Tham khảo tài liệu 'humanoid robots part 9', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Neurophysiological models of gaze control in Humanoid Robotics 193 . Head-free visual orienting movements head-saccadic movements. When the gaze shift becomes large the eye and the head work together. The oculomotor systems transformation the object position into target reference system and then in head reference system Goossens and Van Opstal 1997 Freedman and Sparks 2000 . Many models of these transformations were formulated. Bizzi and colleagues Bizzi et al. 1971 Bizzi et al. 1972 proposed the so-called oculocentric hypothesis. According to this model the head-free gaze is like the head-fixed gaze independently of the occurrence and size of the concomitant head movement. The vestibuloocular reflex VOR is switched-off and cancels any contribution of the head to the gaze. Several experiments showed that the VOR is more or less switched-off during saccades Laurutis and Robinson 1986 Pelisson et al. 1988 Lefevre et al. 1992 . Further experiments validated this hypothesis for gaze shifts smaller than 10 degrees. Differently from the head-fixed in which the hypothesis of eye movements with local feedback of current position is accepted Robinson 1975 in the head-free model it is supposed that the gaze motor-error drive the oculomotor system. According to this so called gaze feed-back hypothesis the gaze saccades can be maintained even if the VOR is suppressed during the movement. The main question is what is the source of the feedback As described in Fig. 3 two hypotheses are being explored. In the first hypothesis the gaze error after decomposition in eye-error and head-error drives both eye and head Fig. 3-A Goossens and Van Opstal 1997 . Differently in the second architecture there exists only a local feedback of the eye-position whereas the head act in open loop Fig. 3-B Freedman and Sparks 2000 Freedman and Sparks 1997 . A B Fig. 3. Two main hypothesis of gaze control architecture. A. The gaze error after decomposition drives both eye and head Goossens and Van
