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R Vogels

Publications and source records attributed to R Vogels.

72 records · Page 4Linked to original sources
PubMed1990

Population coding of stimulus orientation by striate cortical cells.

I have examined the performance of a population coding model of visual orientation discrimination, similar to the population coding models proposed for the coding of limb movements. The orientation of the stimulus is not represented by a single unit but by an ensemble of broadly tuned units in a distributed way. Each unit is represented by a vector whose magnitude and direction correspond to the response magnitude and preferred orientation of the unit, respectively. The orientation of the population vector, i.e. the vector sum of the ensemble of units, is the signalled orientation on a particular trial. The accuracy of this population vector orientation coding was determined as a function of a number of parameters by computer simulation. I have shown that even with broadly orientation tuned units possessing considerable response variance, the accuracy of the orientation of the population vector can be as good as behaviorally measured just noticeable differences in orientation. The accuracy of the population code is shown to depend upon the number of units, the average response strength, the orientation band-width, response variability and the response covariance. The results of these simulations were also compared to predictions derived from psychophysical studies of orientation discrimination.

Animals↗
PubMed1990

Hox-2.3 upstream sequences mediate lacZ expression in intermediate mesoderm derivatives of transgenic mice.

The mouse Hox-2.3 gene contains an Antp-like homeobox sequence and is expressed in a spatially restricted anteroposterior domain during development. To study the molecular basis of this differential gene regulation, we set out to characterize the cis-regulatory elements mediating Hox-2.3 expression during embryogenesis. We show that a fragment extending 1316 base pairs (bp) upstream of the transcription start site, thus corresponding to the Hox-2.4/Hox-2.3 intergenic sequences is capable of mediating luciferase gene transcription in transfected cells in vitro and lacZ expression in transgenic mice. The beta-galactosidase-staining pattern in embryos was found to be strikingly similar to the Hox-2.3 in situ hybridization pattern in intermediate mesoderm derivatives: high levels of both Hox-2.3 transcripts and beta-galactosidase activity were found in the mesonephric duct-derived epithelium of the meso- and metanephric kidney and associated ducts, from the time these structures first appeared on throughout development. The transgene apparently lacks sequences needed for correct Hox-2.3 expression in somitic and lateral plate mesoderm and in neurectoderm. These results document the involvement of distinct regulatory elements in Hox gene expression in subsets of cells with distinct developmental fate, situated at similar positions along the anteroposterior axis of the embryo.

Animals↗
PubMed1990

Expression of the murine homeobox-containing gene Hox-2.3 suggests multiple time-dependent and tissue-specific roles during development.

This study reports the expression pattern of the murine homeobox-containing gene Hox-2.3 during development. Using in situ hybridization, we first detect Hox-2.3 transcripts in the allantois primordium at 7.5 days post coitum (p.c.). One day later transcripts are found in embryonic ectoderm and mesoderm. In 9.5- and 10.5- day embryos Hox-2.3 expression is observed in the central nervous system (CNS) from a rostral boundary in the upper spinal cord to the caudal end. Within this anteroposterior domain, Hox-2.3 expression is also found in the peripheral nervous system, in the mesoderm and in the hindgut epithelium. The rostral boundary in the mesoderm is located at the level of the 11th somite and thus shifted posteriorwards compared to the rostral boundary in the neural tube. During subsequent development, the initially broad expression pattern in the somitic, lateral plate and intermediate mesoderm becomes restricted to structures in the urogenital system. In adults, the spinal cord and the derivatives of the Wolffian and Müllerian ducts continue to express the gene at a high level. The described temporal and tissue-specific changes in expression of Hox-2.3 are suggestive of several levels of regulation as reported for Drosophila homeotic genes and argue for more than one role of the gene during development and in adults.

Animals↗
PubMed1990

How well do response changes of striate neurons signal differences in orientation: a study in the discriminating monkey.

