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Biomedical subjects

D K Boman

Publications and source records attributed to D K Boman.

10 recordsLinked to original sources
PubMed1996

Anticipatory smooth eye movements and predictive pursuit after unilateral lesions in human brain.

Anticipatory smooth eye movements precede expected changes in target motion. It has been questioned whether anticipatory smooth eye movements are a component of the smooth pursuit system. Five subjects with unilateral brain lesions and five control subjects were tested with predictable double-ramp stimuli to determine whether these lesions have a similar effect on horizontal, visually guided smooth pursuit, anticipatory smooth eye movements, and the predictive component of smooth pursuit. All four subjects with a brain lesion involving the parietal or parietal-frontal lobe had parallel velocity asymmetries in all three forms of smooth eye movements, with lowest velocities toward the side of the lesion. A similar uniformity and magnitude of smooth eye movement directional asymmetries were not found in control subjects. Unidirectional attenuation of these three forms of smooth eye movements provides evidence that they are part of a unified smooth eye movement system.

Brain↗
PubMed1992

Interleukin-6 in psoriasis: expression and mitogenicity studies.

Interleukin-6 (IL-6) is a multifunctional cytokine which has been suggested to function as an autocrine mitogen in psoriatic epidermis. We report here the results of several experiments designed to further examine this hypothesis. Blot hybridization was unable to detect 1.3 kb IL-6 transcripts in RNA extracted from normal or psoriatic epidermal (keratome) biopsies, suggesting that IL-6 expression is very low in normal and psoriatic epidermis. Therefore, qualitative and semiquantitative PCR/Southern blot analyses were performed on keratome-derived RNA, and revealed variable but significantly increased IL-6 mRNA levels in lesional psoriatic relative to normal tissue. To further examine the ability of normal human keratinocytes (NHK) to express IL-6, RNA was extracted from rapidly proliferating secondary NHK cultures. IL-6 transcripts were nearly undetectable by blotting in keratinocytes grown in low-calcium serum-free medium, but low levels could be induced by treatment with 1.8 mM CaCl2. IL-6 transcripts were strongly superinduced after cycloheximide treatment, suggesting that a labile protein regulates IL-6 mRNA levels in these cells. Finally, the mitogenic activity of IL-6 was examined in NHK under varying conditions of cell density and added growth factors. IL-6 did not stimulate high density keratinocyte growth in the presence or absence of other growth factors, but did stimulate clonal growth in epidermal growth factor (EGF)-deficient media at high concentrations (> or = 10 ng/ml). The proliferative effects of IL-6, but not of basic fibroblast growth factor, were abrogated by monoclonal antibodies directed against the EGF receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1992

Predictive smooth pursuit eye movements near abrupt changes in motion direction.

The stimulus-response characteristics of predictive smooth pursuit eye movements near the time of predictable, abrupt changes in target motion direction were studied. Expectations about the speed and direction of target motion both before and after the direction change affected specific components of the predictive pursuit responses. We propose that, when the direction of target motion is expected to change, the cessation of motion in one direction and the initiation of motion in a new direction are separately anticipated and that predictive pursuit movements are summated responses to these two events.

Adult↗
PubMed1992

Reading speed with a pixelized vision system.

A visual prosthesis based on electrical stimulation of the visual cortex with an array of penetrating electrodes is expected to produce pixelized visual images consisting of punctate spots of light (phosphenes). We measured reading speed in subjects viewing text with optically simulated phosphene fields in order to obtain estimates of the following design parameters for such an electrode array: pixel number, pixel spacing, and visual-field size. Comparisons were made between scanning the text with eye movements and scanning the text with head movements. The results indicate that a 25 x 25 array of pixels representing four letters of text projected on a foveal visual field of 1.7 degrees is sufficient to provide reading rates near 170 words/min with scrolled text and near 100 words/min with fixed text.

Humans↗
PubMed1989

Motion perception prominence alters anticipatory slow eye movements.

