Vestibular perception of angular velocity in normal subjects and in patients with congenital nystagmus

A technique is described for the assessment of vestibular sensation. The tw o main goals of the study were (i) to compare the perception of angular vel ocity with the eye velocity output of the vestibule-ocular reflex and (ii) to study vestibular function in patients with congenital nystagmus; this wa s needed since most previous studies, based on eye movement recordings, hav e been inconclusive. Subjects indicated their perceived angular velocity by turning by hand a wheel connected to a tachometer. The vestibular stimuli used consisted of: sudden deceleration from rotation at a constant horizont al velocity of 90 degrees/s ('stopping' responses). Eye movements were reco rded simultaneously with electro-oculography. In normal subjects the percei ved angular velocity decayed from the moment of deceleration in an exponent ial fashion. The mean time constant of sensation decay was similar to 16 s. Eye movement velocity decayed with a similar exponential trajectory (time constant 16 s). Congenital nystagmus patients showed markedly shortened ves tibular sensation (mean time constant 7 s). The following conclusions can b e drawn: (i) the similarity of the eye velocity and perceptual responses su ggests that these two systems receive a vestibular signal which has been si milarly processed; (ii) the time constant of the responses indicates that t his vestibular signal probably originates in the same brainstem 'velocity s torage' integrator; (iii) the technique described is useful for clinical as sessment of vestibular function, particularly in patients with ocular motil ity disorders; (iv) patients with congenital nystagmus have short vestibula r time constants, which is probably due to changes induced in velocity stor age processing by the persistent retinal image motion present in these pati ents.