Researchers unravel mechanisms that facilitate precise identification of moving images

An international collaboration elucidates the mechanisms that facilitate the precise identification of moving images. The results were published in Nature Communication

Imagine meeting a friend on the street and imagine that with every step they take, your visual system has to process their image from scratch in order to recognize them. Now imagine if the same thing happened with every object and creature that moves around us. We would live in a constant state of uncertainty and inconsistency. Fortunately, this is not the case.

Our visual system is able to retain the information obtained in motion, thus presenting us with a more coherent picture of our surroundings. These are the conclusions of a study carried out by SISSA, in collaboration with the University of Pennsylvania and the Katholieke Universiteit Leuven and published in Nature Communication, which explains the neural foundations of this phenomenon.

One of the biggest challenges for all sensory systems is to maintain a consistent representation of our surroundings, despite the constant changes that are happening around us. The same goes for the visual system. It is enough to look around us: objects, animals, people, all in motion. We move ourselves. This triggers rapid fluctuations in the signals acquired by the retina, and until now it was not clear whether the same type of variations applied to the deeper layers of the visual cortex, where information is integrated and processed. If this were the case, we would be living in enormous confusion. “

Davide Zoccolan, director of the Visual Neuroscience Laboratory, International School of Advanced Studies

It has long been known that the signals produced by the retina as a result of the presentation of visual stimuli reach a set of consecutive processing steps within the visual cortex, organized in a finely regulated hierarchy. It is this processing sequence that allows us to recognize an object or a face, regardless of its angle or position. This has been demonstrated in the case of static stimuli and is explained by the invariance in the encoding of images which is gradually built up along the cortical hierarchy.

To study the existence of a similar process in dynamic situations, researchers from SISSA, the University of Pennsylvania (Penn) and the Katholieke Universiteit Leuven (KU Leuven), led by Zoccolan, analyzed the signals produced by neurons through different visual cortical areas in rodents after presentation of dynamic visual stimuli. The results were published in Nature Communication.

“We used three separate datasets: one collected by Liviu Soltuzu at SISSA, one collected by Kasper Vinken at KU Leuven in the group led by Hans Op de Beeck and one made available free of charge by the Allen Institute for Brain Science in Seattle, ”the scientist said. “The visual stimuli used in each were of different types. In SISSA we have created dedicated video clips showing objects moving at different speeds. The other data sets were acquired using various types of clips, including from movies. “

Next, the researchers analyzed the signals recorded in the different areas of the visual cortex using a combination of sophisticated algorithms and models developed by Eugenio Piasini and Vijay Balasubramanian of Penn in collaboration with scientists from SISSA (Liviu Soltuzu, Paolo Muratore and Riccardo Caramellino). Researchers have developed a theoretical framework to help connect movie images to the activity of specific neurons to determine how neural signals evolve over different time scales.

“The art in this science was to find a method of analysis to show that the processing of visual images slows down as you go deeper and deeper into the brain,” says Balasubramanian. “Different levels of the brain process information on different timescales – some things could be more stable, others faster. It’s very hard to tell if timescales change in the brain, so our contribution was to design. a method of doing it. “

The results remained consistent regardless of the nature of the visual stimuli: “We observed an increased persistence of neural responses recorded in deeper stages of the visual system, a kind of ‘perceptual constancy’ which guarantees a certain stability in the visual system. encoding information and eliminates fluctuations seen in prior visual areas, ”Zoccolan explains. “And not just that. We also noticed a form of ‘intrinsic’ persistence that increased along the hierarchy of visual areas. In deeper areas, the neural response remains for a few hundred milliseconds even after the stimulus has subsided, which guarantees a minimum time for encoding the images, and this in turn ensures that the information is correctly processed and that the response to the stimulus is correctly calibrated. “