Perceptual Organization Unit 3 – RG 4e Modified PowerPoint from: Aneeq Ahmad -- Henderson State University. Worth Publishers © 2007

Perceptual Illusions To understand how perception is organized, illusions provide good examples. It is as good to study faulty perception as other perceptual phenomena. Line AB is longer than line BC.

Tall Arch Vertical dimension of the arch looks longer than the horizontal dimension when both are equal. Rick Friedman/ Black Star

Perceptual Organization When vision competes with other senses vision usually wins – a phenomenon called visual capture. How do we form meaningful perceptions from sensory information? We organize it! Gestalt psychology helps us organize information into meaningful wholes… but remember…the “whole is different from the sum of it’s parts”

Figure-Ground Organization of the visual field into objects (figures) that stand out from their surroundings (ground). Time Savings Suggestion, © 2003 Roger Sheperd.

Gestalt Grouping Having discriminated figure from ground our perception needs to organize figure into meaningful form using grouping rules.

Grouping & Reality Usually grouping principles help us construct reality but at times lead us astray.

Depth Perception Depth perception enables us to judge distances. Gibson and Walk (1960) suggested that human infants (crawling age) have depth perception. Even new born animals show depth perception. Visual Cliff

Monocular Cues Interposition: Objects that occlude (block) other objects tend to be perceived as closer. Rene Magritte, The Blank Signature, oil on canvas, National Gallery of Art, Washington. Collection of Mr. and Mrs. Paul Mellon. Photo by Richard Carafelli.

Monocular Cues Linear Perspective: Parallel lines like rail road tracks, appear to converge with distance. The more the lines converge, the greater their perceived distance.

Monocular Cues Relative Size: If two objects are similar in size, we perceive one that casts a smaller retinal image as farther away.

Monocular Cues Relative Height: We perceive objects higher in our field of vision as farther away.

Monocular Cues Texture Gradient: Indistinct (fine) texture signals increasing distance.

Binocular Cues Convergence: When two eyes move inward (towards the nose) to see near objects, and outward (away from the nose) to see far away objects…object is perceived as closer the more eyes turn inward

Binocular Cues Retinal disparity: Images from the two eyes differ…the greater the difference between the two objects, the closer the object Try looking at your two fingers half an inch apart about 5 inches away. You will see a “finger sausage” as shown in the inset.

Perception of Movement Stroboscopic motion: our tendency to perceive motion in a series of slightly varied still images flashed in rapid succession

Perception of Movement Phi Phenomenon: When lights flash at certain speed they tend to present illusions of motion. Neon signs use this principle to create motion perception. One light jumping from one point to another: Illusion of motion. Two lights flashing one after the other.

Perceptual Constancy Perceiving objects as unchanging even as illumination and retinal image change. Perceptual constancies include constancies of shape and size. Shape Constancy

Stable size perception amid changing size of the stimuli. Size Constancy Stable size perception amid changing size of the stimuli.

Size-Distance Relationship Moon Illusion What makes this happen? Cues to the objects’ distances at the horizon make the Moon behind them seem farther away than the moon in the night’s sky.

Size-Distance Relationship The distant monster and the top red bar appear bigger because of distance cues. Ponzo Illusion Alan Choisnet/ The Image Bank From Shepard, 1990

Visual Illusions… Straight lines or bowed? Stationary or moving?

How many people/faces do you see? Visual Illusions… How many people/faces do you see? A spiral right?

Visual Illusions… Which line matches with C? It’s actually B… Poggendorf Illusion Old woman or young woman?

These are on drawn on flat surfaces (sidewalks)! Visual Illusions… These are on drawn on flat surfaces (sidewalks)!

Visual Illusions… Julian Beever has made pavement drawings for over ten years. He has worked in the U.K., Belgium, France, The Netherlands, Germany, the USA and Australia.

Visual Illusions…