Role of Brightness Contrast and Brightness Contrast-Reversal in Illusory Contour Formation

1981 ◽  
Vol 52 (2) ◽  
pp. 415-424 ◽  
Author(s):  
Willard L. Brigner ◽  
Joseph T. Hammond
Keyword(s):  
Pupil Size ◽  
Illusory Contour ◽  
Brightness Contrast ◽  
Artificial Pupil

The effects of artificial pupil size and the effects of a power lens upon the relative prominence of illusory contour were evaluated. The perception of illusory contour was facilitated by conditions associated with increased retinal blur and brightness averaging. This was true whether the blur and averaging were achieved using a large artificial pupil or a power lens. The effects of power lens and the effects of artificial pupil size upon the occurrence of brightness contrast and brightness contrast-reversal (or assimilation) were also investigated. Brightness contrast was changed to brightness contrast-reversal by using either a power lens or a large artificial pupil. The occurrence of vivid illusory contour under conditions found conducive to brightness contrast-reversal was interpreted as evidence that contrast-reversal was more crucial in illusory contour formation than brightness contrast.

Parallelism and the Perception of Illusory Contours

Perception ◽  
1993 ◽  
Vol 22 (5) ◽  
pp. 589-595 ◽  
Author(s):  
Marc K Albert
Keyword(s):  
Illusory Contour ◽  
Illusory Contours ◽  
Gestalt Principles ◽  
Contour Strength

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.

Cue-dependent deficits in grating orientation discrimination after V4 lesions in macaques

1996 ◽  
Vol 13 (3) ◽  
pp. 529-538 ◽  
Author(s):  
Peter De Weerd ◽  
Robert Desimone ◽  
Leslie G. Ungerleider
Keyword(s):  
Visual Field ◽  
Normal Control ◽  
Illusory Contour ◽  
Visual Area ◽  
Orientation Discrimination ◽  
Fixation Target ◽  
Illusory Contours ◽  
Pattern Vision ◽  
Area V4

AbstractTo 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 texture, as well as phase-shifted abutting gratings that created an “illusory” contour. The monkeys were trained to maintain fixation on a fixation target while discriminating extrafoveal stimuli, which were located in either a normal control quadrant of the visual field or in a quadrant affected by a lesion of area V4 in one hemisphere. Comparing performance in the two quadrants, we found significant deficits for contours defined by texture and for the illusory contour, but smaller or no deficits for motion-, color-, and luminance-defined contours. The data suggest a specific role of V4 in the perception of illusory contours and contours defined by texture.

scholarly journals Photoreceptor inputs to pupil control

2019 ◽  
Author(s):  
Manuel Spitschan
Keyword(s):  
Retinal Ganglion Cells ◽  
Pupil Size ◽  
Ganglion Cells ◽  
Light Level ◽  
Retinal Ganglion ◽  
Pupil Control ◽  
Data Set

AbstractThe size of the pupil depends on light level. Watson & Yellott (2012) developed a unified formula to predict pupil size from luminance, field diameter, age, and number of eyes. Luminance reflects input from the L and M cones in the retina but ignores the contribution of intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin, which are known to control the size of the pupil. We discuss the role of melanopsin in controlling pupil size by reanalysing an extant data set. We confirm that melanopsin-weighted quantities, in conjunction with Watson & Yellott’s formula, adequately model intensity-dependent pupil size. We discuss the contributions of other photoreceptors into pupil control.

Effect of the Reference Imidazoline Drugs, Clonidine and Rilmenidine, on Rat Eye Pupil Size Confirms the Decisive Role of α2-Adrenoceptors on Mydriasis

2014 ◽  
Vol 10 (8) ◽  
pp. 470-478 ◽  
Author(s):  
Joanna Raczak-Gut ◽  
Teresa Frackowiak ◽  
Antoni Nasal ◽  
Joanna Rietz ◽  
Maja Paszek ◽  
...  
Keyword(s):  
Pupil Size ◽  
Decisive Role ◽  
Α2 Adrenoceptors

The Determinants of Illusory-Contour Perception

Perception ◽  
1981 ◽  
Vol 10 (2) ◽  
pp. 199-213 ◽  
Author(s):  
Diane F Halpern
Keyword(s):  
Illusory Contour ◽  
Experimental Results ◽  
Brightness Contrast ◽  
Apparent Depth ◽  
Primary Role ◽  
Illusory Contours ◽  
Contour Perception

The term ‘illusory contours' refers to contours perceived where none physically exist. Three hypotheses that have been successful in their ability to account for this phenomenon invoke: (i) apparent depth; (ii) brightness contrast; and (iii) use of figural cues. An experiment has been designed to determine the extent to which each hypothesis accounts for the overall variation in subjects' responses to illusory contours when all three hypotheses are considered simultaneously. Experimental results suggest that different processes may assume a primary role in the perception of illusory contours depending upon the type of inducing area and the configuration. The results highlight the multifaceted nature of the processes involved, and indicate that no single theory can explain the perception of illusory contours.

The role of edges and line-ends in illusory contour formation

1993 ◽  
Vol 33 (16) ◽  
pp. 2253-2270 ◽  
Author(s):  
Gregory W. Lesher ◽  
Ennio Mingolla
Keyword(s):  
Illusory Contour

Influence of Accommodation on the Viewing of an Optical Illusion

1968 ◽  
Vol 20 (4) ◽  
pp. 329-335 ◽  
Author(s):  
Michel Millodot
Keyword(s):  
Exposure Time ◽  
Visual Angle ◽  
Pupil Size ◽  
Optical Illusion ◽  
Concentric Ring

This study demonstrates the role of microfluctuations of accommodation in the viewing of the concentric ring illusion. Four experiments were carried out. Experiment I consisted of changing the distance between the illusion and the eyes but retaining visual angle, luminance and pupil size constant. In Experiment II, the accommodation of the eyes is paralysed by a cycloplegic. In Experiment III, the illusion is shown to a monocular aphakic and in Experiment IV, the exposure time is varied between 1/100 and 5 sec. Furthermore, a series of observations compared the concentric ring illusion seen with both eyes simultaneously. The evidence provided by the results of these experiments plus others discussed provide evidence that the concentric ring illusion is caused by the microfluctuations of accommodation.

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