PERCEPTUAL PROCESSES-PSYC 615 (Grau)

 VISION

THE STIMULUS

Electromagnetic waves

wavelength-->hue

amplitude of the waveform-->brightness

complexity of the waveform-->saturation

Distal and Proximal stimuli

Visual angle

THE EYE

Structures of the eye

Cornea

Aqueous humor

Iris

Lens

Ciliary muscles and accommodation

Limits and problems

near point-increases with age

nearsightedness

farsightedness

Retina

Types of cells

Rods, cones, bipolar, ganglion, horizontal and amacrine cells

Orientation seems backwards

Receptors are next to the pigment epithelium

Duplicity theory

The theory

Adaptation

Provides evidence that the cones and rods function under different conditions

Dark adaptation in an uncontrolled situation

Dark adaptation when looking directly at the stimulus

Dark adaptation in a rod monochromat

Evidence adaptation reflects the regeneration of the photopigments

Sensitivity and neural wiring

Acuity and neural wiring

Ganglion cells

Receptive fields

Types of receptive fields

On-center, off-surround

Off-center, on-surround

X (or P) and Y (or M) cells

CORTICAL PROJECTIONS

Optic chiasm

Superior colliculus

Lateral geniculate

VISUAL CORTEX

Layers of the visual cortex

Organization of the visual cortex (Hubel & Weisel)

Location columns

Simple & complex cells

Organization of the location columns

Hypercolumn

Beyond area 17

Hypercomplex cells

Face cells

NEUROCHEMICAL MECHANISMS

Photoreceptors: Inner & outer segment

Photopigment: Opsin & retinal

cGMP gated channels

Allow Na+ (& some Ca++) to flow into the cell

Maintains cell at -40 mVolts

Light --> metarhodopsin

Activates transducin

Activates cGMP phosphodiesterase

Which converts cGMP to 5'GMP

Lowering levels of cGMP --> closing cGMP channels

Causing hyperpolarization (--> -70 mVolts)

Adaptation to light

Guanylate cyclase converts GTP to cGMP

Its inhibited by Ca++

Slowing the flow of Ca++ removes this inhibition

Reestablishing levels of cGMP

Which reopens cGMP channels --> -40 mVolts

Photoreceptors activate bipolar via a decrease in the release of glutamate

On center bipolars are excited (depolarize) by a decrease in glutamate

Off center bipolars are inhibited (hyperpolarize) by a decrease in glutamate

Photoreceptors in the surround

Inhibit photoreceptors in the center via horizontal cells

Caused by depolarizing center photoreceptor

MOVEMENT (M CELLS) AND DETAIL (P CELLS)

Lateral geniculate

Layers 2, 3, 5: ipsilateral

Layers 1, 4, 6: contralateral

Layers 1 & 2: magno (movement)

Layers 3-6: parvo (detail)

Parietal cortex: movement & location

Temporal cortex: object recognition/discrimination

COLOR

The problem of defining color

The need for more than one type of receptor

Color matching

Trichromatic theory of color vision (Young-Helmholtz)

The theory

Evidence for 3 pigments

Deriving their functional properties (Stiles)

Physiological evidence

Explanation of color matching

Opponent process theory

Additional observations

The theory

Deriving their functiona properteis (Jameson & Hurvich)

Physiological evidence (Svaetichin & DeValois)

Relation to trichromatic theory

Color deficiency

Monochromats

Dichromats

The problem of determining what they perceive

Unilateral dichromats

Protanopia

Deuteranopia

Tritanopia

BRIGHTNESS AND CONTRAST

Brightness

Operating characteristics

Tradeoff btw operating range and contrast sensitivity

The role of light and dark adaptation

Brightness constancy

Ratio principle (contrast theory)

Experimental evidence (Gelb)

Contrast

Mach bands

The phenomenon

A physiological explanation

Lateral inhibition

Role of eyemovements in perceiving contours

LINKING PROPOSITIONS

Nature of linking hypotheses

Maps, composite map & bridge locus

Logical structure

Initial proposition, contrapositive, converse, converse contrapositive

Linking propositions

Identity, similarity, simplicity, mutual exlusivitity, analogy

Specific examples (difficulties)

Mach bands

Feature detectors

PERCEPTUAL ORGANIZATION

Figure-ground

Gestalt principles

Law of good continuation

Law of simplicity (pragnanz)

Law of similarity

Law of proximity

Law of closure

Subjective contours

Problems with the Gestalt approach

 

END OF MATERIAL FOR MID-TERM

 

OBJECT PERCEPTION

Associationists (parts) versus Gestalt (wholes)

Integrating the two approaches

Deriving the psychological components

Evidence components may not be consciously accessible

Physiological evidence

Lesions that selectively disrupt properties

e.g., color, motion

Psychological/behavioral evidence

Selective adaptation

Illusory conjunctions

Speeded sorting

Integral & separable dimensions (Garner)

Free classification

Similarity scaling

City block versus Euclidean metric

Converging operations

An alternative approach: Spatial frequency

Fourier synthesis

Fourier analysis

Application to human pattern recognition

Contrast sensitivity function

Evidence for frequency channels

Selective adaptation

Physiological mechanisms

Simple/complex cells & frequency analysis

PERCEPTION OF DEPTH

Binocular cues

Covergence

Binocular disparity

Monocular cues

Accommodation

Pictorial cues

Linear perspective, Relative size, Interposition

Height in the visual field, Atmospheric perspective

Texture gradients

Motion parallax

PERCEPTION OF SIZE

Size-distance invariance hypothesis

Evidence perceived size is influenced by depth

Emmert's law

Illusions of size

Moon illusion, Muller-Lyer, Ponzo illusion

PERCEPTION OF MOTION

Importance of motion perception

Impact of a lesion that destroyed motion perception

Real movement

Factors that influence our perception of real movement

Background

Size of the object

Mechanisms for the perception of real movement

Movement detectors

Corollary discharge

Information in the optic array

Gibsonian approach to motion perception

Vision and balance

Illusory movement

Autokinetic movement

Apparent movement

Examples of phi movement

Waterfall illusion