Courtesy Jorge Otero-Millan

Ed. Note: Elements of this article first appeared in a press release about our research article, from the Barrow Neurological Institute.

A new study from my laboratory at the Barrow Neurological Institute, titled “An oculomotor continuum from exploration to fixation”, was just published in the Proceedings of the National Academy of Science, Volume 110, Number 15, and is now available online for viewing and printing.

The research shows that we explore the world with our eyes in a different way than previously thought, and it advances our understanding of how we interact with and glean critical information from our surroundings. The study was conducted in collaboration with Jorge Otero-Millan, Rachel Langston, and Stephen Macknik, also at Barrow.

Previously, scientists had thought that we sample visual information from the world in two main different modes: exploration and fixation. That is, we used to think that we make large eye movements to search for objects of interest, and then fix our gaze to see them with high detail, but we now know that’s not quite right.

The fact is, even during visual fixation, we use eye movements to scan visual details -- just like we use big eye movements to explore visual scenes, but on a different scale. This means that exploration and fixation are two ends of the same continuum of oculomotor scanning.

Exploration and fixation are the two extremes of an eye movement continuum that depends on image size, a concept illustrated here with diminishing sizes of the same natural image that share a common eye scanning path. Butterfly image from the McGill Calibrated Colour Image Database. Composition courtesy of Jorge Otero-Millan.

Subjects viewed natural images while we measured their eye movements with high-speed eye tracking. The images could range in size from the massive—presented on a unique video monitor array 4 meters wide in the Barrow Neurological Institute’s Eller Telepresence Suite, normally used when Barrow’s surgeons collaborate in brain surgeries taking place in other sites all around the world—to the minute—just half the width of your thumb nail at arm’s length. In all cases, the researchers found that subjects’ eyes scanned the scenes with the same general strategy, along a smooth continuum of dynamical changes.

There was no abrupt change in the characteristics of the eye movements, whether the visual scenes were huge or tiny, or even when the subjects were fixing their gaze. That means that the brain controls eye movements in the same way when we explore and when we fixate.

Scientists have investigated how the brain controls eye movements for over 100 years, and the idea that our study challenges—that fixation and exploration are fundamentally different behaviors-- has been central to the field. We hope that our findings affect future research and bring focus to the study of neurological diseases that impact oculomotor behavior.

Jorge Otero-Millan, Stephen L. Macknik, Rachel E. Langston, and Susana Martinez-Conde. An oculomotor continuum from exploration to fixation. PNAS 2013 ; published ahead of print March 26, 2013, doi:10.1073/pnas.1222715110