Just-noticeable differences (JNDs) in orientation were measured in 2 monkeys using a temporal same-different task, with stationary rectangular gratings as stimuli, and compared to those of humans tested in the same setup. The JNDs of one monkey (1.5 degree) were similar to those of humans; those of the other monkey were larger (5.8 degrees). We recorded from V1 neurons in these monkeys while they were performing the orientation discrimination with the same stimuli and under the same conditions as used in the behavioral testing. In order to determine how small a difference in orientation the V1 neurons can, in these conditions, signal reliably by small changes in firing rate, we performed 2 different receiver-operating characteristic (ROC) analyses. One ROC analysis was performed on the number of spikes evoked by the first of the 2 stimulus presentations as a function of the orientation of this stimulus. Neural JNDs derived from the neurometric curve were obtained in this way for 50 cells. In the second ROC analysis, the difference in the number of spikes evoked by the 2 stimuli presented in succession during 1 trial was analyzed as a function of orientation difference between the 2 stimuli. Neural JNDs were obtained by this procedure for 21 cells. These 2 complementary ROC analyses yielded very similar results. Also, the results were similar for the 2 monkeys. A minor fraction of V1 cells can reliably signal difference in orientation as small as 2.5 degrees, but none could signal differences smaller than 2 degrees. Our results also showed that the neural JND obtained by the ROC analysis depends on the duration of the interval during which spikes are counted. In these experiments, this duration could be chosen rather precisely, because the reaction times of the 2 monkeys were measured. Also, our results showed that the neural JND depends on the point of the tuning curve at which the measurement is made and is smallest when this is done on the steepest part of the tuning curve. Finally, our results show that the discriminative capacity of V1 neurons does not depend so much on each of the tuning characteristics--bandwidth, response strength, and variability--as on the combination of these factors.

Analysis of Variance↗
PubMed1989

The response variability of striate cortical neurons in the behaving monkey.

In order to relate single cell performance to behavioral discrimination one needs measurements of the response variance of the units. We recorded from 183 single units of area V1 of monkeys performing an orientation discrimination task. The response variance was found to increase with increasing response strength. This relationship between response variance and response strength was well described by a power function with a power close to one. The response variance was on average 1.9 times the response strength. Despite important differences in preparation, the behaving monkey data are in good agreement with those previously obtained in paralysed and anesthetised animals.

Animals↗
PubMed1988

The effect of feature uncertainty on spatial discriminations.

Just noticeable differences (JNDs) in orientation and spatial frequency were measured under two conditions. In one condition the subject was cued before stimulus presentation as to the feature to be discriminated on that trial, while in the other condition the subject was cued only after stimulus offset. JNDs were larger in the latter, feature uncertainty, condition. This feature uncertainty effect increased with decreasing stimulus processing time. The results suggest that this feature uncertainty effect is of sensorial origin. They also demonstrate that it is possible for humans to address selectively those mechanisms that are most relevant for a given discrimination task.

Adult↗
PubMed1987

Illusory contour orientation discrimination.

Just noticeable differences (JNDs) in orientation for real lines and illusory contours were compared. JNDs in orientation of an illusory contour and of a real line differ by less than a factor two. JNDs in orientation of an illusory contour showed meridional variations similar to those obtained for a real line. By scaling measurements illusory contours are equally visible at all orientations, so meridional variations in illusory orientation discrimination reflect an anisotropy in orientation processing mechanisms. JNDs in orientation measured at an oblique reference orientation improve with practice for an illusory contour as well as for a real line. However while the effect of practice transfers from an illusory to a real contour, the reverse is not true. These results suggest that there are two paths for processing orientation: one activated only by real lines, the other concerned with both real and illusory contours.

Adult↗
PubMed1987

Influence of a moving textured background on direction selectivity of cat striate neurons.

