Perception

Top-down processing

What do you see?

Perception is different from sensation

• Wundt-Jastrow illusion• The oscillating window illusion• The horizontal-vertical illusion• The Muller-Lyer Illusion

The oblique effect

Brain pathways and perception

• From the retina, axons of ganglion cells travel as the optic nerve to the lateral geniculate nucleus (LGN) of the thalamus

• From LGN cells, axons travel to the primary visual cortex, in the occipital lobe

• From the primary visual cortex, axons project to visual association cortex, in the parietal and inferior temporal lobes

Other visual pathways

• To the SCN (suprachiasmatic nucleus) of hypothalamus

• To accessory optic nuclei of brainstem and to cerebellum: Synchronize eye and head movements

• To pretectum to control pupil diameter• To superior colliculi of the tectum, for control

of visual attention

Information processing

• At each level in the visual pathways, more complex information is drawn from the stream

• Hubel and Wiesel’s method (1977): Microelectrodes

• Receptive fields: On and Off

The Hermann Grid

Receptive fields

• The piece in the visual field to which a given cell responds.

• Receptive fields for rods and cones are simple and round.

Off

On

Examples of receptive fieldson

on

on on

onoff

off

offoff off

offon

Center off-surround on

Center on-surround off

Center-surround Cells:-Ganglion cells, LGN cells (both M and P), and layer IV of striate cortex

Receptive fields and gray dots

Examples...

onoff on

off

Simple cortical cells:Line border respondsbest to -contrasting bars -single straight edges -at a particular angle

Complex cortical cells

• Merge inputs from simple cells to detect– Stimuli over a larger area of the visual field– An edge at a particular angle anywhere in the

field (not “on-off”)– Movement, often directionally

• About half are binocular• Half of the binocular cells show ocular dominance• Some are retinal disparity detectors

Complex cell fieldsNote:- the larger receptive field- no subdivision on-off-orientation responsiveness-directional sensitivity

Visual association cortex

• Combines information from the primary visual cortex to produce– Orientation, movement, and color– Three dimension views – Spatial location of objects

Effects of damage

• Primary visual cortex: Sensory (Scotomas)• Visual association cortex: Perceptual

– Achromatopsia– Loss of movement perception– Balint’s syndrome: Location– Visual agnosias

• Prosopagnosia

Agnosias

• Prosopagnosia– Actually, an inability to identify particular

faces– Duplicated as an inability to recognize

particular cows, doors, cars– Problem is in distinguishing among similar

examples of complex visual stimuli– Damage is inferior temporal

Other agnosias

• Apperceptive visual agnosias– Prosopagnosia– Achromatopsia

• Associative visual agnosias– Inability to name seen objects, although they

can copy them and know the word (“anchor”)– May get the word through circumlocutions (the

milking farmer)

Processes of organization

• Selective attention– Reversible figures– The cocktail party effect– Dichotic listening experiments

• Perceptual illusions– Visual capture

Principles of organization

• Gestalt psychology• Form perception

– Figure-ground– Grouping: Pragnanz

• Closure and completion• Proximity• Similarity• Continuation and Common Fate• Connectedness

Form perception: Figure-ground

Notice the effects of continuous boundaries on the goodness of form perception of thevase figure.

Closing borders

An example of completion at Mt. Rushmore

Subjective contours

Other subjective contours

Gestalt laws of perception

Pragnanz Proximity

More Gestalt principles

C C C B C C CC C C B C C CB B B B B B BC C C B C C CC C C B C C CC C C B C C CC C C B C C CC C C B C C C

Similarity Continuation

More Gestalt Principles...

Common Fate Connectedness

What principles here?

Form and pattern perception

• Templates?• Prototypes

– Humphrey’s monkeys• Interested in individual monkey pictures• Not interested in individual cows and pigs• Exposure increased interest in cows and pigs• Experience sharpens prototypes

Distinctive features

• Rule prototypes: Ulrich Neisser (1964)

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• The man who mistook his wife for a hat

Perceiving distinctive features

• Context cues• Biederman’s (1990) geons• Cusps and joints

Principles of organization

• Depth perception– Monocular cues– Binocular cues– Examples: Fingerpointing, hole in hand

• Motion perception– Size and position– Stroboscopic movement– Phi phenomenon

The phi phenomenon

Monocular Depth cues: Height, Interposition, and Relative Size

What cues are here?

Charles Sheeler, Classic Landscape, National Gallery, Feb. 26, 2000

Perception phenomena

• Perceptual constancy– Size and shape: The swelling hand– Brightness: Overhead

• Perception as interpretation• The grasping visual illusion

Ebbinghaus figures and the grasping illusion

Franz, Gegenfurter, Bulthoff, & Fahle, 2000

Perceptual Constancy and the Moon Illusion

Expectations affect perceptions

• Perceptual set– Expectations or schemas: Numbers and names– Context:

TIME FLIES I CANT THEYRE TOO FASTCHOPHOUSECHOPHOUSE

More context effects

FOLKCROAKSOAK

THE WHITE OF AN EGG

Cognitive set

• LULB• CALEM• NUKKS• SEUMO• BAZER

• NORC• NOONI

• MATOOT• PREPPE

• TEBE

EAP

Social transmission of narrative

• Three men, masked and armed with pistols, robbed the Glenwood State Bank yesterday morning at 9:30 a.m. They escaped in a Ford two-door bearing a 1971 Connecticut license plate, taking $647 in coins and $2,190 in five-dollar bills. A lieutenant in the Marines claims he saw the car going north at noon yesterday.

Backmasking

• Queen, Another one bites the dust• Queen, backwards• Psalm 23, backwards• Excerpt: Jabberwocky, Lewis Carroll• More Jabberwocky