Chapter 9

Question 1

Blindsight and Perception

Answer 1

Patient can’t identify objects in blind area but can accurately tell about changes in visual field

Not conscious that they can register changes in visual field

NS constructs images from bits of information + brain must bind it together to create PERCEPTION

Selective awareness → can only access some part of the info our brain is processing

Question 2

Nature of sensation and Perception

Answer 2

Only input brain receives: series of action potentials originating from external energy and is transduced by sensory receptors → info is passed along Sensory neurons that form pathways

Collective sensory input → transduction→ perception: Perception (how one set of nerve impulses = sound and others = vision) is unknown

Diverse sensory systems: vision, touch, taste, etc.
↳ organized similarity but all leads to different perceptual experience

Question 3

Sensory receptors

Answer 3

Specialized cells that transduce (convert) external sensory energy into neural activity

Each sensory receptors are designed to respond to a narrow band of energy
- vision: light energy → chemical energy
- auditory: air pressure → mechanical energy
- somatosensory → mechanical energy
-taste and olfaction → chemical molecules

Question 4

Receptive field

Answer 4

Region of sensory space that selectively responds to external stimulation → stim. modifies receptors activity

What open eye sees: receptive field
→ each photoreceptor in eye points in slightly different direction: creates a broader sense of perception

RF can help sample sensory info and locate events in space→ very tightly packed

Sensory receptor RF can contrast info each receptor is providing→ many overlap and form a network of communication → contrasting responses and levels of activation: helps localize sensations

Spatial dimension of sensory info produces cortical patterns and maps→form reality

Question 5

Receptor density and sensitivity

Answer 5

Sensory receptors are not evenly distributed across body or organs

Density is important for determining the sensitivity of a sensory system
↳ ex. Visual receptors packed towards Center of visual field = poor peripheral vision

Differences m receptor density determine the special abilities of many animals

Question 6

Neural relays

Answer 6

All receptors connect to cortex through a sequence of intervening neurons
(Visual): Retina → thalamus → V1 area → other cortical regions
(Auditory): Auditory receptors (ear)→ hindbrain → midbrain → thalamus → cortex

Sensory info is modified at each relay stage: each region constructs different aspects of sensory experience

Neural relays allow sensory systems to interact

Question 7

Sensory coding

Answer 7

After transduction: sensory info is encoded by action potentials that travel along peripheral nerves to CNS → action potentials travel on nerve tracks within CNS → to whichever area is needed

Unless a reflex: most people need CNS to process info and input

Presence of a stimulus can be encoded by an increase or a decrease in discharge rate
↳amount of increases/decreases encode stimulus intensity

Changes in visual field encoded by activity in different neurons or different levels of discharge within a Neuron

Question 8

Sensory coding and representation

Answer 8

Neocortex represents sensory field of each sensory modality as a spatially organized neural representation of external world

Topographic map: spatially organized rep. Of external world

Each sensory system has at least one primary cortical area → main relay station where sensory input comes first: MOST input arrives here

May project to secondary areas

Question 9

Topographic map in sensorimotor cortex

Answer 9

Size of its features represent relative proportions of the parts of the human brain responsible for motor and somatosensory function

Features that are exaggerated have largest correlate representations in the brain

Question 10

Sensation vs. Perception

Answer 10

Sensation: registration of physical stimuli from the environment by the sensory organs → no conscious registration

Perception: subjective interpretation of sensations by the brain → visual experience is not an objective reproduction of what is out there; rather a subjective construction of reality manufactured by brain → human senses are incredibly limited and perception is very flawed

Question 11

Structure of Retina

Answer 11

Retina → consists of neurons and photoreceptor cells (cones and rods)
- translates light into action potentials
- discriminates wavelengths (colours)
- works in wide range of light intensities

Fovea→ region at the center of the retina that is specialized for high acuity: Sharp vision
↳ receptive field at the center of the eyes visual field: can see more clearly at center of visual field

Blind spot (optic disk)
- region of retina where axons forming optic nerve leave the eye and where blood vessels enter and leave → no photoreceptors

Question 12

Acuity across visual field

Answer 12

Vision is better in the Center of the visual field than in periphery

Visual system is colour based at Center and black and white in peripheral → Brain just compensates so all vision is cohesive

