The role of prediction in head-free pursuit and vestibuloocular reflex suppression.
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Darkness↗
Biomedical subjects
G R Barnes
Publications and source records attributed to G R Barnes.
Gaze control during head-free pursuit in patients with loss of vestibular function.
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Darkness↗
Interaction of active and passive slow eye movement systems.
Independent target and background motions have been used to generate conflicting activity within the pursuit and optokinetic systems. Subjects were required to pursue a small target against a structured background which moved independently. Selective enhancement of the response to the target generated high-gain active pursuit which dominated the eye movements. Passive eye movements induced during relative target and background motion are not normally directly quantifiable due to their low gain. By reducing the gain of the active pursuit optokinetically induced eye movements were enhanced and quantified. Three techniques are described for degrading active pursuit: tachistoscopic, eccentric and pseudorandom methods of target presentation. Our results demonstrate the synchronous input of active and passive eye movement drives to the oculomotor system and illustrate their interaction.
Eye Movements↗
A quantitative study of eye and head movements during smooth pursuit in patients with cerebellar disease.
Eye and head movements were analysed during smooth pursuit in 16 patients with various forms of cerebellar disease. Smooth pursuit gain was reduced across all frequencies and velocities of target motion for the patient group as a whole, during both sinusoidal and pseudo-random target motion. The graded breakdown in the pursuit response, as pseudo-random target motion became less predictable, was of a similar magnitude in patients and controls, implying that the predictive pursuit mechanisms were intact in these patients. During head-free pursuit, when vestibulo-ocular reflex (VOR) suppression was necessary, performance was not significantly different from that observed during head-fixed pursuit in the patient group. This finding is similar to that noted in control subjects, and is consistent with the observation that the VOR gains associated with head movements in darkness were similar in the patient and control groups. The deficits in pursuit and VOR suppression in patients with cerebellar disease therefore represent a decrease in gain in the closed-loop visual feedback pathways with apparent sparing of the predictive pathways.
Adult↗
Pursuit of intermittently illuminated moving targets in the human.
1. Experiments have been conducted in order to establish the changes in oculomotor activity which take place when the human subject attempts to pursue an intermittently illuminated moving target. 2. In an initial experiment, target motion in the horizontal plane was composed of one or two sinusoids at frequencies between 0.11 and 0.2 Hz. The target was illuminated for varying durations (10-320 ms) at intervals between 40 and 960 ms. As pulse interval was increased or pulse duration was decreased there was a progressive increase in eye velocity gain for the smooth component of eye movement. Some smooth eye movement was generated even when the pulse interval was as large as 960 ms. 3. In a second experiment target motion consisted of a triangular waveform in which target presentation was timed to occur at regular intervals throughout each cycle. Overlaying and averaging the response from several cycles revealed a regular pattern of pulsatile activity associated with each target presentation. This response, which was particularly evident when the pulse interval was greater than 1 s, consisted of an initial build-up of smooth eye velocity followed by an exponential decay with a time constant of 0.5-2 s. When the pulse interval was less than 1 s there was a summation of the transient responses so that eye movement appeared quite smooth when pulse interval was reduced to 320 ms. 4. The pulsatile nature of the response was accentuated when the target was made to execute a staircase-ramp waveform in which the target was illuminated only during the ramp component. The elimination of position change between ramps and the ability to achieve higher target velocity led to clear evidence of the summation of transient oculomotor responses. 5. The summated effects, however, were not simply attributable to the addition of responses to individual target presentations as indicated by the timing of each response. The eye velocity pulse was frequently initiated 200-300 ms prior to target appearance, and well before the time (100 ms) at which visual feedback would be expected to become effective. 6. The effect of target step displacement alone was investigated by examination of the smooth eye movement initiated by varying numbers of steps in the waveform. This showed that the basic step response had a peak velocity of no more than 8-10 deg/s in most individuals.(ABSTRACT TRUNCATED AT 400 WORDS)
Humans↗
Coordination of eye and head movements during smooth pursuit in patients with vestibular failure.
