Upward Eye Movements Research Articles

Summing up: A functional role of eye movements along the mental number line for arithmetic

In Western cultures, small-left and large-right spatial-numerical associations are constantly found in various simple number processing tasks. It has recently been suggested that spatial associations are also involved in more complex number processing, for example that individuals make rightward or upward “mental” movements along the number line during addition, and leftward or downward movements during subtraction. In line with this, it has been shown that participants' spontaneous eye movements on a blank screen during upward and downward counting follow such associations. The present research investigated whether eye movements along the number line are simply an epiphenomenon of the recruitment of a spatial reference frame, or whether they play a functional role for the arithmetic computation. This question was addressed by using multi-step problems (e.g., 59 + 5 + 4 + 3) that show a larger proportion of computation (vs. retrieval) when compared to single-step problems (e.g., 59 + 5), as confirmed in Pretest 1. Moreover, the question was addressed only for addition problems and vertical eye movements, because spatial-arithmetic associations were not found in the other conditions (subtraction, horizontal eye movements) in Pretest 2. In the main experiment, participants (n = 29) solved addition problems while following a moving dot with their eyes (smooth pursuit) either in a congruent (upward) or incongruent (downward) direction, or while keeping their eyes fixated on to the center of the screen, or while moving their eyes freely on a blank screen. Arithmetic performance was faster in the congruent condition (upward eye movements) when compared to the other conditions (downward eye movements, central fixation, free viewing). These results suggest that vertical shifts in spatial attention along the mental number line are functionally involved in addition. The results support the view of shared mechanisms for directing spatial attention in external (visual) and representational (number space). Implications for embodied views of number processing are discussed.

Processing of an ambiguous time phrase in posttraumatic stress disorder: Eye movements suggest a passive, oncoming perception of the future

Metaphorically, the future can be perceived as approaching us (time-moving metaphor) or as being approached by us (ego-moving metaphor). Also, in line with findings that our eyes look more up when thinking about the future than the past, the future's location can be conceptualized in upwards terms. Eye movements were recorded in 19 participants with PTSD and 20 healthy controls. Participants with PTSD showed downward and healthy controls upward eye movements while processing an ego/time-moving ambiguous phrase, suggesting a passive (time-moving) outlook toward the future. If replicated, our findings may have implications for the conceptualization and treatment of PTSD.

Research on Home-Auxiliary Robot System Based on Characteristics of Human Physiological and Motion Signals

A home-auxiliary robot system based on characteristics of the electrooculogram (EOG) and tongue signal is developed in the current study, which can provide daily life assistance for people with physical mobility disabilities. It relies on five simple actions (blinking twice in a row, tongue extension, upward tongue rolling, and left and right eye movements) of the human head itself to complete the motions (moving up/down/left/right and double-click) of a mouse in the system screen. In this paper, the brain network and BP neural network algorithms are used to identify these five types of actions. The result shows that, for all subjects, their average recognition rates of eye blinks and tongue movements (tongue extension and upward tongue rolling) were 90.17%, 88.00%, and 89.83%, respectively, and after training, the subjects can complete the five types of movements in sequence within 12 seconds. It means that people with physical disabilities can use the system to quickly and accurately complete life self-help, which brings great convenience to their lives.

Right Cortical and Axonal Structures Eliciting Ocular Deviation During Electrical Stimulation Mapping in Awake Patients

To investigate the neural network underpinning eye movements, a cortical and subcortical intraoperative mapping using direct electrical stimulation (DES) was achieved in six awake patients during surgery for a right frontal low-grade glioma. We assessed the relationship between the occurrence of ocular deviation during both cortical and axonal DES and the anatomic location for each response. The corresponding stimulation sites were reported on a standard brain template for visual analysis and between-subjects comparisons. Our results showed that DES of the cortical frontal eye field (FEF) elicited horizontal (anterior FEF) or upward (posterior FEF) eye movements in 3 patients, supporting the fact that FEF comprises several distinct functional subregions. In addition, subcortical stimulation of the white matter tracts underneath the FEF evoked conjugate contraversive ocular deviation in 3 other patients. Interestingly, this region seems to be a crossroad between the fronto-striatal tract, the frontal aslant tract, the inferior fronto-occipital fascicle and the superior longitudinal fascicle. No deficits in eye movements were observed following surgery. To our knowledge, this is the first study reporting ocular deviation during axonal electrostimulation mapping of the white matter fibers in awake patients. Therefore, our original data issued from DES give new insights into the cortical and subcortical structures involved in the control of eye movements and their strong relationships with other functional pathways.

