PSYCH 261 Lecture 13 + 14 (Critical periods) - Uncompleted

Gestation  (the period of development inside the womb)

• Exposure to stress or infection during gestation can cause an increased risk of depression, schizophrenia and autism spectrum disorders

• It can then cause a transgenerational effect where other generations are also effected

Impact of enriched environments

• Dendritic arborization: The branching and growth patterns of dendrites

  • In enriched environments, theres more dendrites and the dendrite branches are more spread out

• Spine density: Higher density of dendritic spine which means more connections

The electromagnetic spectrum 13

• A spectrum that shows the range of electromagnetic radiation based on wavelength or frequency

How does light travel? 13

• Light travels in straight lines and can provide info about object location, size, shape and texture

1. Iris: Creates a opening called the pupil so that the light can pass through

2. Pupil: light passes through the pupil and hits the lens

3. Lens: Thickness of the lens is controlled by the ciliary muslces

4. Ciliary muscles: controls refraction of light so that it hits the back of the eye and focuses the image on the retina

5. Retina: at the back of the eye

6. Vitreous humour: A fluid where light travels through

7. Fovea: At the back of the retina and is densly packed with cones

8. Optic disc: At the back of the retina

Normal vision 13

Light focuses on the plane of the retina

Hyperopia 13

Light focuses behind the plane of the retina

• “Far-sighted” = objects close by looks blurry

Myopia 13

Light focuses before the plane of the retina

• “Near sighted” far away objects are blurry

Receptive fields 13

An area in visual space where light has to hit it to excite or inhibit neurons —> Excitation/inhibition of neurons depends on the light

Center-surround receptive fields 13 

Important in understanding how visual information is processed in the eyes retina

??

ON-center / OFF-surround ganglion cell 14

• When the surround of the ganglion cell receptive field is illuminated/ light hits the surround, the firing rate of the ganglion cell is reduced —> inhibition

• When the center of the ganglion cell receptive field is illuminated, the firing rate of the ganglion cell is increased —> Excitation

3 types of ganglion cells - 14

1. Parasol

2. Midget

3. Bistratifed

Parasol ganglion cell 14

• Large receptive field

• Responsive to low spatial frequency

Midget ganglion cells 14

• Small receptive field

• Responsive to high spatial frequency

Colour: trichromatic theory 14

Colour perception occurs through the relative rates of response by three kinds of cones

Red-green colour blindness 14

• Occurs on the X chromosome so more common in males

• People see the world in yellow and blue

• Protanopia: red cones has green opsin

• Deuteranopia: green cones has red opsin

Blue-yellow colour blindness (tritanopia) 14

• Rare

• Retina doesn’t have blue cones

• People see the world in reds and greens

Colour: opponent-process theory 14

Receptive fields of bipolar cells and ganglion cells respond in a center-surround, opponent-process way

Colour constancy 14

Regions producing diff wavelengths of light are perceived as having a similar colour

Retinocollicular pathway 14

??

Geniculostriate pathway 14

??

Cortical magnification - 14

Foveal information is allocated disproportionately more tissue in the primary visual cortex than is peripheral information —> the brain gives more processing power to foveal vision (the center of the visual field) because it provides the most important and detailed visual information.

Simple cells, complex cells and hypercomplex/end-stopped cells in the primary visual cortex (V1) - 14

1. Simple cells

• Has receptive fields with fixed excitatory and inhibitory zones

2. Complex cells

• Responds equally anywhere within a large receptive field 

• Respond mostly to a stimulus moving in a particular direction

3. Hypercomplex/ end-stopped cell

• Has strong inhibitory area at one end of the bar-shaped receptive field

Damage to the left primary visual cortex….

Causes loss of awareness of information presented to the right visual field

Photoreceptor cells - 13

1. Rods

• A lot of it is in the periphery of retina

• Supports night time vision —> so its only responsive (inhibited) at low intensities of light

• Contains rod lamellae (disks)

2. Cones

• There’s a lot of cones in and near fovea

• Supports bright light and is important for colour vision —> is only responsive in bright light

• Has cone lamellae (Sacs)

Transduction in the rod —> How a rod cell in the retina works in the dark - 13

DARK

• Rod cells are depolarized and active in the dark b/c rods are only responsive in the dark

1. In the dark, retinal is in the inactive 11-cis configuration

2. Phosphodiesterase inactive —> leading to high concentration of cGMP

3. cGMP binds to ion channels, which opens them and the rods becomes depolarized

Transduction in the rod —> How a rod cell in the retina works in light - 13

• In light (E.g sunlight), rods becomes hyperpolarized

1. Light activates retina —> changes 11-cis to all-trans configuration

2. cGMP —> changed to GMP. Therefore, the amount of cGMP decreases

3. cGMP doesn’t attach to ion channels, causing ion channels to stay close and rods becomes hyperpolarized

Two ways your eye processes visual information depending on where light hits the retina - 13

1. Foveal vision

• Light hits the fovea (Central part of the retina)

• Has mostly cones, so this vision is helpful for colour perception and focusing on fine/small details (E.g focusing a object only, reading a text)

• Each single photoreceptor (cones) is connected to a single bipolar cell, which creates a high resolution perception —> bipolar cells have a small receptive field —> so can see small details very clearly 

2. Peripheral vision “seeing at the corner of your eye”

• Contains mostly rods

• Many rods connect to a single bipolar cell —> bipolar cells have a large receptive field (receiving light)

  • Large receptive field vision makes it harder to focus on single/small details

• But, it is good for darkness and detecting motion