Question 13

Photoreceptors

Answer 13

Light energy → chemical energy → neural activity

Light arrives at photoreceptors →series of chemical reactions → change in membrane potential → change in release of neurotransmitters onto nearby neurons

Rods → light levels: more numerous than cones, sensitive to low levels of light, one type of pigment only, used mainly for night vision

Cones →colour: highly responsive to bright light, specialized for colour and visual acuity, in fovea only, 3 types of pigment

Question 14

Cones

Answer 14

3 types of cone pigments (absorb over a range of frequencies, but their maximal absorptions are:
→ 419 nm (blue, or short wavelength)
→ 531 nm (green, or middle wavelength)
→ 559 nm (red, or long wavelength)

Equal numbers of red and green cones but fewer blue cones→ random distribution throughout fovea

Question 15

Retinal neutrons → 4 types

Answer 15

Bipolar cell: receives input from photoreceptors into ganglion cells

Horizontal cell: links photoreceptors and bipolar cells

Amacrine cell: links bipolar cells and ganglion cells

Retinal ganglion cell (RGC): gives rise to the optic nerve

Question 16

Ganglion cells → 2 types

Answer 16

Magnocellular cell (M-cell): magno- ‘large’
- receives input primarily from rods
- sensitive to light and moving stimuli

Parvocellular cell (P-cell): parvo- ‘small’
- receives input primarily from cones
- sensitive to colour→ encode features from stimulus such as colour

Question 17

Visual pathways → simplified

Answer 17

Left visual field → processed in right side of brain

Right visual field → processed in left side of brain

Question 18

Optic Chiasm

Answer 18

Junction of the optic nerves from each eye

Axons from the nasal (inside) half of each retina cross over to opposite side of brain

Axons from the temporal (outer) half of each retina remain on the same side of the brain

Question 19

3 routes to the visual brain

Answer 19

2 main pathways lead to visual cortex in occipital lobe:
→ Geniculostriate pathway for processing the objects image: made by ALL P ganglion axons and some M ganglion axons
→ Tectopulvinar pathway for directing rapid eye movements: made by remaining M ganglion axons

Smaller pathway tracks into the hypothalamus:
→ hypothalamic tract: sleep and circadian rhythm’s

Question 20

Geniculostriate System

Answer 20

Projections from the retina to the lateral geniculate nucleus to layer IV of the primary visual cortex

Bridges the thalamus (geniculate) and the striate cortex (primary visual processing)

Lateral geniculate nucleus → striate cortex → other visual cortical areas

Question 21

Striate Cortex

Answer 21

The primary visual cortex (V1) in the occipital lobe
→ shows striped (striations) when stained

Two visual paths emerge from the striate cortex:
→ one route goes to vision-related regions of the parietal lobe
→ one route goes to vision-related regions of the temporal lobe

Question 22

Tectopulvinar System

Answer 22

Projections from the retina to the midbrain’s superior colliculus→ to the pulvinar (part of the thalamus) → to the parietal and temporal visual areas (processed to create perception: colour, motion, etc)

Question 23

Retinohypothalamic tract

Answer 23

Synapses in the tiny suprachiasmatic nucleus in the hypothalamus

Roles in regulating circadian rhythms and in the pupillary reflex

Contains photosensitive RGC’s → ex. Blue light suppresses the release of melatonin

Question 24

Dorsal visual stream

Answer 24

Visual processing pathway from V1 to the parietal lobe → movement relative to objects

Known as the ‘how’ pathway → how action is to be guided towards objects
→ orients perception to create movement

Question 25

Ventral visual stream

Answer 25

V1 to the temporal lobe: object identification and perceiving related movements Known as the 'what' pathway → identifies what an object is All geniculostriate → tectopulvinar doesn't engage in this pathway***

