Apparent Motion of Subjective Surfaces

Perception ◽  
1985 ◽  
Vol 14 (2) ◽  
pp. 127-134 ◽  
Author(s):  
Vilayanur S Ramachandran
Keyword(s):  
Visual Field ◽  
Motion Capture ◽  
Apparent Motion ◽  
Regular Matrix ◽  
Illusory Contours ◽  
Salient Features ◽  
Subjective Surfaces

Apparent motion of an illusory surface was produced by presenting two spatially separated illusory squares in an appropriately timed sequence. Control experiments showed that the effect arose from the illusory contours themselves and not from motion of the cut sectors on the discs. When a template of this movie was superimposed on ‘wallpaper’ composed of a regular matrix of spots, the spots appeared to move with the illusory surface even though they were physically stationary. This effect (‘motion capture’) suggests that the motion of certain salient features in the visual field gets spontaneously attributed to even static elements in the vicinity.

Illusory Contours Do Not Pass through the “Blind Spot”

2007 ◽  
Vol 19 (1) ◽  
pp. 91-101 ◽  
Author(s):  
Marianne Maertens ◽  
Stefan Pollmann
Keyword(s):  
Visual Field ◽  
Blind Spot ◽  
Natural Scenes ◽  
Illusory Contours ◽  
Response Latencies ◽  
Neural Processes ◽  
Specific Performance ◽  
Neural Substrate ◽  
Pass Through ◽  
Kanizsa Figure

Our visual percepts are not fully determined by the physical stimulus input. That is why we perceive crisp bounding contours even in the absence of luminance-defined borders in visual illusions such as the Kanizsa figure. It is important to understand which neural processes are involved in creating these artificial visual experiences because this might tell us how we perceive coherent objects in natural scenes, which are characterized by mutual overlap. We have already shown using functional magnetic resonance imaging [Maertens, M., & Pollmann, S. fMRI reveals a common neural substrate of illusory and real contours in v1 after perceptual learning. Journal of Cognitive Neuroscience, 17, 1553–1564, 2005] that neurons in the primary visual cortex (V1) respond to these stimuli. Here we provide support for the hypothesis that V1 is obligatory for the discrimination of the curvature of illusory contours. We presented illusory contours across the portion of the visual field corresponding to the physiological “blind spot.” Four observers were extensively trained and asked to discriminate fine curvature differences in these illusory contours. A distinct performance drop (increased errors and response latencies) was observed when illusory contours traversed the blind spot compared to when they were presented in the “normal” contralateral visual field at the same eccentricity. We attribute this specific performance deficit to the failure to build up a representation of the illusory contour in the absence of a cortical representation of the “blind spot” within V1. The current results substantiate the assumption that neural activity in area V1 is closely related to our phenomenal experience of illusory contours in particular, and to the construction of our subjective percepts in general.

Peripheral Apparent Motion as a Function of Location, Contrast, and Direction of Stimulus Motion

1989 ◽  
Vol 68 (1) ◽  
pp. 33-34 ◽  
Author(s):  
Woodrow Barfield ◽  
Conrad Kraft ◽  
Ali Piyarali
Keyword(s):  
Visual Field ◽  
Apparent Motion ◽  
Stimulus Location ◽  
Peripheral Visual Field ◽  
Stimulus Contrast ◽  
Stimulus Motion ◽  
Independent Variables ◽  
Main Effect

This study investigated the perception of the direction of peripheral apparent motion as a function of stimulus location in the peripheral visual field, stimulus contrast, and the direction of the apparent motion. Results indicated that each of these independent variables was significant as a main effect while the interactions were not.

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.

Measurements of the Relative Tilt of Corresponding Vertical and Horizontal Meridians in the Two Eyes as a Function of Elevation and Eccentricity in the Visual Field

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 226-226 ◽  
Author(s):  
T Ledgeway ◽  
B J Rogers
Keyword(s):  
Visual Field ◽  
Apparent Motion ◽  
Similar Amount ◽  
Optical Instrument ◽  
Orientation Change ◽  
Orientation Difference ◽  
Apparent Orientation

