Flies do a precise and fast calculation to avoid a specific threat, and they are doing it using a brain that is as small as a grain of salt. They process information so quickly. Flies’ nervous system and muscles are able to control movements to a very, very fine scale. ~ Dutch biomechanist Florian Muijres
According to matterist doctrine, each time you shift your gaze (which you do several times every second), the brain sends a command to the eyes to move. A copy of that same command is issued to the internal visual system. This allegedly allows the brain to predict that it is going to receive a flood of visual information resulting from the body’s movement, and to compensate for the movement by suppressing or enhancing certain neural activity.
A fruit fly or housefly has to do the same thing, with a brain that is a miniscule fraction of yours. But the situation is even more complicated for a fly.
A fly’s eyes are bolted to its head. For a fly to shift its gaze, it must maneuver its whole body like a tiny airplane. Despite the physical encumbrance, a fly still manages to compensate for expected and unexpected visual motion.
A group of motion-sensitive neurons in a fly’s visual system are adjusted during a rapid, intentional turn. The compensation is quite specific: only visual motion along the yaw axis is suppressed. Sensitivity to roll is unimpaired.
This makes sense because a fly must first roll, and then counter-roll, to properly execute an intentional turn. If a fly were to counter-yaw, it could never head off on a new direction. So, the fly’s visual neurons must distinguish visual signals caused by yaw from those related to roll.
Visual neurons quantitatively silence their predicted visual responses to rotations around the relevant axis while preserving sensitivity around other axes. The brain can remove one sensory signal from a circuit carrying multiple related signals. ~ American neurobiologist Gaby Maimon et al
Once again, the assumptive physiological explanation is fantastic. The supposed neural computation is equivalent to tuning out the sound of a single instrument in an orchestra – it simply cannot be done. That a small group of nerve cells can selectively edit multiplexed signals at the speed at which flies fly is beyond belief. The most advanced algorithms that mathematicians and computer scientists have come up with could not accomplish such a fine-tuned feat. The idea that a few neurons could do so literally on-the-fly is absurd.