Depth Perception and Perceptional Illusions

Depth Perception The use of visual cues to perceive the distance or three-dimensional characteristics of objects. Two cues are monocular cues and binocular cues.

Monocular Cues Monocular cues are distance or depth cues that can be processed by either eye alone. The six main Monocular cues are Relative Size, Overlap, Aerial Perspective, Texture Gradient, Linear Perspective, and Motion Parallax. Accommodation-Monocular cue that utilizes information about changes in the shape of the lens of the eye to help us estimate distance. Pictorial Cues-When monocular cues are used by artists to create the perception of distance or depth in paintings.

Relative Size If two or more objects are assumed to be similar in size, the object that appears larger is perceived as being closer.

Overlap When one object partially blocks or obscures the view of another object, the partially blocked object is perceived as being farther away.

Aerial Perspective Faraway objects often appear hazy or slightly blurred by the atmosphere.

Texture Gradient As a surface with a distinct texture extends into the distance, the details of the surface texture gradually become less clearly defined.

Linear Perspective Parallel lines seem to meet in the distance.

Motion Parallax When you are moving, you use the speed of passing objects to estimate the distance of the objects.

Binocular Cues Binocular cues are distance or depth cues that require the use of both eyes. Convergence-The degree to which muscles rotate your eyes to focus on an object.

Binocular Disparity Because our eyes are set a couple of inches apart, a slightly different image of an object is cast on the retina of each eye. When the two retinal images are different, we interpret the object as being close by. When the two retinal images are more nearly identical, the object is perceived as being more far away. Stereogram-A picture that uses Binocular Disparity to create the perception of a three-dimensional image.

Perception of Motion As we follow a moving object wit hour gaze, the image of the object moves across the retina. Our eye muscles make micro-fine movements to keep the object in focus. Our perception of the speed of the object’s approach is based on our perception of the object’s rate of enlargement. Induced Motion-A strong tendency to assume that the background is stationary.

Perceptional Constancies Perceptional constancy is the tendency to perceive objects, especially familiar objects, as constant and unchanging despite changes in sensory input. Size Constancy-The perception of an object as maintaining the same size despite changing images on the retina. Shape Constancy-The perception of a familiar object as maintaining the same shape regardless of the image produced on the retina.

Perceptional Illusions A perceptional illusion is the misperception of the true characteristics of an object or an image. MÜLLER-LYER Illusion-A famous visual illusion involving the misperception of the identical length of two lines, one with arrows pointed inward, one with arrows pointed outward. Moon Illusion-a visual illusion involving the misperception that the moon is larger when it is on the horizon than when it is directly overhead.

Perceptional Sets Perceptual Sets are the influence of prior assumptions and expectations on perceptual interpretations. Influenced by are prior learning experiences. Can exert a strong influence on the perceptional conclusions we reach.