COgn 2nd yr

Visual Field

how much of the outside world the retina can see

Degrees of visual angle

the portion of the retina taken by an object

Anterior chamber

Filled with aqueous humour

Cornea

• Transparent membrane through which light enters the eye

• Lacking blood vessels and nourished by the aqueous humour

• Protects the eye, responsible for some refraction, ensuring visual images are not blurred

Pupil

Opening in the eye - light enters and reaches the retina

Iris

A diaghragm, coloured muscle which regulates light entry to the eye

Lens

Responsible for most refraction, held in place with ciliary bodies

Vitreous humour

Maintains structure and shape of the eye, allows movement of vitamins

Sclera

Protective colouring

Choroid Layer

Continuation of the cornea containing light-absorbing pigment

Optic disc

THe area where retinal blood vessels and fibres of the optic nerve exit the retina

Blind spot

Where the optic nerve and retinal artery enter the eye above the retina

Optic nerve

Bundle of axons from the retina to the brain

Macula

The area of the retina with a high density of photoreceptors

Fovea

Highest visual acuity, more cones

Ophthalmoscope

Device enabling us to peer from pupil to retina

Order of processing in the retina

1. Choroid layer

2. Horizontal cells

3. Bipolar cells

4. Amacrine cells

5. RGCs

Horizontal cells

Lateral inhibition of adjacent cells

Bipolar cells

Form modified 2nd image

Amacrine cells

Form modified 3rd image

RGCs

Produce APs which project to CNS vis optic nerve

What is photoreceptor adaptation

Photoreceptors increase the amount of OPSIN they have

What is OPSIN

Photosensitive protein

Are our perceptions an accurate reflection of reality? Why/

Yes, survival

What kind of process is perception

Active

What does perception being an active process mean

We interpret sensory information to guide interactions with the environment

How many photoreceptors are there in each retina?

100 million

How many cells are there in the brain cortex?

100 billion

How many other cells does each nerve cell make connections to?

4000

What is psychophysics?

The study of quantitative relationships between sensory experience and environmental stimulation?

Who are the two main researchers in psychophysics?

Weber (1834)

Fechner (1860)

What part of psychophysics is Weber influential in?

Ideas

What part of psychophysics is Fechner influential in?

Techniques

How does psychophysics research work?

The subject reports when they detect the presence of a sensory stimulus

What does psychophysics research measure?

The perceptual performance of the entire organism?

What is the central concept of psychophysics research?

The measurement of thresholds

What is the detection threshold?

The weakest stimulus that reliably evokes a sensation in the observer

What is the discrimination threshold?

The smallest difference between two stimuli along a particular dimension that can be detected

What is discrimination threshold also known as?

Just Noticeable Difference

What are the two methods developed by Fechner that are still used?

Limits

Constant Stimuli

What is Limits?

Change stimulus intensity until subject says it is (un)detectable

What is Constant Stimuli?

Present subject with a fixed constant set of stimulus strengths in random order, ask them each time if they detected it

What are the steps involved in a Forced Choice Task?

• Ask subjects to report something about the stimulus

• On each trial present the stimulus at different temporal intervals

• Calculate percentage of correct responses and the threshold

What is the threshold usually?

75%

Signal Detection Theory researcher

Green & Swets (1966)

What is the Signal Detection Theory

Internal noise interfere with perceptual decisions about the world when stimulus is weak

What is Electrophysiology

Recording the electrical activity of cells in sensory pathways

What is Electrophysiology similar to

Neurophysiology

What equipment is used in single cell recording

Microelectrode, Speaker, PSTH

What is PSTH

peri-stimulus-time-histogram

What is PSTH used for in Single Cell Recordings

Plot showing how the firing rate of a cell changes during the time a stimulus is presented withing its receptive field

What do Single Cell Recordings allow us to map

The receptive field of a cell

What is the range of constriction / dilation of the pupil

1-8mm

What happens to the firing rate of ON-centre cells when light hits the centre region?

Increases

What happens to the firing rate of OFF-centre cells when light hits the centre region?

Decreases

Where are the receptive fields of cells smallest?

Fovea

What is the size of receptive fields in the fovea?

0.01mm

What does the size of RFs in the fovea mean for spatial resolution and why?

High spatial resolution - low neural convergence factor

What does centre-surround organisation help us do?

Identift edges in images

What does each RF respond optimally to?

A bar of particular width depending on its size

What do small RFs respond best to and why?

Small objects - good spatial resolution

What do large RFs respond best to and why?

Large objects - bad spatial resolution

What are RGCs sensitive to?

The phase

What is the phase?

The relative position of a grating in its cycle

What are the three subdivisions of the Lateral Geniculate Nucleus?

Magnocellular

Parvocellular

Koniocellular

Proportion of M, P, K cells

10, 80, 10

RF size of M, P, K cells

Large, Small, Medium

Retinal position of M, P, K cells

Peripheral, Central, Peripheral

Axon diameter of M, P, K cells

Thick, Thin, Thin

Conducion velocity of M, P, K cells

Fast, Slow, Slow

Best objects of M, P, K cells

Large Low Cont, Small High Cont, Larg Low Cont

Colour sensitivity of M, P, K cells

No, Yes, Yes

Temporal response of M, P, K cells

Transient, Sustained, Sustained

Info extracted from M cells

Where is it? Does it move?

Info extracted from P cells

What is it? What colout?

Info extracted from K cells

Where is it? How bright?

Which cells in the retina fire action potentials

Ganglion cells

What do cells in the retina apart from ganglion cells respond to stimulation with?

Graded changes in membrane potenial

What do photoreceptors release when depolarised?

Neurotransmitter amino acid Glutamate

Under which circumstances are photoreceptors depolarised?

Dark

Under which circumstances are photoreceptors hyperpolarised?

Light

What is the preferred stimulus for a photoreceptor?

Dark

What are OFF bipolar cells?

Ionotropic glutamate receptors

How do ionotropic glutamate receptors work?

Glutamate-gated channels, influx of sodium ions, classical depolarisation

What does the hyperpolarisation of cone cells cause?

Less neurotransmitter to be released, more hypolarised bipolar cells

What are ON bipolar cells?

Metabotropic G-protein-coupled receptors

How do Metabotropic G-protein-coupled receptors work?

They respond to glutamate by hyperpolarising

Where do APs go from RGCs?

Optic nerve

What is the optic nerve also known as

2nd cranial nerve

What happens to projections from the contralateral hemifield at the optic chiasm?

Switch sides

What is the crossing of fibre bundles called?

Decussation

Where does the optic tract project to?

LGN

Where is the LGN?

Thalamus

Where do optic radiations project to after LGN?

Visual cortex

Which retinal areas view the left hemifield?

Right eye - Temporal

Left eye - Nasal

Which retinal areas view the right hemifield?

Right eye - Nasal

Left eye - Temporal

Where do RGC axons that don’t project to LGN go to?

Superior colliculus

Hypothalamus

What is the superior colliculus involved in

Eye movements

What is the hypothalamus involved in

Circadian rythm

How many layers of the LGN are there?

Six