In this chapter, theoretical arguments plead for a retinotopic (relative) instead of spatiotopic (absolute) coding in the superior colliculus (SC), supporting the idea of a velocity (or relative position) feedback loop to the SC in the control of gaze saccades. Experimental data are also reported that argue objectively for a relative coding of gaze saccades: in humans, head-movement amplitude is proportional to gaze displacement, and not to gaze position in space. Finally, simulation results of a new model are presented that are in agreement with reported data and have several important implications. The chapter first addresses the implications of gaze-velocity versus gaze-position feedback, when the SC is placed inside or outside the gaze control loop. The proposed control modes are compared in terms of: control accuracy, the different collicular networks supporting these strategies, and their respective connectivity. Some experimental data is then presented that give interesting arguments in the context of the alternative between velocity and position feedback, and which report the influence of eye initial position on head-movement amplitude during gaze shifts in humans. On the basis of these arguments, a new eye–head coordination model is proposed that reproduces the further reported experimental data presented in the chapter.
Lefèvre, P. (1993). A new eye–head coordination model based on gaze velocity feedback to the superior colliculus. In Alain Berthoz (ed.), Multisensory Control of Movement (p. p. 269-289). Oxford University Press. https://doi.org/10.1093/acprof:oso/9780198547853.003.0147