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Biomedical subjects

J J Barton

Publications and source records attributed to J J Barton.

At least 37 records · Page 2Linked to original sources
PubMed1998

Ocular search during line bisection. The effects of hemi-neglect and hemianopia.

We examined ocular fixations during line bisection in five patients with left hemianopia, two patients with right hemianopia, nine patients with left hemi-neglect and nine normal control subjects. Compared with measures in control subjects, the median fixation, and left- and rightmost fixations were shifted contralaterally in patients with hemianopia alone and ipsilaterally in patients with hemi-neglect. The fixation with the longest duration and the bisection point were also shifted contralaterally with hemianopia and ipsilaterally with hemi-neglect. However, the number of fixations and the spatial range spanned by fixations did not differ between the groups, showing that ocular exploration was not truncated in any group. Only some patients showed a previously reported directional search bias. Overall, there was no directional bias in saccadic number or amplitude. The distribution of fixations was most dense at the centre of the line in normal subjects, while hemianopic patients fixated most frequently at the ends of lines in their contralateral (blind) hemispace and at a central locus that was biased slightly contralaterally, as was their bisection judgement. This contralateral bias may reflect either an adaptive contralateral attentional gradient or a non-veridical spatial representation within the remaining normal hemifield. Hemi-neglect patients had a broad distribution of fixation peaks in the ipsilateral hemispace. Of two hemi-neglect patients with many fixations, one clustered fixations at a position right of centre, as if a normal fixation pattern was shifted rightward, while the other had two fixation peaks: one to the far right and the other near the centre of the line, reminiscent of the dual peaks of activity seen in some recent hemi-neglect models. These data reveal a heterogeneity in the routes by which right-biased judgements of spatial centre are reached by hemi-neglect patients.

Adult↗
PubMed1998

Ocular tracking of step-ramp targets by patients with unilateral cerebral lesions.

The relationship of sinusoidal smooth pursuit defects to pursuit defects with step-ramp targets in patients with cerebral lesions is unclear. We examined pursuit and saccades to both step-ramp and sinusoidal targets in 17 patients with unilateral cerebral lesions. Two types of pursuit defects were found. One group of three patients had ipsi-directional sinusoidal pursuit defects from lesions to the posterior internal capsule. Their chief abnormality with step-ramp targets was increased contra-directional pursuit. Their ipsi-directional step-ramp pursuit was often normal and disproportionately better than their ipsi-directional sinusoidal pursuit. Another patient with a parietal lesion had a second type of pursuit defect. He had low-normal sinusoidal pursuit bilaterally, but decreased ipsi- and contra-directional step-ramp pursuit. Also, he had an abnormal contra-directional drift after saccades to stationary targets. Despite these pursuit defects, saccadic accuracy did not show poor compensation for target motion in either patient type. The patient with the parietal lesion also had increased latencies for contralateral saccades. Recovery of pursuit was studied in one patient with an infarct of the posterior internal capsule. Initially he had a contra-directional bias that caused decreased ipsi-directional pursuit, increased contra-directional pursuit, and a contra-directional drift after saccades to stationary targets. Four months later, ipsi-directional pursuit and the post-saccadic drift to stationary targets had recovered, but contra-directional pursuit remained abnormally high. We conclude that lesions of descending pursuit tracts in the internal capsule are characterized by a contra-directional bias which recovers partly through a direction-specific adaptation. Lesions that affect the human homologue of posterior parietal cortex cause asymmetric bi-directional defects in pursuit initiation and increased contralateral saccadic latencies.

Adult↗
PubMed1998

Higher cortical visual function.

Higher cortical visual function continues to be explored with both lesion and functional imaging studies. Studies with functional MRI confirm that the fusiform gyri are involved in color and face perception, and show multiple regions participating in motion perception, including V5, V3A, and a new area, the kinetic occipital region. There were numerous blindsight reports, including studies of spatial summation and "inhibition of return," and a refutation of the argument that blindsight is merely a "criterion shift." However, other studies failed to find blindsight-like ocular motor responses to moving stimuli. Occipitotemporal lesions were found to cause defects in perception of both first- and second-order motion. The psychophysical impairments of the motion-blind patient LM were shown to be similar to those of monkeys with V5 ablations, suggesting a close homology between this monkey visual area and the human motion area in the lateral occipitotemporal cortex.

