General Principles of PerceptionGeneral Principles of Perception

Each Receptor is Specialized Each Receptor is Specialized to Absorb One Kind of to Absorb One Kind of Energy & Transduce it into Energy & Transduce it into an Electrochemical Pattern in an Electrochemical Pattern in the Brainthe BrainCoding of visual information in the Coding of visual information in the brain does not duplicate the brain does not duplicate the shape of the objectshape of the object

Law of Specific Nerve Law of Specific Nerve EnergiesEnergiesAny activity by a particular nerve Any activity by a particular nerve always conveys the same kind of always conveys the same kind of information to the braininformation to the brain

The Eye/Brain The Eye/Brain ConnectionConnection

StructureLight enters the eye through the Cornea & the PupilIt is focused by the Cornea & Lens & projected on to the Retina

RetinaThe rear surface of the eye which is lined with visual receptors

The RouteReceptors send messages to the Bipolar Cells, which send messages to Ganglion CellsAmacrine Cells are important for complex processing of visual informationGanglion Cells join together to form the Optic Nerve

The Fovia & the Periphery of the The Fovia & the Periphery of the RetinaRetina

MaculaMaculaPortion of the Retina with the greatest Portion of the Retina with the greatest ability to resolve detailability to resolve detail

FoveaFoveaCentral potion of the Macula specialized for Central potion of the Macula specialized for acute, detailed visionacute, detailed vision

Fovea has the least impeded visionFovea has the least impeded vision

Each receptor connects to a single Bipolar Each receptor connects to a single Bipolar Cell which connects to a single Ganglion Cell which connects to a single Ganglion CellCell

Midget Ganglion Midget Ganglion CellsCellsReceive input from a single coneReceive input from a single cone

Each cone has a direct line to the brainEach cone has a direct line to the brain

Visual ReceptorsVisual ReceptorsRodsAbundant in the periphery of the RetinaFor Periphery & Night Vision

ConesPrimarily in the FoveaFor Visual Acuity & Color VisionPhotopigments:Photopigments: Chemicals that release energy when struck by light

CCoolloorr VViissiioonnRequires Comparing Responses of Different Kinds of ConesShortest to Longest WavelengthsShortest wavelength seen as Violet, longest wavelengths seen as Blue, Green, Yellow, & Red

Two Main TheoriesTrichromatic TheoryOpponent-process Theory

CCoolloorr VViissiioonnRetinex Theory Retinex Theory (The Land (The Land Effect)Effect)Proposed to account for Proposed to account for Color Color ConstancyConstancy

When information from various When information from various parts of the retina reaches the parts of the retina reaches the cortex, the cortex compares cortex, the cortex compares each of the inputs to determine each of the inputs to determine the brightness & color the brightness & color perception for each areaperception for each area

ColorblindnessColorblindnessColor Vision Color Vision DeficiencyDeficiencySeen mostly in MalesSeen mostly in Males

Red-Green Red-Green colorblindness is most colorblindness is most commoncommon

On the X-chromosomeOn the X-chromosome

X-linked disorderX-linked disorder

The Visual The Visual SystemSystem

Rods & Cones Rods & Cones Synapse with Synapse with Horizontal & Horizontal & Bipolar CellsBipolar CellsHorizontal cells make Horizontal cells make inhibitory inhibitory contact onto contact onto bipolar cells which synapse with amacrine and bipolar cells which synapse with amacrine and ganglion cellsganglion cells

Axons of the Axons of the Ganglion Cells Ganglion Cells Form the Optic Form the Optic NerveNerveOptic nerves from both eyes meet at the Optic nerves from both eyes meet at the optic optic chiasmchiasm where ½ of the axons from each eye cross where ½ of the axons from each eye cross to the opposite side of the brainto the opposite side of the brainMost of the ganglion cells go to the Most of the ganglion cells go to the Lateral Lateral Geniculate NucleusGeniculate Nucleus of the thalamus of the thalamus

Mechanisms of Visual ProcessingMechanisms of Visual Processing

Receptive FieldsVisual Field

The area of the world that you can see at any timeReceptive Field

The portion of the visual field to which any neuron respondsLateral Inhibition

The reduction of activity in one neuron by activity in neighboring neurons

This is the retinal technique that sharpens the boundaries of visual objects

Neurons in the Visual Neurons in the Visual PathwaysPathways

Parvocellular NeuronsSmall cell bodies located in or near the fovea with small receptive fields & respond best to details & colorThey synapse only onto cells of the LGN

Magnocellular NeuronsLarger cell bodies distributed throughout the retina & have a larger receptive field responding best to moving stimuliMost synapse onto cells of the LGN, but a few connect to other areas of the Thalamus

Koniocellular NeuronsSimilar in size to Parvocellular Neurons, but distributed throughout the retinaThey have several different functions & their axons connect to the LGN, other areas of the Thalamus, & the Superior Colliculus

In the Cerebral Cortex

Most Axons from the Most Axons from the LGN go 1LGN go 1stst to the Primary to the Primary Visual Cortex (V1)Visual Cortex (V1)V1 sends information to the Secondary Visual Cortex (V2)Connections between V1 & V2 are reciprocalIn the cortex, Parvocellular & Magnocellular pathways split from 2 to 3 pathwaysParvocellular is sensitive to shapeMagnocellular is sensitive to movementThe mixed pathway is sensitive to brightness & color

Object Object RecognitionRecognition

Ventral StreamVentral StreamMade up of parvocellular & magnocelluilar pathwaysGoes through V1, V2, V4 & areas of the Inferior Temporal LobeSensitive to shape, movement & color brightnessSpecialized for object recognition & identification

