bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fusion and Rivalry of Illusory Contours
Authors: Harris J P , Gregory R L 
Published: January 2007

The general question is raised: “Are visual contours given directly from striate-cortex feature-detector activity?‘’ Phenomena of ‘subjective’ or ‘cognitive’ contours are examined to challenge this view, on the ground that contours can be extrapolations across low-probability gaps. The contours may be curved and may have poor ‘gestalt’ qualities—so ‘gestalt closure’ is not appropriate, but may be a sub-class of these phenomena. It is suggested that these illusory contours (and brightness differences) are generated by perceptually postulated masking objects—these being part of perceptual ‘scene analysis strategy’, since strong evidence for nearer objects is provided by improbable gaps. Experiments are reported, in which each eye is given a different ‘cognitive’ contour figure such that there are disparate but illusory contours. It is found that these are fused to give three-dimensional illusory. surfaces bowing in front of the display. Masking objects must be in front of gaps; what happens here with reversal of stereo depth? Switching the eyes often gives rivalry of the illusory contours when masking is incompatible with the stereo depth. Implications for normal stereo vision are discussed.
‘On’ and ‘Off’ Components in the Human Somatosensory Evoked Response
Authors: Feinsod M , Bach-Y-Rita P , Madey J M , Simoes E 
Published: January 2007

The somatosensory evoked response to vibrotactile stimuli was studied in 20 subjects. This type of response to stimuli of 1000 ms duration displays ‘on’ and ‘off’ components. The latter consists of a surface negative deflection of about 100–120 ms peak latency, followed by a slower positive wave. As in the averaged visual evoked response an afteractivity of frequency 8–10 Hz may follow the ‘on’ component. This activity may either mask the ‘off’ component, be initiated by the termination of the stimulus, or its rhythm can be interrupted by the stimulus end. In view of the similarity between the averaged evoked response to visual and vibrotactile stimuli, it is suggested that visual and somatosensory information may be processed according to a common pattern.
Visual Experience or Translation Rules? Drawing the Human Figure by Blind and Sighted Children
Authors: Millar Susanna 
Published: January 2007

Figure drawings by 30 blind and 30 sighted children, tested under blindfold and visual conditions, were compared on positioning and drawing scores. Results showed that the majority of the blind, unlike the sighted made positioning errors, and were unaware of the correct placement rule. The older blind did not differ from the sighted on figure drawing, but the younger blind scored significantly worse. Blindfolded compared to visual conditions produced decrements mainly on cohesion and amount of detail by the sighted. The findings suggest that drawing depends on the acquisition of translation rules for which prior visual experience is a facilitating but not a necessary condition. The absence of visual feedback during drawing seems to have detrimental effects mainly on the articulation of drawing.
Quantitative Studies of Some Dynamic Visual Effects
Authors: Barbur John L 
Published: January 2007

The viewing of rotating or rapidly approaching one-dimensional periodic structures results in the perception of a high-contrast band on a uniform structureless surround. For rotating gratings, the width of the generated band is inversely proportional to the angular speed of rotation and the orientation of the band lags behind the direction perpendicular to the grating lines for both clockwise and anticlockwise rotation of the pattern. The amount of lag is proportional to the angular speed of rotation. The width of the band perceived during the viewing of an approaching or receding grating is inversely proportional to its speed, and the orientation of the generated band is along the direction of the lines in the grating. A model is proposed which explains and predicts the effects observed during the viewing of one-dimensional periodic structures in terms of temporal luminance integration in the visual system. The extent to which temporal luminance integration is responsible for the perception of frame or element movement in multielement stimulus frames is also examined. The results obtained with monocularly or dichoptically presented multielement stimulus frames, as well as other relevant psychophysical and physiological data, suggest that the temporal integration responsible for the observed effects is associated with mechanisms of early-stage visual processing which must be located prior to the lateral geniculate nucleus level.
Amblyopia Cannot Be Explained by considering Only Detection Thresholds
Authors: Hess Robert , Jenkins Steven 
Published: January 2007

Threshold function and suprathreshold performance for nonacuity stimuli are compared for an amblyope who exhibits a low as well as a high spatial frequency threshold abnormality. The results show that (i) a suprathreshold abnormality involving discrimination and localization of easily visible stimuli occurs in amblyopia and (ii) suprathreshold abnormalities occur in amblyopia independent of any threshold dysfunction.
Depth from Dichoptic Edges Depends on Vergence Tuning
Authors: Krol Jodi D , van de Grind Wim A 
Published: January 2007

