Biomedical subjects

H C Goltz

Publications and source records attributed to H C Goltz.

8 recordsLinked to original sources

PubMed2003

Comparison of memory- and visually guided saccades using event-related fMRI.

Previous functional imaging studies have shown an increased hemodynamic signal in several cortical areas when subjects perform memory-guided saccades than that when they perform visually guided saccades using blocked trial designs. It is unknown, however, whether this difference results from sensory processes associated with stimulus presentation, from processes occurring during the delay period before saccade generation, or from an increased motor signal for memory-guided saccades. We conducted fMRI using an event-related paradigm that separated stimulus-related, delay-related, and saccade-related activity. Subjects initially fixated a central cross, whose color indicated whether the trial was a memory- or a visually guided trial. A peripheral stimulus was then flashed at one of 4 possible locations. On memory-guided trials, subjects had to remember this location for the subsequent saccade, whereas the stimulus was a distractor on visually guided trials. Fixation cross disappearance after a delay period was the signal either to generate a memory-guided saccade or to look at a visual stimulus that was flashed on visually guided trials. We found slightly greater stimulus-related activation for visually guided trials in 3 right prefrontal regions and right rostral intraparietal sulcus (IPS). Memory-guided trials evoked greater delay-related activity in right posterior inferior frontal gyrus, right medial frontal eye field, bilateral supplementary eye field, right rostral IPS, and right ventral IPS but not in middle frontal gyrus. Right precentral gyrus and right rostral IPS exhibited greater saccade-related activation on memory-guided trials. We conclude that activation differences revealed by previous blocked experiments have different sources in different areas and that cortical saccade regions exhibit delay-related activation differences.

Adult↗

PubMed2003

Eye movements tell only half the story.

The dramatic improvements of neglect symptoms after prism adaptation (PA) have been interpreted as evidence that PA reorganizes higher levels of spatial representation. Here the authors demonstrate that while the exploratory eye movements of a patient with neglect were clearly shifted toward the left after PA, he still showed no awareness for the left side of the stimuli he was now actively exploring. PA modulates functions of the parietal lobe, such as eye movement control, but fails to influence the underlying mechanisms of neglect.

Aged↗

PubMed1998

Vertical latent nystagmus component and vertical saccadic asymmetries in subjects with dissociated vertical deviation.

PURPOSE: This study was conducted to quantify the vertical component of a latent nystagmus observed in subjects with dissociated vertical deviation (DVD), as well as to provide further evidence for vertical saccadic asymmetries in these individuals. METHODS: Binocular eye movements of subjects with DVD were recorded in two dimensions using a noninvasive video-based eye tracker while cover/uncover tests, alternate cover tests, and vertical saccades were performed. RESULTS: A small amplitude (1.5 degrees or less) vertical component of latent nystagmus can be observed in some subjects with DVD and is larger in the deviating eye than in the viewing eye. The frequency of the vertical nystagmus component is the same in each eye for any given fixation condition but may change depending on which eye is fixating. DVD in the presence of a vertical component of latent nystagmus can be adequately modeled by the algebraic sum of an exponentially decreasing velocity DVD and a nystagmus with an exponentially decreasing slow phase velocity. In general, the occluded eyes of DVD subjects make smaller downward saccades than the viewing eyes. CONCLUSIONS: It is possible but not obligatory that DVD subjects will have a vertical component of latent nystagmus. Algebraic summation of an exponentially decreasing velocity DVD and a vertical component of latent nystagmus provides a more parsimonious explanation of the observed saccadic eye movements than modeling the DVD itself as a combination of vergence and saccadic movements. Subjects with DVD show a range of saccadic yoking from nearly complete saccadic conjugacy to nearly complete dissociation.

Adult↗

PubMed1997

Head turn in 1-eyed and normally sighted individuals during monocular viewing.

OBJECTIVE: To determine the incidence and magnitude of head turn in persons unilaterally enucleated at an early age and in normally sighted persons patched monocularly. SETTING: The Hospital for Sick Children, Toronto, Ontario. PARTICIPANTS: Fifty-two unilaterally enucleated children and adults without nystagmus (median age, 10 years) who were enucleated at an early age (median age, 18 months) due to retinoblastoma and 28 normally sighted children and adults. METHODS: Enucleated subjects were videotaped while walking 15 m toward a camera under 2 conditions: (1) fixation relaxed (just looking at the camera) and (2) fixation forced (trying to identify a small fixation target on the camera). Control subjects were tested in the fixation forced condition only. Head turn incidence and magnitude were independently rated. Three categories of head turn were used: "obvious" (> 10 degrees), "small" (5 degrees-10 degrees), and "no" (0 degree-4 degrees). RESULTS: In the fixation relaxed condition, 22 (42%) of 52 enucleated subjects exhibited head turn; when fixation was forced, the incidence increased to 25 (58%) of 43 subjects. Head turn was virtually always in the direction of the missing eye. Incidence and magnitude of head turn were unrelated to age at enucleation or number of years since enucleation. In the control group, there was no consistent finding of head turn across subjects when 1 eye was patched. CONCLUSIONS: One-eyed children frequently exhibit head turn unrelated to the presence of nystagmus. The direction of the head turn is "adaptive" because occlusion by the nose in the lower contralateral field is reduced.

