Lecture 6: Biopsychology, Vision, Retina, and Visual Processing

What is the primary function of vision for most people?

It defines the world around them and allows movement, recognition of people, and identification of objects.

Where does visual processing begin in the human body?

In the retina.

What is the role of specialized neural photoreceptors in the retina?

They catch light energy to initiate sensory processing.

How does human vision operate in relation to bat echolocation?

Both process reflected environmental signals.

What are photons?

Particles that represent light and are involved in electromagnetic radiation.

What are the two types of optical flaws mentioned?

Myopia (nearsightedness) and hyperopia (farsightedness).

What is presbyopia?

A condition where the lens becomes less flexible with age, requiring reading glasses.

What are the five types of nerve cells in the retina?

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

What is the main function of rods in the retina?

To serve low-acuity vision in dim light.

How many cones are concentrated in the fovea?

Approximately 6 million cones.

What happens to photoreceptors in response to light?

They hyperpolarize (become more negative).

What is rhodopsin composed of?

Opsin protein and 11-cis retinal derived from Vitamin A.

What is required for wavelength discrimination in human vision?

Comparing neural output across different cone classes.

What are the primary colors used in RGB color vision?

Red, green, and blue.

What is the difference between additive and subtractive color mixing?

Additive mixing combines light colors (RGB), while subtractive mixing involves pigments (CMY).

What percentage of males and females are affected by red or green color blindness?

About 8% of males and 0.4% of females.

What do bipolar cells do in the retina?

They transform simple photon reports into spatial border detection.

What are the two types of bipolar cells?

On-center and off-center bipolar cells.

How do on-center bipolar cells respond to light?

They depolarize when light hits the receptive field center.

What do retinal ganglion cells generate?

Action potentials.

What is the role of horizontal cells in the retina?

They provide lateral synaptic connections to receptors and bipolar cells.

What is the significance of the fovea in the retina?

It allows light to hit tightly packed photoreceptors directly for high-acuity vision.

What happens to photoreceptors in the dark?

They exhibit a depolarized resting potential (~ -40 mV).

What initiates the phototransduction cascade in photoreceptors?

Photon absorption by visual pigments.

What is the function of amacrine cells in the retina?

They provide lateral connections between bipolar and ganglion cells.

What is the primary purpose of visual pigments in photoreceptors?

To capture light energy.

What is the effect of aging on the lens of the eye?

It becomes less flexible, leading to presbyopia.

What is the role of ganglion cell axons?

They gather as a bundle across the inner surface to leave as the optic nerve.

What type of ganglion cells fire action potentials to dark center spots?

Off-center ganglion cells

What are the two streams into which optic nerve fibers divide?

Magnocellular and parvocellular ganglion cell streams

What is the primary function of parvocellular (P) cells?

To provide detailed, high-acuity foveal vision

What do magnocellular (M) cells specialize in?

Motion detection with large receptive fields

What do ipRGCs contain and where do they project?

Melanopsin; they project to the suprachiasmatic nucleus for circadian control

What do ganglion cell receptive fields require to evoke action potentials?

Luminance boundaries

How do on-center ganglion cells respond to bright centers with dark surrounds?

They are excited

What happens to bipolar or ganglion cells under uniform illumination?

They fail to activate due to surround cancellation

What accounts for the majority of foveal acuity projections?

Parvocellular P-cells

What type of cells exhibit rapid conduction velocity to report peripheral motion?

Magnocellular M-cells

How do retinal ganglion cells encode complementary colors?

By receiving input from opposing cone pairs

What do achromatic ganglion cells detect?

Brightness borders without color tuning

How are red/green ganglion cells activated?

Excited by red in the center and inhibited by green in the surround

What is the result of staring at a colored image for a prolonged period?

Chromatic afterimages due to opponent-color ganglion cell adaptation

What occurs when neutral white light is exposed after adaptation?

It unmasks adaptation by shifting response balance

What visual field does the left visual field project to?

The right hemiretina

What happens to nasal retinal axons at the optic chiasm?

They decussate across the midline

What is the organization of the lateral geniculate nucleus (LGN)?

It organizes retinal input across six distinct layers

Which layers of the LGN do magnocellular ganglion cell axons project to?

Layers 1 and 2

What type of cells respond to small spots or oriented bars in specific receptive field regions?

V1 simple cells

What do complex cells in V1 respond to?

Appropriately oriented straight-line edges anywhere in the field

What is the function of endstopping in complex cells?

It decreases firing when stimulus bars extend beyond receptive fields

What does the dorsal 'where/how' pathway process?

Spatial location and motion

What is the role of the ventral 'what' pathway?

Object recognition

What do IT neurons possess that is significant for visual processing?

Massive receptive fields that include the fovea

What type of organization does the anterior IT have?

Specialized patches responding selectively to faces, colors, and complex scenes