Contour Interaction Research Articles

A preliminary report of acuity and contour interactions across the amblyope's visual field

Acuity and contour interactions were assessed across the visual field of representative strabismic amblyopes. Acuity profiles display large variations between amblyopes who exhibit the same degree of eccentric fixation; however, in no case was foveal acuity significantly better than that found eccentrically. The acuity abnormality for most amblyopes is visual field locus dependent. Contour interactions are abnormal in both form and magnitude for some amblyopes. This abnormality does not depend upon the acuity deficit, is field locus dependent and cannot be easily accounted for by optical, oculomotor or eccentric fixation factors.

Visual resolution and contour interaction in the fovea and periphery

The experiments provide quantitative data on the nature of contour interaction at the fovea and in the periphery to 10° eccentricity for observers with normal vision. Results with Landolt ring targets similar to those used by Flom et al. (J. opt. Soc. Am. 53, 1026–1032) show that contour interaction effects are greater in peripheral vision. In central vision the increase in minimum angle of resolution (MAR) that occurred with the introduction of bars around the Landolt ring is small and much less than the experimental variation, whereas in peripheral vision bars at any of the ring-bar separations tested produced a consistent increase in MAR. Relationships between MAR and eccentricity are presented and compared with those in the literature. Reasons for the variation between previous studies are suggested.

Ebbinghaus illusions: size contrast or contour interaction phenomena?

Forty-eight graduate and undergraduate students between 17 and 30 years of age judged the size of the central circle in Ebbinghaus figures presented under either simultaneous or successive viewing conditions. Successive presentation eliminated the illusion produced by the normally overestimated figure and diminished that produced by the underestimated figure. Under simultaneous viewing conditions, increasing the number of surrounding circles reduced the magnitude of the reversed illusion produced by the normally overestimated figure but had no effect on the illusion produced by the underestimated figure. Under successive viewing conditions, increasing the number of surrounding circles had no effect on the magnitude of illusion produced by the normally overestimated figure but increased the illusion produced by the underestimated figure. These data were interpreted as inconsistent with a size contrast explanation of the Ebbinghaus illusions and suggested that these illusions may be produced by a contour interaction process.

Spatial distortions within the Poggendorff fig are and its variants: A parametric analysis

Angle size and horizontal separation of the Poggendorff figure and three components (acute angles, obtuse angles, and obliques) were varied parametrically. Two adult trained observers judged the distance between the obliques of the test figure relative to a pair of comparison dots during 250-msec tachistoscopic presentations. Results indicated: (1) the Poggendorff effect is created by an underestimation of intercontour distance, resulting in apparent misalignment; (2) only the obtuse angles can serve as a significant predictor of the classical illusion; (3) the parallel lines play an important contributory role in the Poggendorff illusion when they are present. Findings tended to support a theoretical explanation based on contour interactions.

Effect of contrast level and temporal order on the Ebbinghaus circles illusion

Forty-eight undergraduates between 17 and 24 years of age judged the size of the central circle in Ebbinghaus figures presented under either simultaneous or successive viewing conditions. Successive presentation diminished the magnitude of illusion produced by the underestimated Ebbinghaus figure and totally eliminated the illusion normally produced by the overestimated figure. Variations in lightness contrast of the central and surrounding circles significantly altered the magnitude of illusion produced by both simultaneous Ebbinghaus figures as well as that produced by the successive underestimated figure. These data suggest the presence of a contour interaction process in both simultaneous Ebbinghaus illusions.

Contour interaction and temporal masking in strabismus and amblyopia.

Visual acuity of amlyopic eyes, measured under binocular viewing conditions, was improved by reducing the contrast of targets presented to the normal eye. Improvement was also obtained by adjusting the temporal relationship between inputs to the normal and amblyopic eye. Optimal acuity was obtained by alternately presenting targets to the two eyes at rates centered about 2 and 7 Hz. These results are interpreted in terms of binocular contour interaction and metacontrast suppression. They suggest that a portion of the amblyope's acuity loss during binocular viewing conditions results from excessive masking by the dominant normal eye.

The interaction of thickness contours and dislocations under dynamical diffraction conditions

physica status solidi (a)Volume 33, Issue 2 p. K121-K123 Short Note The interaction of thickness contours and dislocations under dynamical diffraction conditions F. W. Schapink, F. W. Schapink Laboratorium voor Metaalkunde, Technische Hogeschool, DelftSearch for more papers by this author F. W. Schapink, F. W. Schapink Laboratorium voor Metaalkunde, Technische Hogeschool, DelftSearch for more papers by this author First published: 16 February 1976 https://doi.org/10.1002/pssa.2210330252AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume33, Issue216 February 1976Pages K121-K123 RelatedInformation

Inhibition in simultaneous and successive contour interaction in human vision

Inhibition in simultaneous and successive contour interaction in human vision

Orientation effects on contour interaction in the Zöllner illusion

The magnitude of the Zollner illusion was measured as a joint function of the angle of intersection between inducing and test contours and the orientation of the complete display. The intersect angle at which judgmental error was maximal varied as the display was rotated from 0 to 90 deg. An explanation of the Zollner illusion in terms of selective adaptation of neural orientation specific detectors accounts for the interactive effects of display orientation and intersect angle if it is assumed that different orientation detectors have different tuning characteristics.

