A dynamical model of orientation and spatial frequency tuning in a cortical hypercolumn is presented. The network topology is taken to be a sphere whose poles correspond to orientation pinwheels associated with high and low spatial frequency domains, respectively. Recurrent interactions within the sphere generate a tuned response via an ...

Spatial frequency (SF) and orientation tuning are intrinsic properties of neurons in primary visual cortex (area V1). To investigate the neural mechanisms mediating selectivity in the awake animal, we measured the temporal dynamics of SF and orientation tuning. We adapted a high-speed reverse-correlation method previously used to characterize orientation tuning ...

The upper part of the hornet cuticle in the abdominal region reveals several structures. First, situated at intervals of 10 microm or more apart, there are depressions housing a peripheral photoreceptor (PP) and between every two of these, there are horizontal flats resembling an irregular polygon which are mostly elongated ...

The effects of the visual features of prey-like objects on the orienting behaviour of the salamander Plethodon jordani were studied. Two stimuli (cricket dummies, rectangles), moving in opposite directions, were presented simultaneously on a computer screen. They differed in size, contrast, velocity and movement pattern of the entire body or ...

Neurophysiological and psychophysical evidence indicates that neuronal surround modulation at cross-orientation (orthogonal to the preferred orientation of the classical receptive field) plays a key role in intermediate-level visual tasks, such as textural segregation and perceptual pop-out. What is missing is a psychophysical description of cross surround modulation at the spatial ...

A computational model is proposed for spatial orientation processing beyond the initial stage of linear filtering in visual cortex. The model accounts for orientation pop-out, edge location and orientation, and bar location and orientation. It naturally extends to higher order orientation symmetries. The model is consistent with much of the ...

The statistical arrangement of oriented segments in natural scenes was recently proposed to be indicative of a cocircularity rule. In particular, the probability density function of the relative position of two oriented segments was found to be maximal along fixed angles on the plane, consistent with the two segments being ...

In contrast to the abundant literature investigating how orientation coding depends on edges defined by various image features, relatively little is known about how coding of orientation might also depend on the two distinct functional roles that oriented edges commonly play. Oriented lines can delineate outline contours of a figure ...

In this paper, the constructive nature of comparison processes (both similarity- and difference-oriented judgments) is examined through their effects on visual perception. Previous research has shown that comparison processes enhance the tendency to interpret ambiguous objects in the light of the unambiguous objects with which they are compared (Medin, Goldstone, ...

In a previous study we found large systematic errors (up to 40 degrees) when subjects adjusted the orientation of a horizontal test bar until it appeared parallel to a horizontal reference bar, both bars rotating about their vertical axes. The deviations increased linearly with the separation angle but vanished when ...

The frequency of free oscillations of plant stems with apical loads, as found in some cereals, is different depending on whether the stems are oriented vertically or horizontally. Neglecting the stem's own weight the differential equations describing the oscillation can be solved for both cases, although in the vertical orientation ...

We investigated temporal aspects of the cortical mechanisms supporting visual contour integration by measuring observers' efficiency at detecting fragmented contours, composed of Gabor micropatterns, embedded in a field of distractor elements. Gabors consisted of a static Gaussian enveloping a sinusoidal carrier which was temporally modulated by motion or counter-phase flicker. ...

The purpose of this research was to determine the reference axes used by the visual system to specify direction of motion of objects by the visual system at the perceptual level. Ten young adults aligned motion of a moving luminous dot on a computer display to body-fixed and external vertical ...

Li and Zaidi (Li, A., and Zaidi, Q. (2000) Vision Research, 40, 217-242) showed that the veridical perception of the 3-dimensional (3D) shape of a corrugated surface from texture cues is entirely dependent on the visibility of critical patterns of oriented energy. These patterns are created by perspective projection of ...

Perceptual fading of texture targets on similarly textured backgrounds was studied in relation to stimulus salience using texture patterns defined by orientation contrast, shape contrast, and order contrast. In two independent experiments, perceptual salience of the targets was determined. In the first, the textural contrast of the stimuli was varied ...

An individual line or a combination of lines viewed in darkness has a large influence on the elevation to which an observer sets a target so that it is perceived to lie at eye level (VPEL). These influences are systematically related to the orientation of pitched-from-vertical lines on pitched plane(s) ...

Virtual reality technology was utilized to assess the effect of component orientation and component design on the range of motion prior to impingement following total hip arthroplasty. Components were digitized, oriented in the pelvis, and computer animations were performed to assess the likelihood of dislocation with different combinations of component ...

