Image credit: Colin Lloyd via Unsplash (CC0)
On average, we move our eyes three times per second. Where we decide to look next is one of the most frequent choices that our brains make, but how does the brain know where to look? Previous work has established that we tend to look towards elements that ‘pop out’ visually, are relevant for our goals, or places that have previously provided us with information. However, a lot of eye movement behavior cannot be explained by these factors.
Koevoet, Strauch et al. wanted to better understand how our brains decide where to look next. The researchers hypothesized that the ‘cost’ of eye movements (the brain has to compute the visual consequences of the eyes moving in a certain way) might influence where we look. To save resources, more ‘affordable’ eye movements may be preferred over costly ones.
To test this hypothesis, Koevoet, Strauch et al. measured the effort of eye movements by looking at the pupil size before an eye movement is made. A larger pupil size indicates more effort is required to prepare the movement. The measurements showed that the cost of eye movements depended on the direction of the eye movement, and that affordable ones were chosen over more costly ones. These findings indicate that effort drives where eyes move, supporting the more general idea that the brain is highly efficient with its resources.
Koevoet, Strauch et al.’s experiments show that cost predicts where the eyes will move. Future studies should explore where and how the brain stores and uses this information to make decisions, and how cost is integrated with other established factors that drive where we look.
