Only through their senses do humans and other organisms have access to the information in the world surrounding them. In the processing of this sensory information, factors like our expectations and previous experiences come into play. Heleen Slagter, associate professor at the University of Amsterdam, tries to unravel the neural mechanisms involved in the interplay between our expectations and perception. The European Research Council supported her with a fund of 1 500 000 euro.
With this grant, Slagter is able to approach the relation between expectations and perception through three main lines of inquiry. In the first, Slagter and her team try to understand why humans only have one interpretation of reality at any moment. ‘This becomes apparent when we are confronted with noisy input,’ Slagter explains. ‘When you walk down a street at night in pouring rain, you might observe a man with a hat standing on the side walk, but at second glance you realize it’s a sign post. With ambiguous input, you either recognize a man or you recognize a sign post, you never see a morphed version of the two because our prior experience tells us there is no such thing as a man-sign post.’
To determine why only one model is selected and how the brain determines which model this should be, Slagter will combine experimental manipulations of perceptual expectations with neuroimaging. She expects interplay between the basal ganglia and the prefrontal cortex to play a particular role in determining what percept will dominate our conscious experience. Using a pharmacological intervention, Slagter will try to modulate interactions between these brain regions, to see whether this prevents people from updating their expectations of what is out there.
In a more clinical part of this research line, Slagter collaborates with professor Damiaan Denys of the AMC to explore the relevance of basal ganglia in obsessive compulsive disorder (OCD). ‘You could think of OCD as an illness where our models of the world are not adjusted according to reality. For example, people clean their house constantly but don’t perceive their house to be clean. We hope by stimulating activity in the basal ganglia, we can help people update the models they use of reality, thereby helping them to perceive the outside world in a more accurate way.’
In the second line of research, the team tries to understand how attention and expectations influence perception. The amount of information reaching our senses is vast and cannot all be processed by higher brain regions. As human beings we have evolved to process information as efficiently as possible. We can do so first of all based on prior experience, through predictive processing. This means we constantly predict what we are likely to perceive and mainly process the mismatches between our predictions and incoming information. But attention also plays a critical role in guiding information processing, and may determine the extent to which these mismatches make us reconsider our predictions depending on how reliable we consider the mismatch.
Finally, Slagter wants to establish whether the human prediction machine operates automatically, outside our control. ‘I will determine whether it is possible to consciously ‘be in the moment’ and choose to not let previous experiences color our perception. Whether it is possible to perceive every single stimulus as it is, without any expectations.’ To test this, Slagter invites a Buddhist master to her lab and studies the effects of two different meditation styles. ‘I think meditation could help us perceive the world in a less biased way, creating the space to adjust our habitual perception and thoughts. I’m curious to see whether we will find experimental proof to back that up.’
Text: Marieke Buijs