Imagine driving a vehicle on a day when there is a lot of traffic. In a complex task like this one, we need to scan the environment constantly and look at different parts of the scene to monitor everything that is going on. To do this, the visual system not only examines and processes what is in the centre of our gaze — such as a car, a traffic light or a pedestrian — and projects it onto the area of the retina that helps us get a detailed view of the scene — the fovea — but also monitors what is happening in the rest of the visual field, in the periphery.

Now, a study published in the journal Proceedings of the National Academy of Sciences (PNAS) provides new insights into how humans process foveal and peripheral visual information when we direct our gaze to a particular point in the scene during extremely brief fixation periods. The paper reveals that there are differences in the temporal dynamics of visual processing during these fixation periods. This discovery could have important implications for how we understand visual information in complex and dynamic environments, such as during driving and other activities that require high precision.

The study is led by Cristina de la Malla, a researcher of the Faculty of Psychology and the Institute of Neurosciences at the University of Barcelona (UBneuro), and Martina Poletti, researcher at the Department of Neurosciences at the University of Rochester and the Center for Visual Science at the same university (United States).

Understanding the temporal dynamics of visual processing

The paper outlines a new scenario of how the visual system processes information from the foveal and peripheral areas. Specifically, the authors have compared the ability to correctly localize changes that occur in the foveal and peripheral areas during the brief period of fixation according to the exact time at which these changes occur.

“To obtain information from the environment, we direct our gaze towards the part of the scene that we consider most relevant at any given moment. We move from looking at one point to another by moving our eyes very fast, in what we call saccadic movements. After each saccadic movement, there is a brief fixation period of about 250-350 milliseconds, during which the visual system not only obtains detailed information about what is projected onto the fovea, but must also monitor the periphery to be able, for example, to programme the next saccadic movement”, says Cristina de la Malla, a lecturer in the Vision and Control of Action Group of the UB’s Department of Cognition, Development and Educational Psychology.

The study states that, after a saccadic movement — the rapid eye movements that occur between fixations — the processing of changes in the scene varies depending on where and when exactly the change occurs. “There is a lot of previous work showing that saccadic movements affect perception. In contrast, it has generally been assumed that visual processing is stable during short periods of fixation, and foveal and peripheral processing have been compared without considering possible differences that may occur during the period of time that a fixation lasts”, says the expert.

The conclusions suggest that, at the onset of fixation, the visual system is better at localizing changes at the foveal level than at the peripheral level. “At the beginning of fixation, the visual system identifies changes in the foveal domain better than those occurring in the periphery, but as fixation progresses, our ability to detect changes at the peripheral level improves, possibly because of the need to programme and execute the next movement”, says the researcher.

“This is another step towards understanding the temporal dynamics of visual processing. For now, the results have been obtained in controlled environments. It remains to be seen how this process develops in more complex environments. It would also be relevant to know whether this way of processing information changes, for example, as we get older or due to brain lesions”, concludes De la Malla.