vHIT Gain: Instantaneous vs Median vs Regression

10 mins
09 February 2022

The three categories of gain calculation provided by the Interacoustics EyeSeeCam are:

  • Instantaneous gain
  • Median gain
  • Regression gain

 There are in fact three instantaneous gain values provided for lateral impulses, all restricted to less than 100ms after the impulse commences.  These gain values are the ratio of eye and head velocity. Values are provided at 40ms, 60ms and 80ms. Although emphasis is provided for the value at 60ms, the other values are provided because there is an indication that different (e.g. neurological) pathologies can lead to different gain values over the time course of the head impulse (Kremmyda et al., 2012).

In many (perhaps most) cases the instantaneous gain is both sufficient and ideal indication of VOR compensation for the head rotation. However, on occasions the goggle mounted camera can slip in relation to the pupil, causing “slippage” artefacts. Then the instantaneous gain can provide a misleading result.

In these cases we can turn to median gain and regression gain. Both of these values are also restricted to a time course of <100ms, which is important for providing an indication that is specific to VOR gain. These two gain calculations are averaged over the 100ms period, therefore should be less prone to artefactual anomalies present at any given moment in time (e.g. slippage, covert saccades, noise artefacts), although the dynamic information provided by instantaneous gain at multiple time points is lost. The regression gain and not the instantaneous gain would therefore be used routinely when performing RALP and LARP vHIT, since these procedures are more prone to google slippage.

Therefore, these various gain calculation methods are complimentary. A detailed discussion is provided by E. Schneider in an Interacoustics Academy webinar “Gain calculation methods in vHIT”.


Kremmyda, O., Kirchner, H., Glasauer, S., Brandt, T., Jahn, K., & Strupp, M. (2012). False-positive head-impulse test in cerebellar ataxia. Frontiers in neurology3, 162. doi:10.3389/fneur.2012.00162 


Michael Maslin
After working for several years as an audiologist in the UK, Michael completed his Ph.D. in 2010 at The University of Manchester. The topic was plasticity of the human binaural auditory system. He then completed a 3-year post-doctoral research program that built directly on the underpinning work carried out during his Ph.D. In 2015, Michael joined the Interacoustics Academy, offering training and education in audiological and vestibular diagnostics worldwide. Michael now works for the University of Canterbury in Christchurch, New Zealand, exploring his research interests which include electrophysiological measurement of the central auditory system, and the development of clinical protocols and clinical techniques applied in areas such as paediatric audiology and vestibular assessment and management.

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