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H Maes

Publications and source records attributed to H Maes.

At least 55 records · Page 3Linked to original sources
PubMed1990

Selectivity of cat area 18 neurons for direction and speed in depth.

1. Fifty-eight area 18 cells recorded in anesthetized and paralyzed cats were tested for selectivity for direction in depth after their monocular velocity characteristics and static disparity profile were determined. 2. Direction in depth was produced by changing the speed and direction in the two eyes, but keeping the speed along axes in depth constant. 3. Forty-two cells were completely investigated, which means that direction in depth selectivity was tested at least at two different position disparities and two different bar speeds. Seven out of the 42 cells were accepted as direction in depth selective. 4. The 16 remaining cells were incompletely tested. Only one of them was direction in depth selective at the disparity and speed tested and shared all the properties of the seven completely tested direction in depth selective cells. Therefore we estimated that 8/58, i.e., 14% of the area 18 cells are direction in depth selective. 5. The direction in depth selective cells are a very homogeneous class: they all belong to the S family, are velocity tuned, monocular, prefer orientations close to vertical, and have a broad inhibitory or an unmodulated position disparity profile. 6. Direction in depth selectivity arises both from monocular properties and binocular interactions. These binocular interaction profiles can be symmetric or asymmetric. The change of these interaction profiles with changes in base speed can be summarized as changes in level of inhibition for the axes corresponding to equal speed in the two eyes on one hand and changes in the slope of the inhibition gradient centered on these axes of equal speed on the other hand. 7. Nineteen of the 58 cells were tested for selectivity for speed along trajectories in depth. All five direction in depth selective cells tested were also tuned to speed in depth. This suggests that area 18 contributes to the elaboration of a 3D velocity map. 8. A wiring diagram that accounts for the binocular interactions underlying direction selectivity in depth is presented.

Animals↗
PubMed1989

Genetic and environmental variation in the birth weight of twins.

Two novel approaches to the analysis of twin data are illustrated with data from birth weight in twins. First, two possible covariates of birth weight are fitted to the data simultaneously, allowing for linear effects of these variables, and their correlation. Second, information on chorionicity is used to estimate the effects of chorion type on birth weight. The data were collected from a large sample of twins born in East Flanders, Belgium. Variation and covariation in twins were considered as a function of sex, chorionicity, maternal age, gestational age, and genotype. No evidence for sex differences in causes of variation was found. As expected, the largest source of variation in bith weight was associated with gestational age. Other common environmental influences were non-significant. Heritability was significant, constituting approximately 40% of variation not associated with maternal and gestational age. A small but significant effect of chorionicity was found, such that dichorionic twins show a greater similarity than monochorionic.

Birth Weight↗
PubMed1987

The velocity dependence of direction selectivity of visual cortical neurones in the cat.

1. The range of velocities, yielding direction-selective responses, was investigated in a total of 167 direction-selective cells from areas 17 and 18 of the cat, using a high-contrast light bar moving at velocities ranging from 0.6 to 900 deg s-1. 2. 11% of the cells were direction selective over the full range of velocities tested. Most cells (66%) gave only responses at low velocities and thus were not direction selective at high velocities. The remaining cells gave responses over a broad range of velocities but the direction selectivity was limited to either high or intermediate velocities (18 and 5% of the cells, respectively). Cells with direction selectivity at high but not at low velocities had large receptive fields with non-overlapping 'on' and 'off' subregions and they responded quickly and phasically to stationary flashes. This suggests that the latter cells relied on fast and brief interactions over large distances. 3. In thirty cells the spatial and temporal limits of direction selectivity were investigated using a stroboscopically illuminated moving light bar. In all cells direction selectivity depended both on the interflash distance and the interflash time interval. Area 17 cells with large receptive field at high eccentricity tolerated much larger interflash spacings than area 17 cells with small receptive fields near the area centralis. For eleven of the thirty cells the effective interflash distance could be larger than the width of the receptive field. The largest effective interflash time interval varied between 35 and 250 ms. 4. Eight of the thirty cells were direction selective at high but not at low velocities. These eight cells all remained direction selective over large interflash distances and they required brief interflash intervals (less than or equal to 65 ms). 5. Responses to single stroboscopic flashes within the sequence were observed in ten cells, which all responded well at high apparent velocities. While most cells (eight out of ten) showed both response increments in the preferred direction and response decrements in the non-preferred, the decrements constituted the dominant element in the direction selectivity of six out of ten cells while the remaining four cells relied mainly on response increments. 6. It is concluded that the range of direction-selective velocities of some cat visual cortical cells can be predicted from a knowledge of the spatial extent and the time course of the direction-selective interactions.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

