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Biomedical subjects

J A Mather

Publications and source records attributed to J A Mather.

17 recordsLinked to original sources
PubMed1992

Disruption of saccade production during oculomotor tracking in schizophrenia and the use of its changes across target velocity as a discriminator of the disorder.

A clear measure of eye movement disorder (EMD) that reliably separated schizophrenic individuals from others would both give insight into the brain control of the disorder and provide an aid in diagnosis. In the present study, a detailed analysis was carried out of the interactions between the pursuit and saccadic components of eye movements at different target velocities. The subjects comprised schizophrenic patients, unipolar depressed patients, and normal controls. The speed of the slow pursuit component did not differ among the groups, but schizophrenic subjects made more saccadic movements at low target velocities, though they started further away from the target at high target velocities. On the basis of these differences, a slope was computed of the linear function that related the number of saccadic eye movements to the velocity of a ramp visual target. Slope direction was negative for schizophrenic subjects but positive for unipolar depressive and normal subjects, and the correct classification rate for subjects was 84%.

Adolescent↗
PubMed1990

Schizophrenic performance on line bisection: no simple lateralization defects.

Many studies have assessed the possible lateralization deficits of schizophrenics, and the results usually suggest left hemisphere dysfunction. Nevertheless, they have been variable. This may have been due to cognitive demand of the different tasks, not to changes in brain lateralization itself. In order to circumvent this problem, the present study evaluates the performance of schizophrenics on a simple but lateralized task, line bisection. Subjects bisected a line using either visual or tactile information, with the left or right hand, when it was placed in their left or right hemispace or directly in front of them. Schizophrenic subjects were not more erroneous than normals (variable error), nor were they biased differently from normals in either direction with either modality of sensory input (constant error). There were only two significant effects of group on the tactile line bisection, one of position x length x group and one of position x hand x end x length x group, both on constant error (directional bias). The lack of main effects and presence of interactions on these basic tasks suggests that apparent lateralization differences found in schizophrenic subjects are due not to a simple defect of brain lateralization but may stem from task demands and attention allocation.

Attention↗
PubMed1989

Release of saccades in schizophrenics: inattention or inefficiency?

This paper attempts to distinguish between inattention and inefficiency as the cause of the eye movement problems of schizophrenic subjects. It focuses on their release of fast saccadic eye movements in four different situations: interrupting smooth tracking, as double-jumps in refixation, and as inadvertent departures from steady fixation or too-early prediction moves. If an attention deficit causes saccades during tracking, they should be reduced only for schizophrenic subjects in the dark, when there is no contrasting background. Instead the reduction was present for all groups. If double-jumps in saccadic refixations were caused by inattentional instability, they should increase in schizophrenic subjects when the target is a temporary flash of light. Instead, they were reduced in all groups to almost none, suggesting a perceptual processing cause for the excess double jumps. If a global attentional problem of schizophrenia caused saccade release, saccade number should be correlated across the four situations. Instead, there were significant correlations only between departures and predictions in paranoid schizophrenic subjects (r = 0.728) and between predictions and looking in nonparanoid schizophrenic subjects (r = -0.855). This lack of over-all correlations suggests that a common inattentional problem does not produce these eye movement deficiencies. Instead, the perceptual influence on tracking and looking suggests that processing inefficiency is responsible for at least part of the deficit.

Adolescent↗
PubMed1986

Saccadic eye movements to seen and unseen targets: oculomotor errors in normal subjects resembling those of schizophrenics.

Schizophrenic subjects have defects in oculomotor control which appear to be the result of inefficient processing of sensory information, not a problem in controlling the movement itself [Mather and Putchat (1983b) J. Psychiat Res. 17, 343-360]. A demonstration that manipulating sensory information by removing context information alters these same saccadic eye movements in normals is the subject of the present research. Without context information (in the dark) people make more double-jump saccades and overshoot a target, as schizophrenics do usually. Normals have a reduced number of double saccades, a different pattern of eye movement, when the target itself is not visible. These findings reinforce the suggestions that schizophrenics, despite their normal oculomotor reaction time, are less effective than normal subjects at processing the spatial information which guides their eye movement.

Adolescent↗
PubMed1985

Eye movements of teenage children of schizophrenics: a possible inherited marker of susceptibility to the disease.

Teenage children each having one schizophrenic parent showed deficits in oculomotor control which are also found in schizophrenic subjects compared with controls. They made significantly more saccadic eye movements interrupting smooth pursuit ocular tracking. They also made significantly more double-jump saccadic movements in a looking task. Since this latter difference was true only when the visual target was illuminated during the saccade (p less than 0.001), the cause was likely visual processing and not a fixation stability problem. The two measures correlated significantly for all subjects (r = 0.63), and half the experimentals had scores more than two standard deviations above the mean for controls. This suggests that a pattern of oculomotor dysfunction found in schizophrenics which comes from a single source may act as a marker for susceptibility of their offspring to the disease.

Adolescent↗
PubMed1984

Motor control of schizophrenics--II. Manual control and tracking: sensory and motor deficits.

Manual control and tracking of 12 acute and chronic schizophrenics was tested for comparison with their performance in oculomotor tracking. Schizophrenics tended to be slower in a non-timed, non-tracking hand movement, and chronics made even slower movement when the experimental room was illuminated than when it was darkened. Chronics also had a significantly higher reaction time than normal controls. When tracking a constant-velocity visual target, all schizophrenics were significantly slower than normals to high-velocity (50 degrees and 60 degrees/s) targets only. When tracking a sinusoidally moving target, schizophrenics were not less accurate over-all but they showed less improvement than normals when room illumination gave visual information about background and hand position. This complex group of motor deficiencies of schizophrenics, along with their oculomotor control problems, suggests that they have sensory processing, attentional, and motor planning problems when performing orienting tasks.