Animals↗
PubMed1998

Line bisection in hemianopia.

The effect of hemianopia on line bisection is not known. To study this, manual line bisection in 30 patients with unilateral cerebral hemispheric lesions was examined. The mean bisection point in a group of eight patients with left hemineglect was biased rightward (ipsilaterally), as expected. Among the remaining 22 patients, eight had right hemianopic visual defects, eight had left hemianopic visual defects, and six had normal visual fields. Both groups of patients with contralateral visual field defects had mean bisection points biased contralaterally, compared with 68 normal subjects. This bias was less than the ipsilateral (opposite) bias of patients with hemineglect. Contralateral bisection bias was more evident in those whose field defect involved the macular region. No bias was seen in patients with neither field defects nor hemineglect. The contralateral bias in hemianopia may represent either non-veridical spatial representation within a visual hemifield or a consequence of the strategic adaptation of attention into contralateral hemispace after hemianopia.

Adolescent↗
PubMed1998

Induction chemotherapy with docetaxel, cisplatin, fluorouracil, and leucovorin for squamous cell carcinoma of the head and neck: a phase I/II trial.

PURPOSE: A phase I/II trial of docetaxel, cisplatin, fluorouracil (5-FU), and leucovorin (TPFL5) induction chemotherapy for patients with locally advanced squamous cell carcinoma of the head and neck (SCCHN). PATIENTS AND METHODS: Twenty-three previously untreated patients with stage III or IV SCCHN and Eastern Cooperative Oncology Group functional status less than or equal to 2 were treated with TPFL5. Postchemotherapy home support included intravenous fluids, prophylactic antibiotics, and granulocyte colony-stimulating factor (G-CSF). Docetaxel dose was escalated to determine the maximum-tolerated dose (MTD). Fifteen patients were treated with three cycles of TPFL5 at MTD. Patients who achieved either a partial response (PR) or complete response (CR) to three cycles of TPFL5 then received definitive twice-daily radiation therapy. Toxicity and clinical and pathologic response to TPFL5 were assessed. RESULTS: Twenty-three patients received a total of 69 cycles of TPFL5. The MTD was determined to be docetaxel 60 mg/m2. Dose-limiting toxicity (DLT) was neutropenia. Additional significant toxicities at MTD were nausea, mucositis, diarrhea, peripheral neuropathy, and sodium-wasting nephropathy. The overall response rate to TPFL5 was 100%, which included 14 of 23 (61%) clinical CRs and nine of 23 (39%) clinical PRs. Primary-site clinical and pathologic CR rates were 19 of 22 (86%) CRs and 20 of 22 (91%) CRs, respectively. Eight patients had less than a CR in the neck to chemotherapy and, therefore, had postradiation neck dissections, four of which were positive for residual tumor. CONCLUSION: TPFL5 is a tolerable induction regimen in patients with good performance status. The DLT is neutropenia with significant mucositis, diarrhea, peripheral neuropathy, and sodium-wasting nephropathy. The high response rates to TPFL5 justify further evaluation of this combination of agents in the context of formal clinical trials.

Adult↗
PubMed1997

Motion direction discrimination in blind hemifields.

We tested motion direction discrimination with random dot cinematograms (RDCs) projected into the contralateral homonymous visual field defects of 10 patients with unilateral cerebral hemispheric lesions. Five patients had medial occipital lesions that spared the putative motion area in lateral occipitotemporal cortex and the optic radiations and other white matter tracts proximal to this site. The other 5 had lesions involving this area or the proximal optic radiations. Eye position was monitored to ensure fixation. No patient in either group discriminated motion direction in signal/noise RDCs at a level better than chance, and the performance of those with lesions restricted to medial occipital lobe did not differ from those with lateral occipital or optic radiation lesions. A subgroup of patients with medial occipital lesions also performed a "frequency of discrimination" experiment, using 100% coherent dot motion with stimulus velocities ranging as high as 79.4 degrees/sec. Their results on these tests were also no better than chance. Sparing of the putative motion area in lateral occipitotemporal cortex and its input fibers is not a sufficient condition for residual direction discrimination (blindsight) with RDCs in homonymous visual field defects.