The suppressive influence of moving textured backgrounds on responses of cat striate neurons to moving bars.

The suppressive action of a moving textured background on responses to moving bars was investigated in 118 striate neurons, 19 dorsal lateral geniculate neurons, and 5 perigeniculate neurons in paralyzed and anesthetized cats. In standard conditions the background was a two-dimensional (2D) noise pattern, the bar moved at optimal speed, and its contrast level was adjusted to yield 50% of the maximum response. Neuronal responses to the moving bar were suppressed when the background moved at the same speed or faster than the bar. The direction of motion of the bar had little influence. This suppressive effect was equally strong in all three experimental samples. The suppressive effect of the moving background was uniformly distributed among the cortical population, being equally strong in all layers, in all parts of the visual field representation, and for different categories of cortical cells. The suppressive effect of the moving background depended little on the structure of the background or on the speed of the bar. The suppression increased with decreasing contrast of the bar. Many (80%) cortical cells and all geniculate neurons responded to the movement of the 2D noise on its own. Most of these cells responded to isolated features ("grains") in the pattern rather than to movement of the whole pattern. There was no difference in strength of suppression between cortical neurons responsive and unresponsive to the moving 2D noise. The possible origins of this suppressive influence of moving backgrounds and its significance for the processing of visual scenes, more complicated than a single stimulus, are discussed.

Animals↗
PubMed1987

Responses of cat striate neurons to moving light and dark bars: changes with eccentricity.

Responses of area-17 neurons to light and dark bars moving over a wide range of speeds were measured over a range of receptive-field locations in anesthetized and paralyzed cats. For both light bars and dark bars, velocity sensitivity shifted to higher speeds with increasing eccentricity, whereas response strength and direction selectivity hardly changed. The good correlation between response strength and velocity sensitivity for light and dark bars suggests that ON and OFF inputs converge upon most area-17 cells. The correlation between direction selectivities for light and dark bars was not better than that between velocity sensitivities for light and dark bars. Only cells with strong direction selectivity were equally direction selective for light bars and dark bars. Comparison with previous studies done with high-contrast stimuli shows that the shift in sensitivity to higher speeds with increasing eccentricity is contrast dependent.

Animals↗
PubMed1986

Velocity discrimination in the cat.

After considerable training (over 2 years) we measured the just noticeable differences (JNDs) in velocity as a function of reference velocity in three cats. The velocity discrimination curve plotting JNDs in velocity, expressed as Weber fractions as a function of reference velocity is U-shaped with optimal performance at reference speeds between 25 and 60 degrees/sec. The discrimination curve changed little with a tenfold change in slit width. Compared to the human velocity discrimination curve determined with the same test apparatus, the feline curve is narrower and shifted towards faster velocities and larger Weber fractions. These results support our specific linking hypothesis between velocity tuned cells as observed in cortical areas 17 and 18 of the cat, and velocity discrimination.

Animals↗
PubMed1985

Visual cortical correlates of visible persistence.

