Thesis defense Joke Kalisvaart (Donders Series 126)

9 October 2013

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

Visual ambiguity in perception and action

When looking around in daily life, we perceive the world around us as stable and unambiguous. Sometimes, however, we come across a situation in which what we see can be interpreted in different ways. When this happens, the brain has to choose a certain interpretation from the possible options. In my thesis, I describe 4 studies in which we investigated human behavior when presented with several types of ambiguity.
Ambiguity can take different forms. Figures can be ambiguous in itself, but ambiguity can also arise when the left and the right eye are presented with distinctly different images. Unable to fuse the two images into a single 3D percept, the brain then chooses one percept to perceive and suppresses the other and switches the dominant percept every few seconds; a phenomenon known as binocular rivalry. Ambiguity has much in common with visual decision making. When the targets for an eye movement are equally likely, ambiguity also arises.

In the first two studies, we investigated ambiguity in the relation to decision making. Visual decision making and binocular rivalry are usually described with very different models. We propose a combined model featuring key elements from common decision making models and binocular rivalry models and show that such a model is able to predict human behavior in both ambiguous and unambiguous decision making.

In the last two studies, we studied the effect of saccades on binocular rivalry. By comparing the effect of saccades on the rivalry process with the situation in which the stimulus moved instead of the eye, we found that saccades elicit a form of onset rivalry, and that rivalry is modulated by extraretinal eye movement signals.