Biomedical subjects

R Vogels

Publications and source records attributed to R Vogels.

At least 19 recordsLinked to original sources

PubMed1998

The neuronal machinery involved in successive orientation discrimination.

Following our strategy of using simple discrimination tasks to investigate the primate visual system, we trained both human and monkey subjects for two orientation discrimination tasks: an identification and a successive discrimination. Contrasting these two tasks allowed us to isolate the temporal comparison component and to relate this component to activity in right fusiform gyrus using Positron Emission Tomography (PET) and to infero-temporal cortex using a lesion approach in monkeys. Single-cell recordings in infero-temporal cortex demonstrated that neurons in this region can contribute to the three processes underlying temporal comparison: (1) sensorial representation of visual stimuli, (2) maintaining a trace of the preceding stimulus, and (3) comparison of the incoming stimulus with that trace. By the same token, a comparison of these two tasks, which use the same input and the same attribute, demonstrates the task dependency of processing in the human and non-human primate visual system.

Adult↗

PubMed1997

Ocular torsion induced by static and dynamic visual stimulation and static whole body roll.

By means of real-time infra-red video-oculography we studied eye torsion in 12 normal healthy subjects. Ocular torsion was induced by visual stimulation or static whole body roll with and without visual orientation ("head-fixed" or "earth-fixed"). Visual stimulation was achieved by a horizontal grating that oscillated sinusoidally in a frontal plane. The oscillation frequency varied from 0 to 0.6 Hz while amplitude varied from 6 degrees to 33 degrees. Visual orientation during whole body roll was established by mounting a 32 lx illuminated horizontal grating either on a tilting device (head-fixed) or on the wall in the frontal plane (earth-fixed). Maximum visual-induced eye torsion gain was reached at about 0.2 Hz. No eye torsion was observed in static (0 Hz) visual tilts of the grating. Maximum gain was about 0.36 at amplitudes between 6 degrees and 10 degrees. Eye torsion gain decreased with increasing amplitude and increasing frequency (> 0.2 Hz). Static whole body roll in the dark up to 180 degrees clockwise and counterclockwise induced static ocular counter rolling with a maximum amplitude of 12 degrees and a maximum gain of 0.22. Gain decreased with increasing roll down to zero at 180 degrees. Visual orientation with either head or earth fixed did not affect the amplitude or gain of the body roll induced ocular counter-rolling. The results are interpreted in terms of improving the reliability of clinical statolith testing and understanding the processes involved in motion sickness.

Adult↗

PubMed1997

Responses of macaque inferior temporal neurons to overlapping shapes.

We tested whether macaque inferior temporal neurons can signal the presence of their preferred shape independently of other shapes simultaneously present, by comparing the responses and selectivity of TE neurons to shapes (figures), either presented in isolation or overlapping another shape (background). The two overlapping shapes differed in color or texture and thus were easily segmentable. We found that the response and selectivity of TE neurons to the figure can be dramatically altered, most commonly reduced, when the figure is overlapping the background. This reduction in response was also present when the monkey was required to actively discriminate the figures from varying backgrounds during recording. The level of suppression depended on the shape of the background and on whether or not figure and background can be discriminated. These results indicate that responses of TE cells are not only determined by the properties of the figures but also are influenced by the properties of stimuli in the background.

Animals↗

PubMed1997

Effects of inferior temporal lesions on two types of orientation discrimination in the macaque monkey.

Rhesus monkeys with transection of the forebrain commissures were trained in two different tasks in which grating orientation was the discriminandum. In the temporal same-different task, the monkeys had to judge whether or not two successively presented gratings differed in orientation. In the identification task, we measured how well the monkey could judge the orientation of the grating. The performance in any task was affected neither by a unilateral anterior temporal cortical area lesion nor by a subsequent posterior temporal cortical area lesion in the same hemisphere resulting in a two-stage inferior temporal (IT) lesion. However, a single stage IT (combined anterior and posterior temporal cortical areas) lesion of the other hemisphere severely disrupted the performance in the temporal same-different task, but only barely increased just noticeable differences in orientation in the identification task. This indicates that the impairment in a temporal comparison task after an IT lesion is not due to a perceptual coding deficit, but is related to the temporal comparison per se. Thus, IT is involved in the temporal comparison of successively presented stimuli. On the other hand, the two IT lesions, each having a different history (single versus two stage) had dramatically different behavioural effects, suggesting an important role for adult brain plasticity in determining the behavioural outcome of a brain lesion.