Small but reproducible fixation disparities occur in normal subjects when they view certain types of dichoptic stimuli. During dichoptic as well as stereoptic stimulation the motor fusion process determines first the average vergence state of the eyes. The subsequent fine tuning of vergence is shown to depend on the spatial distribution of contrast edges both of the same contrast sign (‘stereoptic edges’) and of opposite contrast sign (‘dichoptic edges’). Stereoptic edges tend to induce superposition attempts of the vergence control system and dichoptic edges tend to antagonise this process. If a single low-contrast dichoptic edge is presented with zero disparity and within a stereoptic reference frame, a fixation disparity of several minutes of arc results. This influences depth vision since dichoptic edges are perceived (as monocular edges) at the actual rather than at the intended fixation distance. The findings explain previous paradoxical results of eg Kaufman and Pitblado who reported seeing depth in opposite-contrast stereograms. Their results seemed to contradict the well-established ‘same-sign rule’ (SSR) which states that the stereoptic system only detects disparities of edges with the same contrast sign. It is concluded that (i) the SSR holds; (ii) dichoptic (and monocular) edges are seen at the horopter; (iii) the vergence fine tuning prevents superposition of dichoptic edges even if this causes a fixation disparity.
Static Depth Cues Do Affect the Perceived Direction of Motion
Authors: Mowafy Lyn 
Published: January 2007

Models of motion perception usually assume that the visual system references spatial displacements to retinal coordinates, and not to three-dimensional coordinates recovered by a parallel process. The present studies investigated whether moving elements viewed in the context of a static random-dot stereogram could lead to the appearance of motion in depth. Observers judged the velocity of a monocular element translating horizontally in the stereo context as ‘same as’ or ‘different to’ that of a standard. Based on velocity constancy, if there was apparent motion in depth, the relative velocity judgments would yield a predictable pattern of errors. The first experiment compared two stereo contexts: a sloped surface versus a fronto-parallel plane at zero disparity. The results indicated an overall increase in the perceived velocity of the element moving in the sloped surface context. A similar pattern of results was found when surfaces differing in incline were compared. Experiment 2 explored the case of fronto-parallel planes at crossed and uncrossed disparities. Here depth differences did not systematically affect observers' judgments. It was concluded that in some cases motion analysis can be affected by three-dimensional disparity information and not by angular displacement alone.
The Detectability of Geometric Structure in Rapidly Changing Optical Patterns
Authors: Lappin Joseph S , Norman J Farley , Mowafy Lyn 
Published: January 2007

Human vision is sensitive to the coherent structure and motion of simple dot patterns undergoing rapid random transformations, even when the component dots are widely separated spatially. A study is reported in which visual sensitivity to translations, rotations, expansions, pure shear, and additive combinations of these transformations was investigated. Observers discriminated between coherent (correlated) movements, in which all the component dots moved simultaneously in corresponding directions and distances, and incoherent (uncorrelated) movements, in which the movements of individual dots were statistically independent. In experiment 1 the accuracy of coherence discrimination was found to be similar for all four of the basic transformations and to increase linearly with the distance of the movements. The discriminability of coherent versus incoherent motion was also found to be similar to the detectability of any motion, suggesting that concurrent movements of individual dots are visually interrelated. In experiments 2 and 3 the visual independence of these four groups of transformations was tested by comparing the accuracy of coherence discrimination of each of the transformations presented alone with that when added to background motions produced by each of the four transformations. Coherence discriminations were less accurate when the target transformation was added to another background transformation, indicating that these transformations are not visually independent. Rotations and expansions, however, were visually independent. In experiment 3 qualitatively similar effects for patterns of several different sizes and dot densities were found. In general, an impressive visual sensitivity to globally coherent structure and motion under several different geometric transformations was observed in these experiments. A basic theoretical issue concerns the local visual mechanisms underlying this sensitivity.
The Reversed Müller-Lyer Illusion and Figure—Ground Organization Theory
Authors: Taya Raiten , Ohashi Yasuhiro 
Published: January 2007

When the shaft is shortened and reaches neither of the vertices of the two pairs of wings, a reversed Müller-Lyer illusion is observed: a shaft between inward-pointing wings appears to be longer than a shaft between the outward-pointing wings. In this paper it is examined whether this illusion can be explained in terms of figure—ground organization. A circle was used as the focal area, instead of a shaft or a pair of dots, so that the figure—ground character could be seen more definitely in this focal area. The apparent size of the focal circle was measured under different conditions with three variables (enclosure, wings direction, and depth). The focal circle appeared to be largest in the condition where the circle should appear most readily as a hole, ie in the single, wings-in, space condition. The circle appeared to be smallest in the condition where the circle should appear most readily as a disc, ie in the separate, wings-out, object condition. This is consistent with an explanation of the usual, as well as the reversed, Müller-Lyer illusion in terms of figure—ground organization theory.
Parallelism and the Perception of Illusory Contours
Authors: Albert Marc K 
Published: January 2007

