All hvHIT examinations were carried out by the same experienced right-handed examiner (M.K.) employing the Otometrics - Natus ICS Impulse device (Taastrup, Denmark) in which the camera captures the right eye movements alone. For the vHIT system used the VOR gain is calculated as the whole area under the curve of the velocity over time recordings of the eye movement divided by that of the head. Physiologically occurring microsaccades characterized by eye movements smaller than 15 minutes of arch with velocity < 50 deg/sec are screened out by the vHIT system (17). The vHIT test was carried out as has been previously described for the Otometrics - Natus ICS Impulse system (16). For each participant 20 repetitions of the head impulse were randomly carried out to the left and right sides.

The outcome measures for the hvHIT were the horizontal canal VOR gain; percentage of gain asymmetry ((rightward gain – leftward gain / rightward gain + leftward gain)*100), head velocity (degrees/sec), RS velocity (degrees/sec), RS latency (msec), and RS frequency ((number of corrective saccades / number of eligible head thrusts) * 100).

42 healthy subjects with no vestibular complaints and normal otoneurological examination had vHIT testing of the horizontal semicircular canals employing the Otometrics - Natus ICS Impulse device (Taastrup, Denmark). All the examinations were carried out by the same experienced right-handed examiner (M.K.). The gain values obtained had normal distribution averaging 0.88+ 0.08 (mean + standard deviation) for the left horizontal semicircular canal and 1+ 0.14 (mean + standard deviation) for the right semicircular canal. Taking into consideration normal range within mean + 2 standard deviations, the calculated normal ranges for the hvHIT gains are 0.72 – 1.04 and 0.72 – 1.28 for the left and right side respectively.