Loss of visual constancy of a fixated target induced by rapid movement of the head

The possibility that various types of conjugate eye movements are not merely a means of efficient perception but also determine the related visual effects is tested by imposing rapid (saccadic) movements upon the (slow) compensatory mechanism. 10 subjects were asked to shake and nod the head, at separate times, with increasing speed while fixating a stationary target. As the head reaches a frequency of resonance, at around 5 Hz, the fixated target appears to be jumping counter-head-wise.