Chapter 8

Chapter 8

Perception

Perception

Bottom-Up Process An analysis of the action of feature detectors

in a sensory experience

Top-Down Process An analysis of the effects of expectations and

prior learning on a sensory experience

Receptive Fieldsand Feature Detectors

Receptive Field The portion of the visual field to which a cell

in the nervous system responds when visually stimulated

Feature Detector A visual neuron that is sensitive to a particular

visual feature

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Ganglion Cell Receptive Fields

On-center cells Ganglion cells that respond in an excited

fashion when light falls in the center and darkness falls on the outside

Equal Lighting

Center On

Center Off

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Ganglion Cell Receptive Fields

Off-center cells Ganglion cells that respond in an excited

fashion when light falls in the surround and darkness falls on the center

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Cortical Feature Detectors

Simple Cells Neurons in the striate cortex that respond to

lines of a particular orientation in their receptive field

Depth Perception

The perception of depth arises from a combination of cues that creates the illusion of three dimensions

Binocular Cues to Depth require both eyes

Monocular Cues to Depth require only one eye

Binocular Cue ofRetinal Disparity

Each eye has a slightly different view of the world The difference in views produces an

impression of depth

Binocular Cue ofConvergence

A cue to depth resulting from the eyes turning inward to see near objects

Monocular Cues to Depth

Interposition

Monocular Cues to Depth

Relative Size

Monocular Cues to Depth

Linear Perspective

Monocular Cues to Depth Relative Clarity

Monocular Cues to Depth

Texture Gradient

Monocular Cues to Depth

Relative Motion

Perceptual Constancies

The perceptual world appears constant even though the retinal image is constantly changing

Perceptual Constancies

Size Constancy The tendency to see a figure as being the same

size, despite changes in its retinal size

Shape Constancy The tendency to see a form as unchanging,

despite changes in its retinal size

Lightness Constancy The tendency to see an object as being the

same, even under different light intensities

Brightness Contrast

Ponzo IllusionMay be due to perspective cues

Mueller-Lyer Illusion

Ambiguous Figures

Conscious & Unconscious Processes in Perception

Blindsight: The case of D.B.Vision loss in left visual field, resulting

from brain surgery (hemianopia)Shown stick in blind field - claims he

cannot see it But, he can accurately determine its

orientation

Hemianopia

The Striate Cortex and Consciousness

Patients with damage to striate cortex (primary visual cortex in the Occipital Lobe) can respond to visual stimuli, even though they are unaware of them

Unconscious Processing in Sighted SubjectsSubjects

presented with moving dots

One quadrant moving in a different direction

Although subjects claim they cannot tell which quadrant is different, they are very accurate

Parallel Processing of Visual Information

Many different brain areas process visual information simultaneously Processing of form, depth, motion and color is

done by different brain areas

Parallel Processing of Visual Information

Evidence for Parallel Processing:Damage to Extrastriate Cortex

Cortical Color Blindness Due to damage to brain area that processes

color

Cortical Motion Blindness Due to damage to brain area that processes

motion

Temporal Lobe Damage

Visual Agnosia A visual disability that is characterized by seeing

without knowing the meaning of what is seen. The case of Dr. P - The Man Who Mistook His Wife

for a Hat.Disconnection syndrome: visual processing occurring, but

meaning has been lost

Prosopagnosia loss of ability to recognize faces resulting from brain

damage

The Stroop Effect

Red

Blue

Green

Purple

Black

Pink

Green

Pink

Red

Blue

Pink

Purple

People find thiscondition the hardest

Gestalt Psychology

Perception is not putting together parts, but seeing the whole The whole is greater than the sum of its parts

- Max Wertheimer

Gestalt: Apparent Movement

The Phi Phenomenon

Principles of Perceptual Organization

We group together elements in a consistent manner

Grouping by Proximity and Similarity

Principles of Perceptual Organization

The Principle of Continuity

People tend to report seeing two continuous lines

Principles of Perceptual Organization

The Principle of Common Movement

Principles of Perceptual Organization

The Principle of Pragnanz (Good Figure)

Principles of Perceptual Organization

Figure-Ground Relationships

Perception of Meaningful Sounds

Language as a meaningful signal may have developed after the development of music

Language and music are controlled by separate brain areas.

Perception of Odors and Tastes

Conscious vs. Unconscious processing of smells Smell influence the onset of women’s menstrual cycle

Women living together in a dorm eventually developed a common cycle

Same results occur when women smell androstenone extracted from axillary areas of other women

Women who sleep with men have a more regular menstrual cycle

Smells and Sexual Attraction

Major Histocompatibility Complex Section of DNA that is similar in closely

related individuals

People with similar MHC genetic profiles have similar smells Women prefer the smell of men who do not

have a similar MHC genetic profile to themselves

The Perception of Touch

Contact Comfort Harry Harlow: Baby monkeys will seek out

soft, warm surrogate mothers, even if they do not provide food