motor responses to non-reportable stimuli

Geometrical symbols are presented to a test subject for short times of 50 ms on a screen. The test subject was instructed to react with a keystroke when recognizing a circle; observed reaction time was about 200ms.
However, If a circle was followed by a square within 60 ms, then the perception of the circle was masked. In these cases the test subject informs to have seen a square only, but no circle. Nevertheless the test subject always reacts with a keystroke; the action caused by the stimulus is carried out although consciousness is not involved.

Ansorge, U., Klotz, W. & Neumann, O. Manual and verbal responses to completely masked (unreportable) stimuli: exploring some conditions for the metacontrast dissociation. Perception 27, 1177-89 (1998).