Animals↗

PubMed1997

Human brain activity related to orientation discrimination tasks.

In order to relate regional activity in the human brain to the different components of discrimination tasks, we compared regional cerebral blood flow, measured with positron emission tomography, under four conditions: successive orientation discrimination, orientation identification, detection and passive viewing. By adding successive discrimination and passive viewing at a second, lower rate we were able to investigate the main effects and interaction between task and presentation rate. Four occipital regions--the posterior calcarine region bilaterally, the right lingual gyrus and the right interior occipital cortex--displayed a main effect of presentation rate. Two regions--a right posterolateral occipital region and a right posterior fusiform region--displayed a significant main effect of task. The involvement of this posterior fusiform region in successive discrimination was also revealed by the subtraction of detection from successive discrimination, as was that of the right middle fusiform gyrus. Finally, a more anterior right middle fusiform region was differentially active in successive discrimination compared to identification, suggesting that activity in this region is related to the temporal comparison of orientation.

Adult↗

PubMed1996

Diazepam decreases performance in a long-term memory task using visual shapes.

We designed a memory task involving visual recognition sensitive enough to demonstrate the long-term amnesic effect of diazepam. Following memorization of a list of abstract visual stimuli (Fourier), subjects were evaluated on recognition performance immediately following acquisition and after a 3-day drug clearance interval. Administration of 15 mg diazepam 1 h before acquisition imposed a significant (10-24%) deficit only in delayed recognition. In contrast, a drug-free acquisition followed by a diazepam-challenged delayed recognition did not influence recognition. Moreover, 1 h after administration, diazepam did not significantly impair detection or visual discriminative performances. Given the persistence of an important deficit in recognition memory in the absence of any drug, this paradigm promises to be useful for studying regional cerebral blood flow during long-term memory performance.

Adolescent↗

PubMed1996

Herpes simplex virus thymidine kinase gene therapy for rat malignant brain tumors.

Transfer of a herpes simplex virus-derived thymidine kinase (HSV-tk) gene into brain tumor cells and subsequent ganciclovir (GCV) treatment has been shown by others to be an effective treatment in rats with intracerebrally inoculated 9L gliosarcomas. Mechanism of action and reproducibility are, however, still a matter of debate. We have used the same model to test the therapeutic effects of both retrovirus- and adenovirus-mediated transfer of the HSV-tk gene followed by GCV treatment. Survival time of rats with intracerebral 9L tumors was significantly prolonged after a single administration of adenovirus carrying a HSV-tk gene as compared to controls. Retrovirus-mediated gene transfer also resulted in significantly prolonged survival time when recombinant retrovirus-producing cells were transplanted. Direct injection of the recombinant retrovirus, HSV-tk-expressing cells, virus-producing cells without GCV administration and recombinant retrovirus-lacZ or interleukin-2 (IL-2)-producing cells did not result in tumor cell kill. In the present study, no significant difference in survival of 9L brain tumor carrying rats was found after treatment with adenovirus as compared to retrovirus-mediated HSV-tk-mediated gene transfer and subsequent GCV treatment.

Adenoviruses, Human↗

PubMed1996

Task dependency of visual processing in the human visual system.

In this review we contrast passive, attribute driven processing in the visual system with an active, task-dependent view and summarize the evidence from our Positron Emission Tomography (PET) work supporting the task-dependent view. The PET studies involved comparison of regional Cerebral Blood Flow (rCBF) in closely related detection and discrimination tasks. The major finding reported is that the same retinal input or input containing only a single cue activates different extrastriate areas depending on the task.

Adult↗

PubMed1996

Coding of stimulus invariances by inferior temporal neurons.

Primates are able to recognize a particular object despite major differences in the retinal images of the object. Inferior temporal cortex is suggested to be involved in this invariant object recognition. Neurons of this cortex show shape selectivity and it has been shown that this shape selectivity is relatively invariant for changes in the position and size of the shape. We show that macaque inferior temporal cortical neurons may respond to shapes that are defined by relative motion or by texture differences. The degree of shape selectivity can vary for the different visual cues, but overall shape preference is invariant for shapes defined either by luminance, by relative motion or by texture. Also, we found that shape selective inferior temporal neurons respond to partial occluded shapes and that their shape selectivity is similar with and without the partial occlusion. These results suggest that inferior temporal neurons, as a population, can code for an abstract, stimulus invariant shape or object part.

Animals↗

PubMed1996

Cost and prevention of pressure ulcers in an acute teaching hospital.

