Our ability to see clearly and resolve visual clutter is much higher at the so-called fovea - the center of gaze - than in the periphery. Therefore, human vision is a process of selection – we constantly move our eyes and place the fovea on different parts of the scene in front of us. This poses a challenge to the visual system. At each moment in time, it needs to decide where to move the fovea next, often based on poor peripheral input. But how does it achieve this feat? How can we select the most relevant parts of a scene before we look at them directly? For a long time, vision scientist modelled this process as a function of low-level image properties. For instance, these models may predict the next eye movement to go to the part of the scene with the highest color contrast. However, more recent work has shown that eye movements are much better predicted by semantic properties of a scene, like the location of objects, faces or text. Furthermore, eye movements differ systematically between observers – they are not just a function of the scene in front of us, but also the person looking at it. INDIVISUAL aims to better understand how eye movements differ from one person to the next, what the sources and consequences of these differences are for individual perception and whether we can use individual eye movements as a diagnostic marker. We also aim to use individual differences as a tool to better understand the general mechanisms allowing the human visual system to efficiently select relevant parts of a scene for eye movements.
After five adventurous years, INDIVISUAL came to several conclusions. Systematic individual differences in gaze predict individual differences in perception. Gaze traits can predict how two people will describe a scene and even how the representation of a movie will differ in their brains. Moreover, how we look at faces can predict how well we do at recognising them and distinguish between 'super recognisers' and controls. Our differences in this regard seem to go back to basic features of the visual system. They are not specific to face, but extend to inanimate objects: Someone who avoids looking at the eye region will also tend to look lower in objects. Individual differences in the visual brain are at least partially heritable (identical twins have more similar visual brains than non-identical ones), but where we move our eyes is also shaped by development. A massive dataset we colected in a museum allowed us to trace the development of eye movements across thousands of children and adults and revealed that gaze behaviour takes surprisingly long to mature, with changes lasting well into teenage and beyond.
