Figure 1.

Electrical stimulation of the right posterior canal influences perception of the subjective visual vertical. In the absence of stimulation, the subjective visual vertical is oriented near true earth-vertical (green bar, 0 Hz). Electrical stimulation of the right posterior canal (indicated by the yellow lightning bolt) results in a leftward rotation of the subjective visual vertical, consistent with the head being perceived as rolled to the right. Increasingly higher stimulation frequencies result in greater rotation from true earth-vertical (blue bar, 100 Hz; purple bar, 200 Hz).