Erratic eye tracking in schizophrenic patients as revealed by high-resolution techniques.

Using high-resolution infrared oculography with digital recording and analysis techniques, we tested several types of eye movements in 19 schizophrenic patients and 11 normal controls. Abnormal slow pursuit eye movements, seen in about half of the patients, were characterized by erratic inaccuracies in position, velocity, and phase. Tracking errors were quantitatively assessed by their root mean square (RMS) error. Position RMS errors fell into two clearly separated groups, with 10 of 19 patients clustering about the normal controls and the remaining 9 having much higher errors than normal. Although several of these poor trackers had an excess of saccades or low pursuit gain, these abnormalities were not primarily responsible for the large erratic tracking errors. Saccades in response to unpredictable target jumps had normal latencies (reaction times) and velocities, but were more hypometric and variable in accuracy than those of controls. These saccadic abnormalities did not correlate with the patients' position RMS errors during slow pursuit.

Visual evoked potentials elicited by circular grating.

In the belief that it would prove a more effective stimulus for eliciting visual evoked potentials, a circular grating was designed so that the relationship between its bar width and visual acuity was held constant, and, therefore, the bars were equally well resolved across the visual field. Visual evoked potentials elicited by the onset presentation of the pattern were evaluated but found to be excessively variable owing to summation of different waveforms generated by equivalent stimulation of different parts of the visual field.

Normal saccadic structure of voluntary nystagmus.

Infrared oculographic recordings in three cases showed that voluntary nystagmus is composed of rapidly alternating small-amplitude saccades with normal velocity-amplitude characteristics. These bursts of reciprocating saccades are routinely associated with oscillopsia. This means in terms of oculomotor control theory that the brain stem mechanism mediating voluntary nystagmus must bypass the level in the oculomotor path where the saccadic corollary discharge (efferent copy) is initiated.

Retinopathy after tilorone hydrochloride.

Two patients, a 34-year-old woman and a 50-year-old woman, received tilorone HCl, an experimental antitumor drug. After taking the drug orally (total dose, 152 g), the first patient developed corneal subepithelial infiltrates and toxic retinopathy characterized by fine pigment mottling of the peripheral fundus and macula with mild arteriolar narrowing. Although visual acuity was 6/6 (20/20) throughout treatment, Goldmann perimetry showed marked peripheral constriction of the visual fields and results of an electroretinogram and an electro-oculogram were abnormal. After taking the drug orally (total dose, 189 g), the second patient developed corneal subepithelial infiltrates, severe bilateral arteriolar narrowing, and mild pigment mottling of the macula. ERG and EOG were moderately attenuated. Visual fields by Goldman perimetry were within normal limits. Tilorone HCl, like chloroquine, may be an antioxidant that affects the free radical scavenging mechanism of the retinal pigment epithelium. Extensive testing should be done on all patients taking tilorone HCl in order to detect the initial manifestations of retinopathy.

The structure of schizotypy: a pilot multitrait twin study.

This report of a pilot study examines 29 pairs of twins from a population-based registry on whom four domains of schizotypy have been measured: personal interview using the Structured Interview for Schizotypy, self-report questionnaire formed from eight published self-report scales, attentional battery of eight individual tests, and root mean square error on smooth pursuit eye tracking. Analyzing the twins as individuals revealed two independent dimensions of clinically rated schizotypy (positive symptom schizotypy and negative symptom schizotypy) and two independent dimensions of self-rated schizotypy (positive trait schizotypy and trait anhedonia). Positive symptom schizotypy was highly correlated with positive trait schizotypy, but not with attentional dysfunction or eye-tracking error. By contrast, negative symptom schizotypy was significantly related to trait anhedonia, attentional dysfunction, and eye-tracking error. Correlations in monozygotic and dizygotic twins suggested that genetic factors were important in all four domains of schizotypy. Except for eye-tracking error, the results are more consistent with a dimensional than a "disease" model of schizotypy. Replication of these results with a larger group of subjects is needed.

Is Fourier analysis performed by the visual system or by the visual investigator.

A numerical Fourier transform was made of the pincushion grid illusion and the spectral components orthogonal to the illusory lines were isolated. Their inverse transform creates a picture of the illusion. The spatial-frequency response of cortical, simple receptive field neurons similarly filters the grid. A complete set of these neurons thus approximates a two-dimensional Fourier analyzer. One cannot conclude, however, that the brain actually uses frequency-domain information to interpret visual images.

The effect of adaptation to the stimulating pattern on the latency and wave form of visual evoked potentials.