Helmholtz first reported that when the horizontal meridians of the two eyes are aligned, the vertical meridians of the two eyes are tilted outwards (with respect to each other) by approximately 2°. We adapted Nakayama's technique (1977 Proceedings of the Society of Photo-Optical Instrument Engineers120 2 – 9) using the minimal apparent motion of alternating dichoptic images to measure the relative tilt of corresponding vertical and horizontal meridians located up to 20 deg away from the fovea. Observers were presented with the alternating dichoptic images of a pair of dots or a pair of extended lines which had a relative tilt (binocular orientation difference) of between −5° and +5°. The images were alternated at a rate of 0.2 Hz. Observers were asked to select the pair of images which produced the smallest amount of apparent orientation change. The vergence angle of the binocularly visible fixation point was varied between 28 cm and infinity. On the assumption that minimal apparent motion is a valid indicator of binocular correspondence, the corresponding vertical meridians of the two eyes remained offset by around 2 deg even when they were located 20 deg eccentrically. The corresponding horizontal meridians remained approximately aligned even when they were elevated by up to 20 deg. Corresponding horizontal meridians were altered when the vergence angle was changed but corresponding vertical meridians were unaffected for most individuals. With the eyes held in an elevated position, both vertical and horizontal meridians were altered by a similar amount when the vergence angle was altered, indicating a change in cyclovergence.

Perception of Subjective Contours in Fish

Perception ◽  
10.1068/p6121 ◽  
2009 ◽  
Vol 38 (4) ◽  
pp. 579-590 ◽  
Author(s):  
Valeria Anna Sovrano ◽  
Angelo Bisazza
Keyword(s):  
Phase Shift ◽  
Luminance Contrast ◽  
Phase Shifting ◽  
Orientation Discrimination ◽  
Illusory Contours ◽  
Geometric Figure ◽  
Spatial Phase ◽  
Spatial Phase Shift ◽  
Subjective Surfaces

The ability of fish to perceive subjective (or illusory) contours, ie contours that lack a physical counterpart in terms of luminance contrast gradients, was investigated. In the first experiment, redtail splitfins ( Xenotoca eiseni), family Goodeidae, were trained to discriminate between a geometric figure (a triangle or a square) on various backgrounds and a background without any figure. Thereafter, the fish performed test trials in which illusory squares or triangles were obtained by (i) interruptions of a background of diagonal lines, (ii) phase-shifting of a background of diagonal lines, and (iii) pacmen spatially arranged to induce perception of Kanizsa subjective surfaces. In all three conditions, fish seemed to generalise their responses to stimuli perceived as subjective contours by humans. Fish chose, correctly, squares or triangles made of interrupted or phase-shifted diagonal lines from uniform backgrounds of diagonal lines, as well as illusory square or triangle Kanizsa figures from figures in which the inducing pacmen were scrambled. In the second experiment, fish were trained to discriminate between a vertical and a horizontal bar with luminance contrast gradients, and then tested with vertically and horizontally oriented illusory bars, created either through interruption or spatial phase-shift of inducing diagonal lines. Fish appeared to be able to generalise the orientation discrimination to illusory contours. These results demonstrate that redtail splitfins are capable of perceiving illusory contours.

Asymmetry of the human visual field in magnetic response to apparent motion

2000 ◽  
Vol 865 (2) ◽  
pp. 221-226 ◽  
Author(s):  
Tomoyuki Naito ◽  
Yoshiki Kaneoke ◽  
Naoyuki Osaka ◽  
Ryusuke Kakigi
Keyword(s):  
Visual Field ◽  
Apparent Motion ◽  
Magnetic Response

Stereoscopic Illusory Contours—Cortical Neuron Responses and Human Perception

2002 ◽  
Vol 14 (7) ◽  
pp. 1018-1029 ◽  
Author(s):  
Barbara Heider ◽  
Lothar Spillmann ◽  
Esther Peterhans
Keyword(s):  
Visual Cortex ◽  
Visual Field ◽  
Cortical Neuron ◽  
Illusory Contour ◽  
Human Perception ◽  
Illusory Contours ◽  
Stimulus Parameters ◽  
The Mean ◽  
Monkey Visual Cortex

In human perception, figure-ground segregation suggests that stereoscopic cues are grouped over wide areas of the visual field. For example, two abutting rectangles of equal luminance and size are seen as a uniform surface when presented at the same depth, but appear as two surfaces separated by an illusory contour and a step in depth when presented with different retinal disparities. Here, we describe neurons in the monkey visual cortex that signal such illusory contours and can be selective for certain figure-ground directions that human observers perceive at these contours. The results suggest that these neurons group stereoscopic cues over distances up to 8°. In addition, we compare these results with human perception and show that the mean stimulus parameters required by these neurons also induce optimal percepts of illusory contours in human observers.

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