Question 26

Geniculostriate pathway

Answer 26

Lateral geniculate nucleus (thalamus) → ganglion cell fibers will eventually distribute to thalamus ↳ right LGN: input from right half of each retina ↳ left LGN: input from left half of each retina Contains 6 layers: projections from the eyes go to different layers ↳ layers 1,4, and 6: input from contralateral retina ↳ layers 2,3, and 5: input from ipsilateral retina ↳ layers 1 and 2: input from mangocellular cells ↳ layers 3 to 6: input from parvocellular cells Visual info has to stay segregated on pathways: each pathway can specialize and do its job well P (colour) and M (movement) retinal ganglion cells can send separate pathways to thalamus→ segregation continues in striate cortex Left and right eyes also send separate pathways to the thalamus→ remain segregated in striate cortex

Question 27

Maintaining separate visual input

Answer 27

After info is segregated in LGN it maintains segregation in primary visual cortex Pattern → alternating regions of the left and right eye Ocular dominance columns » each region is responsible for ocular dominance (segregated and processed selectively)

Question 28

Tectopulvinar pathway → tectum: roof of midbrain

Answer 28

Formed by the axons of remaining M cells Magnocellular cells are sensitive to light but not colour → sensitive to movement but not fine detail Magnocellular cells from the retina project to the superior colliculus (in the midbrain's tectum) ↳ function: orienting movements to detect and focus the eyes towards stimuli Medial pulvinar → sends connections to the parietal lobe Lateral pulvinar → sends connections to temporal lobe Provides info regarding location: damage to this pathway prevents individual from identifying location of stimuli Superior colliculus sends connections to the pulvinar region of the thalamus

Question 29

Occipital Cortex

Answer 29

Composed of at least 6 visual regions (V1, V2, V3, V3A, V4, and V5) Primary visual cortex (V1; Striate cortex)→ receives input from the lateral geniculate nucleus Secondary visual cortex (V2 to V5; extrastriate cortex) → visual cortical areas outside striate cortex, each region processing specific features of visual input

Question 30

Heterogenous laying in V1 area

Answer 30

Blob (V1) → region in visual cortex that contains colour-sensitive neurons Interblob (V1) → region that separates blobs: participates in perception of form and motion Within V1 region input is segregated by type: colour, form, motion → then projected into V2 region

Question 31

Heterogeneous layering in V2

Answer 31

Thick and thin stripes mixed with pale zones ↳ thick stripes receive input from movement-sensitive neurons in region V1 ↳ thin stripes receive input from V1’s colour- sensitive neurons ↳ pale zones receive input from V1’s form-sensitive neurons Visual pathways proceed from V2 to other occipital/temporal regions

Question 32

Coding location in retina

Answer 32

Each RGC responds to stimulation on a small circular patch of the retina→the cells receptive field ↳ represents outer world as seen by a single cell: think pixel of photo ↳ visual field composed of thousands of receptive fields → very overlapped, influenced by intensity of stimuli Coding Location → light falling on one place on retina will activate one ganglion cell

Question 33

Location in LGN and Region V1

Answer 33

Cells in later geniculate nucleus also have receptive fields Each LGN cell represents a particular place Projects to V1 (striate cortex) forming a topographic map→ pattern of neural activation ↳Info in retina retains spatial position: info in top of one topographic map is on top of the next

Question 34

Topographic organization of region V1

Answer 34

Receptive fields of cells in cortex are typically larger than those of retinal ganglion cells More functional cortical tissue devoted to cells in the fovea than in the periphery →higher acuity because density = receptiveness

Question 35

Neural tissue vs. Function

Answer 35

Amount of neural tissue responsible for a particular function is proportional to the amount of neural processing the function requires Sensory areas that have more cortical representation provide a more detailed construct of the external world

Question 36

Receptive -field hierarchy

Answer 36

Ganglion cells → single LGN cell → single V1 cell Receptive fields combine to form next cell level

Question 37

Retinal ganglion cells (RGC’s) On-center vs. Off-center cells

Answer 37

RGC: respond only to presence or absence of light, not to shape → concentric circle arrangement On - Center cells: excited when light falls on the Center portion of the receptive field; inhibited when light falls on the periphery of the receptive field Off-center cells: excited when light falls on the surround of the receptive field; inhibited when light falls on Center

Question 38

Luminance contrast

Answer 38

Ganglion cells tell the brain about the amount of light hitting a certain spot on the retina relative to the average amount of light falling on surrounding retinal regions Allows input from RGC’s to tell brain about shape

