Perception

"Colors, tones, smells, and tastes are mental constructions created by the brain out of sensory experience. They do not exist, as such, outside of the brain. " (Martin, 1991).

Perception is an active, constructive process*

Al Seckel

Does perception exist outside of awareness?

Subliminality

Selective Attention Focus of conscious awareness on a particular stimulus. Cocktail Party Phenomenon

Change and Inattentional Blindness

djs_lab demos

Viewable/Downloadable Examples

Perceptual Organization

• Gestalt Psychology Late 19th/early 20th field that emphasized the human tendency to organize pieces of information into meaningful patterns or wholes (Max Wertheimer, W. Kohler, F. Koffka)

• The brain’s tendency to organize sensory stimuli in order to construct reality helps to explain our susceptibility to illusions

Gestalt Grouping Principles The perceptual tendency to organize stimuli into

coherent groups (Law of Pragnanz or good order). We tend to order experience in a manner that is regular, orderly, symmetric, and most simple

proximity--group nearby figures together similarity--group figures that are similar familiarity—familiar or meaningful pattern continuity--perceive continuous patterns closure--fill in gaps connectedness--spots, lines, and areas are

seen as unit when connected common fate--when objects move in the

same direction, we see them as a unit Gestalt

Illusory and Subjective Contours-Creating images where they do

not exist

Kanizsa’s Illusory Triangle

Perceptual Organization

• Among our most basic perceptual tasks is a type of selective attention where we distinguish objects as separate from their surroundings, a concept known as. . .

Infamous Rubin

Which picture predominates for you, the younger or older woman?

Reversible figures• Like with figure ground images in the following

illustrations the relationship between the objects continually reverses.

• Perceptual hypothesis Contends that we bridge the gap between what’s real and what we see by constantly making and testing hypotheses

The Necker cube

http://dogfeathers.com/java/necker.html

Binocular cues

• Retinal disparity and stereopisis The brain perceives distance and depth by comparing the different images received by each eye

• Convergence Eyes come together as objects are nearer

Stereograms (like 3-D movies) exaggerate retinal disparity by placing two slightly separated images apart. The brain

actively reconstructs the images into a 3-D illusion

Monocular cues

• Interposition/Superposition• Relative clarity/aerial

perspective• Texture gradient• Relative height• Relative size• Light and shadow• Linear perspective• Motion parallax

Paris Street: A Rainy Day Gustave Caillebotte

Pavement Drawings

Julian Beever

Illusions you should know (and their possible explanations)

• Figure-ground• Reversible figures (Necker cube)• Illusory contours (Kanizsa triangle)• Size-distance illusions (Ames Room, Muller-Lyer &

Ponzo illusion)• Impossible figures (role of perceptual set/schema)

• Think gestalt…Top down processing (perceptual hypothesis)

Size-Distance Illusions

• In each of these examples, the top and bottom lines are actually the same length.

• In each case the top line looks longer. Because?

• Mueller-Lyer Illusion

(a) Müller-Lyer illusion

Ames Room

• Monocular depth cues give the illusion that the two people are equally far away Ames

The Ponzo Illusion

What misassumptions cause this illusion?

The monocular cues of linear perspective and relative size are responsible for this illusion. How?

Shepard's Terror Subterra

More Perception Terms

• Real vs. apparent movement– Autokinetic effect/illusion – Stroboscopic motion – Phi Phenomenon PHI Phenomenon Activity

– Induced movement (stationary-moon)– Moving Aftereffect (MAE) –spiral aftereffect/waterfall

illusion Motion Aftereffect– Motion induced blindness (VSR) MIB

• YTMIB

Motion Illusions

Freezing Rotation Illusion

Motion Induced Blindness

“Stepping feet” Motion Illusion

Stereokinetic Phenomenon

Motion-Bounce Illusion

Perceptual Constancy

Perceiving objects as unchanging even as illumination and retinal image change

color shape size

Contrast and Color Illusions

• Grid Illusions: Hering• Wertheimer-Koffka-Ring• Munker-White Illusion• Adelson -- Checker-shadow illusion• Lilac Chaser

• Cool Escher-inspired movie An “impossible” Movie

• Beau Lotto

The Stroop Effect

• Stroop found that the act of reading could interfere with your ability to perform simple perceptual distinctions like naming colors

• Stroop Lab Introduction

Other Misleading Cues and Line Illusions

• Hering Illusion• Café Wall Illusion

Impossible Figures