Perceived motion may be a stimulus for anticipatory slow eye movements. To test this possibility, the production of anticipatory slow eye movements in humans was studied using apparent motion stimuli. Short range apparent motion was produced with random dot stimuli and the anticipatory slow eye movements were isolated from the smooth pursuit responses by occasionally including trials in which the random dot stimulus did not appear. Long range apparent motion was produced with subjective contour stimuli. Both short range and long range apparent motion were found to be effective stimuli for anticipatory slow eye movements. The prominence of perceived motion was altered by changing the spatiotemporal displacement intervals in the short range apparent motion stimuli. Changing the subjective contours also changed the motion percepts of the long range apparent motion stimuli. With both stimuli, the peak anticipatory slow eye velocities that were achieved decreased as the prominence of the motion percepts decreased, while the time-course of the anticipatory responses were similar under the different conditions. These findings indicate that the expectation of perceived motion is necessary for anticipatory slow eye movements.

Adult↗
PubMed1988

Stimulus conditions that enhance anticipatory slow eye movements.

Anticipatory slow eye movements are predictive responses that occur prior to both ramp and step target motions. These low velocity eye movements are enhanced and can be studied in isolation by transient target disappearance before ramp motion onset. Slow eye velocities also decrease prior to the termination of target motion. In experiments using a bistable apparent motion stimulus, it was found that perceived motion is a stimulus for anticipatory slow eye movements. This relationship between motion perception and anticipatory slow eye movements can explain previously noted differences between these predictive movements and the predictive component of smooth pursuit.

Adult↗
PubMed1985

Effect of stimulus parameters on fusional and stereoscopic performance.

The effect of stimulus size and complexity on the horizontal divergent diplopia threshold, stereoscopic range, reappearance of stereopsis, and re-fusion point was examined. It was found that the addition of random-dot (RD) backgrounds significantly increased both the diplopia threshold and re-fusion point, whereas the further addition of multiple depth planes did not. Stereopsis and diplopia were found to coexist in RD stereograms both when the disparity increased past the diplopia threshold and when it was decreasing toward the re-fusion point. This suggests that monocularly distinguishable contours must be added to RD stereograms to render them suitable for the measurement of fusional amplitudes.

Adult↗
PubMed1985

Horizontal fusional responses to stimuli containing artificial scotomas.

Horizontal fusional responses were studied with stimuli containing binocular or monocular, artificial, stabilized, scotomas. Binocular scotomas of 5-deg, 10-deg, and 15-deg diameters were utilized. The fusional responses to scotomatic stimuli were compared with full-field stimulus responses. All responses contained significant motor and nonmotor (sensory) components. Overall motor compensation to stimuli with 10-deg and 15-deg scotomas was reduced, while the overall motor compensation to stimuli with 5-deg scotomas was not. With full-field stimuli and with stimuli containing binocular scotomas, the changes in the two eyes' lines of sight were often asymmetric in response to symmetric disparity changes. This response asymmetry was exacerbated by the presence of monocular scotomas. Fixation was less steady with stimuli containing 10-deg or 15-deg binocular scotomas than it was in response to full-field stimulation. The fusional responses to annular stimuli were similar to those elicited by scotomatic stimuli.

Convergence, Ocular↗
PubMed1985

Fusional responses of strabismics to foveal and extrafoveal stimulation.

Horizontal fusional responses of 11 strabismics, with normal or anomalous retinal correspondence, were studied. These included four small-angle esotropes with amblyopia, one intermittent esotrope (overcorrected intermittent exotrope), two intermittent exotropes (preoperative esotropes), one accommodative esotrope, and three microtropes with amblyopia. Fusional stimuli (with a constant accommodative demand) ranging from very small, central stimuli to those that cover the central, the peripheral, and both the central and the peripheral visual fields were used. All 11 strabismics produced fusional vergence responses. Many of the fusional responses included large nonmotor components. Small central stimuli were not effective in producing fusional vergence, whereas stimuli that covered the visual periphery produced fusional responses that were similar to those by subjects with normal stereoscopic vision.

Adolescent↗