Saccades

Humans’ conscious awareness of objects in their visual periphery is limited. This limit is not entirely the result of reduced visual acuity. Rather, it is primarily caused by crowding—the difficulty identifying an object when it is surrounded by clutter. The effect of crowding on visual awareness in infants has yet to be explored. Do infants, for example, have a fine-grained “spotlight,” as adults do, or do infants have a diffuse “lantern” that sets limits on what they can register in their visual periphery? We designed an eye-tracking paradigm to psychophysically measure crowding in infants between 6 months and 15 months of age. We showed infants pairs of faces at three eccentricities, in the presence or absence of flankers, and recorded infants’ first saccade from central fixation to either face. Infants could discriminate faces in the periphery, and flankers impaired this ability. We found that the effective spatial resolution of infants’ visual perception increased with age, but...

Saccadic eye movements direct the high-resolution foveae of our retinas toward objects of interest. With each saccade, the image jumps on the retina, causing a discontinuity in visual input. Our visual perception, however, remains stable. Philosophers and scientists over centuries have proposed that visual stability depends upon an internal neuronal signal that is a copy of the neuronal signal driving the eye movement, now referred to as a corollary discharge (CD) or efference copy. In the old world monkey, such a CD circuit for saccades has been identified extending from superior colliculus through MD thalamus to frontal cortex, but there is little evidence that this circuit actually contributes to visual perception. We tested the influence of this CD circuit on visual perception by first training macaque monkeys to report their perceived eye direction, and then reversibly inactivating the CD as it passes through the thalamus. We found that the monkey's perception changed; duri...

The time of occurrence of eye, head, and arm movements directed at the same visual target was measured in five human subjects. The latency of activation of the corresponding neck and arm muscles was also measured. It appears that although the overt movements are sequentially ordered (starting with the eye movement, then the head and finally the arm) the EMG discharges are synchronous with respect to the eye movement onset. In addition, eye movement latency appears definitely (though weakly) correlated with either neck or arm EMG latencies. Neck and arm EMG latencies are also mutually correlated. These results indicate a clustering of segmental motor programs for target oriented actions.

This study tested the hypotheses that visual search impairments in schizophrenia are due to a delay in initiation of search or a slow rate of serial search. We determined the specificity of these impairments by comparing children with schizophrenia to children with attention-deficit hyperactivity disorder (ADHD) and age-matched normal children. The hypotheses were tested within the framework of feature integration

Polygraphic recordings were collected for 11 normal subjects during sleep and wakefulness in order to investigate characteristics of the rapid eye movement (REM) associated potentials. EEGs were averaged using 5 different triggering points: (1) saccade onset under the normal ambient illumination, (2) saccade onset in the total darkness, (3) onset of REMs during REM sleep, (4) flash during REM sleep, and (5) flash during stage 2 sleep. In the central area, positive potentials appeared with waking saccades under the normal ambient illumination (P240L) and REMs (P185R). The latency of P185R associated with REMs was significantly shorter than that of P240L associated with waking saccades. These findings suggest that P185R is evoked by PGO waves occurring just before the REM. A small positive potential appeared in the occipital area with waking saccade under the normal ambient illumination (P260L) and REMs in the total darkness (P250R). Conspicuous absence of these waves for waking sacca...

The horizontal head impulse test (HIT) is a valuable clinical tool that can help identify peripheral vestibular hypofunction by the refixation (compensatory) saccade that returns the eyes to the target of interest after the head has stopped. We asked if there were differences in the compensatory saccade responses during the HIT when the head was rotated away or toward straight ahead (outward versus inward). We also investigated the influence of a fixation target. Using scleral search-coils, we tested five patients with chronic unilateral vestibular hypofunction (UVH) and three healthy control subjects. In UVH patients, the latencies of both overt and covert saccades were longer when the head was rotated inward from an initially eccentric position, regardless of a visual target. The proportion of HIT with covert saccades was independent of a visual target. In control subjects no compensatory saccades were observed and there were no differences in either angular vestibulo-ocular refle...