Adult↗
PubMed1981

Eye-hand tracking using afterimages. Evidence that sense of effort is dependent on spatial constancy mechanisms.

Oculomotor tracking of one's unseen hand is greatly enhanced when a positive afterimage of the arm is projected onto its changing apparent position. The "afterimage arm" also influences the perception of real arm motion. The nature of this influence indicates that sense of effort or will derives from spatial computations potentially involving sensory and motor information about the ongoing orientation of the entire body.

Acoustic Stimulation↗
PubMed1981

The influence of efferent, proprioceptive, and timing factors on the accuracy of eye-hand tracking.

Oculomotor tracking of one's moving hand is considerably more accurate than tracking of an external target undergoing comparable motion. To identify the factors contributing to this enhancement of tracking accuracy, the influence of visual, proprioceptive, and efferent cues on tracking performance was assessed. Related observations were made on the influence both of linear and topological transformations between target and hand position on tracking accuracy. The experimental findings indicate that if a target light is attached to one's hand, a) the target can be tracked with comparable accuracy for active and passive limb movements, and b) when the entire hand rather than just the target light is visible, pursuit velocity is higher and more closely matches target velocity. If a linear transformation is introduced between hand and target positions, nearly identical tracking accuracy is found with voluntary and involuntary limb movements. By contrast, topological transformations degrade target tracking accuracy for passive but not for voluntary limb movements. The implications of this finding are discussed.

Adult↗
PubMed1981

Adaptation to visual displacement: contribution of proprioceptive, visual, and attentional factors.

A study is reported of the sensory and oculomotor factors that influence adaptation to visual displacement when only sight of the hand and of a target light is permitted. Ten subjects each participated in five counterbalanced sessions in which the relative contributions to adaptation of limb proprioception, oculomotor pursuit, retinal image displacement, and attention were determined. Recordings of eye position were taken throughout the sessions. A discordance between the visual direction of the hand and the proprioceptively specified position of the hand was essential but not sufficient for adaptation to occur. When such a discordance was present adaptation was enhanced by improving position sense of the arm by moving it passively, maximizing accuracy of visual tracking, and focusing attention on the hand. Attentional factors played a smaller part than has been reported for exposure situations involving error feedback about limb position. Eye-movement recordings showed that tracking the passively moved hand visually was vastly superior to tracking a target light undergoing comparable motion.

Adaptation, Ocular↗
PubMed1980

Multiple sensory and motor cues enhance the accuracy of pursuit eye movements.

Oculomotor pursuit can be elicited by moving visual, tactile, proprioceptive, and occasionally auditory targets presented singly. Both the accuracy and amount of pursuit are enhanced if the position of the target is specified by cues from several sensory modalities. When the motion of the target is topologically related to movements of the subject's arm, the subjects's eyes are more closely phase-locked with the target and reversals of the eyes generally precede target reversal by 10-20 ms.

Acoustic Stimulation↗
PubMed1976

Increased lead absorption with anemia and slowed nerve conduction in children near a lead smelter.

Studies to evaluate the prevalence, sources, and health consequences of lead absorption were conducted among children living near a primary lead smelter. Lead levels in air, soil, and dust were highest at the smelter and decreased with distance. Ninety-nine percent of one- to nine-year-old children living within 1.6 kilometers had blood lead levels greater than or equal 40 mug/dl, indicating increased absorption, and 22% had levels greater than or equal 80 mug/dl. The prevalence of lead levels greater than or equal 40 mug/dl decreased with distance; at 72 kilometers from the smelter it was 1%. Erythrocyte protoporphyrin levels increased with blood lead levels: 17% of children with lead levels of greater than or equal 80 mug/dl were anemic. There was no overt neurologic toxicity. Significant negative correlation was found in 202 five- to nine-year-old children between blood lead levels and motor nerve conduction velocity (r = 0.38, p less than 0.02).

Air Pollutants↗
PubMed1975

Immunization activities of private-practice physicians: a record audit.

A record audit of the office immunization records of 13 private-practice Idaho physicians included 813 2-year-old children. Thirty-six percent had completed all the Public Health Service recommended immunizations for a 2-year-old child. Forty-four percent of the "active" patients (those seen by the physician within the previous 12 months) were complete as opposed to 8% of the "inactive" patients. In general, the children who received immunizations exclusively from their private physician were better immunized (38% complete) than those who received immunizations from both their private physicians and the health department clinics (22% complete). Despite the low percentage of overall completeness, the vaccine-specific immunization levels were at least as high as the levels computed from the National Immunization Survey. While the limitations of the study prevent application of the results to physicians in general, the data suggest that the inability to complete an immunization schedule, once begun, is a major weakness in the immunization activities of private-practice physicians.

Child, Preschool↗
PubMedDate not supplied

Motor control of schizophrenics--I. Oculomotor control of schizophrenics: a deficit in sensory processing, not strictly in motor control.

An in-depth analysis of eye movements of schizophrenics has demonstrated defects in several oculomotor subsystems, likely due to processing of sensory information and not to problems in the motor system itself. Schizophrenic subjects made more pursuit tracking errors, due to higher RMS errors, larger phase lag, and more saccades in pursuit. When making saccadic movements they had normal reaction times, saccade velocity and intersaccadic pause, but made more double-jump saccades and overshot the target. Only some had inability to hold steady fixation, but all had an attentional problem in restraining an inappropriate eye movement. The multiple defects suggest a processing problem that is not strictly motor and does not fit any standard definition of attention.

Adult↗