Visual evoked potentials (VEPs) elicited with a checkerboard stimulus after adaptation to an unpatterned grey field were compared to those obtained after adaptation to the stimulating pattern for an equal interval of time. When 3--4 sec elapsed between the adapting interval and recording of the VEP, the latency of the principal positive peak increased by 4 msec with pattern-reversal, but not with pattern-onset stimulation, while the amplitude was unchanged. However, when the pattern-onset VEP was recorded immediately after adaptation, the principal negative peak of the response was lost and the latency of its principal positive peak increased by 14 msec, causing it to mimic the conventional pattern-reversal VEP in both wave form and latency, and suggesting that adaptation may cause the wave form differences in the VEPs obtained by these two methods.

Two-dimensional analysis of retinal information transfer.

A two-dimensional, time-dependent analysis of the mammalian retina is presented. A computer simulation of experimental data considers ganglion-cell activity as a two-dimensional process. The properties of the simulation model were examined with several input stimuli. Circular receptive fields enhance not only borders, but other spatial complexities, such as ends of lines and angles. The enhancement is remarkably insensitive to the shape of receptive fields. The processing of the input picture by on-center and off-center receptive fields is complementary but the division of labor varies with the task.

Electrical response to vibration of a lipid bilayer membrane.

The discovery and characterization of a vibration response in a black lipid bilayer membrane is the topic of this paper. An electrical vibration response is obtained when the membrane is under voltage clamp and a weaker, but significant, response is obtained under current clamp. The effect arises from an induced variation in the membrane capacitance. It is further shown that the capacitance variation arises from a change in the membrane area as the membrane undergoes drumhead vibration. Possible physiological significance in mechanoreception is discussed.

Pattern-onset visual evoked potentials in suspected multiple sclerosis.

Visual evoked potentials (VEPs) were obtained by monocular stimulation using a checkerboard pattern-reversal and pattern-onset technique. In 11 normal subjects, pattern-onset VEPs were generally larger, better defined, and less ambiguous than those elicited by pattern-reversal, because of the biphasic waveform characteristically obtained with pattern-onset stimulation. In 68 of 105 patients with possible multiple sclerosis, VEPs were normal in latency by both methods, and in nine adequate comparison was not possible. The incidence of normal VEPs to pattern-reversal was similar to that found in several other studies of patients with possible multiple sclerosis. Among the remaining 28 patients in whom VEP abnormalities were found, an increased latency was detected in 75% with the pattern-reversal technique, and in 96% by pattern-onset. In these patients, VEP abnormalities were obtained by monocular stimulation of each of 46 eyes, and among these the pattern-reversal technique yielded abnormalities in 59% and the pattern-onset method in 98%. These results indicate that VEPs elicited by pattern-onset are useful in investigating patients with suspected multiple sclerosis, and the diagnostic yield may be greater than with conventional pattern-reversal techniques.

Myoclonic ocular jerks.

A 39-year-old woman with a familial trait for myoclonic jerks of the neck presented with spontaneous 5- to 40-degree single jerks of the eyes, usually upward, each producing a brief interruption in fixation. Eye movement recordings showed the myoclonic ocular jerks to be saccades with variable intersaccadic intervals. Treatment with 6.0 mg per day of clonazepam reduced her symptoms.

Opposed adducting saccades in convergence-retraction nystagmus: a patient with sylvian aqueduct syndrome.

We report high resolution oculographic recordings on a patient with convergent-retraction nystagmus (Parinaud's Sign). Recordings show opposed adducting saccades which are slightly asynchronous (8 ms), in contrast to the conjugate horizontal saccades which are exactly synchronous (0.3 ms). Normal saccadic velocity of these opposed adductions necessarily implies reciprocal innervation of horizontal and vertical agonist-antagonist pairs. Lateral view cine films show absence of retraction, apparently as a consequence of normal orbital mechanics. We suggest that normal mechanisms for dynamic overshoot saccades are involved in the production of these abnormal opposed adducting saccades.

Disorders in cerebellar ocular motor control. I. Saccadic overshoot dysmetria. An oculographic, control system and clinico-anatomical analysis.

Photoelectric eye movement recording in 9 patients with cerebellar disorders defined three features of saccadic overshoot dysmetria: (i) saccades were hypermetric and successively diminished in amplitude; (ii) saccadic initiation interval averaged 173 ms: and (iii) eye position was constant during the intersaccadic period. These characteristics indicated that the visually evoked saccades subserving foveation had increased gain, and were modelled by computer simulations using a sampled-data control model with increased feed-forward gain. Eight patients with saccadic overshoot dysmetria had cerebellar neoplasms, vermis-splitting surgical procedures and mid-line cerebellar signs. This clinical evidence suggests that vermian dysfunction is responsible for saccadic overshoot dysmetria. Normally, the cerebellar vermis appears to play an adaptive role by continuously adjusting gain of the direct visual motor pathway. When cerebellar disorder exists, adaptive gain modulation is lost, and, if gain then increases, saccadic overshoot dysmetria is a result.

