Fruit flies respond quickly to changes in the visual environment, Seeing is the essence of contrast perception. When lighting conditions change, the eye needs a certain amount of time to adjust and be able to assess the contrast correctly again.
These processes are relatively well understood.
However, researchers have discovered a mechanism used by the fruit fly Drosophila melanogaster that broadens our understanding of visual perception.
Their results explain why the eye can correctly assess contrast even in suddenly altered lighting conditions. Fruit flies can do this because they have nerve cells in their visual system that respond to brightness.
These nerve cells allow flies to improve their behavior when visual stimuli change dynamically, the researchers explain. Fruit flies respond quickly to changes in the visual environment.
The sensory systems of living organisms have developed in such a way that they mark changes rather than absolute sensory data. For example, you can forget that you wear a necklace during the day, but when an insect lands on your skin, you can feel it immediately. The vision of such functions can be adjusted and designed to respond to changes in the environment.
Many nerve cells react to contrast rather than brightness. For this reason, many animals have a visual system that works very well at dawn, at night, during the day, or in a rapidly changing environment.
Retinal photoreceptor productivity plays a key role in vertebrates and invertebrates. These photoreceptors ensure that contrast is captured without regard to backlighting.
This retinal adjustment itself cannot explain the mechanism that overcomes sudden changes, such as when an animal moves fast or when it sees objects moving from bright sunlight to shadows. In such cases, the backlight can change in milliseconds. Fruit flies respond quickly to changes in the visual environment.
During their study, the team of neurologists focused on processes that occur directly downstream of the photoreceptors in the nervous system.
They pay special attention to signaling pathways that involve laminated neurons that specialize in detecting an increase or decrease in contrast.
Contrast-sensitive nerve responses alone are not enough to explain the behavioral responses of changes in visual stimulation and suggest a correction signal that measures contrast-sensitive responses when background brightness suddenly decreases.
We can show that light information acts as a correction signal which intervenes when it suddenly goes dark. This means that lighting information is needed to accurately identify contrast, Researcher added.
So far, it has been assumed that the relative contrast transmitted from other neurons to the lamina must look right, even with lighting conditions that change rapidly, so that the visual reaction can be calculated correctly, for example, when football moves from light to shadow.
Neurologists can demonstrate this by measuring calcium signals in nerve cells using a two-photon microscope. This technique allows them to determine the activity of individual nerve cells in living fruit flies. Our measurements show that there are cells that do not respond to brightness and contrast.
The team confirmed this result through a behavioral experiment in which flies were made to run on small balls with airbags with dynamically changing backgrounds.
In addition, we can show that these brightness-sensitive cells are needed to respond to flies if the background is dark quickly, the researchers said. When Lamina L3 neurons are inactive, there is no adequate behavioral response.
In this way, researchers have identified a new mechanism that explains how precise image processing works in dynamically changing lighting conditions. Contrast sensitivity alone is not enough to consider behavioral responses to visual stimuli.
The researchers concluded that light intensity, the most important input to the visual system, is also an important factor in controlling the behavioral response of visual input. They suggest that this is a common visual processing strategy that can also be used by the human eye.