Question 39

Processing shape in V1

Answer 39

V1 neurons receive input from multiple RGC’s ↳ have much larger receptive field than RGC’s ↳ respond to stimuli more complex than light on/off Cells behave like orientation detectors → excited by bars of light oriented in particular directions Simple cells: receptive field with a rectangular on-off arrangement Complex cells: maximally excited by bars of light moving in a particular direction through receptive field Hypercomplex cells: maximally responsive to moving bars but also have a strong inhibitory area at one end of receptive field

Question 40

V1 receptivity

Answer 40

RGC respond maximally to spots of light (not orientation) V1 input comes from ganglion cells aligned in a row

Question 41

Processing shape → temporal cortex

Answer 41

Maximally excited by complex visual stimuli (ex. Face or hands) → very selective Stimulus equivalence: recognizing that an object is the same across different viewing orientations Complex features are necessary for activation of most neurons in area TE → include a combination of characteristics such as orientation, size, colour, and texture Neurons with similar but not identical responsiveness to particular features tend to cluster in columns → functional column

Question 42

Subtractive colour mixing → seeing colour

Answer 42

Obtains entire range of colours by mixing only 3 colours→ property of the cones in the retina Light of different wavelengths stimulates the 3 cone receptor types in different ways Ratio of activity of these 3 receptor types forms our impressions of colours

Question 43

Trichromatic theory

Answer 43

Explanation of colour vision based on the coding of the 3 primary colours Colour we see is determined by the relative responses of the different cone types → all equally active = we see white Can explain different types of colour blindness » lacking one cone receptor type = colour blind Limitation: cannot explain afterimages and 4 basic colours: red, green, yellow blue

Question 44

Opponent-process theory

Answer 44

Explanation of colour vision that emphasizes the importance of the opposition of colours → red vs. Green → blue vs. Yellow Opponent processing occurs in retinal ganglion cells ↳ on-off and center-surround receptive fields ↳about 60% of retinal ganglion cells Cells excited by red are inhibited by green and vice versa ( red-green and blue - yellow = colour opponents)

Question 45

Opponent-colour contrast response

Answer 45

Center of receptive field is excitatory in some cells and inhibitory in other cells Stimulation to the periphery has the opposite effect → Center is responsive to one wavelength and the surround is responsive to another

Question 46

Opponent process → V4

Answer 46

Neurons in cortical region V4 do not respond to particular wavelengths but are responsive to various perceived colours → Center is excited by certain colour, and surrounding is inhibited May be important for colour constancy → perceived colour is constant relative to other colours, regardless of changes in illumination

Question 47

Neuronal activity in dorsal stream

Answer 47

Posterior parietal cortex → involved in processing visual information for action » the ‘how' stream ↳ neurons in this area are silent to visual stimulation when a person is under anesthesia Some cells in this area process the visual appearance of an object to be grasped ↳these cells will fire even when a monkey watches another monkey picking up an object

Question 48

Monocular blindness

Answer 48

Destruction of the retina or optic nerve of one eye, producing loss of sight in that eye → some info still travels into both hemispheres Optic nerve is very difficult to damage

Question 49

Homonymous hemianopia

Answer 49

Blindness of an entire left or right visual field → cuts in the optic track, LGN, or V1

Question 50

Quadrantanopia

Answer 50

Blindness of one quadrant of the visual field

Question 51

Scotoma

Answer 51

Small blind spot in the visual field caused by a small lesion or migraines of the visual cortex Visual white noise essentially

Question 52

Injury to ‘what’ pathway → 3 types

Answer 52

Visual-form agnosia → inability to recognize objects or drawings of objects Color agnosia (achromatopsia) → inability to recognize colours Face agnosia (prosopagnosia) → inability to recognize faces

Question 53

Injury to the ‘how’ pathway

Answer 53

Optic ataxia → deficit in the visual control of reaching and other movements Damage to the parietal cortex Retention of the ability to recognize objects normally

Question 54

Dorsal and ventral visual stream damage

Answer 54

People with damage to the parietal cortex in the dorsal visual stream can see perfectly well→ cannot accurately guide their movements on the basis of visual information People with damage to the ventral stream cannot perceive objects because object perception is a ventral stream function → these same people can guide their movements to objects on the basis of visual information