During pursuit of smoothly moving targets with combined eye and head movements in normal subjects, accurate gaze control depends on successful interaction of the vestibular and head movement signals with the ocular pursuit mechanisms. To investigate compensation for loss of the vestibulo-ocular reflex during head-free pursuit in labyrinthine-deficient patients, pursuit performance was assessed and compared under head-fixed and head-free conditions in five patients with isolated bilateral loss of vestibular function. Target motion consisted of predictable and unpredictable pseudo-random waveforms containing the sum of three or four sinusoids. Comparison of slow-phase gaze velocity gains under head-free and head-fixed conditions revealed no significant differences during pursuit of any of the three pseudo-random waveforms. The finding of significant compensatory eye movement during active head movements in darkness in labyrinthine-deficient patients, which were comparable in character and gain to the vestibular eye movement elicited in normal subjects, probably explains the similarity of the head-fixed and head-free responses. In two additional patients with cerebellar degeneration and vestibular failure, no compensatory eye movement response was observed, implying that the cerebellum is necessary for the generation of such responses in labyrinthine-deficient patients.
Adult↗
Visual-vestibular interaction during head-free pursuit of pseudorandom target motion in man.
Recordings of head and eye movement were made during pursuit of mixed-frequency, pseudorandom target motion to study the mechanism of vestibulo-ocular reflex (VOR) suppression during head-free pursuit. When high velocity stimuli were used, slow-phase gaze velocity gains decreased significantly with increases in both absolute target velocity and the velocity ratio between the frequency components. These changes occurred independently of changes in the head displacement gain, which remained relatively constant at the lower frequency and were directly attributable to impaired suppression of the VOR. Similar effects were seen when visual feedback was degraded by tachistoscopic illumination of the target. The results indicate that visual feedback, rather than an efference copy of the head velocity signal, is essential for suppression of slow-phase vestibular eye movement during head-free pursuit. When head-free and head-fixed pursuit were compared, striking similarities were seen for both slow phase gaze velocity gain and phase, indicating that gaze control during smooth pursuit is largely independent of the degree of associated head movement. This suggests that the VOR is not switched off during head-free pursuit. An estimate of the underlying VOR gain was obtained by recording the vestibular response produced by active head movements in darkness. The rather higher estimates of VOR gain obtained using an imaginary earth-fixed target paradigm were found to predict head-free gains more closely than the gains obtained during imaginary pursuit of a moving target, suggesting that such measures may be more representative of the underlying VOR gain.
Eye Movements↗
Predictive mechanisms of head-eye coordination and vestibulo-ocular reflex suppression in humans.
Head and eye movements of human subjects have been recorded during head-free pursuit in the horizontal plane of a target executing sinusoidal motion at a frequency of 0.26 to 0.78 Hz and a peak velocity of +/- 96 degrees/s. The target was not presented continuously but was exposed for brief durations of 120 to 320 ms as it passed through the centre of the visual field at peak velocity. This technique allowed the timing of each response to be assessed in relation to the onset of target appearance. During the first 3 to 4 target presentations, there was a progressive buildup of both head velocity and the smooth component of gaze velocity, while, simultaneously, the responses became more phase-advanced with respect to target onset. In the steady state, similar temporal response trajectories were observed for head and gaze velocity, which were initiated approximately 500 ms prior to target onset, rose to a peak that increased with the duration of target exposure, and then decayed with a time constant of 0.5 to 1 s. Whenever the target failed to appear as expected, the gaze and head velocity trajectories continued to be made, indicating that predictive suppression of the vestibulo-ocular reflex (VOR) was taking place in darkness. In a further experiment, subjects attempted to suppress the VOR during whole body oscillation at 0.2 or 0.4 Hz on a turntable by fixating a head-fixed target that appeared for 10 to 160 ms at the time of peak head velocity. Again, VOR suppression was initiated prior to target appearance in the same manner as for natural head movements, and when the target suddenly disappeared but rotation continued, predictive VOR suppression was observed in darkness. The similarity of these predictive effects to those obtained previously for head-fixed pursuit provides further support for the hypothesis that both pursuit and visual suppression of the VOR are controlled primarily by identical visual feedback mechanisms.
Dark Adaptation↗
The mechanism of prediction in human smooth pursuit eye movements.