A high-resolution binocular video-oculography system: assessment of pupillary light reflex and detection of an early incomplete blink and an upward eye movement

BackgroundThe pupillary light reflex characterizes the direct and consensual response of the eye to the perceived brightness of a stimulus. It has been used as indicator of both neurological and optic nerve pathologies. As with other eye reflexes, this reflex constitutes an almost instantaneous movement and is linked to activation of the same midbrain area. The latency of the pupillary light reflex is around 200 ms, although the literature also indicates that the fastest eye reflexes last 20 ms. Therefore, a system with sufficiently high spatial and temporal resolutions is required for accurate assessment. In this study, we analyzed the pupillary light reflex to determine whether any small discrepancy exists between the direct and consensual responses, and to ascertain whether any other eye reflex occurs before the pupillary light reflex.MethodsWe constructed a binocular video-oculography system two high-speed cameras that simultaneously focused on both eyes. This was then employed to assess the direct and consensual responses of each eye using our own algorithm based on Circular Hough Transform to detect and track the pupil. Time parameters describing the pupillary light reflex were obtained from the radius time-variation. Eight healthy subjects (4 women, 4 men, aged 24–45) participated in this experiment.ResultsOur system, which has a resolution of 15 microns and 4 ms, obtained time parameters describing the pupillary light reflex that were similar to those reported in previous studies, with no significant differences between direct and consensual reflexes. Moreover, it revealed an incomplete reflex blink and an upward eye movement at around 100 ms that may correspond to Bell’s phenomenon.ConclusionsDirect and consensual pupillary responses do not any significant temporal differences. The system and method described here could prove useful for further assessment of pupillary and blink reflexes. The resolution obtained revealed the existence reported here of an early incomplete blink and an upward eye movement.Electronic supplementary materialThe online version of this article (doi:10.1186/s12938-015-0016-6) contains supplementary material, which is available to authorized users.

A novel spelling system for locked-in syndrome patients using only eye contact

Purpose: We developed and evaluated a novel spelling system for patients with locked-in syndrome: patients with tetraplegia, not able to talk, and only able to blink their eyes. Method: A new communication grid was compared with existing non-technical communication methods for practical daily use. The means of the number of decision steps to reach a full sentence were compared testing 10 sentences relevant in daily care. These 10 sentences together encompass all letters of the alphabet. Results: The new communication grid is organised alphabetically in 4 columns and 2 main rows, with each row subdivided in three rows. The first column contains vowels while the other columns contain consonants. Letters in each column are alphabetically ordered. When spelling a sentence the conversation partner counts the columns, until the patient indicates by an upward eye movement that the column contains the intended letter. Hereafter, the patient indicates by looking straight ahead or by looking down, whether the intended letter is in the upper or in the lower main row, respectively. The conversation partner will then read out the letters until the patient indicates the intended letter. Compared to other spelling systems, this system requires only vertical eye movement, is easier to memorise, and faster in use. The comparison of means of decision steps to reach the 10 full sentences for different communication grids shows that using the new communication grid is approximately one-third to three times faster than the existing spelling systems (p = 0.005). Conclusion: This new grid is a valuable communication tool, especially in situations, such as bathing, getting dressed or out of house activities where no devices are available.Implications for RehabilitationCommunication with patients with locked-in syndrome is a complicated and strenuous task.Communication methods, such as the alphabet board and brain-computer interfaces, are time consuming or too sophisticated to use in daily life tasks.This communication grid is fast, easy to use and memorise and requires only vertical eye movement.