The role of symmetry in the perception of illusory contours has been a subject of controversy ever since Kanizsa proposed his theory of illusory contours based on Gestalt principles. Today it is widely agreed that illusory contours do not necessarily occur more readily with inducers that can be ‘amodally’ completed to symmetrical objects than with inducers that cannot. But the question of whether symmetrical inducers produce weaker illusory contours than do unsymmetrical ones is still controversial. A novel determinant of illusory contour strength, parallelism, is proposed. Experiments are reported which indicate that illusory contours induced by ‘blobs’ which have boundaries that are nearby and parallel to the illusory contour are weaker than illusory contours induced by blobs that do not have this property. It is suggested that the display that has been most widely used by researchers to support their claims for a weakening of illusory contours with symmetrical inducers is weak primarily because of parallelism.
Discrimination of the Shape of the Masked Inducing Figure Precedes Perception of the Illusory Triangle
Authors: Muise J Gerard , LeBlanc Renaud S , Blanchard Louis C , de Warnaffe Alain 
Published: January 2007

Using the Kanizsa triangle in a free-inspection paradigm, Gellatly has shown that subjects report seeing an illusory triangle while apparently not phenomenally aware of the inducing areas. It is argued that Gellatly's procedure may induce response processes which camouflage early sensory processes. By forcing subjects to choose between two response alternatives, it was shown that when they could just perceive the illusory triangle, they could also correctly discriminate the shape of the inducing elements. Under the free-inspection procedure, the duration threshold for seeing the illusory triangle was about 9 ms while the threshold for discriminating the shape of the inducing elements was about 2 ms. A static representation of the dynamic procedure used by Gellatly has been derived, which shows a novel effect of contour completion across boundaries resulting in a ghostly white triangle.
Haptic Discrimination of Doubly Curved Surfaces
Authors: Kappers Astrid M L , Koenderink Jan J , Pas Susan F te 
Published: January 2007

Active haptic discrimination of mathematically well-defined surfaces was investigated. The quadric surfaces were defined in terms of ‘shape index’—a quantity describing shape—and ‘curvedness’—a quantity describing overall curvature. In these experiments shape index was varied and curvedness kept constant. The influence of laterality (unilateral versus bilateral discrimination) was tested in separate sessions. No influence of shape on the discrimination of solid objects was found. From the results an estimate can be made of the just-noticable difference in terms of shape-index units. There was a significant effect of laterality on discrimination: performance with unilateral (successive) examination (both with left and with right hand) was better than with bilateral (simultaneous) examination.
Decay and Interference Effects in Visuospatial Short-Term Memory
Authors: Hole Graham J 
Published: January 2007

The method of constant stimuli was used to examine the accuracy with which two-dimensional spatial information can be represented in mental images. In experiment 1, subjects had to decide which of two successively presented two-dot separations was wider. Over the range of interstimulus intervals employed (0 to 30 s), there was a linear relationship between interstimulus interval and spatial interval thresholds. In experiment 2 subjects' abilities to represent accurately more than one spatial interval at a time was investigated. Three dot pairs were presented, but only two pairs were to be compared, the third being completely irrelevant to the task. This manipulation doubled thresholds (relative to a two-dot-pair control condition), whether or not subjects were obliged to attend to the irrelevant dots. Overall, the results suggest that mental representations of spatial information may be temporally durable, but only in the absence of extraneous stimuli. The latter not only disrupt memory for spatial information, but appear to have obligatory access to it.
The Half-Zöllner Illusion
Authors: Ninio Jacques , O'Regan J Kevin 
Published: January 2007