1. Experiments have been conducted on human subjects to determine the role of prediction in smooth eye movement control. Subjects were required to actively pursue a small target or stare passively at a larger display as it moved in the horizontal plane. 2. Target motion was basically periodic, but, after a random number of cycles an unexpected change was made in the amplitude, direction or frequency of target motion. Initially, the periodic stimulus took the form of a square waveform. In subsequent experiments, a triangular or sawtooth waveform was used, but in order to examine the timing of the response in relation to stimulus appearance, the target was tachistoscopically illuminated for 40-320 ms at the time that it passed through the mid-line position. 3. When subjects either actively pursued the target or stared passively at the larger display a characteristic pattern of steady-state eye movement was evoked composed of two phases, an initial build-up of eye velocity that reached a peak after 200 ms, followed by a decay phase with a time constant of 0.5-2 s. The build-up phase was initiated prior to target displacement for square-wave motion and before onset of target illumination for other waveforms. 4. The peak eye velocity evoked gradually increased over the first two to four cycles of repeated stimulation. Simultaneously, the response became more phase advanced, the reaction time between stimulus onset and the time at which peak velocity occurred decreasing from an average of 300 to 200 ms for triangular waveform stimuli. 5. When there was a sudden and unexpected change in amplitude and direction of the stimulus waveform, the eye movement induced had a peak velocity and direction that was inappropriate for the current visual stimulus, but which was highly correlated with the features of the preceding sequence in the stimulus. 6. When there was a sudden change in the frequency of the stimulus waveform the predictive eye movement was induced with a timing appropriate to the periodicity of the previous sequence but inappropriate to the new sequence. 7. The results indicate that prediction is carried out through the storage of information about both the magnitude and timing of eye velocity. The trajectory of the averaged eye velocity response was similar in form irrespective of the duration of target exposure or basic stimulus frequency, suggesting that the predictive estimate is released as a stereotyped volley of constant duration but varying magnitude under the control of a periodicity estimator.(ABSTRACT TRUNCATED AT 400 WORDS)
Humans↗
Vestibulo-ocular reflex suppression during high velocity head-free pursuit in normal subjects.
Recordings of head and smooth pursuit eye movement were made during head-free pursuit of a pseudo-random target motion stimulus. The pseudo-random stimulus was composed of 2 high velocity sinusoids, of frequency 0.4 and 1.3 Hz, with the velocity of the higher frequency being varied as a ratio of the lower frequency velocity between 0 and 2. Slow-phase gaze velocity gain for the lower frequency component decreased significantly with an increase in velocity ratio, and with an increase in target velocity above 60 degrees/s. Gaze velocity gain was frequently less than head displacement gain which remained fairly constant, indicating that the eyes had been driven in the opposite direction to head movement as a result of inability of suppress the vestibulo-ocular reflex. Similar effects were seen when visual feedback was degraded by tachistoscopic illumination of a target composed of 2 low velocity sinusoids (0.11 and 0.13 Hz). These results indicate that visual feedback, rather than head displacement, is essential for suppression of slow-phase vestibular eye movement during head-free pursuit, even at high stimulus velocities.
Feedback↗
The assessment of predictive effects in smooth eye movement control.
Predictive mechanisms in pursuit were studied by requiring subjects to track a moving target which appeared for a brief period (40-320 ms) at regular intervals. With successive presentations the timing of the eye velocity trajectory became progressively more predictive of target appearance, whilst simultaneously increasing in peak velocity. Sudden changes in periodicity or velocity resulted in inappropriate eye movements correlated highly with previous stimulus cycles. The results suggest that prediction involves storage of velocity information and its release under the control of a periodicity estimator.
Humans↗
The effect on motion sickness and oculomotor function of GR 38032F, a 5-HT3-receptor antagonist with anti-emetic properties.
1. The 5-hydroxytryptamine (5-HT3) receptor antagonist, GR 38032F, which possesses potent anti-emetic properties in vomiting induced by cancer chemotherapeutic drugs, has been tested to determine its value in the prophylaxis of motion sickness induced by cross-coupled stimulation. The double-blind trial compared GR 38032F with both a placebo (lactose) and with hyoscine. In addition, studies of ocular pursuit and saccadic eye movements were carried out following the administration of each drug. 2. The prophylactic effect of GR 38032F on motion-induced nausea was indistinguishable from that of placebo, whereas following hyoscine subjects showed a highly significant (P less than 0.001) increase in tolerance to cross-coupled stimulation. Tests of oculomotor function showed no effect on saccadic eye movement from either drug. However, both drugs produced a significant (P less than 0.05) though small reduction in eye velocity gain during pursuit eye movement. 3. These findings suggest that the 5-HT3 receptor is not involved in the neural pathways that bring about motion sickness, but that it may have a role in the control of ocular pursuit. The absence of an anti-motion sickness effect from a drug that is effective in the treatment of vomiting induced by cancer chemotherapy serves to emphasize that different neural mechanisms are involved in the generation of motion sickness.
