Lecture 2 - Light, Eye and Retina: First Steps in Seeing

Question 1

How does light travel, and what 3 things can happen to it?

Answer 1

In straight lines from a light source - can be absorbed, reflected or refracted

Question 2

What are human eyes known as?

Answer 2

Image forming eyes which enable us to see and understand the information from the light and interpret them

Question 3

We have two lenses, what are they called and what do they do?

Answer 3

Called lens and cornea, they focus light onto the retina by allowing light to pass through whilst changing its direction (due to the curved, transparent material).

Question 4

What happens after light passes through the lenses (in general)

Answer 4

Hits the back of the eye, known as the retina

Question 5

What is the retina?

Answer 5

A sheet of photosensitive neruones that turns light energy into electircal signals to communicate with the brain

Question 6

What are the 3 main components of the retina?

Answer 6

Photo receptors (rods and cones), Interneuones (horizontal, bipolar and amacrine cells) and axons to brain via optic nerve (ganglion cell)

Question 7

Describe Rods (5 bits of info)

Answer 7

Many receptors (100mil), one type of photo pigment (colour blind, only register light), very sensitive to light (so used in dim light - scotopic vision), poor spatial resolution, high temporal resolution and most sensitive to green light.

Question 8

Describe cones (5 bits of info)

Answer 8

Less receptors (6mill), Have S, M and L cones - wavlengths, less senstive to light (photopic vision), high spatial resolution, poor temporal resolution, more sensitive to yellow light

Question 9

Explain why rods have poor spatial resolution but cones have high

Answer 9

For every ganglion cell in the retina, there are 4 possible rods and only one cone. This means, if the rods (and therefore then ganglion cell) is activated, it cannot determine specifically which space the info is coming from. However, since there is just one cone for every ganglion cell, the localisation of activation is easy to identify.

Question 10

Discuss the distribution of photoreceptors (Fovea, peripheral)

Answer 10

Photoreceptors are not equally distributed across the retina. Cones are concentrated in the central area (fovea) but rods are completely absent from this area and located in the periphery.

Question 11

describe the blind spots in the retina

Answer 11

There is a gap in both retinas which is where the optic nerve is to communicate the electrical information to the brain so we have blind spots in each eye. However, we do not see this because these are located in different points in both eyes.

Question 12

Define the receptive field

Answer 12

A specific region of sensory space in which an appropriate stimulus leads to a response in a sensory neuron.

Question 13

Describe the following section of the receptive field definition: region of sensory space

Answer 13

This refers to the spatial resolution of rods and cones - ganglion cells retrieving information about light from a specific, corresponding region of the photoreceptors.

Question 14

Describe the following section of the receptive field definition: an appropriate stimulus

Answer 14

Some photoreceptors are negatively connected (causing inhibitory response) to ganglion cells and some are positively connected (excitatory response). An appropriate stimulus is when the light hits enough the positive photoreceptors to cause more activation than the baseline (instead of hitting negative which inhibits activation).