Adolescent↗

PubMed1997

Vertical eye position control in darkness: orbital position and body orientation interact to modulate drift velocity.

How stable is vertical eye-in-head position control in darkness when no visual targets are present? We evaluated this while varying both body-in-space orientation and eye-in-orbit position in six subjects who were free from oculomotor/vestibular disease. Vertical eye movements were monitored using a CCD-video tracking system, and results were confirmed on one subject with the magnetic search coil. Three body orientations were used: (1) seated upright; (2) supine; and (3) prone. In each of these body orientations starting eye-in-orbit position was varied in quasi-random order from -20 to +20 deg, while vertical eye drift was monitored for a 90 sec period at each position. Subjects were instructed to hold their eyes as steady as possible. The relationship between body orientation/eye position and vertical eye drift velocity was examined using a linear regression technique. In contrast to prior clinical reports, normals exhibit a vertical nystagmus/drift in darkness. Moreover, slow-phase eye velocity was found to be dependent on eye-in-orbit position in the upright and supine body orientations. This pattern of eye drift mirrors Alexander's Law, with significantly increased drift velocities when subjects looked in the direction of their re-centering saccades (P < 0.05 or better). Body-in-space orientation also modulated the eye drift velocity, with significant differences in rate of eye drift (P < 0.05 or better) between extremes of body orientation (supine and prone) for five out of six subjects. The stability of the vertical oculomotor control system in the absence of visual input is strongly affected by body-in-space orientation and eye-in-orbit position: manipulating either of these variables results in non-random patterns of drift. These results are discussed using a multiple-input model of vertical eye-in-head position control.

Adult↗

PubMed1993

The effect of gravity on the resting position of the cat's eye.

We measured rotation (horizontal, vertical and torisonal) and translation (horizontal and vertical) of the paralysed cat's eye in response to 45 degrees steps of orientation presented in a pseudorandom order around the roll and pitch axes (with respect to the horizontal canals). During changes of position of the animal in the roll plane, the eyes rotated towards the lowest part of the orbit (left with left ear down; top when the cat was upside down, etc.) by an average of 0.55 degree. Changing orientation in the pitch plane evoked vertical rotations of +/- 1.42 degrees (upwards eye movement during forwards head pitch) and torsional rotations of +/- 1.3 degrees. All these rotations taken together suggest that the centre of mass is in front of, below and temporal to the centre of rotation. The eyes translated temporally (thus separating by 0.72 mm) during forward pitching and there was a small vertical displacement (0.23 mm) when the animal was upside down. These findings are discussed with respect to a possible role of the extraocular proprioception system.

Animals↗

PubMedDate not supplied

Visual alignment from the midline: a declining developmental trend in normal, strabismic, and monocularly enucleated children.

Children, 1.8 to 5.0 years of age, were asked to sight through a tube at targets. There were three groups tested: children with normal binocular vision, children with strabismus, and children with one eye enucleated. The younger normal and strabismic patients placed the tube midway between the two eyes. Surprisingly, the younger enucleated children also placed the tube at the midline. This "Cyclops effect" diminished as the children grew older, with a transition to sighting monocularly by the age of 4 years. The tendency to align with the midline by the younger children, regardless of the degree of their binocular vision, presumably is a natural response to a cyclopean projection center in the midline. As children mature, they learn to meet the demands of monocular preference tasks by aligning objects in front of one eye.

Child, Preschool↗

PubMedDate not supplied

Dissociated vertical deviation: head and body orientation affect the amplitude and velocity of the vertical drift.

PURPOSE: Five subjects with dissociated vertical deviation (DVD) were studied to determine if the amplitude or velocity of the vertical components of the DVD were affected by head/body orientation with respect to gravity. METHODS: Deviations were measured in head upright, head supine, and supine positions, with head hanging postures using a binocular CCD video-based infrared eye tracker. Subjects were required to fixate a target presented in the primary position during alternate or cover/uncover tests. RESULTS: Amplitude and velocity of DVD both in onset and recovery were affected by head/body orientation with respect to gravity. In four of five subjects, the amplitude of the DVD was asymmetric between the two eyes when the head was upright. When the head/body was moved from an upright to a supine with head hanging backward condition, the amplitude of the DVD in the two eyes inverted. The eye with the larger DVD in the upright position had a smaller DVD in the head-hanging orientation. A similar relationship existed between velocity and head/body orientation. We found that DVD velocity increased with amplitude. CONCLUSIONS: Passive effects of gravity on the eye-inorbit do not influence DVD magnitude or frequency of occurrence. The data suggest, however, that otolithic and possibly neck afferent inputs play a role in DVD magnitude and may be a part of the etiology of the condition.

Adult↗