Experimental procedures are described which respectively enlarge stimulus duration in vestibular peracceleratory tests, and allow to rule out direct thermal effects on the vestibular nerve during long term calorisations. First experimental results indicate that time course of nystagmus during prolonged stimulations differs markedly in rotational and caloric tests. Whereas there is a distinct decline of response during rotation (in accordance to the predictions of current mathematical models), in caloric tests nystagmus reaches a steady state level, maintained for at least 15 min. Caloric and vestibular stimulations produce nystagmus, the slow phase velocity (SPV) of which is proportional to cupular displacement. However, it is a wellknown fact that during prolonged stimulation (leading to a constant cupular displacement) there is a decline of SPV, indicating that adaptation occurs in the vestibulo-ocular reflex (Ek et al., 1960;Malcolm and Jones, 1970;Young and Oman, 1968) 9 Fernandez andGoldberg (1971) showed that this adaptation is already present in the peripheral vestibular nerve.
Mathematical descriptions of the vestibulo-ocular reflex consider this adaptation effect by assuming an exponential decay of SPV to zero in response to a constant cupular displacement (Young and Oman, 1968;Malcolm and Jones, 1970;Schmid et al., 1971). These models were shown to be in good agreement with experimental results of the common rotational and caloric tests 9 Experiments using prolonged rotational stimuli of up to 84 s duration (Guedry and Lauver, 1961;Collins and Guedry, 1962) showed