Attention is a mechanism to select sensory information. It is a modulatory process which normally cannot be observed as overt responses. We have studied spatial attention using a new visual illusion of motion--line-motion effect: a line, which was presented physically at once, was perceived to be drawn from one side ...

The effects of a texture surround composed of line elements on a stimulus within which a target line element segregates, were studied. Detection and discrimination of the target when it had the same orientation as the surround were impaired at short presentation time; on the other hand, no effect was ...

Recent models of the visual system in primates suggest that the mechanisms underlying visual perception and visuomotor control are implemented in separate functional streams in the cerebral cortex. However, a little-studied perceptual illusion demonstrates that a motor-related signal representing arm position can contribute to the visual perception of size. The ...

Inhibition of return (IOR) is the name that has been assigned to a response time (RT) delay to a stimulus presented at a recently stimulated spatial location. A commonly held explanation for the origins of IOR is that perceptual processing in inhibited and that this inhibition translates into slower RT. ...

Sensory interaction and sensory adaptation in short- and long-lasting space flights (SF) and the dynamics of stability of adaptive shifts were studied by the phenomenology of spontaneous and visually induced illusory reactions. It was shown that perceptive impairment developed during the initial adaptation to microgravity should be considered regular reactions ...

The role of allocentric cues on movement control was investigated in the present study. Pointing movements directed to the more distant vertex of closed and open configurations of the Muller-Lyer illusion, as well as to the vertex of control lines, were studied in four experimental conditions. In the first (full-vision ...

To examine the role of visual area V4 in pattern vision, we tested two monkeys with lesions of V4 on tasks that required them to discriminate the orientation of contours defined by several different cues. The cues used to separate the contours from their background included luminance, color, motion, and ...

Wheels turning in the movies or in other forms of stroboscopic presentation often appear to be rotating backward. Remarkably, a similar illusion is also seen in continuous light. The occurrence of this perception in the absence of intermittent illumination suggests that we normally see motion, as in movies, by processing ...

During smooth pursuit eye movements made across a stationary background an illusory motion of the background is perceived (Filehne illusion). The present study was undertaken in order to test if the Filehne illusion can be influenced by information unrelated to the retinal image slip prevailing and to the eye movement ...

A spatial perturbation paradigm was used to determine equivalent intrinsic uncertainty and spatial integration efficiency in bisection. Specifically, three-line bisection thresholds were measured in the fovea of four normal observers with stimulus lines comprised of discrete dark dots distributed randomly around the mean line position according to a Gaussian function. ...

The turning responses of clawed toads (Xenopus laevis) to surface waves were examined in animals with an intact lateral line or with different combinations of lateral lines reversibly inactivated by CoCl2. The responses were characterized with respect to response frequency, turning accuracy, turning side, response time, and swim distance. After ...

The Mach book is a two-dimensional figure which looks three-dimensional. Despite the impression of depth in the figure, the apparent shape has not been determined. It has been suggested that the book appears as part of a 'cubic corner', 'as flat as possible', or with each half rotated about its ...

The physical elevation that appears to correspond to eye level (VPEL), as measured with a small visual target, changes systematically with the orientation in depth ('visual pitch') of a visual field consisting of one or two pitched-from-vertical lines in darkness. The influence is large and, with a one-line stimulus, is ...

A line, presented instantaneously, is perceived to be drawn from one end when a dot is flashed at that end prior to the presentation of the line. Although this phenomenon, called illusory line motion, has been attributed to accelerated processing at the locus of attention, preattentive (stimulus-driven) motion mechanisms might ...

The Zollner figure contains stacks of short parallel segments oriented obliquely to the direction of the stack. Adjacent parallel stacks of opposite polarity seem to diverge where their top segments form an arrowhead. To probe whether or not the opposite polarities are necessary to the illusion, three 'half-Zollner' configurations were ...

The perception of brightness differences in Ehrenstein figures and of illusory contours in phase-shifted line gratings was investigated as a function of the contrast polarity of the inducing elements. We presented either continuous lines or line-like arrangements composed of aligned dashes or dots whose spacing was varied. A yes/no procedure ...

Tracing movements (hand-following the stationary contours of three two-dimensional figures: square, triangle and circle by means of a computer mouse-operated lightspot) were analyzed during five consecutive days. All three figures consisting of four (square, circle) or three (triangle) segments had the same circumference. Three parameters were chosen to express the ...