The influence of a moving textured background on direction selectivity for a moving bar was tested in 118 striate neurons and in 19 dorsal lateral geniculate neurons of anesthetized and paralyzed cats. In the standard conditions the background was a two-dimensional noise pattern, the bar moved at optimal speed, and its contrast was adjusted to the level producing 50% of the maximum response. These experiments revealed a new typology of cortical cells based on relative direction selectivity. Six different relative-direction-selectivity types are described. Two types of cells were found to have opposite kinds of relative direction selectivity: antiphase direction-selective cells (5% of the cortical sample) preferred the direction of the bar opposite to the direction of background motion, and absolutely direction-selective cells (20% of the cortical sample) kept their direction selectivity for bar motion independently of the background motion. Three types of cortical cells were direction selective for bar motion only in restricted background motion conditions: conditionally direction-selective cells (20% of cortical sample) only expressed their direction selectivity when the bar and the background moved in antiphase, differencing direction-selective cells (5% of the cortical sample) only expressed their direction selectivity when the bar and the background differed in speed, and limited direction-selective cells (20% of the cortical sample) only expressed their direction selectivity for near zero background speeds. The sixth type, relative nondirection-selective cells (30% of the cortical sample and all of the geniculate cells) were direction selective for none of the background motion conditions. These different relative-direction-selectivity types differed in RF organization, in ocular dominance, velocity sensitivity, in laminar distribution, and in distribution in the visual field. The relative-direction-selectivity types were invariant for changes in the contrast and bar speed. The construction of these relative-direction-selectivity types from the geniculate input requires some inhibitory, but mainly facilitatory, intracortical interactions. These experimental findings suggest that area 17 in the cat has the neuronal machinery to extract depth from motion (limited direction-selective cells) and to segregate visual scenes by motion cues (antiphase, conditionally and differencing direction-selective cells).

Animals↗
PubMed1986

Decision processes in visual discrimination of line orientation.

The contribution of decision factors to the meridional variations in line orientation discrimination was determined for two-alternative forced-choice experimental designs. Using Johnson's (1980) formalization of decision processes in discrimination tasks, we identified three decision factors: the decision rule, memory variance, and criterial noise. In a first experiment, we showed the effect of experimental design on orientation discrimination to be similar at horizontal and oblique standard orientations, indicating that the meridional variations in orientation discrimination were not due to a decision rule anisotropy. In a second experiment, the effect of the interstimulus interval was also found to be similar at both standard orientations, suggesting that the memory variance is isotropic in the orientation domain. The results of two other experiments supported the hypothesis that the meridional variations in orientation discrimination are not due to a criterial noise anisotropy. These different results strongly suggested that the oblique effect in line orientation discrimination is due to sensorial factors rather than to decision factors. Therefore, they further support the hypothesis linking the anisotropy of the preferred orientation distribution of Area 17-S cells (a single physiologically defined class of cells in the primary visual cortex) and the meridional variations in line orientation discrimination.

Adult↗
PubMed1986

Human orientation discrimination: changes with eccentricity in normal and amblyopic vision.

The authors measured orientation discrimination of a single line as a function of eccentricity, line length, and standard orientation. Orientation discrimination improved with increasing line length at all eccentricities. The shortest length at which orientation discrimination was optimal increased with eccentricity. When a line length was used for which discrimination was optimal at all eccentricities, it was found that orientation discrimination performance changed little with increasing eccentricity. Under the same conditions, the oblique effect in orientation discrimination decreased with increasing eccentricity. Similar results were also obtained in both eyes of strabismic amblyopes. The difference between the just noticeable differences in orientation of the amblyopic and nonamblyopic eye decreased with increasing line length for central vision. This interocular difference also decreased with increasing eccentricity. The absence of the oblique effect in orientation discrimination at large eccentricities support the hypothesis that the area 17 S-cell orientation anisotropy underlies the oblique effect in orientation discrimination of long lines since this sensorial anisotropy is limited to the central visual field.

Adult↗
PubMed1985

The effect of practice on the oblique effect in line orientation judgments.

Line orientation discrimination improves with selective practice for oblique orientations and not for principal orientations. This training effect was observed with an identification task as well as with two alternative forced choice tasks. Despite the improvement for oblique orientations, just noticeable differences in orientation are still larger for the practised oblique orientation than for the principal orientations after 5000 practice trials. These findings suggest that the oblique effect in line orientation has at least two sensorial components, one of which is attributed to the meridional variations in the preferred orientation of area 17 S-cells.

Adult↗
PubMed1984

Human orientation discrimination tested with long stimuli.

Human orientation discrimination was measured for single long lines presented sequentially. Orientation sensitivity is better for a narrow range of orientations around the principal meridians. Both the orientation sensitivity and its meridional variation increase with stimulus length. Control experiments show that the "oblique effect" can be obtained as well with a signal detection method as with the method of constant stimuli and that the subjects used a visual orientation cue in their judgments. Comparison of these findings with properties of visual cortical cells suggest that cells similar to S cells of cat and monkey striate cortex, carry the neuronal representation used in the decision process. And indeed the meridional variation in orientation sensitivity can be predicted from the number of monkey S cells preferring different orientations.