Disorders in cerebellar ocular motor control. II. Macrosaccadic oscillation. An oculographic, control system and clinico-anatomical analysis.

A distinctive cerebellar ocular motor disorder, macrosaccadic oscillation, evolved simultaneously with an acute cerebellar syndrome in 4 patients, 2 with haemorrhagic metastatic melanoma deep in the vermis, a third with a presumed cerebellar haematoma and a fourth with focal demyelinating disease. Ocular oscillations were conjugate, horizontal, symmetrical, occurred in bursts of several seconds duration, had amplitudes of 30 degrees to 50 degrees, and were evoked whenever the patient attempted to shift visual fixation or pursue a moving target. Photo-electric recordings in one patient with tumour defined features of this disorder of saccadic eye movement: (i) oscillation was composed of saccades, (ii) frequency was 2 Hz, (iii) bursts occurred with amplitude first increasing and then decreasing, (iv) intervals between beginnings of saccades averaged 260 ms and (v) eye position did not exhibit systematic drift during the intersaccadic period. These features documented the inreased gain and instability of the visually guided saccadic system. By using increased feed-forward gain in a sampled-data control model we simulated the pattern of macrosaccadic oscillation. We belive that the acute loss of the calibrator function of the cerebellum accounts for the gain abnormality underlying macrosaccadic oscillation.

Clinical significance of transient visual phenomena in the elderly.

To evaluate the significance of transient visual phenomena in the elderly patient, a retrospective study of 43 patients over 40 years of age (mean, 58) presenting between 1971 and 1982 was conducted. Historical, clinical and diagnostic features were collated and analyzed by computer. The study revealed that 31 patients were diagnosed as migraine and 12 as vertebrobasilar insufficiency based on features identified in this review. Follow-up was obtained in 90% of the patients with a mean follow-up of 2.4 years. In general, prognosis proved to be excellent, with two deaths of cardiac origin and an 81% incidence of remission or symptomatic improvement of the visual events. No retinal or cerebral strokes were observed and TIAs occurred in only 9% of the population. This study suggests that transient visual phenomena in the elderly are benign.

Mixture analysis of smooth pursuit eye movements in schizophrenia.

The goal of this study was to replicate and extend previous findings indicating that the eye movement data of schizophrenic patients is best represented by the mixture of two groups, one of which has distinctly poor performance. Forty-nine schizophrenic patients and 32 normal controls had their smooth pursuit eye movements quantified by calculating the root mean square (RMS) deviation between the target and eye waveforms. Based on the finding of mixture in the distribution of RMS error, the patients were divided into low (better tracking) and high (worse tracking) RMS error subgroups. The high RMS error patients had abnormally decreased gain. Both patient subgroups had abnormally increased frequency of catch-up saccades and increased phase lag. Distinguishing between these two subgroups may be useful in clarifying the pathophysiology of abnormal pursuit and its relationship to heterogeneity in schizophrenia.

Oculomasticatory myorhythmia: a unique movement disorder occurring in Whipple's disease.

We describe two patients and a previously reported patient who acquired unique pendular vergence oscillations of the eyes and concurrent contractions of the masticatory muscles, i.e., oculomasticatory myorhythmia (OMM). The smooth disjunctive eye movements cycled with a frequency of 0.8 to 1.2 Hz. An analysis of peak velocities (15 to 200 degrees/sec) with respect to peak amplitudes (5 to 25 degrees) revealed dynamics characteristic of normal vergence movements. The pathological alterations resulting in pendular vergence oscillations implicate a separately functioning, physiologically normal vergence system within the brainstem. In addition to paralysis of vertical gaze, each patient also experienced progressive somnolence and intellectual deterioration. An intestinal biopsy in 1 patient established a diagnosis of Whipple's disease, which led to appropriate treatment and amelioration of the OMM. A pathological diagnosis of Whipple's disease of the central nervous system was made in the other 2 patients; results of an intestinal biopsy in one of these patients were normal. No patient had palatal myoclonus, and olivary pseudohypertrophy was not found in two autopsy examinations. Thus, OMM is a distinct movement disorder and has been recognized only in Whipple's disease. We conclude that patients with OMM should be treated presumptively for Whipple's disease of the central nervous system, even if a jejunal biopsy is normal.