eye movement, visual scene and motor action in horses. We believe this is the first time a mobile eye tracker has been successfully demonstrated in any species other than humans. Practical significance: The technique has potential wide application in welfare related research as it allows the direction of visual attention to be related to motor actions and dynamic events in the visual scene. Acknowledgements: Development of the eye tracker was funded by the EPSRC, we gratefully acknowledge Kat Daniels and Margie Craib for assistance with organising and providing facilities for experimental work, and Olivia Phelps and Vicky Haile for performing analysis of the eye tracker data.