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At least 757 records · Page 42Linked to original sources
PubMed2003

Measuring V1 receptive fields despite eye movements in awake monkeys.

One difficulty with measuring receptive fields in the awake monkey is that even well-trained animals make small eye movements during fixation. These complicate the measurement of receptive fields by blurring out the region where a response is observed, causing underestimates of the ability of individual neurons to signal changes in stimulus position. In simple cells, this blurring may severely disrupt estimates of receptive field structure. An accurate measurement of eye movements would allow correction of this blurring. Scleral search coils have been used to provide such measurements, although little is known about their accuracy. We have devised a range of approaches to address this issue: implanting two coils into a single eye, exploiting the small size of V1 receptive fields and developing maximum-likelihood fitting techniques to extract receptive field parameters in the presence of eye movements. All our investigations lead to the same conclusion: our scleral search coils (which were not sutured to the globe) are subject to an error of approximately the same magnitude as the small eye movements which occur during fixation: SD approximately 0.1 degrees. This error is large enough to explain the SD of measured vergence in the absence of any real changes in vergence state. This, and a variety of other arguments, indicate that the real variation in vergence is much smaller than coil measurements suggest. These results suggest that monkeys, like humans, maintain very stable vergence. The error has a slower time course than fixational eye movements so that search coils report the difference in eye position between two consecutive trials more accurately than the eye position itself on either trial. Receptive field estimates are unlikely to be improved by assuming the coil record is veridical and correcting for eye position accordingly. However, receptive field parameters can reliably be determined by a fitting technique that allows for eye movements. It is possible that suturing coils to the globe reduces the artifacts, but no method has been available to demonstrate this. These receptive field measurements provide a general means by which the reliability of eye-position measurements can be assessed.

Animals↗
PubMed1992

Scanning eye movements in schizophrenic patients. Relationship to clinical symptoms and regional cerebral blood flow using 123I-IMP SPECT.

Eye movements during the Benton Visual Retention Test were examined using an eye-mark recorder in 32 schizophrenic patients and 32 normal controls. The patients had significantly fewer eye fixations, longer mean duration of fixation and shorter length of mean scan path than the controls. In the patients, these eye movement parameters were significantly correlated with the negative symptom score but not with the positive symptom score on the Positive and Negative Syndrome Scale. These parameters had a significant correlation with the composite score on the Scale for the Assessment of Negative Symptoms (SANS). In particular, they were highly correlated with avolition-apathy and affective flattening or blunting scores on SANS subscales. Thus, examination of scanning eye movements seemed to be a good objective index of negative symptoms. Secondly, regional cerebral blood flow (rCBF) was examined using N-isopropyl-p-[123I]iodoamphetamine (123I-IMP) and single photon emission computer tomography in 17 of 32 patients. With regard to the relationship between the eye movement parameters and rCBF, the mean duration of fixation was negatively correlated with 123I-IMP uptake in the left superior frontal area and left basal ganglia. The mean length of the scan path was correlated with uptake in the left superior frontal area. These findings suggest that the characteristic eye movements of schizophrenic patients are likely to be related with dysfunction of the frontal-basal ganglia neural circuit.

Adult↗
PubMed1989

The value of measuring saccadic eye movement in the investigation of non-compressive myelopathy.

Saccadic eye movement recording was performed in 53 patients with non-compressive myelopathy. Twenty one patients (40%) had subclinical abnormalities of saccadic movement, supporting a diagnosis of probable multiple sclerosis. When used in addition to the measurement of visual evoked potentials and brainstem auditory evoked responses, the detection of subclinical abnormalities increased from 40% to 57%. The detection rate of abnormalities by saccadic eye movement recording was equal to that of visual evoked responses, but more than of brainstem auditory evoked responses. Prolonged latency of gaze was the most common saccadic latency abnormality detected. The majority of saccadic velocity abnormalities could be explained by disease in the medial longitudinal bundle. An unusual finding was that abduction velocity was increased in six patients. It is concluded that the simple measurement of saccadic eye movement is a valuable addition to other ancillary investigations for the diagnosis of multiple sclerosis. It also allows analysis of oculomotor function, commonly disordered in multiple sclerosis, but rarely investigated.

