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R Vogels

Publications and source records attributed to R Vogels.

At least 55 records · Page 3Linked to original sources
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↗
PubMed1994

Activity of inferior temporal neurons during orientation discrimination with successively presented gratings.

1. We recorded from inferior temporal (IT) cells in three monkeys while they performed an orientation discrimination task with successively presented gratings. Histological reconstruction of two monkey brains indicated that most recordings were from TE3. The task was exactly the same as the one used in a previous V1 study, allowing direct comparison. 2. One quarter of IT cells were responsive to the grating. Response strength and variability of the cells excited by the grating (n = 341) were similar to those in V1, whereas response latency was on average 40 ms longer than in V1. 3. In one third of the responsive cells orientation had a significant effect. Sensitivity for orientation was captured by the orientation sensitivity index, which ranged from 0 to 0.95 with a median of 0.23. Orientation sensitivity of IT cells was on average much less than that of V1 cells. More cells preferred horizontal and vertical than oblique orientations. 4. The differences in responsiveness and orientation sensitivity among individual animals could be accounted for by the anterior/posterior difference in recording position. 5. Task-related behavioral effects were examined in 283 cells that were responsive to the visual stimuli. Order effects were examined in "same" trials and occurred in half of the IT cells in each of the three monkeys. In these cells there was on average a threefold difference in response between the first stimulus (S1) and the second stimulus in same trials (S2same). In two monkeys the average response to S2same was less than that to S1, whereas in the third monkey the average response to S1 was smaller than that to S2same. 6. IT cells also exhibited same/different effects, whereby response to a physically identical second stimulus differed between same and "different" trials. Generally cells responded more to the second stimulus in different trials than to S2same but the opposite also occurred. For a subset of these cells we could show that the correct/error type of the trial had no effect and that the response occurred before the saccadic response. 7. These context effects were modulations of the gain of the orientation tuning curves for the different types of responses. The tuning for orientation of these different responses was similar. 8. One third of the responsive IT cells exhibited an increased activity in the interstimulus interval (ISI), fitting the definition of delay cells. This activity was maintained when the ISI was lengthened from 300 to 800 ms. The orientation tuning of this response was similar to that for S1 responses.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Different perceptual tasks performed with the same visual stimulus attribute activate different regions of the human brain: a positron emission tomography study.

To investigate the processing of visual form in human cerebral cortex, we used the PET (positron emission tomography) activation technique to compare the human brain regions that are involved in a visual detection task and two orientation discrimination tasks: the temporal same-different (TSD) task, which includes a short-term memory component, and the identification (ID) task, which is without this component. As a control task we used passive viewing. Stimuli were identical in all four tasks. Subtraction of passive viewing from detection showed that the detection task activates early visual cortical regions (areas 17/18) as well as several motor brain regions, while decreasing activity in several higher order frontal, temporal, and parietal regions. Comparing the ID task to the detection task revealed no further visual cortical activation, while comparison of the TSD task to the detection task revealed an activation of several right visual cortical regions, one of which remained significant after the subtraction of ID from TSD (right area 19). These experiments demonstrate the task dependence of visual processing, even for very closely related tasks, and the localization of the temporal comparison component involved in orientation discrimination in human area 19.

Adult↗
PubMed1993

Cue-invariant shape selectivity of macaque inferior temporal neurons.

The perception of shape is independent of the size and position of the shape and also of the visual cue that defines it. The same shape can be recognized whether defined by a difference in luminance, by motion, or by texture. Experiments showed that the shape selectivity of individual cells in the macaque inferior temporal cortex did not vary with the size and position of a shape and also did not vary with the visual cue used to define the shape. This cue invariance was true for static luminance and texture cues as well as for relative motion cues--that is, for cues that are processed in ventral and dorsal visual pathways. The properties of these inferior temporal cells meet the demands of cue-invariant shape coding.

Animals↗
PubMed1993

Proximal cis-acting elements cooperate to set Hoxb-7 (Hox-2.3) expression boundaries in transgenic mice.