The cost of pressure ulcer treatment is much greater than the cost of prevention. Treating a pressure ulcer incurs considerable cost to the patient and hospital, especially if the pressure ulcer has advanced beyond stage one. In this paper, the cost of the intensive treatment required for patients who developed a pressure ulcer for two procedures, coronary artery bypass and hip replacement, in an Australian teaching hospital for the three years 1990, 1991 and 1992 was investigated. The average length of stay for all patients who had these two procedures was calculated and compared with the average length of stay for those patients who suffered a pressure ulcer. Results indicated statistical significance at the 5% confidence level for coronary artery bypass (t-test = 8.85, p = < 0.01) and for hip replacement (t-test = 5.39, p = < 0.01) for the three years 1990, 1991 and 1992. Preventive strategies were evaluated and results in this study indicated that the incidence rate improved when the pressure ulcer was detected earlier, and when positioning and appliance use were better reported, which was demonstrated for hip replacement in 1992.

Confidence Intervals↗

PubMed1995

Cortical correlate of pattern backward masking.

The perception of a briefly presented shape is strongly impaired when it is followed by another pattern, a phenomenon called backward masking. We found that the vast majority of a sample of shape-selective neurons in the macaque inferior temporal cortex respond selectively to backward-masked shapes, although these shapes could not be discriminated by human and monkey subjects. However, this selective response was brief, since it was either interrupted by the mask or overridden by a response to the mask itself. We show that reliable discrimination of briefly presented shapes by single neurons depends on the temporal integration of the response. Presentation of the mask, however, reduces the number of spikes available for integration, explaining backward masking. These results also provide direct neurophysiological evidence for the "interruption theory" of backward masking.

Action Potentials↗

PubMed1995

Human perceptual learning in identifying the oblique orientation: retinotopy, orientation specificity and monocularity.

1. Human perceptual learning in discrimination of the oblique orientation was studied using psychophysical methods. Subjects were trained daily to improve their ability to identify the orientation of a circular 2.5 deg diameter unidimensional noise field. Dramatic improvements in sensitivity to contour orientation occurred over a period of 15-20 days. The improved performance persisted for several months. Improvement was more evident between daily sessions than within sessions. This was partly due to fatigue interfering with the learning effect. Moreover, a consolidation period seemed to be required. 2. Improvement was restricted to the position of the stimulus being trained. This position dependency of the learning effect proved very precise. After training at a specific stimulus position, merely displacing the stimulus to an adjacent position caused a marked increase in thresholds. 3. No transfer of the training effect was observed between orientations. Following a shift of 90 deg away from the trained orientation, performance fell, even below the initial level. 4. We observed complete to almost complete transfer between the two eyes. 5. Our results suggest plastic changes at a level of the visual processing stream where input from both eyes has come together, but where generalization for spatial localization and orientation has not yet occurred.

Discrimination, Psychological↗

PubMed1995

A motion area in human visual cortex.

We have localized an area in the human brain involved in the processing of contours defined by motion differences (kinetic contours) by comparing with positron emission tomography the regional cerebral blood flow in tasks performed with kinetic and luminance-defined gratings. These tasks included passive viewing, counting the total number of grating stimuli, and counting the number of gratings of a given orientation. Comparison between the counting tasks and passive viewing with a given type of contour revealed a set of active areas that were similar for both luminance-defined and kinetic contours. Comparisons between these two types of contours revealed a single focus in the right hemisphere that did not overlap with the many regions activated by uniform motion. In particular this "kinetic focus" was clearly separated from the area previously defined as the human homologue of V5/middle temporal. Activity in this kinetic focus was stronger when orientation had to be processed than in the other two tasks. These results and control experiments with uniformly moving random dot patterns suggest the existence of an area in the human visual system that is activated much more by kinetic contours than by luminance contours or uniformly moving random dots. Up to now, such an area has not been described in the monkey visual system.

Animals↗

PubMed1995

Regulation of the Hoxb-8 gene: synergism between multimerized cis-acting elements increases responsiveness to positional information.

