The effect of the perceptual set was studied using the different stimuli of various lengths and the motor estimation task. The subjects estimated the lengths of pairs of segments located one above the other, presented on the touch screen. The task was to draw the line (as it was on the screen) with the index finger of their right hand. Movements were carried out from left to right, from top to bottom. In the set series, we used the pairs of segments of differing lengths, while in the test series the segments were equal. We did not find classical perceptual set effect in the task of the motor estimation of the line length. This result is consistent with the hypothesis of two subsystems of visual perception, according to which direct actions with objects do not require the use of memory, and therefore the contrast or assimilation effects is not to be found. The results were compared with the effects of the perceptual set using the illusory stimulus (Ponzo and Muller-Lyer illusions). The perceptual set effect was not formed with the Muller-Lyer illusion, and with the Ponzo illusion, there was the assimilative effect. It is concluded, that the effect in the motor assessment of the Ponzo illusion probably could be due to the involvement of the cognitive mechanisms in the formation of the Ponzo illusion. And it could be due to the effect of the repetition error in the recognition of equal segments as differing.