A neural computational model is suggested in this paper for investigating the stimulus dependence of spiking patterns and the neural representation of alpha-oriented moving light bars in the cortex. In this model, a stimulus-directed cortical developing algorithm is introduced for training the neural network. Three classes of computer simulations concerned ...

Both psychophysical and neurophysiological evidence suggest that there are two visual cortical processing streams, a linear stream that processes first-order stimuli and a nonlinear stream that also processes second-order stimuli. This evidence also suggests that before the extraction of the second-order signal, the nonlinear pathway broadly but not completely pools ...

We analyzed how the visual response to orientation modulation in texture patterns varied as a function of the magnitude of orientation contrast. Using a contrast-discrimination technique, we measured threshold increments of orientation contrast (the orientation contrast required for discriminating between two textures) at various pedestal-orientation contrasts. The orientation-contrast-response function estimated ...

OBJECTIVE: The purpose of this study was to perform a quantitative evaluation of the effect of static magnetic field orientation on cartilage transverse (T2) relaxation time in the intact living joint and to determine the magnitude of the magic angle effect on in vivo femoral cartilage. MATERIALS AND METHODS: Quantitative ...

Several studies have attempted to determine the effects of orientation on a horse's ability to maintain balance during transportation. The results have often been contradictory because of differences in trailer design and lack of simultaneous comparisons. In this study, three replications of two forward-facing and two rear-facing horses were transported ...

A field study was conducted to observe the standing orientation and behaviour among a group of meat type goats during transit by road. Randomly selected goats were observed from 10 runs (10 goats per run) carried out on the same road and the duration of each run was about 50min. ...

A shape can be more difficult to identify when other shapes are near it. For example, when several grating patches are viewed parafoveally, observers are unable to report the orientation of the central patch. This phenomenon, known as 'crowding,' has historically been confused with lateral masking, in which one stimulus ...

We analysed the temporal-frequency characteristics of two functional processes involved in orientation-based texture segregation: local orientation coding and subsequent orientation-contrast coding. Two texture images, in which each micropattern was rotated by 90 degrees, were alternated at various temporal frequencies. A micropattern was a second-derivative (D2) of a Gaussian that loses ...

Detection of a uniquely oriented line element in a background field of uniformly oriented line elements depends on the orientation of the background field. Is the orientational reference frame for this anisotropy entirely dependent on the orientations of structures outside the line-element display, the spatial regularity of the stimulus elements, ...

The effect of light and gravity on orientation was studied in cercariae of 4 echinostome species: Pseudechinoparyphium echinatum, Echinostoma revolutum, Hypoderaeum conoideum, and Isthmiophora melis. The cercariae were placed into vertical and horizontal cuvettes, illuminated with 2 different light intensities from various directions, and their distribution recorded for 6 hr ...

The structure of orientation maps computed from a different number of stimulus orientations was studied in visual cortical area 18 of the cat. Single condition maps (SCMs) were obtained to 16 stimulus orientations, of which angle maps were generated using 4, 8, and 16 SCMs corresponding to multiples of 45, ...

In the classic oblique effect contrast detection thresholds, orientation discrimination thresholds, and other psychophysical measures are found to be smallest for vertical or horizontal stimuli and significantly higher for stimuli near the +/-45 degrees obliques. Here we report a novel inverse oblique effect in which thresholds for detecting translational structure ...

It is a well-established fact that the cortical filters selective for spatial frequency and orientation have a limited spatial extent. The present study investigated how information from local filters is integrated into global shapes. Specifically, we were interested in whether identification of a global pattern consisting of small oriented, spatially-bandpass ...

Prevalence of certain celestial and terrestrial cues was tested in the zonal recovery behavior and orientation of the fiddler crab Uca cumulanta. Experiments were conducted in the field bordering a mangrove forest on the eastern Venezuelan coast. Uca cumulanta exhibited zonal recovery behavior based on different orientational references, including celestial ...

Li and Zaidi (Li, A., and Zaidi, Q. (2000) Vision Research, 40, 217-242) showed that the veridical perception of the 3-dimensional (3D) shape of a corrugated surface from texture cues is entirely dependent on the visibility of critical patterns of oriented energy. These patterns are created by perspective projection of ...

Desert ants (Cataglyphis fortis) were trained to follow a fixed route around a barrier to a feeder. Their homeward trajectories were recorded on a test field containing a similar barrier, oriented either as in training or rotated through 22 or 45 . Under one set of experimental conditions, the homeward ...

