[Neck-deep immersion effects on gaze fixation by primates]

Effects of load deprivation on gaze fixation were studies in two primates (Macaca mulatta) immersed neck-deep twice with a two-week interval. Gaze fixation was traced using electrooculography and measurement of head turn velocity in 5 hours since the beginning of immersion. Decrease of the maximum head velocity and vestibuloocular reflex gain in both animals were significantly higher in the second compared with the first period of immersion and the results of previous investigations with three primates repeatedly immersed chest-deep. During the second neck-deep immersion, loss of head velocity in both animals was accompanied by changes in the pattern of head movements toward the target that included emergence of a dual-wave velocity profile in one animal and noticeably earlier start of the head vs. saccade reaction in the other. To conclude, the longer load deprivation, the more profound changes in the memory-assisted central programming of eye-head movement coordination in the course of gaze fixation.