Adaptation Of Eye Movements Research Articles

Eyelid movement abnormalities in progressive supranuclear palsy.

We systematically videotaped eyelid movements in a community-based series of 38 patients with progressive supranuclear palsy (PSP). Ten patients (26%) had blepharospasm, "apraxia" of lid opening and/or "apraxia" of lid closing. These patients as a group had more severe upgaze paresis but no greater disease duration than the patients without supranuclear lid dysfunction. Patients used a variety of synkinetic movements to overcome lid-movement abnormalities. One patient displayed "slow blinks," a phenomenon not previously described in PSP. Blink rate in PSP, 3.0/min, was markedly lower than that in patients with Parkinson's disease (PD), 12.5/min, and patients with PSP but not PD increased their blink rate during command versional eye movements.

Concomitant direction and distance aftereffects of sustained convergence: A muscle potentiation explanation for eye-specific adaptation

Fixating a target for 6 min was shown to produce distance aftereffects that varied in direction and magnitude as a linear function of the convergence angle. Eye-specific direction aftereffects also were obtained in a nasal direction under conditions that produce increased perceived dtstance and in a temporal direction under conditions that produce decreased perceived distance. These aftereffects were shown to be sensitive to the range of horizontal versional eye movements that accompany the near or far convergence positions maintained during exposure. The results provide a logical alter­ native to perceptual learning accounts of eye-specific adaptation. Maintaining the eyes in a fixed or restricted range of convergence positions may induce a muscle potentiation aftereffect in the subset of extraocular muscles innervated to achieve and sustain those postures. Muscle potentiation refers to an involun­ tary component of continued innervation in the direction of previous muscular stimulation. Since the increase in muscle tension is involuntary, registra­ tion of eye-position information based on the monitoring of voluntary motor signals should be in error to the degree that the potentiation effect must be overcome. Assuming that the potentiation effect itself is not registered via an inflow from proprio­ ceptive units in the extraocular muscles, it follows that any perceived spatial dimension that requires compensation for or registration of ocular rotation should undergo changes consistent with the felt position of the eyes. Accordingly, changes in per­ ceived distance should occur whenever the eyes have been maintained predominantly in near or far con­ vergence positions. For example, if the medial recti of each eye are potentiated by maintaining the eyes in a near convergence position, then it would be as if each eye was being involuntarily pulled nasally. Therefore, in order to fixate a visual target, the observer would have to overcome the additional innervation due to potentiation by the same amount of voluntary innervation in the opposite direction, i.e., in a temporal direction that would normally result in a smaller convergence angle. This change in

Accommodative vergence in the alert monkey. Motor unit analysis

The behavior of both abducens nucleus and oculomotor nucleus motoneurons during accommodative vergence eye movements is examined in the alert monkey. This behavior is compared with that of the same neurons during versional eye movements. The behavior is found to be identical, which indicates that oculomotor unit discharge is determined by fixation angle without regard to the type of movement used to reach that angle. Detailed statistical analysis of unit firing rate also suggests that the separate inputs controlling vergence and version are probably combined at some supranuclear level before the motoneuron. The firing rates of motoneurons during the dynamic phase of a vergence movement is examined and compared to that during pursuit movements in an attempt to correlate neuron discharge with the mechanical dynamics of the orbit.