Thesis defense Peter Kok (Donders Series 149)

22 May 2014

Promotor; Prof.dr. P. Hagoort, copromotor: dr. F. de Lange

On the role of expectation in visual perception: A top-down view of early visual cortex

Perception is not solely determined by the light that hits our eyes. Instead, what we perceive is strongly influenced by our prior knowledge of the world. Your prior experiences also help you predict what will happen next, based on what you have learned about the world. For example, a proficient tennis player uses her opponent’s stance and the swing of her arm to predict the trajectory of the ball, even before it is hit – if she did not, but instead merely reacted to the ball as it approached her, she would not stand a chance. These kinds of predictions are pervasive in daily life, though we may not realise it. Every day, you could ride your bike home and open your door without paying any attention to the details of these operations, yet if someone slightly raised your bike seat, or replaced the door handle with a differently shaped knob, you would notice it immediately – things are not as you expected.
This thesis discusses several ways in which expectation influences perception, focusing on how expectation modulates neural processing in the visual cortex. Overall, the findings indicate that expectations affect neural processing already at the earliest stages. Specifically, when stimuli clearly violate prior expectations, they evoke more activity in early visual cortex, but this increased activity contains less information about the presented stimulus. Furthermore, expectation can change not only how well information is represented in visual cortex, but also what is represented. These findings indicate that expectations play a fundamental role in sensory processing.