Leonard R. Proctor

Eye-Tracking Patterns in Schizophrenia

A significant number of schizophrenic patients show patterns of smooth pursuit eye-tracking patterns that differ strikingly from the generally smooth eye-tracking seen in normals and in nonschizophrenic patients. These deviations are probably referable not only to motivational or attentional factors, but also to oculomotor involvement that may have a critical relevance for perceptual dysfunction in schizophrenia.

Smooth-pursuit eye movements, and diazepam, CPZ, and secobarbital

This study examined the effects on smooth-pursuit eye tracking of single doses of CPZ (0.667 and 1.334 mg/kg), diazepam (0.071, 0.142, and 0.284 mg/kg), and secobarbital (100 mg). Only the barbiturate significantly affected the ability to follow a moving target with smooth-pursuit eye movements. In repeated testing of a single subject, 130 mg of secobarbital disrupted smooth-pursuit movements at least until 24 hrs after ingestion.

The several qualities of attention in schizophrenia.

EVER since systematic observation of madness began-and history records ancient descriptions of syndromes quite similar to those we know today-disturbances in the ability to attend have been given a prominent place either in explanations or descriptions of the abnormalities. In this paper we present evidence for an impairment of a non-voluntary form of attending in schizophrenia, the study of which has important implications for exploring the psychological and neurophysiological aspects of schizophrenia.

SMOOTH PURSUIT EYE MOVEMENTS IN TWINS DISCORDANT FOR SCHIZOPHRENIA

IN A SERIES of studies we reported that between 65 and 80 % of schizophrenic patients have disordered pursuit eye movements, compared with about 15 “/;, in other psychiatric populations and 6 % in the normal population. Of equal interest was the finding that about 45-50 “/,; of first-degree relatives of the schizophrenics also showed the same kind of eye-tracking impairments, compared with a prevalence in the families of other psychotic patients that was no greater than that found in the normal population. 1,~ This association of disordered pursuit eye movements with schizophrenia and with members of the families of schizophrenics suggested that deviant pursuit eye movements may represent a genetic indicator of schizophrenia. This hypothesis would obtain confirmation if monzygotic (MZ) and dizygotic (DZ) twins who are discordant for schizophrenia were concordant for deviant eye tracking. This paper describes such a study. Smooth pursuit eye movements are those attendant upon following a moving target, and the speed of the target determines almost exactly the speed of the eyes. Rapid or saccadic movements are those that occur when fixation shifts, as when a person looks about a room from one object to another. In saccadic shifts, the eye can move at very rapid speeds, at times up to 600 degrees a second. In contrast, following movements break down into saccadic shifts if the target moves faster than about 40 degrees a second. A simple test of pursuit eye movements simply requires a subject to follow a pendulum. The pendulum, of course, oscillates at a continuously varying velocity, at first accelerating to a maximum and then decelerating to zero velocity. Electronystagmographic recording permits the investigator to obtain a permanent record of eye movements during the pursuit task.‘,2 In good pursuit eye movements the eyes should reproduce the sinusoidal wave form of the pendulum. Figure 1 shows four examples of pursuit movements. Normal eye tracking is represented in Figs la, lb. Deviations in eye tracking, such as those illustrated in Figs lc and Id are found in persons with some hemispheric and brain-stem lesions, multiple sclerosis, Parkinson’s disease, and some drug intoxications, particularly barbiturate and alcohol.3 In our studies we found that deviant eye tracking patterns in young schizophrenic patients occurred without the presence of organic disease and in a large number of their first-degree relatives the poor tracking occurred without either the presence of clinical schizophrenia or of organic pathology. Indeed, none of the relatives examined had visited a psychiatric facility for treatment for themselves and all were functioning quite adequately in the social

Acute vestibular paralysis in herpes zoster oticus.

A case of herpes zoster oticus is presented in which the lateral and superior semicircular canals of the labyrinth were affected unilaterally. The results of several electronystagmographic examinations are described and correlated with the patients description of symptoms. This case study indicates that disease affecting the lateral semicircular canal is reliably detected by the conventional caloric test. However, the fact that the posterior semicircular canal remained intact could not be inferred from the results of the caloric test in this case. Also, the appearance of nystagmus upon eye closure appears to have been a more sensitive index of the state of the disease process than was the caloric test.

Stimulation of the Vestibular Receptor by Means of Step Temperature Changes During Continuous Aural Irrigation

A technique for rapid, balanced hot/cold stimulation of the vestibular receptor is presented. During continuous aural irrigation the temperature of the irrigation fluid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. Application of the test to 32 clinical subjects demonstrated that the heat conduction model and the analysis used in timing the sequence of thermal pulses was accurate. We expect that, with further refinements, the new technique will prove superior to conventional caloric test methods in the detection and measurement of subtle as well as gross abnormalities of the vestibular system.

Reference Values for Serial Vestibular Testing

This study defines the normal limits of day-to-day variation in vestibular function. A short-acting caloric test was used and nystagmus intensity was measured by means of an interactive computerized technique. Data were analyzed from 30 normal subjects tested on three successive days and from ten of these subjects who were also tested on 11 additional occasions. Individual caloric test scores generally remained between 55% and 170% of their initial value; narrower ranges resulted when scores were averaged together. There was very little habituation of caloric responses. The upper normal limits of test-retest variation in scores for right-left difference and directional preponderance of caloric responses were 24% and 22%, respectively.

New Approach to Caloric Stimulation of the Vestibular Receptor

A new caloric testing method is described. During continuous aural irrigation, fluid is switched between hot and cold values at times computed according to a mathematical model of heat conduction in the labyrinth area. As a result, the induced temperature difference across the lateral semicircular canal describes an approximately sinusoidal time course, reaching peak values of equal magnitude but opposite sign. The magnitude of the caloric stimulus may be selected by choosing appropriate irrigation durations from a graph or table. Application of the test to clinical subjects demonstrated that the heat conduction model and analysis used in timing the sequence of thermal pulses was accurate. The new procedure causes less patient discomfort and requires less time to complete than does the conventional Fitzgerald-Hallpike test.

Results of new air caloric testing method among normal subjects. I. Biphasic testing.

A new air caloric testing method is described in which the temperature of a continuous aural irrigation is switched between hot and cold values at times calculated to control the intensity of the resulting vestibular stimulation. Applications of low or high caloric stimulus intensities to normal subjects were well tolerated and reliably produced appropriate low or high intensity nystagmic responses. Nystagmus intensity values obtained from this study were compared with predicted intensity values from a computerized simulation of the actual test conditions, and also with values obtained when using biphasic water irrigations. As a result, further improvements in our methodology have been effected.

Construction of a practical and inexpensive air stimulator for caloric vestibular testing

An inexpensive and practical method for delivering air into the aural canal at a selected stable temperature is described. A water‐air heat exchanger utilizing the external circulation of a constant‐temperature water bath brings the temperature of the air stream to a chosen value. Measurements indicate stable air outflow temperatures are maintained when proper nozzle design and air flow rates are employed. The apparatus is easy to construct and has proven convenient and effective when used in the clinical vestibular laboratory.