Inhibition of saccade and vergence eye movements in 3D space

Abstract

Inhibitory capacity was investigated by measuring the eye movements of normal subjects asked to fixate a central point, and to suppress eye movements toward visual distracters appearing in the periphery or in depth. Eight right-handed young adults performed such a suppression or distracter task. In different conditions, the distracter could appear at 10 degrees left or right at a distance of 20, 40, or 150 cm (calling for horizontal saccades), or in a central position far or close (calling for convergence or divergence), or 7.5 degrees up or down at 40 or 150 cm (calling for vertical saccades). Eye movements were recorded binocularly with an infrared light eye-movement device. Results showed that (1) suppression performance was not perfect, as the subjects still produced eye movements; (2) errors were distributed unequally in three-dimensional space, with more frequent errors toward distracters calling for convergence, or leftward and downward saccades at a close distance; (3) distracters calling for saccade suppression yielded saccades in the direction of the distracter (that we called prosaccades), and saccades directed away from it (that we called spontaneous antisaccades); (4) for vergence, only distracters calling for convergence yielded errors, which were always promovements; (5) in addition, a small convergent drift was found for convergence distracters. Differences in the errors between saccade and vergence suggest that different inhibitory mechanisms may be involved in the two systems. Spatial left/right, up/down, and close/far asymmetries are interpreted in terms of attentional biases.

Saccades during symmetrical vergence

“…However, the latter was correlated neither to visually-guided saccades, to express saccades, nor to erratic saccades in the antisaccade task [24]. In a recent study using a distracter task, we also observed a rightward bias in microsaccadic activity, particularly at close distance [12]. This set of results suggests that we do not explore visual left and right spaces similarly.…”

“…Monophasic square wave intrusions (MSWI), biphasic square wave intrusions (BSWI), single saccadic pulses (SSP) and double saccadic pulses (DSP) have been previously described by Abadi and Gowen during fixation [1]. For MSWI, we used an upper limit of 500 ms as inter-saccadic delay [12]. Among SSP occurring during vergence, we distinguished between SSP followed by a backward drift (SSPbd) and SSP followed by an ownward drift (SSPod).…”

Dorsolateral Prefrontal Cortex Prevents Short-latency Saccade and Vergence: a TMS Study

“…In all, we suggest that the short-latency triggering described to date for saccades can generalize symmetrical convergence (without the contribution of saccades) under particular conditions of spatial arrangement and prefrontal disinhibition. This assumption is supported by a recent study showing that unwanted short-latency convergence could occur when a convergence distracter has to be ignored (Coubard and Kapoula, 2005).…”

“…Anticipated divergence contrasted convergence that was little anticipated and could be explained by some passive relaxation of the eyes. Against this hypothesis is our recent observation in a distracter task: when normal subjects were asked to fixate a position on the median plane and ignore distracters presented in depth (either in front of or behind the fixation location), they almost never diverged spontaneously but, in contrast, were prone to produce convergence erratic movements or a convergent drift (Coubard and Kapoula, 2005). Thus, the anticipatory mode of triggering for divergence, also described in prior studies (Takagi et al, 1995;Coubard et al, 2004), would rather be a volitional behavior that may correspond to a phylogenetic survival of an oculomotor function aiming to rapidly detect a predator or a prey.…”

“…Shorter mean latencies at near might be due to higher rates of express latencies, but this was not investigated. Coubard and Kapoula (2005) showed that the ability to inhibit an eye movement towards a distracter presented at various locations in direction or in depth was poorer when the distracter was close to the observer (20 or 40 cm) than when it was farther. Based on these observations, the present study aimed (i) to create favourable conditions for the emergence of short latencies for both saccades and vergence; and (ii) to test under such conditions whether TMS over the DLPFC promotes further short-latency triggering.…”