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LIP seems to encode decision variables for saccade direction.

Excitatory burst neurons (EBNs) in the paramedian pontine reticular formation (pprf) (pons) initiate saccades.

These neurons receive direct excitatory input from SC and inhibitory input from the nucleus raphe interpositus (RIP) (brainstem).

Wang et al. provide evidence that SC might during saccades turn of RIP inhibition through the central mesencephalic reticular formation (cMRF) while it drives EBNs.

Electrical stimulation of the cat SC can evoke saccades.

Typically, these saccades go into that general direction in which natural stimuli would lead to activation in the area that was electrically stimulated.

The SC may play a major role in the selection of stimuli—as saccade targets or as reaching targets.

Since we analyze complex visual scenes in chunks by saccading from one location to another, information about saccades must be used to break the constant stream of data coming from the eyes into chunks belonging to different locations in the visual field.

By contrasting performance in a condition in which their test subjects actually made saccades to that in a condition when only the image in front of their eyes was exchanged, Paradiso et al. showed that explicit information about saccades --- not just the change of visual input itself --- is responsible for resetting visual processing.

While the signal indicating a saccade could be proprioceptive, the timing in Paradiso et al.'s experiments hints at corollary discharge.

There are parallels between visual attention and eye movements because both serve the purpose of directing our processing of visual information to stimuli from a region in space that is small enough to handle for our brain.

Since visual attention and eye movements are so tightly connected in the process of visual exploration of a scene, it has been suggested that the same mechanisms may be (partially) responsible for guiding them.

There is evidence suggesting that one cannot plan a saccade to one point in space and turn covert visual attention to another at the same time.

Born et al. provided evidence which shows that preparing a saccade alone already enhances visual processing at the target of the saccade: discrimination targets presented before saccade onset were identified more successfully if they were in the location of the saccade target than when they were not.

Born et al. showed that, if the color of a saccade target stimulus is task relevant, then identification of a discrimination target with that same color is enhanced even if it is not in the same location.

• either there are separate, competing fixation and motion systems,
• or there is competition between neurons in the SC coding for different motions.

According to Casteau and Vitu, a fixation population, if it exists, is probably located not in the SC but in the brainstem omnipause region.

According to Casteau and Vitu, a fixation population, if it exists, is probably located not in the SC but in the brainstem omnipause region.

Omnipause neurons (OPN) receive input from neurons across the SC, though more strongly from the rostral part.

Distractors close to a saccade target do not seem to affect saccade latency but change their landing sites.

Casteau and Vitu see the lack of a change in saccade latency due to distractors close to the saccade target as evidence against the lateral-inhibition theory of saccade generation.

Casteau and Vitu's results seem to show that it's not proximity between target and distractor but the ratio of their excentricities that saccade delay is dependent of.

The in-vitro study of the rat intermediate SC by Lee and Hall did not find evidence for the long-range inhibitory/short-range excitatory connection pattern theorized by proponents of the neural-field theory of SC fixation.

Rucci et al.'s neural network learns how to align ICx and SC (OT) maps by means of value-dependent learning: The value signal depends on whether the target was in the fovea after a saccade.

Rucci et al.'s model of learning to combine ICx and SC maps does not take into account the point-to-point projections from SC to ICx reported later by Knudsen et al.

Saccades evoked by electric stimulation of the deep SC can be deviated towards the target of visual spatial attention. This is the case even if the task forbids a saccade towards the target of visual spatial attention.

Activation builds up in build-up neurons in the intermediate SC during the preparation of a saccade.

Activation build-up in build-up neurons is modulated by spatial attention.

Visual sensitivity is strongly reduced during saccades.

Visual sensitivity is strongly enhanced after saccades.

According to Quaia, the Robinson model of saccade generation introduced the idea that saccades are controlled by a feedback loop in which the current eye position is compared to the target eye position and corrective motor signals are issued accordingly.

This idea was integrated in a family of later models.

After ablation of the SC, accurate saccades are still possible. Initially, trajectory and speed are impaired, but they recover.

Quaia et al. present a model of the saccadic system involving SC and cerebellum, which reproduces the fact that the ability to generate fast and precise saccades recovers after ablation of the SC.

Lesions to the cerebellum can permanently affect the accuracy and consistency of saccades.

Activity in the SC drives the saccade burst generators which are oculomotor neurons in the reticular formation.

Tabareau et al. propose a scheme for a transformation from the topographic mapping in the SC to the temporal code of the saccadic burst generators.

According to their analysis, that code needs to be either linear or logarithmic.

Girard and Berthoz review saccade system models including models of the SC.

Except for two of the SC models, all focus on generation of saccades and do not consider sensory processing and in particular multisensory integration.

