For example, if a neuron were to receive signals coming from five other neurons, three of these signals could be of activation and two of inhibition. If the result of the signals were to be greater than a previously established program value, the receptor neuron would set off a new impulse, which would be transmitted to the following layer. If the sum were to be below this value, known as a limit, a real physiological property, the neuron would remain inactive, without passing on the information. It is this communication based on convergence and divergence, summed to the time taken for its completion, which explains the phenomenon known as flash-lag.

Baldo and Caticha believe that the model applied to flash-lag could help in explaining other visual illusions, such as the Fröhlich Effect, when an object in movement seems to be behind another, static, and hinders the formation of details of the start of the trajectory. Imagine a wildcat jumping out from behind a tree: probably it will not be possible to identify its mouth and snout, which are the first to turn up from behind the tree, and the image of the wildcat would be built up starting from either the left or the right sides of its face. A better understanding about the different visual illusions also represents the possibility of knowing in greater detail the general working of vision itself. Baldo does not discard the hypothesis of any image formed, even those called normal, which in theory do not suffer interferences, could be considered an illusion, since they will never be an exact representation of reality. “I believe that all of us look at the same person or at the same scenario with differences in details, not always subtle”, he suggested. “Vision is always an interpretive reading of the world and there is no absolute precision.”

Late images – Flash-lag began to catch people's attention in 1958, with an article from the physicist Donald MacKay, from the University of Keele, England, published in Nature. In this work, physicist MacKay described a phenomenon that would remain for many years without an explanation: when he had agitated a lamp and had illuminated it with another source of stroboscopic light – which goes on and off at regular intervals, in successive flashes –, one had the impression of seeing the filament to the front, as if it were outside of the lamp. Only in 1994 did the Indian psychologist Romi Nijhawan, currently at the University of Sussex, also in England, offered the first explanation about the phenomenon, when stating that all of the objects are seen with a delay.

Thus, a car that is coming down a road could already be a meter in front when the brain manages to process the image. According to Nijhawan, the evolution of the human brain must have developed a mechanism to automatically eliminate the difference in phase of space and the delay in the perception of the image, but only when the trajectory is already known. If there is a surprise the brain will not be capable of making these adjustments– and flash-lag will pop up. For this reason the risk of being knocked down by a car that seems to have come ‘all of a sudden’ around the corner is greater.
In 1995, Baldo and the American physicist Stanley Klein, from the University of California, United States, also published in Nature another study concerning flash-lag, showing that this type of visual illusion could well come from lack of attention. The idea was simple: as one’s attention is drawn to the object in movement, it takes a longer time to perceive and determine the position of any new element that appears on the scenario like a flash and calls one’s attention to it.

Neurons in neutral – Very similar arguments were used three years later, in 1998, by two independent groups of researchers: one headed by the American professor of optometry, Harold Bedell, today at the University of Houston, United States; the other one coordinated by two psychologists, David Whitney, currently at the University of Western Ontario, in Canada, and Ikuya Murakami, from the NTT Communication Science Laboratories, in Japan. The two teams had been working with the perspective of time differences in the perception of objects – or latencies. They held that the brain, already accustomed with the previously identified scene, had the need to go through a type of warming up process in order to return to its neural activity and to register a new object. It is as if the neurons were already in a position of resting, in neutral, and thanks to the sudden stimulus they saw themselves obliged to pass again through first, second and third gears until they recover their normal velocity. The model from the two physicists unifies these theories, showing that the proposals previously showing discrepancies or even contradictions are, in truth, facets of the same phenomenon looked at from different angles.

Now, a warning. Before they presented the mathematical model that they created and that will shortly be published in the magazine Vision Research, Baldo and Caticha usually  invite for a test people who visit them for the first time. They ask that the visitor sit in front of a switched on computer and they would off the light in the room, full of archives and papers spread over the desk. With just a click on the mouse a small line appears on the screen, always moving horizontally, in a straight line. When it reaches a fixed point, predetermined and marked, a luminous flash –a second  line – blinks on the screen. The task is to say where this second point had appeared. Most of the times the reply from this reporter was: “Before the other one”. The researchers smiled with satisfaction, faced with yet another victim of the effect of flash-lag: in truth, the two lines had been in line. The explanation that the two physicists then offer clarifies why many times we are betrayed by vision, and allows us to look with more sympathy at the difficulties confronted by linesmen on a football field, under the eyes of thousands of fans.