Adult↗
PubMed1977

Vertical eye movement related unit activity in the rostral mesencephalic reticular formation of the alert monkey.

Eye movement related unit activity was recorded in the rostral mesencephalic reticular formation (MRF) of the alert monkey. Most units (78 out of 117) were activated with a short activity burst starting before the eye movement and were otherwise silent. The activity was the same whether movements occurred spontaneously in the light or dark, or were fast phases of vestibular or optokinetic nystagmus, and could be related to parameters of a vector representing the eye movement such as amplitude, position changes along certain planes or direction of movements. Units coding position changes or direction of movement had their preferred direction always close to the vertical. Other units (18 out of 117) showed some tonic activity, which was also only related to vertical eye position. It is suggested that this region of the rostral MRF acts an an immediate supranuclear structure, mediating eye movements in the vertical plane.

Action Potentials↗
PubMed1976

Visual masking during pursuit eye movements.

In three experiments, targets and masking stimuli were briefly flashce while observers visually tracked a moving dot. Masking stimuli were more effective when they appeared to be in the same place as the target but stimulated different parts of the retina than when they stimulated the same parts of the retina but appeared displaced because of of an intervening pursuit eye movement. Visual masking during pursuit eye movements thus depended on the apparent position of the stimuli, not their retinal positions as such, which is in disagreement with previous studies of visual masking during saccadic eye movements. The apparent conflict can be explained in terms of the functional significance of visual masking in tracking and saccardic movements: Retinal position masking after saccadic eye movements may erase previous images, and apparent position masking during pursuit eye movements may make moving targets more visible.

Eye Movements↗
PubMed1992

Abnormal eye movements in Gerstmann-Sträussler-Scheinker disease.

Gerstmann-Sträussler-Scheinker disease is a familial disorder of progressive ataxia and dementia in adulthood with extrapyramidal signs in some families. Neuro-ophthalmic examinations and eye movement recordings were performed in members of a large Indiana kindred. Five affected members and 11 members at risk were studied. Eye movements were recorded with videotape, electro-oculography, and/or magnetic scleral search coil. All affected members had abnormal eye movements characteristic of extrapyramidal diseases and cerebellar disorders. Nine members at risk had normal eye movements, but two others had slightly abnormal eye movements. Neuro-ophthalmic examination and eye movement recordings might be helpful in detecting early signs of Gerstmann-Sträussler-Scheinker disease in persons at risk.

Adolescent↗
PubMed1994

Eye movement desensitization: a partial dismantling study.

Twenty-three PTSD subjects were exposed to either: (1) standard eye movement desensitization (EMD), (2) a variant of EMD in which eye movements were engendered through a light tracking task, or (3) a variant of EMD in which fixed visual attention replaced eye movements. All three interventions produced significant positive changes in all dependent measures and these changes were maintained at follow-up. No significant differences between groups were observed. It was concluded that the eye movements peculiar to EMD are not essential to treatment outcome. The implications of the present findings and previous reports are discussed and recommendations for future research provided.

Adolescent↗
PubMed1984

Saccadic eye movements--use in ergophthalmology.

Saccadic eye movements are the fast "catching movements" we use to bring a new object to the foveal region. They can be measured and analysed quantitatively e.g. with electrooculography. Saccades are sensitive to drugs, alcohol and fatigue and thus their measurement seems to be a promising method for research in toxicology and ergonomics.

Ergonomics↗
PubMed2006

The temporal and spatial limits of compensation for fixational eye movements.