Adult↗
PubMed1997

Impaired visual search in patients with unilateral neglect: an oculographic analysis.

The attentional deficit underlying hemispatial neglect was examined through a detailed analysis of the eye movement performance of a group of neglect patients. Relative to normal subjects and to patients with hemianopia without neglect, patients with left neglect make fewer fixations and have shorter inspection time on the contralesional left side. They also start their search to the right of the midline and make significantly more fixations and longer fixations on the ipsilesional right side. A positive linear relationship between horizontal location and frequency of fixations was noted for the neglect group as a whole, as well as for most of the individual patients. These findings strongly endorse the view that the attentional deficit in neglect follows a left right gradient. The peak of the maximum fixations, however, is not on the extreme right, as might be predicted by a strict gradient account, and is more consistent with recent views that the midsagittal plane of the viewer is redirected rightwards. These findings provide a detailed analysis of the eye movement patterns in neglect patients and demonstrate the robustness of oculographic analysis for examining their altered spatial representation.

Aged↗
PubMed1997

Smooth pursuit and saccades to moving targets in blind hemifields. A comparison of medial occipital, lateral occipital and optic radiation lesions.

We tested smooth pursuit and saccades to targets within the contralateral homonymous visual field defects of 10 patients with unilateral cerebral hemispheric lesions. Four patients had medial occipital lesions that spared the putative motion area in lateral occipitotemporal cortex and the optic radiations proximal to this site. The other six had lesions involving this area or the proximal optic radiations. From current hypotheses, that surviving extra-striate cortex is responsible for 'blindsight', we expected that the patients with lesions restricted to medial occipital cortex would be more likely to have residual ocular motor responses to moving targets. We found, however, that these patients with sparing of the lateral motion area did not show significantly better correlations of either post-saccadic eye velocity with target velocity or initial saccadic amplitude with the position of the moving target, compared with the other six patients. With increased target velocities against a background of darkness, two patients had weakly positive ocular motor correlations. However, in one patient this finding was replicated by a normal control stimulating the patient's scotoma and, in the other patient, the correlation disappeared when the eye with a residual monocular temporal crescents was occluded. These features indicate an artifact from light scatter. Only one other patient demonstrated a consistent, but weak, correlation of ocular tracking with target motion in the blind region; paradoxically, this patient had a lateral occipitotemporal lesion. We conclude that sparing of the lateral motion area is not sufficient condition for residual tracking of moving targets in homonymous visual field defects, and may not even be necessary.

Adult↗
PubMed1996

Functional MRI of lateral occipitotemporal cortex during pursuit and motion perception.

We performed functional imaging with a conventional 1.5-T magnetic resonance scanner in 9 normal subjects. We used a gradient-echo technique to examine changes in signal between periods when subjects viewed a stationary black-and-white grating, a moving grating, and when they followed a moving spot. We located image pixels with significant differences between the viewing conditions. In 7 subjects, these occurred in the lateral occipitotemporal cortex, a region previously identified as a putative human homologue of the motion-sensitive middle temporal area (MT, or V5) of monkeys. Signal intensity was greater during pursuit of the moving dot than during viewing of the moving grating with the eyes still, despite the fact that the moving grating generated more retinal image motion. In contrast, signal intensity in striate cortex was least during pursuit of the moving dot. These findings suggest that the lateral occipitotemporal cortex has extraretinal signals during pursuit. Such signals may include attentional input, corollary eye movement information, or even a pursuit command. Extraretinal signals suggest that the lateral occipitotemporal cortex may contain a human homologue not only of MT but also of other components of the monkey V5 complex, such as the medial superior temporal area.

Adult↗
PubMed1996

Optical blur and the perception of global coherent motion in random dot cinematograms.

