Wolfgang H. Zangemeister and Lawrence Stark, Experimental Neurology Volume 75, Issue 2, February 1982, Pages 389-406
Head movement latencies are greater than eye movement latencies because of dynamic biomechanical lags. Our EMG recordings show equal latencies in the controller signals to eye movement and to head movement. The increased dynamic lag of head movement leads to the classical gaze pattern. First a rapid saccadic eye movement directs gaze onto target; a slower head movement follows. Its accompanying vestibular ocular reflex exchanges head position for eye position; the eye stays on target throughout. At the end of the movement, the eye is returned to the primary position. Head movement latencies are readily modified by experimental conditions such as instructions to the subject, frequency and predictability of the target, amplitude of the movement, and development of fatigue. They are affected by neurological disease processes. Effects on head latency are mirrored by idiosyncratic or covarying changes in eye movement latency. Covariance of latency in head and eye movements is attributed to concomitant higher level neurological processing because it is sensitive to stimulus predictability and to neural fatique. These experimental results may be readily demonstrated using a gaze latency diagram. They are also illustrated in a table derived from a branching model assignment of latencies according to a hypothetical neurological schema. The potential of these coordinated gaze latency studies for neurological diagnosis is illustrated in patients with homonymous hemianopia.