High-fidelity eye tracking is combined with a perceptual grouping task to provide insight into the likely mechanisms underlying the compensation of retinal image motion caused by movement of the eyes. The experiments describe the covert detection of minute temporal and spatial offsets incorporated into a test stimulus. Analysis of eye motion on individual trials indicates that the temporal offset sensitivity is actually due to motion of the eye inducing artificial spatial offsets in the briefly presented stimuli. The results have strong implications for two popular models of compensation for fixational eye movements, namely efference copy and image-based models. If an efference copy model is assumed, the results place constraints on the spatial accuracy and source of compensation. If an image-based model is assumed then limitations are placed on the integration time window over which motion estimates are calculated.

Eye Movements↗
PubMed2004

Movement perception, directionally selective ganglion cell responses and the involuntary eye movements. Neurophysiology at the level of information processing.

Two neural circuits in the retina are described, that involve neural interaction generated by image movement. One circuit increases the sensitivity in detecting movement in the visual field while the other circuit generates ganglion cell signals when an image moves in one preferred direction but not when moves in the opposite direction, explaining the observation of directionally selective ganglion cell responses described by Barlow and Hill (1963). In agreement with the recorded potentials, the circuit generates ganglion cell responses also when the light stimulus is stationary. This ambiguity in ganglion cell signals to the visual center limits the signals usefulness to images that are in constant movement. The only known such movement is that caused by the involuntary eye movements. The function of the circuit is therefore to stabilize the retinal image when transmitted to the visual center.

Animals↗
PubMed1977

Bilateral lesions of the medial longitudinal fasciculus in monkeys: effects on the horizontal and vertical components of voluntary and vestibular induced eye movements.

Bilateral transections across the brainstem interrupted the medial longitudinal fasciculus (MLF) in three monkeys trained to make eye movements while subjected to horizontal or vertical angular accelerations. Eye movements measured before and after the lesion revealed deficits in both voluntary and vestibular compensatory eye movements; the deficits differed in the horizontal and vertical directions. Vertical saccades in both directions were normal but eccentric positions of fixation could not be maintained; a drift toward the midline followed by a corrective saccade produced vertical fixation nystagmus. Furthermore, the vertical vestibulo-ocular reflex (VOR) was abolished and vertical smooth pursuit was impaired. Along the horizontal meridian, adduction across the midline could not be achieved during either saccades, smooth pursuit, or the VOR. Temporal saccades were normal whereas nasal saccades were considerably slowed. If the eye was not required to cross the midline, the phase shift during the VOR was within 15 deg of normal in each eye. The gain of the VOR was reduced to about 0.4 immediately after the lesion, but recovered within one month. These findings suggest that the MLF transmits quite different kinds of information to horizontal and vertical oculomotoneurons and that deficits in vertical eye movements may be a sensitive indicator of anterior internuclear ophthalmoplegia.

Animals↗
PubMed2001

The eye movements of pure alexic patients during reading and nonreading tasks.

We compared the eye-movements of two patients who read letter-by-letter (LBL) following a left occipital lobe lesion with those of normal control subjects and of hemianopic patients in two tasks: a nonreading visual search task and a text reading task. Whereas the LBL readers exhibited similar eye-movement patterns to those of the other two groups on the nonreading task, their eye movements differed significantly during reading, as reflected in the disproportionate increase in the number and duration of fixations per word and in the regressive saccades per word. Importantly, relative to the two control groups, letter-by-letter readers also made more fixations per word as word length increased, especially as word frequency and word imageability decreased. Two critical results emerged from these experiments: First, the alteration in the oculomotor behavior of the LBL readers during reading is similar to that seen in normal readers under difficult reading conditions, as well as in beginning readers and in those with developmental dyslexia, and appears to reflect difficulties in processing the visual stimulus. Second, the interaction of length with frequency and with imageability in determining the eye movement pattern is consistent with an interactive activation model of normal word recognition in which weakened activation of orthographic input can nevertheless engage high-level lexical factors.

Adult↗
PubMedDate not supplied

The effect of a moving distractor on the initiation of smooth-pursuit eye movements.

