Fig. 3. The vergence eye movements are shown separately for the convergence (a, b) and divergence (c, d) components of the vergence position (a, c) and the relative lid position (b, d). Eye movements during the blink condition (black solid traces) are compared with those during the no blink condition (dotted trace). All traces are aligned to vergence onset. For better illustration, the onset of two phases of the vergence components is indicated by vertical dotted lines. In phase 1, a convergence-divergence movement is found in the convergence (a) and in the divergence (c) paradigms. Note that vergence duration exceeds blink duration; modified after Rambold et al. 2002 [42], with permission.

explain the outlined behavioral effects. Further evidence comes from a saccadic brainstem model that incorporates rebound inhibition firing of the mediumlead burst neurons [81].

Blinks and Vergence Eye Movements

Vergence may be divided into two subsystems: a transient and a sustained vergence system [82, 83]. The transient vergence system is elicited by large retinal disparity errors, which cannot be fused on the retina; the sustained vergence is largely elicited by similar images, small disparity errors, or velocities of less than 4 /s [83, 84]. Blinks affect both subsystems of vergence. Following blink-associated eye movements, the subsequent transient vergence is increased in duration and decreased in velocity when a voluntary blink is elicited (fig. 3).

Fig. 4. Eye position traces are shown for vergence position (a, b) and lid position (c, d) in one healthy subject. The two different vergence directions, convergence (a, c), and divergence (b, d) are shown separately. a–d Thick solid lines indicate the mean of the control condition (without blinks), while the dashed lines show recordings during the blink condition. The long dashed line indicates the end of the blink. The gray inset (a, b) represents the part shown below at higher resolution and as vergence velocity in e, f . e, f Thick solid lines indicate the vergence velocity in the control condition (dotted lines 1 standard deviation), and thin solid lines vergence velocity in the blink condition. The arrows mark the late peak vergence velocity. All traces are aligned to blink onset and shifted for better comparison; modified after Rambold et al. [68], with permission.

This effect is also time dependent; the earlier blinks start before the vergence onset, the more their duration is increased and peak velocity decreased [42].

The blink effect on transient vergence movements may be related to changes in the brainstem premotor circuit, including the OPNs [68], since OPNs also control vergence burst neurons [85]. Accordingly, stimulation of the OPN area slows vergence movements [85]. The peak of vergence velocity depends on the stimulus direction when a reflexive blink is elicited during sustained vergence [68] (fig. 4). This velocity peak shows oscillations (1.7–3.3 Hz) similar to vergence oscillations [25, 83]. These oscillations may be caused by the inhibition of OPNs leading to a disinhibition of the vergence systems.

Blinks and Saccade-Vergence Interaction

To perform saccades in space, conjugate and vergence eye movements are elicited together [86]. Blinks also exert a distinct influence on combined

Fig. 5. Eye velocity responses of step-ramp smooth pursuit (target: thin, solid line) are shown for the blink paradigm (gray lines) in rightward (1st trace) and leftward (2nd trace) directions. The mean desaccaded control pursuit velocity (control paradigm; bold solid line) is superimposed. Below each plot, the lid position is shown (3rd trace). Blink-associated eye movements are marked by asterisks. The other fast peaks in eye velocity reflect saccades that occur with some pause before or after the blink, but not during the blink. After the blinkassociated eye movements, there is a velocity decrease compared to control for both directions and subjects. b The pursuit velocity (mean: solid black line; individual data: thin gray lines) in the blink and control paradigms are subtracted for rightward (1st trace) and leftward (2nd trace) pursuit directions for the interval indicated by the dashed rectangle in a. All data are aligned to maximal lid closure during the blink. Negative velocity indicates a decrease compared to that of the control; modified after Rambold et al. [65], with permission.

saccade-vergence eye movements: both components are decreased in peak velocity, acceleration, deceleration, and increased in duration [42]. This effect might be related to the inhibitory effect of blinks on the OPNs [79, 80, 87].

Blinks and Smooth Pursuit Eye Movements

Introducing a blink just before target onset in a step-ramp smooth pursuit paradigm causes a decrease in pursuit latency of about 10 ms. This effect is on the average less than the gap effect of 35 ms in a gap paradigm (extinguishing the visual stimulus before target onset) when using a comparable gap and blink duration [41]. Saccades are suppressed during the blink but not during the gap [65].

When a reflexive blink is introduced during ongoing smooth pursuit there are blink-associated eye movements, which are followed by a decrease in pursuit velocity (fig. 5). This decrease is independent of the direction and the blink