Module 19

Visual Organization and Interpretation

❖ Perceptual Organization

■ German psychologists noticed that people who are given a cluster of sensations tend to organize them into a gestalt

● Gestalt: an organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.

➢ Form Perception

■ Figure and Ground

● Figure-ground

◆ The organization of the visual field into objects (the figures) that stand out from their surroundings (the ground).

■ Grouping

● The perceptual tendency to organize stimuli into coherent groups.

● Our mind brings order and form to other stimuli by following certain rules for grouping

◆ These rules illustrate how the perceived whole differs from the sum of its parts

◆ Examples:

➢ Proximity

■ We group nearby figures together

➢ Continuity:

■ We perceive smooth, continuous patterns rather than discontinuous ones

➢ Closure:

■ We fill in gaps to create complete, whole object

◆ These principles help us construct reality, but sometimes they lead us astray

➢ Depth Perception

■ The ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.

■ From the two-dimensional images falling unto the retinas, it can organize three-dimensional perceptions that allow us to estimate distance

■ Eleanor Gibson

● She wondered: Would a toddler peering over the rim perceive the dangerous drop-o and draw back?

◆ To answer the question, Gibson and Richard Walk designed a series of experiments using a visual cliff

➢ Visual cliff: a laboratory device for testing depth perception in infants and young animals.

➢ They tried to convince infants to crawl out onto the glass—an area that looked like the edge of a cliff—but most infants refused to do so, which indicated that they could perceive depth

◆ Depth perception is partly innate and partly learning

■ Binocular Cues

● A depth cue, such as retinal disparity, that depends on the use of two eyes.

● Binocular cues are used to judge the distance of nearby objects

● Cues:

◆ Convergence

➢ The inward angle of the eyes focusing on a near object

◆ Retinal disparity

➢ A binocular cue for perceiving depth. By comparing retinal images from the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.

■ Monocular Cues

● A depth cue, such as interposition or linear perspective, available to either eye alone.

● Helps us judge (for example) whether a person is 10 or 100 meters away

➢ Motion Perception

■ The brain, normally, computes motion based partly on its assumption that shrinking objects are retreating and enlarging objects are approaching, but people are imperfect at motion perception

● The brain is sometimes tricked into believing what it is not seeing

● When large and small objects move at the same speed, the large objects appear to move more slowly

■ The brain perceives a rapid series of slightly varying images as continuous movement

● We construct that motion in our heads

■ Phi phenomenon

● An illusion of movement created when two or more adjacent lights blink on and off in quick succession.

■ Visual Organization and Interpretation

● Relative height

◆ We perceive objects higher in our field of vision as farther away

● Relative size

◆ If we assume two objects are similar in size, most people perceive the one that cast the smaller retinal images as farther away

● Interposition

◆ If one object partially blocks our view of another, we perceive it as closer

● Relative motion

◆ As we move, objects that are actually stable may appear to move

● Linear perspective

◆ Parallel lines appear to meet in the distance

● Light and shadow

◆ Shading produces a sense of depth consistent with our assumption that light comes from above

➢ Perceptual Constancy

■ Perceiving objects as unchanging (having consistent color, brightness, shape, and size) even as illumination and retinal images change.

■ Regardless of the viewing angle, distance, and illumination, we can identify people and things in less time than it takes to draw a breath

■ Color and Brightness Constancies

● Our experience of color depends on an object’s context

● Color constancy

◆ Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object.

● Because we construct our perceptions, we can simultaneously accept alternative objective and subjective realities

● Brightness constancy similarly depends on context

◆ We perceive an object as having a constant brightness even as its illumination varies

◆ This perception of constancy depends on relative luminance

➢ The amount of light an object reflects relative to its surroundings

● Context governs our perceptions

■ Shape and Size Constancies

● Sometimes an object whose actual shape cannot change seems to change shape with the angle of our view

● Size constancy helps us perceive an object as having an unchanging size, even while our distance from it varies

● Even in size-distance judgements, the object’s context is always considered

● The interplay between perceived size and perceived distance helps explain several well-known illusions

● Perpetual organizations applies to other senses as well

◆ Listening to our own language, we can automatically hear distinct words

◆ We can organize a string of letters into words that make an intelligible phrase

➢ THEDOGATEMEAT is more likely seen as “the dog ate meat”, rather than “the do gate me at”

❖ Perceptual Interpretation

■ Immanuel Kant

● German philosopher

● Maintained that knowledge comes from our inborn ways of organizing sensory experiences

■ John Locke

● British philosopher

● Argued that through our experiences we also learn to perceive the world

➢ Experience and Visual Perception

■ Restored Vision and Sensory Restriction

● William Molyneux

◆ Wondered whether “a man born blind, and now adult, taught by his touch to distinguish between a cube and a sphere” could visually distinguish the two

➢ John Locke answered no as the man would never have learned to see the difference

➢ Was put to test with adults who were born blind but later gained sight, but remained unable to visually recognize objects

■ Perceptual Adaptation

● The ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field.

● Humans can adapt to distorting lenses quickly

◆ Even when given a lens that turns the world upside down

◆ Experience guides, sustains, and maintains the brain pathways that enable our perception