Adolescent↗
Factors affecting the predictability of pseudo-random motion stimuli in the pursuit reflex of man.
1. Experiments have been performed on human subjects to determine the principal mechanisms underlying the break-down in performance during ocular pursuit of pseudo-random target motion stimuli composed of a mixture of two, four or six sinusoids. As observed in a previous experiment there was a reduction in the ratio of eye velocity to target velocity (eye velocity gain) for lower-frequency components of the stimulus whenever the highest frequency exceeded 0.4 Hz, but the following effects were also observed. 2. Using a combination of four sinusoids in which the three lowest frequencies (0.11, 0.24 and 0.37 Hz) had a constant peak velocity (3 or 6 deg/s) it was shown that an increase in the velocity of the highest frequency (0.78 or 1.56 Hz) caused a progressive decline in gain of the low frequencies and a significant reduction in phase lag for the highest-frequency component. 3. Using a combination of two sinusoids (0.44 and 1.56 Hz), in which the peak velocity was varied over a wide range (4-32 deg/s), it was shown that the reduction in low-frequency gain was dependent on the velocity ratio between the frequency components rather than their absolute velocity. 4. Experiments using a combination of either four or six sinusoids in which the two highest frequencies were very close have revealed a true enhancement in the gain of the highest-frequency component in relation to other frequency components of the stimulus. 5. In the same experiments the phase relationships in the response were shown to vary according to the frequency range of the stimulus in such a way that phase advance was normally present at the lowest frequency even when this ranged up to 0.89 Hz. 6. When the oculomotor system was passively stimulated by allowing the subject to fixate a tachistoscopically illuminated stationary target, pseudo-random target motion induced a response which exhibited characteristics similar to those of active pursuit; that is, enhancement of the gain of the highest frequency and phase advance at the lowest frequency. 7. During passive stimulation the changes in gain of the low frequencies with increasing frequency of the highest-frequency component were not consistent with those of active pursuit. However, increasing the velocity of the highest-frequency component to simulate the retinal velocity error conditions of normal active pursuit caused a significant decrease in low-frequency gain and a subjective effect of high-frequency dominance similar to that observed during active pursuit.(ABSTRACT TRUNCATED AT 400 WORDS)
Eye Movements↗
Head-free pursuit in the human of a visual target moving in a pseudo-random manner.
1. Head and eye movements have been recorded in man during head-free pursuit of a target moving in a pseudo-random manner in the horizontal plane with a motion stimulus composed of the sum of four sinusoids. 2. In an initial experiment the three lowest frequencies remained constant at 0.11, 0.24 and 0.37 Hz, whilst the highest frequency (F4) took values of 0.39, 0.78, 1.56 and 2.08 Hz. Peak velocity of each component was 10 deg/s. When F4 was 0.39 Hz gaze displacement (i.e. the sum of head and eye displacement) was relatively smooth and had a mean velocity gain of 0.95. As F4 was increased gaze displacement contained more saccadic activity and gaze velocity gain for the three lower-frequency components was significantly (P less than 0.001) reduced to a minimum level of 0.66 when F4 was 1.56 Hz. 3. A similar reduction in gain of the lower-frequency components was obtained when the velocity of F4 was increased as a ratio of the velocity of the lower frequencies from 0 to 4. 4. When the frequency composition of the stimulus was varied so that the two highest frequencies were closely spaced, gaze velocity gain for the highest frequency was always significantly higher than that of the next lower frequency, indicating a true enhancement of the highest-frequency component. 5. Changing the lowest-frequency component of the stimulus resulted in a significant shift in the gaze velocity phase profile as a function of frequency, so that phase advance was always associated with the lowest frequency even when this was as high as 0.89 Hz. 6. These changes in gain and phase of gaze velocity with the frequency content of the stimulus were similar to those previously described for head-fixed pursuit and visual suppression of the vestibulo-ocular reflex (VOR) and implicate the frequency-dependent, non-linear visual feed-back mechanisms in gaze control. 7. A number of the non-linear characteristics of gaze velocity were also observed in a somewhat modified form in the head displacement gains and phases, implying that the drive to the neck muscles is also derived from the same non-linear visual feed-back source. 8. The role of the VOR in head-free pursuit was tested by exposing the subject to whole-body motion on a turntable which countered the volitional head movement generated by the subject.(ABSTRACT TRUNCATED AT 400 WORDS)
Eye Movements↗
Head-free pursuit of pseudo-random target motion.
