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Biomedical subjects

J Pola

Publications and source records attributed to J Pola.

At least 19 recordsLinked to original sources
PubMed1997

Offset dynamics of human smooth pursuit eye movements: effects of target presence and subject attention.

Subjects made smooth pursuit eye movements with a target moving horizontally at 15 deg/sec. At a specified location the target either: (1) suddenly vanished; or (2) jumped to the fovea with target retinal velocity and feedback becoming 0 (target stabilized at the fovea). In each type of trial, the subjects either: "looked" at the target, "pushed" the target, or "passively" gazed. When the target vanished, eye velocity decreased exponentially with a short time-constant (tau approximately 0.10 sec), regardless of whether the subjects were "looking," "pushing" or "passively" gazing. However, some subjects while "pushing" (using an imaginary target) did generate low velocity smooth movement (1-2.5 deg/sec) late in the offset. When the target was stabilized at the fovea, eye velocity also decreased, but with a relatively long time-constant (tau = 0.4-0.8 sec). The time-constant was the same with both "looking," and "pushing", but was shorter for some subjects with "passive" gazing (tau = 0.1-0.5 sec). These findings show that smooth pursuit offset is influenced by the presence of a target, but is relatively independent of attentional mode. All of the pursuit offset responses can be simulated using a model of the pursuit system with target velocity and position inputs, and an internal positive feedback loop enabled by target presence.

Attention↗
PubMed1995

Visual fixation of a target and suppression of optokinetic nystagmus: effects of varying target feedback.

The ability to maintain foveal fixation of a target with either a stationary or moving background is often assumed to depend primarily on a difference (in velocity and/or position) between fovea and target. However, when subjects look at a target stabilized at the fovea presented against sinusoidal motion of an optokinetic stimulus field, optokinetic nystagmus (OKN) is suppressed. This suppression is not simply the absence of movement but instead most subjects show some amount of residual slow eye movements roughly counterphase to the field motion. We have varied the visual feedback of the target from 0 (stabilized) to -1 (stationary in space); as feedback increased, amplitude and phase lag of residual eye movements decreased systematically. The mechanism responsible for residual movements appears to operate for all feedback values (including the "real world" value of -1), which suggests a new view of the role played by retinal slip during fixation of a target and suppression of OKN.

Eye Movements↗
PubMed1995

Optokinetic nystagmus (OKN) suppression by fixation of a stabilized target: the effect of OKN-stimulus predictability.

In previous work, subjects looked at a target stabilized at the fovea, superimposed on a sinusiodally moving OKN stimulus. The stabilized target (no retinal-slip) suppressed OKN leaving residual eye movements that were often in counterphase with the OKN stimulus motion. In the present study we explored how this type of suppression of OKN is influenced by OKN stimulus predictability: OKN stimulus motion was either sinusoidal or a random walk of half-sinusoids. During fixation of a stabilized target with sinusoidal stimulus motion, OKN was suppressed leaving residual eye movement whose amplitude was typically less than OKN and with a phase lag of about 180 deg (roughly in counterphase with stimulus motion). With random-walk stimulus motion, the residual movement amplitude was even smaller, and at higher frequencies the phase lag decreased to become the same as for OKN. For both stimulus motions, OKN was suppressed when the target was present, but counterphase residual movements appear to depend on stimulus predictability.

Eye Movements↗
PubMed1994

Smooth pursuit eye movements with imaginary targets defined by extrafoveal cues.

Initiation of smooth pursuit eye movements was studied using imaginary targets defined by pairs of small spots ("cues") moving together in step-ramp motion. The arrangement of cues and imaginary target were either "two-sided"--cues far apart and imaginary target midway between, or "one-sided"--cues 4 deg apart and imaginary target to one side of the cue pair. (1) Pursuit of two-sided stimuli was much better than pursuit of one-sided stimuli and was often as good as pursuit of a real foveal target. (2) Experiments with various cue configurations suggest an attribute required for vigorous pursuit: "foveal enclosure". Configuration information is available to the pursuit system immediately after the onset of motion. (3) Pursuit of imaginary targets is markedly degraded by a background; the effect is strongest for a background at the fovea and weaker for an eccentric background, including one at the cue location.

Cues↗
PubMed1992

Suppression of optokinesis by a stabilized target: effects of instruction and stimulus frequency.

Subjects viewed a foveally stabilized target presented against a background field of dots moving sinusoidally. Several different modes of viewing the target were used (subjects were instructed to gaze, look, or hold), and the frequency of sinusoidal field motion was varied from 1/32 to 2 Hz. In line with previous findings, the presence of a stabilized target resulted in substantial suppression of optokinesis. The characteristics of this suppression (gain and phase of slow residual eye movements) were dependent on both the mode of viewing the target and the frequency of field motion. When subjects used an imaginary target, little suppression occurred. These findings provide an overall profile of dynamic characteristics of mechanisms involved in the suppression of optokinesis. They support the view that this suppression is significantly determined by the presence of a target against a moving background (even without retinal slip), and by the mode of attending to the target.

Adult↗
PubMed1991

Adverse cutaneous reactions due to macrolides.

Macrolides, which are widely prescribed and seldom produce hypersensitivity reactions, are considered to be safe drugs. We present five patients with generalized skin reactions due to erythromycin and/or spiramycin, proved by oral challenge tests. One patient showed reactions to both erythromycin and spiramycin. All skin prick and patch tests and histamine release tests with both macrolides were negative.