Calretinin inputs are confined to motoneurons for upward eye movements in monkey

Motoneurons of extraocular muscles are controlled by different premotor pathways, whose selective damage may cause directionally selective eye movement disorders. The fact that clinical disorders can affect only one direction, e.g., isolated up-/downgaze palsy or up-/downbeat nystagmus, indicates that up- and downgaze pathways are organized separately. Recent work in monkey revealed that a subpopulation of premotor neurons of the vertical eye movement system contains the calcium-binding protein calretinin (CR). With combined tract-tracing and immunofluorescence, the motoneurons of vertically pulling eye muscles in monkey were investigated for the presence of CR-positive afferent terminals. In the oculomotor nucleus, CR was specifically found in punctate profiles contacting superior rectus and inferior oblique motoneurons, as well as levator palpebrae motoneurons, all of which participate in upward eye movements. Double-immunofluorescence labeling revealed that CR-positive terminals lacked the γ-aminobutyric acid (GABA)-synthesizing enzyme glutamate decarboxylase, which is present in inhibitory afferents to all motoneurons mediating vertical eye movements. Therefore, CR-containing afferents are considered to be excitatory. In conclusion, a strong CR input is confined to motoneurons mediating upgaze, which derive from premotor pathways mediating saccades and smooth pursuit, but not from secondary vestibulo-ocular neurons in the magnocellular part of the medial vestibular nucleus. The functional significance of CR in these connections is unclear, but it may serve as a useful marker to locate upgaze pathways in the human brain.

Upward gaze and head deviation with frontal eye field stimulation

Using electrical stimulation to the deep, most caudal part of the right frontal eye field (FEF), we demonstrate a novel pattern of vertical (upward) eye movement that was previously only thought possible by stimulating both frontal eye fields simultaneously. If stimulation was started when the subject looked laterally, the initial eye movement was back to the midline, followed by upward deviation. Our finding challenges current view of topological organisation in the human FEF and may have general implications for concepts of topological organisation of the motor cortex, since sustained stimulation also induced upward head movements as a component of the vertical gaze shift. [Published with video sequences].

Sources of calretinin inputs to motoneurons of extraocular muscles involved in upgaze.

Recent monkey studies showed that motoneurons of the oculomotor nucleus involved in upward eye movements receive a selective input from afferents containing calretinin (CR). Here, we investigated the sources of these CR-positive afferents. After injections of tract-tracers into the oculomotor nucleus (nIII) of two monkeys, the retrograde labeling was combined with CR-immunofluorescence in frozen brainstem sections. Three sources of CR inputs to nIII were found: the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), the interstitial nucleus of Cajal, and the y-group. CR is not present in all premotor upward-moving pathways. The excitatory secondary vestibulo-ocular neurons in the magnocellular part of the medial vestibular nuclei contained nonphosphorylated neurofilaments, but no CR, and they received a strong supply of large CR-positive boutons. In conclusion, the present study presents evidence that only specific premotor pathways for upward eye movements--excitatory upgaze pathways--contain CR, but not the up vestibulo-ocular reflex pathways. This property may help to differentiate between premotor up- and downgaze pathways in correlative clinico-anatomical studies in humans.

Intraocular Neuromuscular Choristoma: A Case Report and Literature Review

Neuromuscular choristomas (NMCs) are rare benign tumors of the peripheral nerves. Although histopathological characteristics of this unusual lesion have been recognized, in this regard, neuroimaging findings have not been well described previously. We report the first intraconally located NMC affecting the oculomotor nerve, with histopathological and radiological characteristics. A 10-year-old girl presented with sudden-onset left temporal and retro-orbital pain. Magnetic resonance imaging scans demonstrated a small, capsulated, retro-orbital, intraconal solid lesion that was diagnosed as an atypical dermoid cyst preoperatively. The tumor was resected subtotally. Postoperatively, the patient became pain free, but ipsilateral ptosis and upward eye movement failure developed. Histologically, the lesion consisted of well-differentiated striated muscle fibers intermingled with mature nerve elements consistent with the NMC. Although intracranial NMCs need histological confirmation for diagnosis, neuroimaging might contribute to the preoperative diagnosis and management strategy of treatment. We report the first intraconal NMC, which should be considered in the differential diagnosis of intraorbital tumors.

Inferior displacement of the lower eyelid during intraoperative quantification in blepharoptosis surgery

Purpose:To examine inferior displacement of the lower eyelid during eye closing in intraoperative quantification of blepharoptosis surgery.Methods:A series of lower eyelid movements during eye closing in intraoperative quantification of blepharoptosis surgery were examined in 30 eyelids of 15 patients (6 males and 9 females; mean age 70.0 years; range 43–81 years) with bilateral aponeurotic blepharoptosis.Results:Inferior displacement of the lower eyelid was observed in all eyelids examined, although the extent varied in each patient (range 2.0–4.5 mm; mean 3.2 mm). Inferior displacement occurred with upward eye movement caused by Bell’s phenomenon. Many wrinkles were simultaneously observed as a result of contraction of the orbicularis oculi muscle. After maintaining the inferiorly displaced state for several seconds, 20 lower eyelids in 10 patients naturally moved superiorly to a resting position. On the other hand, 10 lower eyelids in 5 patients remained in the same inferior position for more than 5 seconds, after which we had to manually elevate them to a resting position. The eyes then moved inferiorly to their resting position with a decrease in the number of lower eyelid wrinkles. Once the patients opened their eyes, inferior displacement of the lower eyelid completely disappeared.Conclusions:Inferior displacement of the lower eyelid during eye closing increases the amount of lagophthalmos. This phenomenon needs to be considered for quantifying the intraoperative lagophthalmos level during blepharoptosis surgery.

