Caloric diagnosis maximum stimulus and suppression of habituation effects

The relation between randomized caloric stimuli of 30 degrees - 5 degrees C to the parameters: duration, maximum frequency and maximum intensity was electronystagmographically examined on 25 persons. The duration and the maximum frequency showed only a slight correlation to the stimulus. There was a linear correlation to the maximum intensity and the stimulus between 30 degrees and 15 degrees C. But with temperatures below 15 degrees C the reaction did not increase. So the maximum intensity corresponds best to the characteristics of the temperature wave in the petrous bone and thus to the cupula deviation. By mathematical correction of the randomized stimulus sequence it was possible to show that habituation effects can be suppressed by certain test conditions, e.g. a constant degree of alertness of the subject and free head movements in the intervals. It is recommended to replace the 30 degrees C stimulus by a 17 degrees C stimulus: by this strong stimulus extra-vestibular interference and the influence of a latent spontaneous nustagmus are relatively suppressed and hypoexcitability is more accurately determined. Temperatures below 15 degrees C are not recommendable: the vestibular stimulus is not stronger but more painful and pseudocaloric effects are accentuated. When ascertaining correctly a spontaneous nystagmus we propose to refrain from the determination of directional preponderance, the value of which seems questionable.