Three special angles associated with the external reflection of light at the surface of an absorbing medium are well known: the principal angle, the pseudo-Brewster angle, and the second Brewster angle. Another significant angle has been identified recently by Azzam and El-Saba [Appl. Opt. 28, 1365 (1989)]. At this angle, ...

When a wheel rolls along a flat surface, a point on its perimeter traces a cycloid trajectory, forming a sequence of adjacent semicircle-like scallops. However, when mentally visualizing this point's trajectory, participants erroneously describe the point's path as looping back on itself between each scallop or phase of the cycloid, ...

The generation of illusory contours is closely related to distinct parts of a pattern such as dots, line ends, and corner points. On the other hand, the remarkable property is that gaze at one point of the contours diminishes the illusion and a return of gaze to the whole pattern ...

This study determined how contour interaction (the degradation of visual acuity by the presence of nearby contours) is affected by the incessant retinal image motion that occurs in observers with congenital nystagmus (CN). Visual acuity was measured for single, high-contrast, black Landolt Cs, presented without and with flanking bars (contour-to-C ...

We studied how the visual system integrates locally ambiguous velocities into global unambiguous coherent motion in the presence or absence of a textured background. Line drawings of complex figures were presented through invisible (i.e. same luminance and hue as the background) circular apertures such that only straight line segments were ...

Results from three experiments using spatial forced-choice techniques show that an illusory contour improves the detectability of a spatially superimposed, thin subthreshold line of either contrast polarity. Furthermore, the subthreshold line is found to enhance the visibility of the illusory contour. Stimuli which do not induce illusory contours, but reduce ...

We discuss three motion illusions, the fluted square wave illusion, the reverse phi illusion and the Pantle illusion. In these illusions reversed apparent motion is either induced or eliminated by the introduction of a blank inter-frame-interval between the frames of the apparent motion sequence. In order to simulate these effects ...

RATIONALE AND OBJECTIVES: We investigated whether the left thoracic paraspinal line represents an actual change in optical density corresponding to the posterior pleural reflections or whether it represents a Mach band effect. METHODS: Using photodensitometry, we obtained averaged light intensity tracings across the left thoracic paraspinal line in 14 normal ...

A circle was attached to one of three lines which were changing in length and direction simultaneously. This configuration of moving lines had been found previously to induce the perception of depth. Of 26 observers 20 reported that the moving circle appeared smaller in size than a physically equal stationary ...

Periodical stimulation of the otoliths during linear horizontal displacement leads not only to motion and displacement perception but also to the "Hilltop Illusion", which is the perception of being transported not on an earth-horizontal path, but over a small hill. This phenomenon is explained by the partial reinterpretation of the ...

A previously unreported motion illusion is described. Oblique lines that drift smoothly on the retina in a vertical direction appear to be displaced laterally. The effect occurs both for moving lines under fixation and for stationary lines under ocular tracking of an external target. Orientation, length, and homogeneity of the ...

The visual angle subtended by the frame seems to be an important determinant of the contribution of orientation contrast and illusion of self-tilt (ie vection) to the rod-and-frame effect. Indeed, the visuovestibular factor (which produces vection) seems to be predominant in large displays and the contrast effect in small displays. ...

The visual field exerts powerful effects on egocentric spatial localization along both horizontal and vertical dimensions. Thus, (1) prism-produced visual pitch and visual slant generate similar mislocalizations of visually perceived eye level (VPEL) and visually perceived straight ahead (VPSA) and (2) in darkness curare-produced extraocular muscle paresis under eccentric gaze ...

In two studies the effect of the distance between the tip of the rod and the frame sides (gap) in the rod-and-frame (RF) illusion was examined and the effect of a full-square condition was compared with that of two different frame amputations. In both studies, there were more rod-setting errors ...

The study of illusory brightness and contour phenomena has become an important tool in modern brain research. Gestalt, cognitive, neural, and computational approaches are reviewed and their explanatory powers are discussed in the light of empirical data. Two well-known phenomena of illusory form are dealt with, the Ehrenstein illusion and ...

The effect of curvature on visual interpolation in partly occluded figures was examined. In experiments 1 and 2, the shape of a visually interpolated contour was measured by using a partially occluded triangle or a partially occluded circle as the target figure. The targets were cut off at both sides, ...