Loss of vertical gaze - the Parinaud syndrome

Introduction: Loss of vertical gaze in combination with oculomotoric disturbances are called Parinaud-syndrome. The variable loss of vertical gaze is caused by unilateral tegmental lesions in the mesencephalon. Upward eye movement cause convergence reactions and nystagmus. The often large pupils react slowly to light and pathological eyelid-retraction may occur. Tumours, multiple sclerosis or disrupted blood supply are mainly responsible for the Parinaud syndrome.

Vertical nystagmus: clinical facts and hypotheses

The pathophysiology of spontaneous upbeat (UBN) and downbeat (DBN) nystagmus is reviewed in the light of several instructive clinical findings and experimental data. UBN due to pontine lesions could result from damage to the ventral tegmental tract (VTT), originating in the superior vestibular nucleus (SVN), coursing through the ventral pons and transmitting excitatory upward vestibular signals to the third nerve nucleus. A VTT lesion probably leads to relative hypoactivity of the drive to the motoneurons of the elevator muscles with, consequently, an imbalance between the downward and upward systems, resulting in a downward slow phase. The results observed in internuclear ophthalmoplegia suggest that the medial longitudinal fasciculus (MLF) is involved in the transmission of both upward and downward vestibular signals. Since no clinical cases of DBN due to focal brainstem damage have been reported, it may be assumed that the transmission of downward vestibular signals depends only upon the MLF, whereas that of upward vestibular signals involves both the MLF and the VTT. The main focal lesions resulting in DBN affect the cerebellar flocculus and/or paraflocculus. Apparently, this structure tonically inhibits the SVN and its excitatory efferent tract (i.e. the VTT) but not the downward vestibular system. Therefore, a floccular lesion could result in a disinhibition of the SVN-VTT pathway with, consequently, relative hyperactivity of the drive to the motoneurons of the elevator muscles, resulting in an upward slow phase. UBN also results from lesions affecting the caudal medulla. An area in this region could form part of a feedback loop involved in upward gaze-holding, originating in a collateral branch of the VTT and comprising the caudal medulla, the flocculus and the SVN, successively. Therefore, it is suggested that the main types of spontaneous vertical nystagmus due to focal central lesions result from a primary dysfunction of the SVN-VTT pathway, which becomes hypoactive after pontine or caudal medullary lesions, thereby eliciting UBN, and hyperactive after floccular lesions, thereby eliciting DBN. Lastly, since gravity influences UBN and DBN and may facilitate the downward vestibular system and restrain the upward vestibular system, it is hypothesized that the excitatory SVN-VTT pathway, along with its specific floccular inhibition, has developed to counteract the gravity pull. This anatomical hyperdevelopment is apparently associated with a physiological upward velocity bias, since the gain of all upward slow eye movements is greater than that of downward slow eye movements in normal human subjects and in monkeys.

Prolonged Asymmetric Smooth-Pursuit Stimulation Leads to Downbeat Nystagmus in Healthy Human Subjects

Downbeat nystagmus (DBN) is a typical ocular motor sign in patients with lesions of the vestibulocerebellum. A vertical vestibular tone asymmetry, an upward shift of the eyes' null position for vertical gaze holding, or an imbalance of vertical smooth-pursuit signals have been proposed as mechanisms of DBN. The purpose of this study was to elaborate a possible link between an imbalance in the vertical smooth-pursuit system and DBN by relying on a healthy human model. Healthy subjects (n=6) were exposed to continuous asymmetric smooth-pursuit stimulation over 20 minutes. Prolonged asymmetric smooth-pursuit stimulation induced a drift lasting >5 minutes in the direction of the prior pursuit. Upward drift was faster than downward drift and showed eye-position dependence in accordance with Alexander's law, but no increase of drift velocity with lateral gaze. Upward drift violated Listing's law in three of four subjects tested. An experimentally induced vertical smooth-pursuit imbalance leads to DBN in healthy human subjects. Accordingly, because in patients with cerebellar disease upward smooth-pursuit eye movements are typically better preserved than downward, the resultant sustained imbalance of vertical smooth-pursuit input may play a major role in the generation of DBN.

