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Behavioural Neuroscience - BN Vision

22 important questions on Behavioural Neuroscience - BN Vision

What is the name of the fluid that fills the eyeball?

Vitreous humour

How does light enter the eye? And how does the image that enter the eyes get focused?

Light enters the eye through the cornea. Behind the cornea is the lens, which is made up of a number of transparent layers. The shape of the lens can be altered to help focus the image onto the back of the eye, which is lined by a light-sensitive structure called the retina.

Describe the light sensitive cells (photosensitive)

Located at the back of the retina - so light must pass through each of the other layers to get to them.

Two types of these photoreceptors: rods and cones.

The rods and cones contain photopigments. These pigments break down when exposed to light. This leads to the neural impulses that are eventually conveyed to the brain by the optic nerve

What are cones important for? Where are they concentrated at?

Seeing fine detail

Concentrated in a region of the retina called the fovea,

Responsible for ability to see colour - different types of cones are also sensitive to different wavelengths of light

What do rods do? Do rods discriminate between different wavelengths?

No, they do not discriminate between different wavelengths

They cannot discriminate fine visual detail.

Much more sensitive to light than cones - so they are used in dim environments

In dim environments, we cannot perceive colour because we are using rods

What do ganglion cells do?

Ganglion cells send their axons through the optic nerve (the second cranial nerve), which conveys visual information to the brain.

The other two cell types in the middle layer of the retina called the horizontal cells and amacrine cells, combine messages from several photoreceptors

Do photoreceptors and bipolar cells produce action potentials? If not, what do they do?

No, they do not produce action potentials. Rather, they release neurotransmitters that increase or decrease the firing rate of action potentials generated by the ganglion cells

What is the optic chiasm?

After leaving the eye, the axons of retinal ganglion cells are bundled together to form the optic nerves. These go to the optic chiasm

At the optic chiasm, roughly half the axons from the retina of each eye cross over to the opposite side of the brain. This causes visual information from the right visual field to be conveyed to the left hemisphere and vice-versa

Where is the LGN located and is there one in each hemisphere?

Thalamus. Yes

Where do neurons in the LGN form synapses with other neurons?

Neurons in the LGN send their axons posteriorly where they form synapses with neurons in the primary visual cortex

Do all LGN axons terminate in the primary visual coretx?

No, 90% of LGN axons terminate in the primary visual cortex. The remaining 10% project to other areas, including the superior colliculus (part of the midbrain) and pulvinar nucleus of the thalamus.

What is orientation preference?

The cells receptive field organisation is such that each cell will fire preferentially to light coming from bars and edges of one particular orientation (e.g., vertical, horizontal, 45° clockwise from vertical, etc.).

This is the beginning of being able to identify the spatial structure in the visual scene.

Areas of the Primary Visual Coretex

Primary visual cortex (V1)

Area V4 - neurons that are sensitive to the colour of visual inputs

Area MT - responsible for moving visual stimuli

Inferior temporal cortex - contains neurons that are selectively responsive to complex objects and faces

Damage to area V1 - When can it occur? What happens if that area is affected?

Occur after a stroke affecting the posterior cerebral artery in the brain.

Damaged - Blind to all visual stimuli arising to the contralateral side of their present point of fixation, e.g., damage to V1 in the right hemisphere will cause blindness in the left visual field.

This disorder is called hemianopia

Damage to Area V4 - What happens if that area is affected?

Achromatopsia (vision without colour).

These individuals continue to see forms and movement, so they are not completely blind.

Instead, one half of the world looks like a black and white movie.

Are patients with pure achromatopsia rare?

Yes, because the strokes that cause brain damage typically affect large areas of cerebral tissue, and almost never damage just one small functional area in isolation

Damage to Area MT - What happens if that area is affected?

Akinetopsia - lose ability to perceive motion but retain ability to perceive shapes and colours

Damage to Inferior part of the temporal cortex

Visual object agnosia - Selective loss of the ability to recognise familiar objects when they see it. But they know it. Because they know what it means when they touch it or hear the word

Are face processing different from other processing? What effect is this?

Face Inversion Effect - People are able to learn to recognise pictures of faces they have never seen before, but they have difficulty learning to recognise pictures of faces when they are turned upside-down.

Thatcher Illusion - We fail to notice even quite striking visual anomalies when a face is shown upside-down.

What part of the brain is responsible for face recognition?

Fusiform gyrus - Located in the inferior part of the temporal lobe

Damage to fusiform gyrus

Prosopagnosia - May have a selective impairment in recognising familiar faces, even though their ability to recognise other objects may still be relatively good

How is a blindspot formed?

The rods and cones in the retina send their axons out of the eye from the optic disk. Because there are no photoreceptors at the optic disk, so it causes a blindspot

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Behavioural Neuroscience - BN Vision

22 important questions on Behavioural Neuroscience - BN Vision

What is the name of the fluid that fills the eyeball?

How does light enter the eye? And how does the image that enter the eyes get focused?

Describe the light sensitive cells (photosensitive)

What are cones important for? Where are they concentrated at?

What do rods do? Do rods discriminate between different wavelengths?

What do ganglion cells do?

Do photoreceptors and bipolar cells produce action potentials? If not, what do they do?

What is the optic chiasm?

Where is the LGN located and is there one in each hemisphere?

Where do neurons in the LGN form synapses with other neurons?

Do all LGN axons terminate in the primary visual coretx?

What is orientation preference?

Areas of the Primary Visual Coretex

Damage to area V1 - When can it occur? What happens if that area is affected?

Damage to Area V4 - What happens if that area is affected?

Are patients with pure achromatopsia rare?

Damage to Area MT - What happens if that area is affected?

Damage to Inferior part of the temporal cortex

Are face processing different from other processing? What effect is this?

What part of the brain is responsible for face recognition?

Damage to fusiform gyrus

How is a blindspot formed?

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