The Hox genes have been proved to be instrumental in establishing the positional identity of cells along the embryonic anteroposterior (A-P) axis. Studying the regulation of these genes is a first step toward elucidating the molecular basis of regionalization during embryogenesis. We report here on the identification of cis-acting elements controlling the expression of Hoxb-7 (Hox-2.3). We show that elements driving A-P restricted gene expression are located within the 3.5 kb proximal upstream sequences of the Hoxb-7 gene. A deletion analysis provides evidence for at least three cis-acting control elements upstream from Hoxb-7, and for cooperative interactions between some of these elements in generating the A-P restricted transgenic pattern. One element, conferring by itself Hox-like expression boundaries to the transgene, has been studied in more detail and found to act in an orientation-and promoter-dependent manner. Together the 3.5 kb sequences proximal to Hoxb-7 mediate A-P restricted Hoxb-7/lacZ gene expression in a domain showing rostral boundaries more posterior than those of Hoxb-7. The evolution throughout embryogenesis of the expression pattern of a transgene carrying these sequences has been analysed and shown to mimick that of the endogenous gene, except for a slight delay in the initial expression. We conclude that the transgenes that we tested, spanning a total of 27 kb genomic sequences, do not reproduce all the features of the Hoxb-7 expression pattern. The differences in expression between Hoxb-7 and the transgenes may reveal an aspect of the Hox regulation for which either remote cis-acting control elements and/or gene clustering is required. Additional features that may have favoured maintenance of clustered organisation during evolution are partial overlap of transcription units with the regulatory regions of the neighbouring genes, and cis-regulatory interactions between multiple Hox genes: not only do cis-acting control elements of the Hoxb-7 gene map in the 3' untranslated sequences of the Hoxb-8 (Hox-2.4) gene, but our experiments suggest that Hoxb-7 control sequences modulate expression of the Hoxb-8 gene as well.

Animals↗
PubMed1991

Quantitative study of striate single unit responses in monkeys performing an orientation discrimination task.

Contour orientation discrimination accuracy is determined by the orientation bandwidth, response variance and response strength of single units that code for orientation. We measured the latter three properties for V1 cells of monkeys which were performing an orientation discrimination of the grating stimulating the cell under study. We recorded from 285 cells, of which 76% responded to the grating. The orientation bandwidth, measured as full width at half height of the tuning curve, varied over a wide range amongst cells. The median bandwidth was 41 degrees. The response variance of the cells also varied considerably between cells; on average it was about two times the response strength. We also studied the temporal properties of the responses. Most of our cells had a latency between 40 and 100 ms. The response variance was found to be smaller in the initial phases of the response than at the later response stages. In some cells the orientation tuning varied in successive stages of the response, while in others the orientation bandwidth and preferred orientation remained stable throughout the response. However, all orientation sensitive cells were orientation tuned from the start of the response, a property which contribute to the fast and reliable coding of contour orientation. These results provide for the first time an estimation of the orientation tuning properties of V1 cells during visual orientation discrimination. They will be very useful to compare single cell properties of other areas to as well as in simulation studies of models of primate visual discriminations.

Animals↗
PubMed1991

The mouse homeobox gene, S8, is expressed during embryogenesis predominantly in mesenchyme.

The murine S8 gene, originally identified by Kongsuwan et al. [EMBO J. 7(1988)2131-2138] encodes a homeodomain which resembles those of the paired family. We studied the expression pattern during mid-gestation embryogenesis of S8 by in situ hybridization. Expression was detected locally in craniofacial mesenchyme, in the limb, the heart and the somites and sclerotomes all along the axis, and was absent from the central and peripheral nervous system, splanchnopleure, and endodermal derivatives. This pattern differs considerably from that of most previously described homeobox containing genes. By genetic analysis, the gene was located on chromosome 2, about 20 cM from the HOX-4 cluster.

Amino Acid Sequence↗