Experiments have been conducted in which subjects were required to pursue a target moving in the horizontal plane with co-ordinated movements of the head and eyes. Target motion was pseudo-random in form, composed of four sinusoids. The three lower frequencies of the stimulus were maintained at 0.11, 0.24 and 0.37 Hz with a peak velocity of 10 degrees/s, whilst the frequency and velocity of the highest frequency component (F4) were varied. When all frequencies were below 0.4 Hz, eye movements were smooth and gaze velocity gain was high (0.95), but when F4 was increased up to 1.56 Hz or when the velocity of F4 was increased up to 40 degrees/s, gaze velocity gain decreased significantly. When voluntary head movements were countered by whole-body rotation to eliminate the input to the semicircular canals, gaze velocity gain increased because there was no longer any requirement to suppress the vestibulo-ocular response to head rotation. The results are in accord with those of previous experiments involving head-fixed pursuit and vestibulo-ocular suppression.
Eye Movements↗
Eye movements induced by linear acceleration are modified by visualisation of imaginary targets.
Lateral eye movement responses to linear acceleration in the lateromedial axis of the head have been examined in normal human subjects who were seated within a cabin, free to move on a horizontal linear track. The motion stimulus was either sinusoidal (0.2-0.8 Hz) or pseudo-random (0.11-1.25 Hz) in form, with a peak acceleration of 1.5 m.s-2. In darkness, while carrying out mental arithmetic, the mean ratio of slow-phase eye velocity to linear cart velocity increased from 2.8 degrees/m at 0.2 Hz to 10.5 degrees/m at 0.8 Hz during sinusoidal stimulation. When subjects were instructed to imagine a near head-fixed target in darkness, eye velocity decreased by 25%-48% during both sinusoidal and pseudo-random stimulation. When subjects were instructed to visualise an earth-fixed target during sinusoidal stimulation eye velocity was augmented by 47% when imagining a target 3 m distant and by 175% when visualising a target 0.6 m distant. Response augmentation was not as great during pseudo-random stimulation. The results indicate that the otolith-ocular response is highly modifiable by mental set.
Acceleration↗
High-dose cisplatin and vinblastine infusion with or without radiation therapy in patients with advanced non-small-cell lung cancer.
Non-small-cell lung cancer (NSCLC) patients with locally advanced or metastatic measurable disease were given a combination of cisplatin, 200 mg/m2 divided in five daily doses, and simultaneously, vinblastine, 7.5 mg/m2 as a continuous intravenous (IV) infusion over five days. Five courses of chemotherapy were planned. Afterwards or on progression, patients were randomized to receive maximally tolerated radiation to all sites of disease v observation only. Forty males and seven females were entered. Median age was 60 years (range, 37 to 74), median Karnofsky performance status was 70 (range, 30 to 90). Five patients had previous brain radiation therapy for metastatic disease, all others were previously untreated. Side effects in the 87 courses of chemotherapy administered included leukopenia (WBC less than 1,000/microL following nine courses) and thrombocytopenia (platelets less than 20,000/microL following four courses). Ten patients became septic, nine of them while leukopenic. Elevations of serum creatinine followed eight courses; in all cases the level was less than 3.0 mg/dL. Nausea and vomiting were mild to moderate. Five patients experienced mild hypoacusis and six had sensory polyneuropathy. The deaths of three patients were considered drug-related. The response rate was 28%. The median survival for the group was 22 weeks, 63.2 weeks for responders and 17.9 weeks for nonresponders. Twenty-six patients received radiation therapy, 16 randomized to this arm as planned, ten to palliate symptoms. Median survival of all irradiated patients was 24.8 weeks. Seven responders to chemotherapy were randomized to receive radiotherapy; their median survival was 25 weeks. In six responders randomized not to receive radiation, the median survival was 77.8 weeks (P greater than .3). Among nonresponding patients, the median survival of those radiated was 22.2 weeks, while that of nonradiated patients was 11 weeks. This regimen is cumbersome and toxic. It has offered no major survival benefits, or improvement in response rates, therefore, we do not recommend it for the standard treatment of NSCLC.
Adult↗
Sound spectography in the diagnosis of equine respiratory disorders: a preliminary report.
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Animals↗