In order to evaluate their possible role in visible persistence, cortical cells from area 17 of the cat were investigated with a stationary light bar flashed for different durations. Thirteen out of 72 cells with non-overlapping On and Off subregions were able to respond to the briefest On stimulus (12.5 msec) for low and moderate contrasts. The responses of these cells outlasted brief On stimuli and this neural persistence increased as the On duration was shortened, mimicking the inverse duration effect of visible persistence. The 30 cells with overlapping On and Off subregions were all able to respond to brief stimuli but their neural persistence was independent of stimulus duration. At very high contrast levels, the inverse duration effect, observed in cells with non-overlapping subregions, disappeared since the On responses were followed by Off rebound discharges regardless of stimulus duration. It is suggested that the latter responses are a possible cortical equivalent of positive afterimages.

Afterimage↗
PubMed1985

Velocity selectivity in the cat visual system. III. Contribution of temporal factors.

In 149 units from area 17 and 48 units from area 18 the responses to stationary stimulation of different durations were compared with the responses to the same stimulus (a 0.3 degrees-wide light or dark bar) moving at different velocities. The aim was to test the hypothesis that the range of effective velocities depends on the time needed for the bar to cross the receptive field. Forty-two percent of the area 17 cells and 8% of the area 18 cells responded poorly or not at all to briefly presented stationary stimulation. These cells were unable to respond at high velocities, and for these "duration-sensitive" cells the velocity characteristics are well predicted on the basis of responses to stationary stimulation of different durations. Cells that responded equally well to periods of stationary stimulation ranging from 12.5 to 3,200 ms ("duration-insensitive cells") were found to be able to respond at all equivalent velocities, but their preference for either high, low, or intermediate velocities was not reflected in differences in responsiveness to the different durations tested. Duration-sensitive cells in area 17 tended to have a receptive field near the area centralis, and 73% of them were classified as S-family cells, one third being end-stopped S-cells. In contrast only 18% of the duration-insensitive cells were of the S family, and these S-family cells were rarely end-stopped (1/12) or rarely had receptive fields within 5 degrees of the fovea (3/12). Duration-sensitive cells had very long latencies (median 285 ms) in response to a stationary flashed light bar of 1 s duration but much shorter latencies (median 91 ms) when tested with a slowly moving light bar. This difference was not seen in duration-insensitive cells (median latencies = 61 and 59 ms). The ability to respond at high velocity was contrast dependent. At a low contrast level all cells failed to respond to brief stimulation, whether moving or stationary. At high contrast levels only the duration-insensitive cells showed an increased responsivity to brief stimuli. The absence of responses in duration-sensitive cells to brief stimuli of high contrast may depend upon suppressive influences reaching these cells before the excitatory influences. We conclude that the velocity upper cutoff of most S-family cells with a central receptive field can be predicted from a knowledge of the minimum duration of stationary presentation required for their activation (median ON duration threshold, 200 ms).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Velocity discrimination in central and peripheral visual field.

Just-noticeable differences (jnd's) in velocity were measured as a function of reference velocity for central and peripheral vision. The velocity discrimination curves plotting jnd's in velocity, expressed as Weber fractions, as a function of reference velocity were U shaped at all eccentricities. Under almost every stimulus condition the increase in jnd in velocity with increasing eccentricity was significantly larger at low reference velocities than at high reference velocities. Consequently the shift toward higher velocities with increasing eccentricity was much clearer for the lower end of the velocity-discrimination curve than for the upper end. These results are in agreement with the predictions derived from the response characteristics of velocity-tuned cells. Control experiments involving direction discrimination have shown that the impossibility of making fine velocity judgments at high speeds is due not to too weak a contrast for the stimulus motion to be visible but to a limitation in the neural apparatus analyzing velocity.

Adult↗
PubMed1984

Factors influencing velocity coding in the human visual system.

Differential velocity detection in the fovea was measured over a wide range of velocities (0.25-256 degrees/sec). Differential thresholds were minimum (about 6%) for intermediate velocities (4-32 degrees/sec). Velocity judgements were shown not to depend on duration judgments. The U-shaped curve relating differential velocity detection and velocity was preserved at different background levels and different contrasts. The physiological correlates of these observations are discussed.

Differential Threshold↗
PubMed1982

Receptive field structure of area 19 as compared to area 17 of the cat.

