Ch 6 The Visual System

Question 1

wavelength is to ___ what intensity is to ____

Answer 1

colour, brightness

Question 2

why does it help to have eyes on front of head

Answer 2

3D perceptions from 2D images

convergence

Question 2

sensitivity vs acuity

Answer 2

sensitivity: ability to detect dimly lit objects

acuity: detail

Question 3

how does the lens move to accommodate to distance

Answer 3

ciliary muscles will flatten lens for far away objects, and bend for closer ones to refract light onto the retina

Question 4

binocular disparity

Answer 4

○ Difference in the position of the two retinas
○ Greater for closer objects
○ Can use this to make 3D perceptions

Question 5

5 types of neurons in the retina

Answer 5

Receptors (rods and cones)

Horizontal cells

Bipolar cells

Amacrine cells

Retinal ganglion cells

Question 6

inside out structure of eye

Answer 6

Light Path: Light passes through the retina layers before reaching the receptor layer. Once activated, receptors send neural signals back through the layers to the retinal ganglion cells.

Question 7

features of blind spot

Answer 7

Located where the bundle of ganglion cell axons exit the eye.

This creates a gap in the receptor layer.

The brain compensates for this by filling in the gap with surrounding information (completion).

Question 8

surface interpolation

Answer 8

brain takes limited info cues light edges/general shapes and fills it in - perception comes from the partial image

Question 9

what kind of vision is each rods and cones

Answer 9

rods: Scotopic

cones: photopic

Question 10

Differences in Convergence

Answer 10

Scotopic Vision: Many rods (hundreds) converge onto a single ganglion cell. This helps to summate signals for maximum light sensitivity but loses detail.

Photopic Vision: Fewer cones converge onto a ganglion cell, allowing for high detail and colour perception but less sensitivity to light.

Question 11

Purkinje Effect:

Answer 11

In bright light, yellow/red colors appear brighter.

In low light, blue/green colors appear brighter.

This is because the eye’s sensitivity to different wavelengths changes depending on light conditions.

Question 11

Types of Fixational Eye Movements:

Answer 11

Tremor: Small, high-frequency movements.

Drift: Slower, low-frequency movements.

Saccades: Small jerky movements.

Question 12

why do eyes move a little

Answer 12

neurons really just respond to changing images

Question 13

describe visual transduction

Answer 13

rods contain rhodopsin, and in the dark is red and have absorbing capacity (bright light bleaches and it loses ability)

rhodopsin is g-coupled protein

In the dark:
Sodium channels are partially open.
Rod is slightly depolarized.
Glutamate is continuously released, causing inhibition of downstream neurons.

In light:
Sodium channels close.
Rod hyperpolarizes.
Glutamate release decreases, allowing downstream neurons to become activated.

Question 14

basis of the retina-geniculate-striate pathway

Answer 14

Conducts signals from each retina to the primary visual cortex via the lateral geniculate of the thalamus

Question 15

Visual Field Representation: pathway from eye to pvc

Answer 15

Signals from the left visual field are processed in the right primary visual cortex.

Ipsilateral: Temporal hemiretina (same side).

Contralateral: Nasal hemiretina (opposite side, via optic chiasm).

Question 16

Lateral Geniculate Nucleus (LGN):

Answer 16

Composed of 6 layers.

Receives contralateral visual field input (3 layers from each eye).

top 4 P layers (small cell bodies)

bottom 2 layers M layers (large cell bodies)

Question 17

P vs M layers

Answer 17

P
Responsive to color, fine patterns, and stationary or slowly moving objects.
Cones contribute to P layer input.

M
Responsive to motion.
Rods contribute to M layer input.

Question 18

striate cortex

Answer 18

LGN projects onto layer IV

Question 19

mach bands

Answer 19

part of contrast enhancement

Enhance the contrast at each edge and make the edge easier to see

Question 20

Foveal neurons have ____ than peripheral neurons (consistent with higher acuity).

Answer 20

smaller receptive fields

Question 21

things known about receptive fields in the eyes

Answer 21

All monocular: each neuron had a receptive field in one eye but not the other

Had receptive fields that comprised an excitatory area and an inhibitory area separated by a circular boundary

On-center cells: Respond to light in the center, inhibited by light in the periphery.

Off-center cells: Inhibited by light in the center, excited by light in the periphery.

Question 22

on and off centre cells respond best to

Answer 22

contrast

Question 23

Simple Striate Cells:

Answer 23

Monocular (one eye). Respond to straight lines (not diffuse light). Prefer specific orientations and positions of lines.

Question 23

Complex Striate Cells:

Answer 23

Binocular (both eyes). Larger receptive fields than simple cells. Responsive to straight-edge stimuli at a specific orientation, regardless of position. Some ocular dominance: Respond more to one eye over the other.

Question 24

Binocular Complex Striate Cells:

Answer 24

Retinal disparity: Role in depth perception. display some ocular dominance (better in one eye than the other) Respond to stimuli in both eyes, with slight differences in retinal positions.