This study examined the range and reliability of individual differences in several oculomotor measures. One thousand participants were tested using standard smooth pursuit and pro- and antisaccade paradigms. In the smooth pursuit task, the variables of interest were the root mean square error of eye position, gain (ratio of eye velocity to target velocity), and number and type of intruding saccades. In the saccadic tasks, the variables of interest were accuracy, latency distribution and velocity characteristics. We report the range and distribution of these variables, as well as correlations between them. We also report a number of internal consistency reliability measures for these variables, as well as test–retest reliabilities based on a randomly selected 10% of the sample.

Oculomotor disturbances and nystagmus are seen in many diseases of the nervous system, the vestibular apparatus, and the eyes, as well as in toxic and metabolic disorders. They often indicate a specific underlying cause. The key to diagnosis is systematic clinical examination of the patient's eye movements. This review deals mainly with central oculomotor disturbances, i.e., those involving smooth pursuit, saccades, gaze-holding, and central types of nystagmus. We searched the current literature for relevant publications on the diagnosis and treatment of oculomotor disturbances and nystagmus, and discuss them selectively in this review along with the German Neurological Society's guidelines on the topic. A detailed knowledge of the anatomy and physiology of eye movements usually enables the physician to localize the disturbance to a specific area in the brainstem or cerebellum. The examination of eye movements is an even more sensitive method than magnetic resonance imaging ...

The most widely applied model relating drug concentrations to effects is the Emax model. In practice, concentration-effect relationships often deviate from a simple linear relationship but without reaching a clear maximum because a further increase in concentration might be associated with unacceptable or distorting side effects. The parameters for the Emax model can only be estimated with reasonable precision if the curve shows sign of reaching a maximum, otherwise both EC50 and Emax estimates may be extremely imprecise. This paper provides a solution by introducing a new parameter (S0) equal to Emax/EC50 that can be used to characterize potency adequately even if there are no signs of a clear maximum. Simulations are presented to investigate the nature of the new parameter and published examples are used as illustration.

Aim: The main aim of this study was to evaluate the Neuro-Linguistic Programming (NLP)
assumption concerning the eye-movement in terms of cognitive tasks (narrative memory,
imagination, object recognition and spatial attention). Literature up to now, decline NLP as a
science based on non-neuropsychological evaluation. Hence, this research clarified cerebrum
topography via the cognitive tasks and tried to evaluate the role of amygdala on facial
behaviour cues. Amygdala is responsible for emotional processing and it is part of limbic
system which via hippocampus activation connects with narrative memory (biographical and
autobiographical memory). Hippocampus and amygdala triggers Prefrontal Cortex in terms of
executive functioning (i.e decision making, and morality)
Methods: Twenty six (13 male and 13 female) students (healthy participants) were recruited
from city unity and 6 female Multiple sclerosis (MS) patients from Policlinic of Evaggelismos
hospital. The first picture of Thematic Apperception Test (TAT) was used in order to
stimulate emotional memories and imagination. More to this, the Edinburgh Handiness
Inventory was used for clarifying whether participants were right or left handed. All of the
participants were above 18 and they were right- handed. A video camera was used to record
the participants’ saccades during the experimental tasks.
Results: Healthy population results indicated a partial support to NLP claims concerning the
association between saccades and cognitive tasks. More specific, NLP claims of associating
right saccades to the imagination task were confirmed, while NLP claims regarding the
association between left saccades and recall task were not supported. Further, the bilateral
activation of amygdala was confirmed via right saccades associating to left amygdala,
reflecting emotional arousal. On the contrary, MS patients’ results confirmed the
bilateralization of amygdala via the dislocation of emotional functionality. Hence MS patients
partially confirmed NLP theory, in terms of cognitive tasks, while in terms of constructing a
story, this research findings were not supportive to NLP theory, as prefrontal cortex seems to
have a crucial role in this part.
Conclusion: NLP was neuropsychologically evaluated, and it was indicated the crucial role of
amygdala and prefrontal cortex. Such results indicate, also the role of saccade reactions in the
therapeutic alliance. Yet, further research should be done.
Keywords: NLP, saccades, amygdala, hippocampus, PFC, cognitive tasks.