Visual stimulation of a region outside the receptive field of single cells in visual cortex often results in the modulation of their responses. The modulatory effects are thought to be mediated through lateral connections within visual cortex. Research on lateral interactions commonly shows suppression. There has been no systematic study ...

This paper examines the interaction between first- and second-order contours in the orientation domain. Using the simultaneous tilt illusion (TI), we show that the apparent rotation of a vertical test grating away from that of a surrounding inducing grating (repulsion effect) occurs when both the inducing and test grating are ...

From the intracellularly recorded responses to small, rapidly flashed spots, we have quantitatively mapped the receptive fields of simple cells in the cat visual cortex. We then applied these maps to a feedforward model of orientation selectivity. Both the preferred orientation and the width of orientation tuning of the responses ...

The aim of this study was to examine the effect of body and head tilts on the haptic oblique effect. This effect reflects the more accurate processing of vertical and horizontal orientations, relative to oblique orientations. Body or head tilts lead to a mismatch between egocentric and gravitational axes and ...

Foveal visual acuity is impaired by the presence of contours that surround the target (contour interaction (CI)). In order to determine the roles of various surrounding contours, visual acuities for a square C were measured in the presence of four and two flanking bars. Bars of different orientations relative to ...

Recent research on texture synthesis suggests that characterisation of those properties of textures to which human observers are sensitive may be provided by the histograms of the coefficients of a wavelet decomposition. In this study we examined the properties of wavelet histograms that affect texture discrimination by measuring observer sensitivity ...

To understand how the human visual system analyzes images, it is essential to know the structure of the visual environment. In particular, natural images display consistent statistical properties that distinguish them from random luminance distributions. We have studied the geometric regularities of oriented elements (edges or line segments) present in ...

Orientation detection and discrimination thresholds were measured for Gabor 'envelopes' formed from contrast-modulation of luminance 'carriers'. Consistent with previous research differences between carrier and envelope orientation had no effect on sensitivity to envelopes. Using plaid carriers in which the proportion of contrast modulation 'carried' by each plaid component was systematically ...

Regan and Beverley [Regan, D., & Beverley, K. I. (1985). Postadaptation orientation discrimination. Journal of the Optical Society of America A, 2(2), 147-155] previously demonstrated that adapting to an oriented visual stimulus improves sensitivity to subtle orientation differences while impairing contrast sensitivity. Here, we investigated whether practice-based improvements in orientation ...

We investigated whether the response of a motion sensor was related to the specificity of sensory information (orientation and direction of motion) used to compute motion energy. This was done in two ways. First, we assessed whether orientation discrimination of a target line, which segregated by an orientation difference from ...

Naturally occurring visual stimuli are rich in examples of objects delineated from their backgrounds simply by differences in luminance, so-called first-order stimuli, as well as those defined by differences of contrast or texture, referred to as second-order stimuli. Here we provide a brief overview of visual cortical processing of second-order ...

To assess temporal and spatial variations in the emission of the odour guiding them to the nipples, we exposed newborn rabbits, Oryctolagus cuniculus, to lactating females in a series of simultaneous olfactory choice tests. They showed a clear preference for females in early, rather than late, lactation, and in the ...

We apply an adaptation technique to explore the neural code for the visual location of textures defined by modulation of orientation over space. In showing that adaptation to textures modulated around one orientation shifts the perceived location of textures modulated around a different orientation, we demonstrate the existence of a ...

This paper considers the problem of position/orientation tracking control of wheeled mobile robots via visual servoing in the presence of parametric uncertainty associated with the mechanical dynamics and the camera system. Specifically, we design an adaptive controller that compensates for uncertain camera and mechanical parameters and ensures global asymptotic position/orientation ...

We examine how differently oriented components contribute to the discrimination of motion direction along a horizontal axis. Stimuli were two-frame random-dot kinematograms that were narrowband filtered in spatial frequency. On each trial, subjects had to state whether motion was to the left or the right. For each stimulus condition, Dmax ...

Stimuli composed of two overlapped faces, one rotated 45 degrees clockwise and the other 45 degrees counterclockwise, produce perceptual rivalry whereby both faces cannot be simultaneously perceived. We obtained subjective and quantitative measures of this rivalry effect and examined if it persists with inverted stimuli. Our results show that upright ...

Feedforward models of visual cortex appear to be inconsistent with a well-known property of cortical cells: contrast invariance of orientation tuning. The models' fixed threshold broadens orientation tuning as contrast increases, whereas in real cells tuning width is invariant with contrast. We have compared the orientation tuning of spike and ...