Question 25

organization of the primary visual cortex

Answer 25

functional vertical columns (at right angles to the cortical layers) all neurons in the same column respond to the same type of stimuli neurons with simpler preferences converge on those with more complex ones (retina->thalamus->cortex)

Question 26

retinal ganglion cells vs lateral geniculate cells

Answer 26

Retinal Ganglion Cells: Distinct types: Monocular, on-center/off-center, responsive to orientation, motion, and direction. Lateral Geniculate Cells: Some are sensitive to more than just contrast: Orientation, motion, direction of motion.

Question 27

what is component theory for processing of colour

Answer 27

3 kinds of colour receptors with diff spectral sensitivity any colour we see is from a combo of those 3 receptors (mixing 3 wavelengths of light)

Question 28

colour constancy

Answer 28

an object can stay the same colour even though it can reflect diff wavelengths of light (dark room vs lit room) the colour is the same although we perceive it differently

Question 28

opponent theory of colour vision

Answer 28

two classes of cells for colour, one for brightness the colour ones have opposite/complementary colours depending if they hyper or depolarize complementary cannot exist at smae time (make black or white)

Question 29

location and role of primary visual cortex

Answer 29

Location: Posterior region of the occipital lobes. Role: The first cortical area involved in processing visual information.

Question 29

retinex theory

Answer 29

has to do with colour constancy The colour of an object is determined by its reflectance—the proportion of light of different wavelengths that a surface reflects. Key Points: The efficiency of absorption and reflection of different wavelengths by the surface does not change. The visual system compares the light reflected by adjacent surfaces across at least three different wavelengths and calculates the reflectance.

Question 30

location and role of secondary visual cortex

Answer 30

Gets input from: The primary visual cortex. Components: Prestriate Cortex: Band of tissue in the occipital lobe surrounding the primary visual cortex. Inferotemporal Cortex: Located in the inferior temporal lobe.

Question 31

location and role of the visual association cortex

Answer 31

Gets input from: Secondary visual cortex and other secondary areas. Location: Several parts of the cerebral cortex, with the largest area in the posterior parietal cortex.

Question 32

what is a scotoma? why do people often not notice they have one

Answer 32

area of blindness caysed by damage to primary visual cortex completion

Question 33

dorsal vs ventral streams for visual perception

Answer 33

Dorsal Stream Pathway: Primary visual cortex → Dorsal prestriate cortex → Posterior parietal cortex. Function: Processes spatial stimuli (e.g., "where" things are located in space). Ventral Stream Pathway: Primary visual cortex → Ventral prestriate cortex → Inferotemporal cortex. Function: Processes characteristics of stimuli (e.g., "what" things are).

Question 34

Control of Behaviour vs Conscious Perception ventral vs dorsal

Answer 34

Dorsal Stream: Mediates direct behavioural interactions with objects. Ventral Stream: Mediates conscious perception of objects.

Question 35

prosopagnosia

Answer 35

inability to recognize faces FFA occipital face area (OFA) lateral prefrontal cortex

Question 36

akinetopsia

Answer 36

A deficiency in the ability to see movement progress in a normal smooth fashion ○ See only periodic snapshots of the world middle temporal area of the cortex

Question 37

functions of V1, V4 and MT

Answer 37

V1: straight lines, analysis of orientation, movement and colour V4: colour MT: movement perception (speed and direction)

Question 38

Ocular Dominance Columns

Answer 38

Definition: The separation of input from the right and left eyes in V1. Development: During early development, inputs from both eyes may overlap. As the brain matures, distinct ocular dominance columns form, where each column responds primarily to one eye. These columns alternate between the right and left eyes, and each V1 cell may fire more strongly in response to one eye's stimulation.

Question 39

Orientation columns

Answer 39

Definition: Clusters of cells in V1 that respond to the same orientation of visual stimuli (e.g., vertical or horizontal lines). Systematic Arrangement: Each column in V1 has a slightly different orientation preference, creating a full 360-degree representation of orientations.

Question 40

blobs

Answer 40

Regions in the center of ocular dominance columns that contain neurons sensitive to colour.

Question 41

amblyopia/lazy eye

Answer 41

A condition that occurs when visual input from one eye is not fully functional during early development. can shift ocular dominance solve by patching eye

Question 42

What is the Binding Problem?

Answer 42

Question: How does the brain combine activity from different areas of the cortex into a unified, conscious perceptual image? The brain must integrate information from many different sources, like motion, shape, color, and location, to create one coherent perception of an object or scene.

Question 43

Hypotheses to Address the Binding Problem

Answer 43

1. Single Neuron/Feature Detector Hypothesis Idea: Specialized neurons are responsible for detecting specific features of an object (e.g., a "Taylor Swift neuron" that activates when seeing Taylor Swift's face). Issue: The brain has a limited number of neurons, making it unlikely for there to be a unique neuron for every object or feature we encounter. 2. Assembly Coding/Distributed Recognition System Idea: Rather than a single neuron, the brain combines the activity of neurons across different areas to form a unified perception. Distributed System: Different areas of the brain specialize in processing different features (e.g., color, shape, movement), and their combined activity leads to the formation of a complete visual perception.