Analysis of the interaction of thickness extinction contours and dislocations in weak-beam electron microscopy

Bending of thickness extinction contours close to a dislocation in weak-beam images is analysed using a simplified model for the diffraction. In this model the depth-dependent orientation of the crystal within a particular column is replaced by an average effective orientation. For a screw dislocation parallel to the foil surface the experimentally observed contour profiles can be satisfactorily explained; the slope of the contour lines near the dislocation core is a function of both foil thickness and the dislocation depth in the foil. It is shown that surface relaxation of the dislocation stress field changes the slope of contours near the dislocation core by a factor of 1.5 to 2, depending on the dislocation position in the foil. For an edge dislocation with Burgers vector parallel to the foil surface analogous results are found. On the other hand, the interaction between dislocation and thickness contours is negligible for an edge dislocation with Burgers vector perpendicular to the foil surface. Die Wechselwirkung zwischen Versetzungen und Dickenkonturen wird unter Annahme eines stark vereinfachten Beugungsmodells berechnet, indem die tiefenabhängige Orientierung des Kristalls durch eine mittlere effektive Orientierung ersetzt wird. Für eine Schraubenversetzung parallel zur Folienebene ergibt sich eine befriedigende Übereinstimmung zwischen berechneten und gemessenen Konturen. Die Neigung der Dickenkonturen in der Nähe einer Versetzung ist abhängig von der Foliendicke und dem Versetzungsort in der Folie, und wird um einen Faktor 1,5 bis 2 durch Relaxation des Spannungsfeldes geändert. Åhnliche Ergebnisse werden für eine Stufenversetzung mit Burgers-Vektor parallel zur Folienebene gefunden, während die Wechselwirkung mit einer Stufenversetzung mit Burgers-Vektor senkrecht zur Folienebene vernachlässigbar ist.

Maskability of visual targets varying in brightness contrast

Duration thresholds of visual targets varying in brightness contrast were measured under backward masking and nonmasking conditions. As expected, thresholds varied as a function of target contrast in the nonmasking condition; thresholds were elevated for all targets in the masking condition. These results bear on the interpretation of a previously reported finding that targets with increasing numbers of internal contours were both increasingly hard to detect and hard to mask. The attribution of that finding to mechanisms underlying contour interaction continues to be worthy of consideration: in particular, the previous results do not reflect a general relation between target detectability and target maskability.

Attraction of parallels as a function of intercontour distance.

Pollack (1964) found attraction of simultaneously presented parallel lines under fixation. Using the Delboeuf figure, Ogasawara ( 1952) found that attraction of concentric circles increased, then decreased as separation between the contours increased. Widening the space between the parallels of the Poggendorf figure results in an increased illusory effect (e.g., Hill, 1971), suggesting that attraction increases as separation increases. The distance between a pair of parallel lines was varied from 3 to 15 rnm. in 2-mm. steps. Lines were located to one side of a central fixation dot, with comparison dots, whose spacing varied about that of the corresponding test lines, equidistant on the opposite side. Control stimuli merely substituted dots for tesc lines. No stimulus exceeded a total visual angle of 3. Stimuli were presented tachistoscopically for 250 msec. to two trained adult Ss, who judged the spacing of the dots relative to that of the lines. A modified method of constant stimuli was used, converting attraction magnitudes into percentages by subtracting control PSEs from tesc PSEs over 16 trials. For both Ss, attraction was small (0 to 4%) for 3- to 9-mm. separations, but a sharp increase occurred at 11 mrn. ( 13% co 14% ). For S1, attraction with wider separations increased and leveled off, while the effect declined and leveled off for S2. Results are considered consistent with Ogasawara's findings. (With wider separations, the effect would be expected to decrease for S1.) The occurrence of attraction under the present restricted viewing conditions suggests that it is a basic contour interaction process. Implications for explanation of the Poggendorf illusion are currently under investigation.

Facilitation of foveal letter recognition by metacontrast

Foveal letter recognition is improved in the presence of a flanking letter context. Signal detection analysis is used to examine sensitivity changes attributable to specific contour interactions between target and context letters.

Contour interactions in visual masking.

Contour interactions in visual masking.

Spatial determinants of visual masking: Effects of mask size and retinal position

Visual masking was studied in three observers by measuring the threshold for detection of a small black disc (test target) with and without prior exposure to a concentric larger black disc (masking target). Independent variables were size of mask and retinal position. Results showed that: (1) for all retinal positions, decreasing the size of the masking target produced a greater masking effect; (2) for each size of mask, there was a greater masking effect in the periphery than in the fovea; (3) in the fovea, the largest mask produced a lowered threshold for test target detection, suggesting summation or facilitation. These results were discussed in terms of contour interaction and signal-to-noise ratio.

EFFECTS OF PROLONGED STIMULATION BY COMPONENTS OF THE MUELLER-LYER FIGURE UPON THE MAGNITUDE OF ILLUSION.

Based upon data concerning contour orientation and interaction and the stimulus variables affecting the Mueller-Lyer illusion, an explanation for the illusion was advanced. Predictions made for the effects of prolonged fixation of each of the component figures were experimentally confirmed. The theoretical rationale proposed was discussed in terms of possible difficulties which require further empirical investigation.

CONTOUR INTERACTION AND VISUAL RESOLUTION: CONTRALATERAL EFFECTS.

Detection of the gap in a four-position Landolt C presented to one eye is impaired by critically spaced surrounding bars seen only by the other eye. The intensity and spatial extent of this contralateral contour interaction match those obtained ipsilaterally. These results indicate that the neural site for this loss of visual information is supraretinal.

VISUAL RESOLUTION AND CONTOUR INTERACTION.

Detecting the position of the gap in a Landolt C is adversely affected by black bars placed tangential to the C and at a certain distance from it. The maximum bar separation affording interaction is proportional to the minimum angle of resolution, even in cases of amblyopia where resolution is presumably not limited by optical spread of the image. It is suggested that this contour interaction is related to the size of the receptive field (and hence to the resolving capacity) associated with the retinal region used to fixate the target.