Eye movements evoked by selective saccular nerve stimulation in cats

Objective: Because of technical obstacles in controlling current spread to adjacent peripheral nerve, eye movements evoked by activation of the otolith organs have not been investigated in detail compared to eye movements evoked by activation of the canal organs. We attempted to solve this problem by applying more sensitive methods using fine needle and strictly controlling stimulus current intensity compare with filed potential for selective stimulation. Methods: Eye movements evoked by selective, unilateral saccular (SAC) nerve stimulation were investigated using both electrooculography (EOG) and video recording in decerebrated cats in the presence or absence of anesthesia. Electrical stimulation was applied to the SAC nerve through implanted acupuncture needles. Results: In the absence of anesthesia and with stimulus intensities less than (3.1±2.7)×N 1T, we found supraduction in both eyes or in either the ipsilateral or contralateral eye of different cats. We observed downward eye movements using a stronger stimulus intensity ((6.2±2.9)×N 1T). The threshold for downward eye movements was significantly greater than that for upward eye movements ( P<0.05). In anesthetized cats, only downward eye movements were observed when stimulus intensities less than 10×N 1T ((7.8±2.3)×N 1T) were used. Conclusion: These results confirm the known sacculo-ocular anatomical connections, which are involved predominantly in vertical eye movements. Because the sacculo-ocular connections are relatively weak, the normal supraduction evoked by SAC activation can be easily modified by factors such as level of anesthesia and the method of stimulation.

GABAergic neurons in the rostral mesencephalon of the macaque monkey that control vertical eye movements.

The mesencephalic reticular formation is important for the generation of vertical eye movements, but up until now the location of inhibitory premotor neurons is not known in primates. With tract-tracer methods combined with immunocytochemistry or in situ hybridization, we investigated the location of GABAergic premotor neurons in the rostral interstitial nucleus of the medial longitudinal fascicle (riMLF) and interstitial nucleus of Cajal (iC) in macaque monkeys. In the present work, only the premotor pathways of the downward pulling eye muscles, superior oblique (SO) and inferior rectus (IR), were studied. We found that very few, small GABAergic neurons are present in the riMLF, and none of them was found to project to the oculomotor nuclei, suggesting the presence of exclusively excitatory projections from the riMLF to the oculomotor neurons. However, in the iC, medium-sized and large GABAergic neurons were identified projecting contralaterally to the SO and IR motoneurons, and presumably the iC of the other side. These commissural GABAergic projections are well suited to inhibit the SO and IR motoneurons and possibly premotor down-burst-tonic neurons during upward eye movements.

A mathematical analysis of the characteristics of the system connecting the cerebellar ventral paraflocculus and extraoculomotor nucleus of alert monkeys during upward ocular following responses.

Movements of the visual scene evoke short-latency ocular-following-responses (OFR). Many studies suggest that a neural pathway containing the cerebellar-ventral-paraflocculus (VPFL) mediates OFR. The relationship between eye movement and simple-spike firing in the VPFL during OFR has been studied in detail using an inverse dynamics approach. The relationship between eye movement and cell firing in the extraoculomotor nucleus (MN) has already been reported. However, no studies have examined the information transformation that occurs between the VPFL and the MN during OFR. In this paper, using an inverse dynamics approach, we derive a transfer function that represents the characteristics of the structure connecting the VPFL and the MN during upward OFR. This structure appears to contain a kind of neural integrator, which constructs eye-velocity-and-position information from eye-acceleration-and-velocity information. We propose a diagram for the neural integration commonly at work during all types of upward eye movement. This is a closed-loop circuit containing a low-pass filter. The low-pass filter can construct eye-velocity-and-position information from an eye-acceleration-velocity-position command similar to the final motor command used commonly for all upward eye movements. Anatomical and electrophysiological data suggest that the vestibular nuclei-interstitial nucleus of Cajal-vestibular nuclei loop might perform such neural integration.