As a step toward understanding the mechanism by which targets are selected for smooth-pursuit eye movements, we examined the behavior of the pursuit system when monkeys were presented with two discrete moving visual targets. Two rhesus monkeys were trained to select a small moving target identified by its color in the presence of a moving distractor of another color. Smooth-pursuit eye movements were quantified in terms of the latency of the eye movement and the initial eye acceleration profile. We have previously shown that the latency of smooth pursuit, which is normally around 100 ms, can be extended to 150 ms or shortened to 85 ms depending on whether there is a distractor moving in the opposite or same direction, respectively, relative to the direction of the target. We have now measured this effect for a 360 deg range of distractor directions, and distractor speeds of 5-45 deg/s. We have also examined the effect of varying the spatial separation and temporal asynchrony between target and distractor. The results indicate that the effect of the distractor on the latency of pursuit depends on its direction of motion, and its spatial and temporal proximity to the target, but depends very little on the speed of the distractor. Furthermore, under the conditions of these experiments, the direction of the eye movement that is emitted in response to two competing moving stimuli is not a vectorial combination of the stimulus motions, but is solely determined by the direction of the target. The results are consistent with a competitive model for smooth-pursuit target selection and suggest that the competition takes place at a stage of the pursuit pathway that is between visual-motion processing and motor-response preparation.

Animals↗
PubMed1996

Single neurons in posterior cingulate cortex of behaving macaque: eye movement signals.

1. Posterior cingulate cortex, although widely regarded as a part of the limbic system, is connected most strongly to parietal and frontal areas with sensory, motor, and cognitive functions. To gain insight into the functional nature of posterior cingulate cortex, we have recorded from its neurons in monkeys performing oculomotor tasks known to activate parietal and frontal neurons. We have found that posterior cingulate neurons fire during periods of ocular fixation at a rate determined by the angle of gaze and by the size and direction of the preceding eye movement. 2. The activity of 530 posterior cingulate neurons was monitored while rhesus macaque monkeys made visually guided eye movements to spots projected on a tangent screen. 3. In 150/530 neurons, a statistically significant shift in the rate of discharge occurred around the time of onset of saccadic eye movements. The preponderant form of response was an increase in activity (142/150 neurons). 4. In 142 neurons exhibiting significant excitation after saccades in at least one direction, the level of discharge was analyzed as a function of time relative to onset of the saccade. Across the neuronal population as a whole, activity increased sharply at the moment of onset of the saccade, rising to a maximum after 200 ms and then declining slowly. The net level of discharge remained well above presaccadic baseline even after > 1 s of postsaccadic fixation. 5. In 63 neurons, the postsaccadic rate of discharge was analyzed relative to the angle of the eye in the orbit by monitoring neuronal activity while the monkey executed saccades of uniform direction and amplitude to four targets spaced at 16-deg intervals along a line. The postsaccadic firing level was significantly dependent on orbital angle in 44/63 neurons. 6. In 45 neurons, the postsaccadic rate of discharge was analyzed relative to saccade direction by monitoring neuronal activity while the monkey executed 16-deg saccades to a constant target from diametrically opposed starting points. The postsaccadic level of activity was significantly dependent on saccade direction in 20/ 45 neurons. 7. In 58 neurons, the postsaccadic rate of discharge was analyzed relative to saccade amplitude by monitoring neuronal activity while the monkey executed saccades, which varied in amplitude (4, 8, 16, and 32 deg) but which were constant in direction and brought the eye to bear on a constant endpoint. The postsaccadic level of activity was significantly dependent on saccade amplitude in 24/58 neurons. In all neurons exhibiting significant amplitude-dependence, stronger firing accompanied larger saccades. 8. The activity of 10 neurons was monitored during smooth pursuit eye movements (20 deg/s upward, downward, leftward, and rightward). The level of firing varied as a function of both the position of the eye (9 neurons) and the velocity of the eye (6 neurons). 9. We conclude that posterior cingulate neurons monitor eye movements and eye position. It is unlikely that they participate in the generation of eye movements because their shifts of discharge follow the onset of the movements. Eye-movement-related signals in posterior cingulate cortex may reflect the participation of this area in assigning spatial coordinates to retinal images.

