Chapter 6: Perception

Perception – the awareness, integration, and organization of sensory stimuli Bottom-up processing – organization of information without the use of prior knowledge – beginning with the individual elements that are structured together to form a whole Each part is given attention and not until individual elements are connected is the whole recognized or identified. Putting together a puzzle by looking at how the pieces fit together Top-down processing – organization of information that uses prior knowledge to form the whole The final whole is already known and then the individual elements are identified Putting together a puzzle by looking at the picture on the box

Selective Attention- Focusing of conscious awareness on a particular stimulus Cocktail Party Effect- The ability to attend selectively to only one voice among many Inattentional Blindness - When people show a lack of awareness of happenings in their visual environment Change Blindness Change Deafness Choice Blindness

Perceptual Organization Gestalt Psychology- group of German psychologists interested in how the mind organizes sensations into perceptions Gestalt – When given a cluster of sensations, we tend to organize them into a gestalt – a “form” or a “whole” “In perception, the whole may exceed the sum of its parts” Gestalt Principles: Figure-ground - Ability to distinguish between the figure as the foreground and the ground as the background

Gestalt Principles cont. Grouping – Our mind follows certain rules for grouping stimuli together Proximity – Tendency to perceive objects that are close together as belonging together Similarity – Tendency to group similar objects together to make a whole Continuity – Tendency to see an object continuing despite an obvious break Connectedness – Tendency to see objects that are uniform and linked as one unit Closure - Tendency to fill in the gaps to complete a whole object

Depth Perception Biology predisposes our sense of height; experience amplifies it. Depth Perception (seeing objects in 3 dimensions) Visual Cliff Experiment-Eleanor Gibson & Richard Walk designed experiment prove depth perception is innate

Depth Perception – Binocular Cues Depend on both eyes (depth cues) Retinal disparity – by comparing images from two eyes, the brain computes the difference, the greater the distance between the two images, the closer the object 3-D movies rely on retinal disparity Convergence - muscles rotate inward when viewing an object nearby; the greater the inward strain, the closer the object

Depth Perception – Monocular Cues Relative Size - Objects which appear to be smaller, we view as farther away and larger objects are closer

Depth Perception – Monocular Cues Interposition (overlap) - when objects block or otherwise obscure our view of other objects, we perceive obscured object as farther away

Depth Perception – Monocular Cues Relative Clarity - Objects further away appear blurry or hazy - caused by atmosphere

Depth Perception – Monocular Cues Texture Gradient- The coarseness or smoothness of an object is used as a cue for distance. Objects far away appear smaller and more densely packed.

Depth Perception - Monocular Cues Relative Size: If two objects are similar in size, we perceive the one that casts a smaller retinal image to be farther away.

Depth Perception – Monocular Cues Motion Parallax (Relative Motion) - When moving, farther objects move slower.

Depth Perception - Monocular Cues Linear Perspective: Parallel lines, such as railroad tracks, appear to converge in the distance. The more the lines converge, the greater their perceived distance.

Depth Perception – Monocular Cues Light and Shadow: Nearby objects reflect more light into our eyes than more distant objects. Given two identical objects, the dimmer one appears to be farther away. From “Perceiving Shape From Shading” by Vilayaur S. Ramachandran. © 1988 by Scientific American, Inc. All rights reserved.