Staring spells in children: Descriptive features distinguishing epileptic and nonepileptic events

To identify questions sensitive and specific for staring spells of epileptic (absence seizures [AS]) or nonepileptic etiology to increase the yield of history taking. A questionnaire was completed by parents of 40 children who presented with staring spells. Results from 17 children with AS and 23 with nonepileptic staring (NES) were compared. Features with moderate sensitivity (43% to 56%) but high specificity (87% to 88%) for NES included preserved responsiveness to touch, lack of interruption of playing, and initial identification by a teacher or health professional. These features were more frequent in NES than in AS (P = .013, .016, .030). Body rocking occurred only in NES, but sensitivity was low (13%). Features with high specificity (91% to 100%) for AS included limb twitches, upward eye movements, and urinary incontinence; but sensitivities were low (13% to 35%). In children with normal interictal electroencephalography findings and without neurologic disease, staring spells are most likely nonepileptic when parents report preserved responsiveness to touch, body rocking, or initial identification by a teacher or health professional without limb twitches, upward eye movements, interruption of play, or urinary incontinence. In these cases a diagnosis of NES may be confidently applied, with confirmation based on long-term follow-up.

Smooth pursuitlike eye movements evoked by microstimulation in macaque nucleus reticularis tegmenti pontis

1. Smooth pursuitlike eye movements were evoked with low current microstimulation delivered to rostral portions of the nucleus reticularis tegmenti pontis (rNRTP) in alert macaques. Microstimulation sites were selected by the observation of modulations in single-cell firing rates that were correlated with periodic smoothpursuit eye movements. Current intensities ranged from 10 to 120 microA and were routinely < 40 microA. Microstimulation was delivered either in the dark with no fixation, 100 ms after a fixation target was extinguished, or during maintained fixation of a stationary or moving target. Evoked eye movements also were studied under open-loop conditions with the target image stabilized on the retina. 2. Eye movements evoked in the absence of a target rapidly accelerated to a constant velocity that was maintained for the duration of the microstimulation. Evoked eye speeds ranged from 3.7 to 23 deg/s and averaged 11 deg/s. Evoked eye speed appeared to be linearly related to initial eye position with a sensitivity to initial eye position that averaged 0.23 deg.s-1.deg-1. While some horizontal and oblique smooth eye movements were elicited, microstimulation resulted in upward eye movements in 89% of the sites. 3. Evoked eye speed was found to be dependent on microstimulation pulse frequency and current intensity. Within limits, evoked eye speed increased with increases in stimulation frequency or current intensity. For stimulation frequencies < 300-400 Hz, only smooth pursuit-like eye movements were evoked. At higher stimulation frequencies, accompanying saccades consistently were elicited. 4. Feedback of retinal image motion interacted with the evoked eye movements to decrease eye speed if the visual motion was in the opposite direction as the evoked, pursuit-like eye movements. 5. The results implicate rNRTP as part of the neuronal substrate that controls smooth-pursuit eye movements. NRTP appears to be divided functionally into a rostral, pursuit-related portion and a caudal, saccade-related area. rNRTP is a component of a corticopontocerebellar circuit that presumably involves the pursuit area of the frontal eye field and that parallels the middle and medial superior temporal cerebral cortical/dorsalateral pontine nucleus (MT/MST-DLPN-cerebellum) pathway known to be involved also with regulating smooth-pursuit eye movements.

Short-latency compensatory eye movements associated with a brief period of free fall

The vertical eye movements induced by a brief period of free fall were recorded from three monkeys (Macaca mulatta) using the electromagnetic search coil technique. Free fall was initiated in total darkness immediately following binocular fixation of one of six target lights located at viewing distances ranging from 20 to 107 cm. Responses consisted of an initial transient downward eye movement (anticompensatory direction) with a latency of a few milliseconds at most followed by a sustained upward (compensatory) eye movement. The early transient was independent of viewing distance and attributed to an artifact, whereas the later component was a linear function of the inverse of the prior viewing distance and attributed to the translational vestibulo-ocular reflex (TVOR). Response latencies for the four nearer viewing distances were determined from the individual eye velocity traces using a computerized algorithm: after removing the initial transient by subtracting the mean response obtained with the most distant viewing, a regression line was fitted to the initial rising phase of the residual response and then extrapolated back to the baseline to determine the onset. When so determined, median latencies for the nearest viewing ranged from 16.4 to 18.5 ms, values appreciably shorter than any in the literature.