We evaluated the effect of +3.25 dioptres of optical blur on the discrimination of motion direction in random dot cinematograms. Dot displacement between frames varied from 2.1 to 63' of visual angle while the temporal interval was held constant. Optical blur worsened discrimination in three normal subjects at displacements below 16', but improved discrimination at displacements of 21' or more. In a second experiment, two subjects viewed equivalent velocity stimuli constructed with different combinations of temporal interval and spatial displacement. Results showed that the effect of blur was specific to displacement and not velocity. Furthermore, varying the dot density of the display showed that the effect of blur correlated with dot displacement and not the probability of dot mismatches. Since optical blur attenuates high spatial frequencies, this suggests that high spatial frequencies are important for motion perception when dot displacements are less than 16' to 21', but reduce motion perception at larger dot displacements. The use of random dot cinematograms in populations must take into account stimulus displacement and optical causes of reduced spatial acuity.

Contrast Sensitivity↗
PubMed1996

Directional defects in pursuit and motion perception in humans with unilateral cerebral lesions.

We tested motion perception and smooth pursuit in 26 patients with unilateral cerebral hemispheric lesions. We used random dot cinematograms to test motion direction discrimination. We measured pursuit gain as they followed a predictable sinusoidal target moving horizontally at three different frequencies, and an unpredictable horizontal step-ramp target in the ipsilateral hemi-field. Six patients had defects in motion perception when the targets were moving towards the side of the lesions ('ipsi-directional' defects) and two had bi-directional defects. Motion perception defects occurred with lesions of the junction of Brodmann areas 19 and 37, a putative human homologue of the monkey V5 complex. Seven patients had ipsi-directional pursuit defects, five of whom had damage to the posterior limb of the internal capsule. Only two patients had ipsi-directional defects of both motion perception and sinusoidal smooth pursuit. Four patients had ipsi-directional defects of motion perception alone, and five patients had ipsi-directional pursuit defects alone. The two patients with bi-directional defects in motion perception had normal sinusoidal smooth pursuit. Patients with lesions at the 19/37 junction and defects of motion perception alone had normal pursuit of unpredictable step-ramp targets in the ipsilateral hemi-field. In contrast, patients with ipsi-directional sinusoidal pursuit defects had decreased ipsi-directional and increased contra-directional velocities with step-ramp targets. No patient group had a motion-specific directional defect in saccadic accuracy. We conclude that neither predictable nor unpredictable pursuit is necessarily impaired by lesions of the 19/37 junction that cause ipsi-directional defects of motion perception. These dissociations between smooth pursuit and motion perception provide evidence that the pursuit system operates as an interconnected network with parallel pathways, rather than as a simple sequential hierarchy of cortical areas.

Adult↗
PubMed1995

Retinotopic and directional defects in motion discrimination in humans with cerebral lesions.

We investigated the discrimination of motion direction in peripheral and central vision in 23 patients with unilateral cerebral hemispheric lesions on computed tomography or magnetic resonance imaging. We used random dot cinematograms that determined a percent coherence motion threshold for 16 points in the peripheral field and for four directions separately in central vision. We measured asymmetry of right- versus left-field peripheral discrimination (retinotopic defects) and asymmetry of central discrimination for rightward versus leftward motion (directional defects), compared with normal subjects. Five patients had directional asymmetries of foveal motion perception, all worse for motion toward the side of their lesions. One patient had a bidirectional defect for the perception of horizontal motion. For 3 of these 6, the average of all horizontal and vertical motion discrimination thresholds was also elevated. Two had contralateral retinotopic defects. One of these also had an ipsidirectional foveal defect, but the other did not. The remaining 5 patients with ipsidirectional foveal defects had hemianopias that precluded testing for coexistent retinotopic defects. The lesions of the 6 patients with ipsidirectional defects overlapped in white matter underlying the lateral temporo-occipital cortex, at the junction of Brodmann areas 19 and 37. In contrast, lesions of patients without directional defects spared this region.

Adult↗
PubMed1995

Bilateral central ptosis in acquired immunodeficiency syndrome.