Adult↗
PubMed1984

Meridional variations and other properties suggesting that acuity and orientation discrimination rely on different neuronal mechanisms.

It has been widely reported that both grating acuity and orientation discrimination show meridional variations: performance is better for targets oriented horizontally or vertically than for those with oblique orientations. In spite of such similarities, we now present both behavioral and psychophysical evidence from cats and humans to show that grating acuity and orientation discrimination depend upon different neuronal mechanisms.

Animals↗
PubMed1984

Meridional variations in orientation discrimination in normal and amblyopic vision.

Orientation discrimination for single long lines presented in a frameless environment was measured with a method of constant stimuli in 18 normal subjects and in both eyes of 9 amblyopes. Orientation discrimination was tested at four meridians (horizontal, vertical, left, and right oblique). Although the normal subjects showed considerable individual variability in their just noticeable differences in orientation, each subject showed a consistent oblique effect. In amblyopic subjects, the interocular differences were strongly meridian-dependent and individually variable. Across amblyopic subjects, a two-fold increase in just noticeable differences ( JNDs ) was observed for the principal meridians, while the impairments were not significant for the oblique meridians. These small impairments in orientation discrimination strongly contrast with the high losses in acuity for the same subjects, which suggests that different mechanisms underly acuity and orientation discrimination.

Adolescent↗
PubMedDate not supplied

How task-related are the responses of inferior temporal neurons?

The responses of inferior temporal (IT) neurons may depend on the behavioral context of the stimuli; e.g. in Konorski tasks responses to two successively presented physically identical stimuli can be markedly different. This effect has been interpreted as being linked to the behavioral task, and to be involved in short-term memory and/or the temporal comparison of successively presented stimuli. We tested whether this behavioral context effect also occurs when the monkey is not executing a Konorski task, i.e. no temporal comparison of stimuli is being performed. Responses of the same IT neurons under two behavioral conditions were compared using the same temporal stimulus sequence (but different stimuli): a Konorski task and a Fixation task. We found that the occurrence of the behavioral context effect did not depend on the execution of the short-term memory task. The observed decline in the level of responses to repeated presentation of similar stimuli is interpreted as being a passive mechanism involved in recency detection, which occurs even if the recency information is not useful for the task. The importance of these results in the interpretation of "task-related" neuronal responses is discussed.

Animals↗
PubMedDate not supplied

Assessment of stereopsis in rhesus monkeys using visual evoked potentials.

Rhesus monkeys can have deficiencies in stereo vision, making it necessary to screen monkey subjects intended for single cell studies of stereo-based depth processing. We measured VEPs in two monkeys using a dynamic random-dot display in which a stereo-defined checkerboard reversed in depth. Monkeys fixated upon a small dot during stimulus presentation. One monkey showed clear evoked potentials in response to changes in disparity that were similar to those obtained in human subjects, using an identical stimulus paradigm. Controls with presentations of the monocular stimulus sequences (in which no depth reversal can be perceived) yielded no or much weaker VEPs. In the other animal, however, there was no difference in evoked potential between the two conditions. These electrophysiological findings closely match the performance of these same two subjects in a disparity discrimination task in which they were previously trained. We conclude that VEPs using this type of stimulus display can be used to screen monkeys for single cell or behavioral studies of stereopsis.

Animals↗
PubMedDate not supplied

Relating priming and repetition suppression.

We present a prototype of a recently proposed two stage model of the entorhinal-hippocampal loop. Our aim is to form a general computational model of the sensory neocortex. The model--grounded on pure information theoretic principles--accounts for the most characteristic features of long-term memory (LTM), performs bottom-up novelty detection, and supports noise filtering. Noise filtering can also serve to correct the temporal ordering of information processing. Surprisingly, as we examine the temporal characteristics of the model, the emergent dynamics can be interpreted as perceptual priming, a fundamental type of implicit memory. In the model's framework, computational results support the hypothesis of a strong correlation between perceptual priming and repetition suppression and this correlation is a direct consequence of the temporal ordering in forming the LTM. We also argue that our prototype offers a relatively simple and coherent explanation of priming and its relation to a general model of information processing by the brain.

Animals↗