Hox genes play a key role in the specification of regional development in the vertebrate embryo. They are expressed in regionally restricted domains along the anterior-posterior axis, generally extending from a sharp rostral boundary toward the posterior end. We have studied the regulation of the murine Hoxb-8 gene in vivo using reporter constructs and found that 11 kb of genomic sequences upstream of Hoxb-8 confer a Hox-like pattern of expression on a lacZ reporter gene fused in-frame to the first exon of Hoxb-8. Reporter gene expression was detectable from early stages onwards, but reached rostral expression boundaries in mesoderm and neurectoderm that were more posterior than those of the endogenous gene. Within the upstream region, we have identified several cis-acting elements which are individually capable of driving regionally restricted expression in combination with the Hoxb-8 promoter, and we have investigated their relative contributions to the expression pattern. The results suggest that, in this experimental context, these upstream elements, as well as previously identified elements located within the Hoxb-8 gene, cooperate in setting the rostral expression boundaries. Furthermore, we show that multiple identical copies of cis-acting elements can cooperate, causing a pronounced anterior shift in the expression boundaries. This indicates that the rostral extent of expression is limited by the activity of a transcription factor binding to these elements and that this activity was, at some point in development, higher in precursors of more posterior structures than in precursors of anterior structures. This factor is thus very likely to be involved in the transduction of positional signals.

Animals↗

PubMed1995

Responses of monkey inferior temporal neurons to luminance-, motion-, and texture-defined gratings.

1. We recorded from neurons responsive to gratings in the inferior temporal (IT) cortices of macaque monkeys. One of the monkeys performed an orientation discrimination task; the other maintained fixation during stimulus presentation. Stimuli consisted of gratings based on discontinuities in luminance, relative motion, and texture. 2. IT cells responded well to gratings defined solely by relative motion, implying either direct or indirect motion input into IT, an area that is part of the ventral visual cortical pathway. 3. Response strength in general did not depend on the cue used to define the gratings. Latency values observed for the two static grating types (luminance- and texture-defined gratings) were similar, but significantly shorter than those measured for the kinetic gratings. 4. Stimulus orientation had a significant effect in 27%, 27%, and 9% of the cells tested with luminance-, kinetic-, and texture-defined gratings, respectively. 5. Only a small proportion of cells were orientation sensitive for more than one defining cue. The average preferred orientation for luminance and kinetic gratings matched; the tuning width was similar for the two cues. 6. Our results indicate that IT cells may contribute to cue-invariant coding of boundaries and edges. We discuss the relevance of these results to visual perception.

Animals↗

PubMed1995

Selectivity of macaque inferior temporal neurons for partially occluded shapes.

Humans are able to recognize shapes even when they are partially occluded by another pattern. We determined whether inferior temporal (IT) units of awake rhesus monkey remain selective for shapes that are partially occluded by other patterns. In order to link the shape selectivity to shape discrimination, we established that the monkey, like humans, can discriminate partially occluded shapes. We found that IT units are selective for shapes partially occluded by static or moving patterns. The responsiveness, however, decreased with the degree of occlusion. The shape-selective responses to the occluded shapes required longer stimulus durations compared to nonoccluded shapes, matching the better shape discrimination performance at short durations in the no-occlusion compared to the occlusion conditions. Occluder visibility had no effect for shape outlines, indicating that (amodal) shape completion, which is absent when the occluder is invisible, is not necessary for shape selectivity. These data indicate that IT neurons can, indeed, contribute to the invariance of shape perception for changes in retinal input caused by partial occlusion of the shape.

Animals↗

PubMed1994

Hemispheric lateralization in rhesus monkeys can be task-dependent.

Two rhesus monkeys with transection of the forebrain commissures were trained on two grating orientation-discrimination tasks. In one task, the simultaneous orientation identification task, monkeys had to decide which of two simultaneously presented gratings was horizontal. In the other task, the temporal same-different task, the monkey had to decide whether or not two successively presented gratings differed in orientation. Both monkeys showed a statistically significant individual asymmetry in the performance on the same-different task with the left hemisphere supporting superior performance compared with the right hemisphere. No such consistent lateralization was found for the identification task. These results show that the demonstration of a behavioral asymmetry depends on the type of discrimination task performed and suggest that the asymmetry is related to interhemispheric differences in higher order stimulus (cognitive) processing and not to a lateralization of early visual processes.

Animals↗

PubMed1994

Orientation discrimination of motion-defined gratings.

Spatial boundaries can be defined by discontinuities in motion. However, several types of motion contrast exist, each corresponding to the involvement of different spatio-temporal cues. We examined the contribution of two motion cues: a difference in direction of motion (relative motion) and a dynamic occlusion cue. We measured just noticeable differences in the orientation of boundaries defined by one or both of these visual cues. Just noticeable differences in orientation were similar to those reported for luminance gratings, and the presence of two cues in place of one, lowered the thresholds. These results show that relative motion as well as dynamic occlusion can yield precise spatial boundary information.

Adult↗