Abstract: In the course of a 21-day Dry Immersion (DI), we studied the strength of Ponzo and Müller–Lyer visual illusions with the help of verbal response and two variants of the motor response by means of “tracking” (with the presence and absence of visual feedback). The studies were performed with the participation of ten subjects before the start of DI, on the 3rd, 10th, and 20th day of DI, as well as at the end of it. It was shown that DI mainly affects the motor response. Changes in reducing the strength of visual illusions were more pronounced for a more complex motor task performed in the absence of visual feedback. The results are in agreement with the data that we previously obtained under the conditions of a 5-day DI. One of the possible mechanisms of the observed changes in the illusions estimates may be hyperactivation of the dorsal visual pathway due to gravitational unloading.