A total of 139 cells from area 19 along with a comparison sample of 172 cells from area 17 were classified using a system proposed by Orban and Kennedy, following Henry and consisting of 4 basic cell 'families', namely S, C, A and B, each having an end-stopped member: HS, HC, HA and HB. The two basic parameters separating the 4 families are firstly spatial overlap of ON and OFF subregions and secondly receptive field (RF) width. Spatial overlap was studied quantitatively in a number of these cells using multiple presentations of stationary slits or moving light and dark edges. RF width was determined quantitatively using bars moving at different velocities across the RF. It was found that cells with spatially nonoverlapping and overlapping subregions are present in both areas. S and HS cells, which show similarities with simple cells, were encountered in area 19 but they constituted only 18% of the population as opposed to 55% in area 17. C and HC cells, reminiscent of complex cells, were about as common in area 19 as in area 17. In both areas C cells were the only group which consistently discharged equally well or better in response to diffuse light turned on and off than when presented with light bars. A and B families formed a minority in both areas. Area 19 contained a larger proportion of nonoriented and undriveable units, as well as a special category of cells preferring stimuli with a width larger than the length ('rectangle cells'). RF width was generally larger in area 19 than in area 17 and its distribution in area 19 showed distinct peaks. In the part of area 19 subserving central vision these peaks appeared with a periodicity of 0.8 degrees, suggesting that cells in this zone are supplied by one or more rows of a uniform set of afferents having a RF center diameter of about 0.8 degrees. The identification of this population as W-relay cells is supported by the long latencies found in cells from this part of area 19. It is concluded that basic principles underlying the structure of the RF are similar in both areas 19 and 17.

Animals↗
PubMed1981

Velocity sensitivity of areas 17 and 18 of the cat.

Velocity sensitivity of areas 17 and 18 of the cat has been evaluated by preparing neuronal velocity-response (VR) curves in paralyzed and anaesthetized cats. VR curves suggest two possible mechanisms for neuronal coding of stimulus velocity as well as criterion for distinguishing between cells involved in analysis of stationary or moving objects. VR curves differ between cortical areas and with retinal eccentricity. Neurones with larger receptive fields (RFs) become, on the average, sensitive to faster velocities. Parallels with human psychophysics are pointed out as support of the suggestion that the present results are relevant for our insights in human motion perception.

Animals↗
PubMed1980

Functional changes across the 17-18 border in the cat.

Changes in velocity sensitivity, receptive field (RF) position, and RF size were investigated in long oblique penetrations crossing the 17-18 border. The penetrations were histologically reconstructed and the border determined by cytoarchitectonics. In cortex subserving central and paracentral vision change in velocity sensitivity allowed a reasonable physiological identification of the 17-18 border. The physiological border correlates well with the histological border zone, best with its medial edge. Changes in RF position and RF size are of little use for physiological identification of the border in this region. In this cortical region area 18 representation of the vertical meridian (VM) has a high magnification factor. In cortex subserving peripheral vision, the change in velocity sensitivity was small and the change in RF position coincided with the cytoarchitectonics.

Animals↗
PubMed1980

Time course of feeding induced by pentobarbital-injections into the rat's VMH.

Chemical blockade of the ventromedial hypothalamus (VMH) by single microinjections of pentobarbital in ad lib fed male Wistar rats induced a meal that did not outlast a 10-min postinjection period. When food was presented only after this period, feeding was nearly absent. Repeating the injection after 10 and 20 min led each time to eating, although the amount consumed decreased. Scanning behaviour was drastically depressed during the 4-min postinjection period but then recovered within 6-11 min. Sniffing into the litter was enhanced for about the same interval (8-10 min). Fixed-ratio lever pressing for food upon pentobarbital-blockade of the VMH also tended to disappear after this period, whether many (low ratios) or few (high ratios) food pellets were obtained. The limited meal size after VMH-blockade therefore presumably resulted from the waning of the anaesthetic effect (e.g. diffusion) in this brain site.

Animals↗