Donders Institute for Brain, Cognition and Behaviour
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Thesis defense Tom van Grootel (Donders Series 47)

4 March 2011

Promotor: Prof.dr. A.J. van Opstal

On the role of eye and head position in spatial localisation behaviour

In reading this text, our eyes quickly jump about three times per second. Despite a constant shift of the visual world, we don’t perceive the book in front of us has changed position. Hence, we perceive the world as stable even during eye and head movements. This thesis tries to surface some of the involved neurocomputational processes.

An important observation is when during a fast eye/head movement visual targets are flashed, rhesus monkeys (Macaca Mulatta) as well as humans are able to localise these targets correctly. In order to achieve this, the brain must have access to information about instantaneous eye and head position. Previous studies suggested that this information is based on accumulation of all prior eye and head displacements. Unfortunately this seems unlikely. Despite many preceding eye displacements, localisation responses towards auditory targets are still perfect. Displacements do not hamper the localisation performance. Even auditory responses following unconscious eye displacements are still accurate.

Presumably, information about eye and head orientation is combined with target position early in the auditory system in programming a goal directed response. Auditory properties influence the amount of compensation of eye and head position. Individual tone frequencies bring about different compensation strengths.

However, maintaining a stable world is not fail-safe. This can be observed in side-ways tilted subjects, who make large errors in localisation estimates of sound targets straight-above (parallel to gravity). This effect is renowned in visual research, but has never been identified in auditory experiments.


Tom van Grootel