Animals↗
PubMed1992

Alterations of saccadic eye movements in myotonic dystrophy.

Saccadic eye movements were examined by means of infrared reflection oculography in 8 patients having myotonic dystrophy and in 65 control subjects. In 7 patients typical alterations of the saccades could be observed. In comparison with the normal controls the saccades were significantly hypometric, of longer duration, of lower peak velocity, and showed a typical pattern of velocity and acceleration.

Adult↗
PubMed1975

Depression in the excitability of relay cells of lateral geniculate nucleus following saccadic eye movements in the cat.

1. The excitability of relay cells of the lateral geniculate nucleus during a saccadic eye movement was studied in alert cats. Excitability was assessed by the firing probability of the cells in response to electrical stimulation of the optic chiasm. Modifications in the excitability were evaluated during the period following eye movements, by triggering a stimulator from potential shifts in electro-oculogram and altering delays in the stimulus pulse. 2. The cells were classified into S and T cells, based on their response properties and the latencies to chiasmatic stimulation. With a saccade in a stationary patterned field, T cells showed a burst discharge, while the discharges of S cells were completely suppressed. 3. The excitability was depressed in both S and T cells for 150-200 msec after a saccade, when the eye movement occurred in light. However, the depression did not occur in complete darkness. 4. The depression occurred also in the absence of eye movement, when the patterned visual field was moved in a saccadic fashion. 5. The depression in S cells occurred during an inhibitory period. Since S cells do not receive signals on image movement directly from the retina, the depression was due to a recurrent inhibition by signals transferred through the T ganglion-relay cell channel. 6. The depression in T cells occurred concomitantly with the burst discharge. Since the recurrent inhibition was operating less effectively during the period, the depression may be due to a phasic occlusion of the test impulse by coincident high-rate firings in the same cell. 7. The impairment in transmission of visual information through the lateral geniculate nucleus during the period following eye movements has been discussed in connexion with a neurophysiological basis for saccadic suppression.

Animals↗
PubMed1989

Eye movements during voluntary head motion with minimized cervical input.

Eye movements were recorded using DC-electro-oculography in 20 healthy subjects during sinusoidal voluntary head movements and during similar voluntary head movements with minimized cervical input. The eye movements during these conditions were compared to the vestibulo-ocular reflex (VOR), to the cervico-ocular reaction (COR) and to the active COR (i.e., voluntary stabilization of the head in space while the trunk was moved sinusoidally). Each subject sat with eyes covered on a rotating chair. Sinusoidal movements having an amplitude of +/- 20 degrees and either 0.1 or 0.2 Hz were performed. Voluntary head movements and head movements with minimized cervical input showed no difference in the gain of the slow-phase velocity of the nystagmus, the saccadic activity (cumulated amplitude/time) and the maximum eye deviation. The distribution of saccades around the reversal of head movement in space represents the only significant difference between these conditions. While the saccades appear promptly after reversal during sinusoidal voluntary head movement, they appear during voluntary head movement with minimized cervical input just before the reversal of head movement in space. The direction of saccades always depends on the displacement of the head related to the trunk and is due to cervical input and/or central influences.

Adult↗
PubMed1975

The left: lateral eye movements and ideology.

The lateral eye movements of 24 college students were videotaped as they reflected on spatial and analytical questions. As predicted, participants with more initial movements to the left had significantly higher scores on the leftist (or humanistic) index of the Tomkin's Polarity Scale. The direction of this relationship was reversed for the rightist index (right movers scoring higher) but this difference was not significant. Results are interpreted as additions to evidence which suggests a connection between the left and right sides of the human body and more global dichotomies of ideology or personality.

Adolescent↗