The cerebellum is implicated in maintaining the saccadic subsystem efficient for vision by minimizing movement inaccuracy and by learning from endpoint errors. This ability is often disrupted in degenerative cerebellar diseases, as demonstrated by saccade kinetic abnormalities. The study of saccades in these patients may therefore provide insights into the neural substrate underlying saccadic motor control. We investigated the different extent of saccade dynamic abnormalities in spinocerebellar ataxia type 2 and late-onset cerebellar ataxias, genetically undefined and with prevalent cerebellar atrophy. Reflexive and voluntary saccades of different amplitude (10°-18°) were studied in seven patients with spinocerebellar ataxia 2, eight patients with late-onset cerebellar ataxia and 25 healthy controls. Quantitative analysis of saccade parameters and measures of saccade accuracy were performed. Detailed neurological, neurophysiological and magnetic resonance imaging assessment was obtained for each patient. Genetic and laboratory screening for spinocerebellar ataxias and other forms of late-onset cerebellar ataxias were also performed. A lower peak saccade velocity and longer duration was observed in patients with spinocerebellar ataxia 2 with respect to those with late-onset cerebellar ataxia and controls. Unlike subjects with spinocerebellar ataxia 2, patients with late-onset cerebellar ataxia showed main sequence relationships to similar saccades made by normal subjects. Saccades were significantly more inaccurate, namely hypometric, in late-onset cerebellar ataxia than in spinocerebellar ataxia 2 and inaccuracy increased with saccade amplitude. The percentage of hypometric primary saccades and of larger secondary corrective saccades were consistently higher in late-onset cerebellar ataxia than in spinocerebellar ataxia 2 and controls. No other significant differences were found between groups. Two different mechanisms were adopted to redirect the fovea as fast and/or accurately as possible to peripheral targets by the two groups of cerebellar patients. Patients with spinocerebellar ataxia 2 maintained accuracy using slow saccades with longer duration. This reflects prevalent degenerative processes affecting the pontine burst generator and leading to saccade velocity failure. On the other hand, patients with late-onset cerebellar ataxia reached the target with a number of fast inaccurate, mostly hypometric saccades. Different degrees of cerebellar oculomotor vermis involvement may account for differences in optimizing the trade-off between velocity and accuracy in the two groups. In addition, as suggested by spinocerebellar patients having slow saccades that are no longer ballistic, visual feedback might be continuously available during the movement execution to guide the eye to its target.

Our visual system is fovea-heavy, which means that in-depth processing occurs only in the centre of
the retina, forcing the eyes to make constant movements in order to bring visual elements into focus. Despite this, eye movements go largely unnoticed and the environment is perceived as visually stable. Pre-saccadic shifts of attention might be guaranteeing this stability by easing the transition from one foveated image to another. Before an eye movement attention shifts to the location where the eyes will land and visual elements presented there are preferentially processed. A similar mechanism, also based on the allocation of attention in eye-centred coordinates, is known as remapping. It allows attention to be maintained on locations of interest across eye movements, while accounting for the retinal displacement caused by each upcoming movement. In the current thesis, we are concerned with how the visual elements present in the environment shape the allocation of attention before eye movements. We first aimed to determine whether pre-saccadic shifts of attention are a precondition of all saccades, irrespective of goals. We showed that whether the saccade was goal-directed, to the intended target, or involuntary, erroneously directed to a capturing distractor, made little difference to the pre-saccadic shift of attention. Retinal displacement caused by involuntary saccades was also accounted for by the visual system. Next, the project focused on how the presented visual elements affect the programming of eye movements, by investigating how the decision to make an eye movement is affected by the number of target alternatives. We saw evidence that a larger set-size can reduce saccadic reaction times without increasing the error rate, a finding not predicted by a popular model. Further, whether the presence of visual elements in and around the saccade landing point influences the shifts of attention was investigated. We demonstrate that objects and their arrangement shape the distribution of attention, and that the effect is not driven by saccade metrics alone. Finally, we look at the spatial and temporal distribution of visual attention when a saccade target is removed shortly before the eye movement.