Illusory contours are invoked by the visual system to account for otherwise inexplicable gaps in the image. We report three sets of novel observations on illusory contours. First, when an illusory square is superimposed on a checkerboard pattern there is a considerable enhancement of the contours so long as they ...

The enhanced maneuverability aircraft of the future will expose pilots to combinations of conventional translational accelerations as well as extraordinary angular accelerations. This flight regime, combined with the intense concentration required for combat maneuvering, will make motion-induced illusions more perilous than in existing aircraft. Although there are many causes for ...

The use of fixed print size to measure amplitude of accommodation by the push-up method will result in a range of angular sizes of the print at the nearpoint for patients with different amplitudes. We investigated the effect of this on measured amplitude of accommodation in 60 subjects aged 25 ...

The elevation at which an observer sets a target to appear at eye level (VPEL) is systematically related to the angle of pitch of the visual field and is only a little less for a visual field consisting of a single line in darkness than for a complexly structured field ...

We tested five patients with marked left-sided visuo-spatial neglect and two control subjects on a test of line bisection. A series of horizontal lines was presented to each subject, who had to indicate the centre with a projection light-pen. All five patients misplaced the centre to the right, in accordance ...

Single elements in textures segregate preattentively from the background if they differ in special features from surrounding elements (pop-out). Oblique targets on a background of vertical line elements are more easily detected than vertical targets on a ground of oblique elements. We wanted to find out whether this perceptional asymmetry ...

It is well known that a staircase luminance profile is not seen veridically, but appears as the scallopy-like Chevreul illusion. We have shown that adding thin lines (either light or dark) to the centre of each step creates an illusory brightness change at the point of the line. The regions ...

The relationship between objective measures and subjective experiences of sensory stimuli is described by a power law, psi = K phi beta, in which psi represents the psychological value and phi the physical value. The constant (K) and the exponent (beta) are empirically derived. This relationship is often assumed to ...

The present study constituted an initial experimental effort to examine the fragmentation characteristics of subjective contours within the photopic and upper scotopic ranges of illumination. Four stimulus factors known to influence the visibility of subjective contours-target luminance, inducing area size and contrast, and contour orientation--were examined. Results indicated that subjective ...

An analysis of the reset of visual cortical circuits responsible for the binding or segmentation of visual features into coherent visual forms yields a model that explains properties of visual persistence. The reset mechanisms prevent massive smearing of visual percepts in response to rapidly moving images. The model simulates relationships ...

A method for measuring the variation of one stimulus parameter with respect to another is applied to show how line intensity affects the perceived tilt of lines, internal angle of chevrons, and curvature of circular arcs. Perceived curvature increased with increasing line intensity, but analogous effects were found only for ...

The idea that low spatial-frequency information in the Mueller-Lyer figure accounts for a major part of the illusion was tested in a series of five studies. In Study 1, subjects were selectively adapted to high or low square-wave spatial-frequency gratings with no difference in the magnitude of illusion they experienced. ...

Psychophysical studies of interactions between contours defined by different image attributes report that luminance-defined and illusory contours show little if any interaction. Because the contours defined by these attributes may vary in perceptual saliency, we employed the tilt aftereffect (TAE) and a cross-adaptation procedure to evaluate interaction effects between luminance-defined ...

It is demonstrated that lightness perception can be affected by shape from stereopsis. The starting point was a report by Knill and Kersten that the perceived lightness of a monocularly viewed surface can be affected by outline-contour cues indicating that the surface is three-dimensional (3-D). In that study stimuli consisted ...

Evidence from visual-search experiments is discussed that indicates that there is spatially parallel encoding based on three-dimensional (3-D) spatial relations between complex image features. In one paradigm, subjects had to detect an odd part of cube-like figures, formed by grouping of corner junctions. Performance with cube-like figures was unaffected by ...

Earlier work has confirmed that (i) observers can judge divergent receding lines, placed directly in front of them, to be parallel, and (ii) converging lines which are displaced laterally, so that they are viewed obliquely, can also be judged to be parallel. The former observation is in accord with traditional ...

In a series of experiments, the selective-adaptation paradigm was applied to the rotating-trapezoid illusion in an effort to demonstrate neural-adaptation effects in the figural reversal of this classic illusion. Prior to viewing the standard trapezoid, the observer adapted to a rectangle rotating unambiguously in the same direction as the trapezoid ...