Adult↗
PubMed1989

The oculomotor "twitch"--a transient response to target motion.

The oculomotor "twitch" is a small, transient eye movement that occurs in response to onset of target motion during both passive and active regard of the target (Wyatt and Pola 1985 a, 1987). Among the properties described here, primarily tested with subjects remaining passive, the twitch (i) is elicited extrafoveally, but maximally at and near the fovea, (ii) often persists as a distinct early transient response even when target motion is onset of a simple ramp, and (iii) remains approximately constant over a wide range of target motions, varying only with direction. We suggest that the twitch reflects the working of a mechanism analyzing the direction in which a target starts to move.

Adult↗
PubMed1989

The perception of target motion during smooth pursuit eye movements in the open-loop condition: characteristics of retinal and extraretinal signals.

During smooth pursuit eye movement, the perception of target motion appears to come from retinal and extraretinal influences. To explore this, two open-loop conditions (experimental stimuli stabilized at the retina) were used: one to look at the combined effect of retinal and extraretinal signals on perception (using sinusoidal target motion); and the other to look at the characteristics of an extraretinal signal alone (using a complex target and square-wave motion). In both conditions subjects tracked target motion in the dark, and subsequently compared it to motion of a similar target in the light. The main findings of the study are that the magnitude of the extraretinal signal decreases with frequency, and that the retinal and extraretinal signals combine additively. This system appears to involve a transport-time, which could be in the form of a time advance. These features of perception have a variety of implications for motor control.

Eye Movements↗
PubMed1989

Accommodation to size and blur changing in counterphase.

We explored the influence of changing size and blur on accommodation by presenting the two stimuli sinusoidally in counterphase. The frequency response of the accommodative system (0.05 to 1 Hz) was determined using a high-speed infrared optometer while the subject viewed the target in a Badal optometer. Blur was provided by moving the target dioptrically toward and away from the subject, and size of the target was altered by a variable aperture. Both stimuli were varied sinusoidally at the same frequency, but in counterphase. We find that both size and blur can have an influence on accommodation: blur is particularly powerful at low temporal frequencies, whereas size becomes effective at moderate and high temporal frequencies.

Accommodation, Ocular↗
PubMed1988

Predictive behavior of optokinetic eye movements.

Optokinetic nystagmus is often thought of as a "primitive" oculomotor response, while smooth pursuit is thought of as a "higher" one. We have used conditions that are usually thought of as eliciting optokinetic responses; i.e., large-field stimuli confined to the retinal periphery, and instructions to subjects to respond passively. In spite of this, the responses showed predictive behavior similar to that described for smooth pursuit.

Eye Movements↗
PubMed1988

"Passive suppression" of optokinesis by stabilized targets.

Subjects gazed passively at a sinusoidally oscillating optokinetic stimulus. They made no attempt to look at a target which appeared, stabilized on the retina at one of several locations, yet the appearance of the target caused rapid and prolonged suppression of optokinesis. Suppression declined (optokinesis increased) as target eccentricity increased, but could be observed for eccentricities up to 15-20 deg. We propose that a target moving relative to a background is a stimulus for suppression of optokinesis, depending substantially on the visual properties of the target and not the act of attending to it.

Adult↗
PubMed1988

Farm animal feeders: another group affected by cereal flour asthma.

Asthma induced by cereal flour is a long recognized entity. We present studies of three patients affected by asthma related to exposure to cereal flour contained in animal formula feeds. Skin prick test performed with the formula feed components showed positive reactions to cereal flours (wheat, rye and barley) and negative to the other substances in these formulas. Specific anti-wheat, rye and barley flour IgE antibodies were found by RAST. Bronchial provocation tests (BPT) with wheat flour (patients 1 and 2) and barley flour (patient 3) all showed immediate responses. These findings suggest that our patients' symptoms were caused by an IgE-mediated hypersensitivity to cereal flours from animal formula feeds. We call attention to the importance of cereal flours in animal formula feeds as a cause of occupational asthma in farm and animal feeders.

Adolescent↗
PubMed1988

Severe anaphylactoid reaction to nalidixic acid.

We present the case of a 58-year-old non-atopic woman who suffered an adverse reaction to orally administered nalidixic acid, which had been prescribed for the treatment of a urinary tract infection. The single-blind oral provocation test was positive; the patient presented the clinical features of an anaphylactoid reaction 3 min after administration of nalidixic acid. Both the skin test and the histamine release test were negative. These results suggest that we are dealing with an anaphylactoid reaction not described before with this drug.

Anaphylaxis↗
PubMed1987

Dioptric and non-dioptric stimuli for accommodation: target size alone and with blur and chromatic aberration.

The frequency response of the accommodative system (0.05-1 Hz) was determined for various combinations of stimuli: changing target size was presented alone, together with defocus blur, and with both defocus blur and chromatic aberration. A high-speed infrared optometer monitored accommodation while the subject viewed the target in a Badal optometer. Target size was varied sinusoidally and blur was provided by moving the target towards and away from the subject at the same frequency. Chromatic aberration was controlled by using either monochromatic (590 nm) or white (3300 K) light. The target was presented under open-loop conditions when size was the only stimulus. We find that besides the conventional dioptric stimuli, changes in target size that result in changes in apparent distance can have substantial effects on accommodation.

Accommodation, Ocular↗