Dorsal StreamDorsal StreamMostly magnocellular pathwaysFrom V1 to Parietal & to Temporal LobesIntegrates vision & movement leading to the Parietal Lobe

Categories of Neurons in Categories of Neurons in the Cerebral Cortexthe Cerebral Cortex

Simple CellsNeurons with fixed excitatory & inhibitory zones in their receptive fieldsNeurons with fixed excitatory & inhibitory zones in their receptive fields

Found only in the Primary Visual Cortex (V1)Found only in the Primary Visual Cortex (V1)

Complex CellsReceive input from a combination of Simple CellsReceive input from a combination of Simple Cells

Have receptive fields that respond to particular orientations of light but cannot be Have receptive fields that respond to particular orientations of light but cannot be mapped into fixed excitatory & inhibitory zonesmapped into fixed excitatory & inhibitory zones

Located in V1 or V2Located in V1 or V2

End-stopped (Hyper-complex) CellsStrongly resemble complex cells but have an inhibitory area at one end of its bar-Strongly resemble complex cells but have an inhibitory area at one end of its bar-shaped receptive fieldshaped receptive field

Recognition of Recognition of ShapeShape

Cells in the Visual Cells in the Visual Cortex are in ColumnsCortex are in ColumnsSet perpendicular to the Set perpendicular to the surface according to response surface according to response orientationorientation

Feature DetectorsFeature DetectorsNeurons whose responses Neurons whose responses indicate the presence of a indicate the presence of a particular featureparticular feature

Inferior Temporal Inferior Temporal CortexCortexProvides information about Provides information about complex shaped stimulicomplex shaped stimuliImportant in Important in Shape ConstancyShape Constancy

Disorders of Object Disorders of Object RecognitionRecognition

Visual AgnosiaVisual AgnosiaThe inability to recognize objects despite otherwise normal vision

ProsopagnosiaProsopagnosiaThe inability to recognize faces without an overall loss of vision or memory

The Fusiform Gyrus in the Inferior Temporal Cortex is specialized for face recognition

This area is also activated when identifying car models, bird species, and so on

Color, Motion, Color, Motion, & Depth& Depth

Color Perception Depends on Parvocellular & Koniocellular PathwaysBlobsPatches of cells in V1 highly sensitive to color areasIncludes Parvocellular & Koniocellular neurons for color & Magnocellular for brightnessOutput is sent to V2, V4, & Posterior Inferior Temporal Cortex

Creating Stereo Images

Anaglyph 3-DUses red/blue lenses on glasses

Cross-eyed 3-DMust cross eyes to create a single image or use lenses that create the image

Polarized Lens 3-DUse of polarized lenses on glasses

Motion Motion DetectionDetection

Medial Temporal CortexMiddle Temporal Cortex & Medial Superior Temporal Cortex important in motion detection

Mechanisms to Distinguish between Moving Objects & Head ChangesDamage to Medial Temporal Cortex results in motion blindness

Importance of V1 AreaActivation & feedback to V1 area necessary for attention or conscious awareness of a Activation & feedback to V1 area necessary for attention or conscious awareness of a stimulusstimulus

Binding Necessary for ConsciousnessSynchronized activity of the 2 hemispheres necessary to see something that crosses Synchronized activity of the 2 hemispheres necessary to see something that crosses the midline of vision as a single objectthe midline of vision as a single object

A limited amount of visual processing takes place without being consciousA limited amount of visual processing takes place without being conscious

BlindsightBlindsight

Some people with extensive damage to V1 can localize visual objects with a Some people with extensive damage to V1 can localize visual objects with a blind visual fieldblind visual field

Development of the Visual Development of the Visual SystemSystem

Infant VisionInfant VisionInfants have better vision than once imaginedInfants have better vision than once imagined

Spend more time looking at faces, circles, or stripes than at patternless Spend more time looking at faces, circles, or stripes than at patternless displaysdisplays

They have trouble shifting their gaze until about 6 monthsThey have trouble shifting their gaze until about 6 months

The Effects of The Effects of ExperienceExperience

Lack of Early StimulationIn One Eye: Most neurons in the Visual Cortex receive binocular input. Deprivation leads to blindness in the one eye

In Both Eyes: If both eyes are deprived of stimulation, cortical cells will remain sluggishly responsive in both eyes

People born blind but acquiring vision later have trouble identifying shapes & objects & find newly gained vision almost useless

Sensitive or Critical PeriodA stage of development when experiences have a particularly strong & long-lasting influence

Effects of abnormal experiences on cortical development depend on the length of the sensitive period

In humans, even a brief abnormal experience can result in deficits

Restoring Response after Restoring Response after Early DeprivationEarly Deprivation

Depends on WhenIf normal experiences begun soon enough, sensitivity can be restored

AmblyopiaLazy Eye, can be treated by putting a patch over the active eye

Stimulation in Both EyesStimulation in Both EyesRetinal DisparityRetinal DisparityThe discrepancy between the left & the right eye seesIt is necessary for stereoscopic depth perceptionThe fine-tuning of binocular vision depends on experience

StrabismusStrabismusThe eyes do not point in the same directionCannot perceive depth better with 2 eyes as opposed to 1

AstigmatismBlurring of Vision in One DirectionCaused by an asymmetric curvature of the eyes

Corrective lenses in early childhood improve the vision

Early BlindCertain portions of the Visual Cortex in people blind early in life become responsive to auditory or touch stimuli