The Puzzle of Perception

The human eye only resolves a small patch of the visual field in detail - not much more than your thumbnail when you look at it with an outstretched arm. That is why the eyes are constantly in motion. When looking at a photograph or reading this text, rapid jumps of the eye (called saccades) move the center of vision several times per second. The eyes fixate on each point for a brief glance and soon continue their hunt to collect more pieces of the jigsaw puzzle to assemble a seemingly complete picture of the world. But this puzzle is never completed, because selectivity is inseparably built into perception.

My research aims to understand the puzzle of perception a little better. In which ways do attention and memory contribute to conscious experience? How does memory influence what we focus our attention on? How does attention determine how we experience the world and what we learn from it? I am trying to find some answers to to these questions by investigating human performance in visual and memory tasks, analyzing gaze behavior, and studying the neural and behavioral correlates of attention, memory and conscious perception.

The Interplay of Attention and Memory

In one of my favorite projects we investigate the interaction between attention and memory whiles viewing natural scenes in photographs or edited films. Using eye tracking, we investigate how viewers direct their attention when viewing a familiar scene (or a scene that relates to what they have seen before). We realized that attention is very flexible and temporarily adapts to the situation. For example, when it comes to following an edited film or recognizing a familiar photo, attention is quickly and accurately directed to locations that have been viewed before or that are at least very similar to what was seen before. This preference for familiarity seems to be necessary for accurate recognition of pictures and allows to understand how successive shots in an edited film relate to each other. We also try to understand the capacity and stability of this memory and aim to identify its neural correlates in the brain. This could bring us one step closer to understanding how we learn new things from our everyday perceptual experience.

Selected references

The Individual View of the World

In everyday life, different people usually seem to agree on what they see in front of them - and yet there are sometimes considerable differences between people in how they experience objects in the world. This almost became commonly known when a (somehow low quality) photograph of a dress went viral. Many people disagreed about its color, with everyone being particularly convinced that they were right. Such striking individual differences in perception illustrate that there is no one-to-one relationship between the world's objective characteristics and how it is perceived. Instead, various factors contribute to how sensory signals are ultimately interpreted as subjective perceptual experience. I am particularly interested in understanding why there are stable individual differences in which stimuli capture human attention, and to which degree contextual information determines the outcome of a perceptual moment.

Selected references

At the Limits of Perception

In every moment, we only experience a small part of all aspects of our environment consciously. However, we seem to be able to process certain aspects of the world very efficiently without perceiving them consciously. With experimental techniques, it is possible to eliminate or delay conscious experience effectively. A powerful method that I am using in my current projects is Continuous Flash Suppression, which is based on the fascinating phenomenon of binocular rivalry. In Binocular Rivalry and Continuous Flash Suppression, different images are presented to the left and the right eye of the same viewer. Despite both pictures being right in front of the eyes, the viewers perceive only one of them. A perceptual switch occurs only after a few seconds, and the formerly invisible image is eventually consciously experienced. In our current projects, we use behavioral measures and electrophysiological markers to investigate to what extent an invisible image could influence the participants' actions and thoughts. Through this project, we also want to understand how attention and memory can alter and improve conscious experience of particularly weak sensations of the external world.

Selected references

Experimenting and Sharing

In laboratory perception experiments, we often reduce the complexity of everyday situations and present our viewers with very simplified objects, which we can easily control with regards to their visual features and their structure and randomness over time and space. Developing experiments usually involves a lot of trial and error before we end up a suitable setup to test a specific research hypothesis. This process of tinkering and experimentation is rewarding in itself, as it often leads to spontaneous and unanticipated insights. It is also important to keep in mind that our everyday environment is usually much more complex but, at the same time, less randomized, more meaningful than the stimuli we often present in laboratory experiments. For this reason, I try to keep the right balance in my projects between using strongly simplified experimental stimuli and more natural settings, for example by using photographs or real-world scenes, or even virtual reality environments. I also aim to make any of my new research open, transparent, and reproducible. For this reason, I release experimental code, sets of stimuli that I assembled, and data sets and analysis scripts for the experiments I conducted.