A man with acquired immune deficiency syndrome suddenly developed bilateral complete ptosis and minor vertical gaze limitation. Magnetic resonance imaging revealed a lesion in the midbrain surrounding the sylvian aqueduct in addition to bilateral masses in the caudate nuclei. Pathologic examination showed that the caudate lesions were central nervous system lymphoma of B cell origin, but the midbrain lesion contained only signs of AIDS encephalopathy. The periaqueductal lesion involved the caudal central subnucleus and probably also the subnuclei of the superior and inferior recti of the oculomotor nuclear complex bilaterally.

Acquired Immunodeficiency Syndrome↗
PubMed1995

Saccadic duration and intrasaccadic fatigue in myasthenic and nonmyasthenic ocular palsies.

We measured the duration and amplitude of saccades in three normal subjects, eight patients with myasthenia gravis, and eight patients with nonmyasthenic ocular palsies. Saccades were examined at the start of a repetitive saccade task, after 3 minutes of activity, and 1 minute after administration of edrophonium. The duration of saccades was prolonged initially in both myasthenic and nonmyasthenic palsies. Activity did not produce significant differences among the three groups in either the slope of the duration-amplitude relationship or the predicted durations of saccades of 5 degrees, 10 degrees, or 15 degrees. However, durations decreased in myasthenia but increased in nonmyasthenic palsies after edrophonium. Much of this decrease in myasthenic saccadic duration was due to reduction in deceleration time, indicating resolution of intrasaccadic fatigue after edrophonium administration. However, the relation of deceleration fraction (deceleration time divided by total duration) to total duration remained constant in all subject groups. Analysis of saccadic duration is a useful means of interpreting responses to edrophonium because it incorporates data from saccades of a wide range of amplitudes into a linear relation between duration and amplitude.

Adult↗
PubMed1995

Blink- and saccade-induced seesaw nystagmus.

A 29-year-old woman with bitemporal hemianopia persisting after a suprasellar germinoma was resected twelve years previously had brief periods of pendular seesaw nystagmus after blinks and horizontal or vertical saccades. Nystagmus may have been suppressed during fixation, and escaped only when fixation was interrupted by blinks or saccades.

Adult↗
PubMed1995

'Saccadic jitter' is a quantitative ocular sign in myasthenia gravis.

PURPOSE: To examine the variability of saccadic peak-velocity amplitude relationships in myasthenic and nonmyasthenic ocular palsies. METHODS: The authors measured centrifugal saccades in nine patients with myasthenia gravis, nine patients with proven nonmyasthenic ocular palsies, and three normal subjects. Patients made repetitive saccades for 8 minutes. Saccades were analyzed at the start of the task, after 3 minutes of the task (fatigue), and at 1 minute after edrophonium. The authors fitted an exponential function to individual data and averages for amplitude bins and calculated the root mean square error of the curves. They then subtracted the root mean square error of curves fitted to bin averages from that of curves fitted to individual saccades: The result was an index of the variability of saccadic peak velocity, which they called saccadic jitter. RESULTS: Compared to those without myasthenia, the saccades of patients with myasthenia showed more variability in the initial and the fatigue periods. The change induced by edrophonium did not distinguish between the groups. CONCLUSIONS: Signal detection analysis indicated that saccadic jitter has little value as a screening tool but is a useful diagnostic sign in 42% of myasthenic saccadic analyses.

Adult↗
PubMed1994

Muscarinic antagonists in the treatment of acquired pendular and downbeat nystagmus: a double-blind, randomized trial of three intravenous drugs.

We performed a double-blind, randomized trial of intravenous scopolamine, benztropine, and glycopyrrolate in 7 patients with acquired nystagmus and oscillopsia. Five patients had pendular nystagmus and 2, downbeat nystagmus. We recorded eye movements with a magnetic search coil technique and tested visual acuity and motion perception before and after administration of each drug. Scopolamine reduced nystagmus in all patients. Benztropine was moderately effective and glycopyrrolate had a negligible impact. Visual acuity improved only with scopolamine; motion discrimination and oscillopsia improved significantly with scopolamine and benztropine. Pendular and downbeat nystagmus respond to intravenous antagonists of central muscarinic receptors.

Adult↗