The Zöllner 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-Zöllner’ configurations were designed, containing stacks of a single polarity. The ‘orientation profile’ of these configurations was studied, that is, the way the strength of the perceived illusion varies with the orientation of the stacks. The subjects had to align two stacks or align stacks with target segments situated at a slight distance from them. All three half-Zöllner configurations produced errors that could be assimilated to global-orientation misjudgments. These errors were of opposite sign for the two types of stacks and varied with the orientation of the stacks as in the standard Zöllner illusion. A further study was conducted in which the effect of several configurational parameters was explored for a single observer. The standard Zöllner illusion increases with the separation of the stacks. The illusion is also increased when the orientations of the segments in different stacks are orthogonal, independently of the particular longitudinal orientations of the stacks. When the ends of the short segments are curved so that at their endpoints they become precisely perpendicular to the axis of the stacks, the standard and half-Zöllner illusions are reduced, but not abolished. Therefore, they cannot be entirely accounted for by a mechanism of alignment of illusory contours generated at these endpoints. The results are consistent with the existence of a single common mechanism at work in both the standard and the half-Zöllner illusion. It is suggested that the illusion itself is not a rotation of the stacks but either a shear deformation in which the segments of a stack slide with respect to one another, or an expansion of the stacks orthogonally to the segments.
Frame-of-Reference and Hierarchical-Organisation Effects in the Rod-and-Frame Illusion
Authors: Zoccolotti Pierluigi , Antonucci Gabriella , Daini Roberta , Martelli Maria Luisa , Spinelli Donatella 
Published: January 2007

Two hypotheses proposed as alternatives by Rock—frame of reference and hierarchical organisation of perception—were tested in a series of experiments with the use of the rod-and-frame illusion. This illusion produces errors in the apparent vertical due to the presence of a tilted frame surrounding the test rod. The apparent vertical is shifted in the direction of the frame tilt. When an upright square was added inside the tilted frame, rod-setting errors varied according to the visual characteristics of the display. In the case of a large display presented in the dark (experiment 1), there continued to be large errors in the direction of the outer-square tilt. This finding supports the frame-of-reference hypothesis, which proposes that the orientation of all objects in the visual field is dominated by the most peripheral reference. In the case of a small display presented in a lit environment (experiments 2 and 3), the direction of errors was the opposite. This latter finding was taken to indicate that the rod was set with reference to the perceived tilt of the inner upright square. Thus, according to a hierarchical-organisation hypothesis, the orientation of an object in the visual field is influenced by objects in the immediate surroundings not by outermost reference. Overall, the results confirm the presence of two qualitatively different classes of orientational phenomena: one is concerned with the definition of egocentric coordinates and one with an object-centred visual representation.
Stimulus Context and View Dependence in Object Recognition
Authors: Newell Fiona N 
Published: January 2007

The effect of stimulus factors such as interobject similarity and stimulus density on the recognition of objects across changes in view was investigated in five experiments. The recognition of objects across views was found to depend on the degree of interobject similarity and on stimulus density: recognition was view dependent when both interobject similarity and stimulus density were high, irrespective of the familiarity of the target object. However, when stimulus density or interobject similarity was low recognition was invariant to viewpoint. It was found that recognition was accomplished through view-dependent procedures when discriminability between objects was low. The findings are discussed in terms of an exemplar-based model in which the dimensions used for discriminating between objects are optimised to maximise the differences between the objects. This optimisation process is characterised as a perceptual ‘ruler’ which measures interobject similarity by stretching across objects in representational space. It is proposed that the ‘ruler’ optimises the feature differences between objects in such a way that recognition is view invariant but that such a process incurs a cost in discriminating between small feature differences, which results in view-dependent recognition performance.
The dominant role of side‐chain backbone interactions in structural realization of amino acid code. ChiRotor: A side‐chain prediction algorithm based on side‐chain backbone interactions
Authors: Spassov Velin Z. , Yan Lisa , Flook Paul K. 
Published: January 2007

AbstractThe basic differences between the 20 natural amino acid residues are due to differences in their side‐chain structures. This characteristic design of protein building blocks implies that side‐chain–side‐chain interactions play an important, even dominant role in 3D‐structural realization of amino acid codes. Here we present the results of a comparative analysis of the contributions of side‐chain–side‐chain (s‐s) and side‐chain–backbone (s‐b) interactions to the stabilization of folded protein structures within the framework of the CHARMm molecular data model. Contrary to intuition, our results suggest that side‐chain–backbone interactions play the major role in side‐chain packing, in stabilizing the folded structures, and in differentiating the folded structures from the unfolded or misfolded structures, while the interactions between side chains have a secondary effect. An additional analysis of electrostatic energies suggests that combinatorial dominance of the interactions between opposite charges makes the electrostatic interactions act as an unspecific folding force that stabilizes not only native structure, but also compact random conformations. This observation is in agreement with experimental findings that, in the denatured state, the charge–charge interactions stabilize more compact conformations. Taking advantage of the dominant role of side‐chain–backbone interactions in side‐chain packing to reduce the combinatorial problem, we developed a new algorithm, ChiRotor, for rapid prediction of side‐chain conformations. We present the results of a validation study of the method based on a set of high resolution X‐ray structures.