Spatial attention can enhance the activity of SC neurons whose receptive fields overlap the attended region

FEF stimulation elicits saccadic eye movements.

The motor map is not monotonic across the entire FEF, but sites that are close to each other have similar characteristic saccades.

Schenck summarizes three neurorobotic studies in which he evaluates visual prediction, and, more specifically, predictive remapping. He argues that his experiments support a claim in psychology saying that pre-saccadic activation of neurons whose receptive fields will contain the location of a salient stimulus after the saccade is not just pre-activation but actually a prediction of what the visual field will be like after the saccade.

Certain neurons in the deep SC emit bursts of activity before making a saccade.

It has long been known that stimulating the SC can elicit eye movements.

Currently, three types of saccade-related neurons are distinguished in the deep SC:

• Burst- and build-up neurons on the one hand,
• fixation neurons on the other.

Onset times of visually guided saccades have a bimodal distribution. The faster type of saccades are termed express saccades'. Ablation of the SC but not of the FEF makes express saccades disappear.

Removing both SCs and both FEFs leads to permanent deficits:

• a decrease in fixation accuracy,
• a neglect of the peripheral visual field,
• the range of saccadic eye movements is reduced.

Schiller et al. did not observe the visuospatial neglect and stark loss of oculomotor function as did Sprague and Meikle.

The cerebellum is involved in saccade generation.

Certain Purkinje cells in the oculomotor vermis of the cerebellum have saccade-related activity: Helmchen and Büttner found neurons which displayed:

• a saccade-related burst (most of them),
• a saccade-related burst, followed by a pause,
• either a pause or a burst, depending on the direction of the saccade.

Unilateral deactivation of the caudal fastigial nucleus in the cerebellum leads to hypermetria of saccades to the ipsilateral and hypometria of saccades to the contralateral side.

Deactivation of the caudal fastigial nucleus in the cerebellum increases the variability of saccades.

There are neurons in the supplementary eye field which are related to

• eye movements,
• arm movements,
• ear movements,
• spatial attention.

It is possible that learning of saccade target selection is influenced by reward.

The question is whether this happens on the saliency- or selection side.

McHaffie et al. speculate that loops through various subcortical loops might solve the selection problem, ie. the gating of competing inputs to shared resources.

In the SC, this means that the basal ganglia decide which of the brain structures involved in gaze shifts access to the eye motor circuitry.

Goldberg and Wurtz found that neurons in the superficial SC respond more vigorously to visual stimuli in their receptive field if the current task is to make a saccade to the stimuli.

Lesions to SC and FEF individually do not eliminate saccades. Lesions to both do eliminate saccades.

Brainstem activation is very similar to actual muscle behavior.

Fujita models saccade suppression of endpoint variability by the cerebellum using their supervised ANN model for learning a continuous function of the integral of an input time series.

He assumes that the input activity originates from the SC and that the correction signal is supplied by sensory feedback.

In the first experiment by Brouwer et al, people fixated different parts of a shape depending on whether the task was just to look at it or grasp it.

So the question for saccade control is: is there time and where does sensory data come from?

Are there representations, forward models of saccade controls in the SC?

Auditory signals gain relevance during saccades as visual perception is unreliable during saccades.

It would therefore be a good candidate for feedback if saccade control is closed-loop.

The SC is also involved in eye, head, whole-body, ear, whisker and other body movements.

Omnipause neurons in the reticular formation tonically inhibit the saccade-generation circuit'.

It seems unclear what is the original source of SC inhibition in preparation of anti-saccades. Munoz and Everling cite the supplementary eye fields (SEF), dorsolateral prefrontal cortex (DLPFC) as possible sources, and the substantia nigra pars reticulata (SNpr).

Trappenberg presents a competitive spiking neural network for generating motor output of the SC.

During reading, the further a saccade lands from the center of a word, the greater the probability of a re-fixation.

Pajak and Nuthmann found that saccade targets are typically at the center of objects. This effect is strongest for large objects.

Lateral prefrontal cortex (LPFC) and frontal eye fields (FEF) are frontal cortex regions involved in visual attention and target selection.

The direction of a saccade is population-coded in the SC.

There exist two hypotheses for how saccade trajectory is population-coded in the SC:

• the sum of the contributions of all neurons
• the weighted average of contributions of all neurons

The difference is in whether or not the population response is normalized.

According to Lee et al., the vector summation hypothesis predicts that any deactivation of motor neurons should result in hypometric saccades because their contribution is missing.

According to the weighted average hypothesis, the error depends on where the saccade target is wrt. the preferred direction of the deactivated neurons.

Lee et al. found that de-activation of SC motor neurons did not always lead to hypometric saccades. Instead, saccades where generally too far from the preferred direction of the de-activated neurons. They counted this as supporting the vector averaging hypothesis.