Sensory Systems and Perception

Question 1

What happens when sensory input is disrupted, why?

Answer 1

We become lost very quickly.

What we see in front of us is not reality but rather what our minds have constructed. Our conscious experience is a construction of our minds and the way we see this reality is based on this construction.

Question 2

What is the very first things that happens when you see an object?

Answer 2

You begin to identify patterns in the environment.

Question 3

What are some features of the environment that aid in pattern recognition?

Answer 3

Light and Shade
Contours
Adjacent parts where light parts connect to dark parts

Question 4

What does ‘noise’ have to do with our visual field?

Answer 4

When information is initially processed in the back of the eye images are distorted, upside down and contain scrambled noise. It is this noise that needs to be extensively processed, filtered and enhanced in the brain in order to make sense of things.

Question 5

What is a complication of our visual field?

Answer 5

We are only able to interpret what we can see.

Question 6

What are photoreceptors and how are they spread around the retina?

Answer 6

They are specialised cells for detecting light. They are extremely sensitive and direct light can kill them, overtime UV poisons them and they become weaker.

They are spread around the retina in different densities with the most dense pocket being in the Fovea.

They turn light into electric signals.

Question 7

What is the retina?

Answer 7

The retina contains millions of light-sensitive cells (rods and cones) that receive and organise visual information. The retina sends this information to your brain through your optic nerve , enabling us to see.

Question 8

What is the Fovea and what is its function?

Answer 8

It is at the back of the retina, where densely packed photoreceptors are stored. It has the highest level of visual acuity in the eye. The Fovea is the first structure light will hit serving to focus our attention.

Question 9

What is an illusion of our perception?

Answer 9

The vision outside of things you are looking at is quite poor, making the point you are looking at, or focused on, quite acute. Images are filtered to pay particular attention to the things you are directly looking at.

Question 10

What is the blind spot?

Answer 10

A part of the retina where there are no photoreceptors. Cells loop out and back covering this part of the retina. The brain is unaware of of this ‘big hole’ in the visual field and compensates by ‘filling in’ information that we perceive to be there.

Question 11

What is the optic nerve?

Answer 11

It transmits sensory information for vision in the form of electrical impulses from the eye to the brain.

Question 12

What are the 3 main layers of cells in the Retina?

Answer 12

Bipolar Cells
Ganglion Cells
Photoreceptors

Question 13

How do photoreceptors store information?

Answer 13

Light is captured and streamed in from different sources in the environment. Each photoreceptor receives a quantum of light relative to where you are looking. Photoreceptors have memory and preserve where the light is coming from, creating a map in your brain.

Question 14

How does light move through the eye?

Answer 14

light hits the retina (a light sensitive area at the back of the eye). It then penetrates 3 dense layers of cells, bouncing off the back of the eye into the photoreceptors.

Question 15

What happens before light reaches the retina?

Answer 15

It moves into the choroid, which is jet black, and serves to absorb light before reflecting back into the photoreceptors. This is because light is toxic to photoreceptors.

Question 16

How do we turn light into seeing objects/lines/shapes?

Answer 16

Firstly, we find edges, discontinuity, heaps of light, heaps of dark, at the retinal ganglion level we register these edges and discontinuities as possible shapes.

Question 17

What is the first step at the ganglion cellular level in processing light into seeing objects/shapes/lines?

Answer 17

1. Begins in the outermost point of the cellular layers.

light enters and bounces back off the choroid and enters the photoreceptors . depending on the type of light the photoreceptor wants to see, it will fire, generating an action potential. Thus, releasing neurotransmitters.

Question 18

What are bipolar cells?

Answer 18

They are cells that bridge signals from photoreceptors to ganglion cells.

Multiple retinal photoreceptors converge onto one single bipolar cell, creating a tapestry of small receptive fields across the retina representing a region of space.

Question 19

What are ganglion cells?

Answer 19

They are the most complex information processing systems in the retina and are the final output neurons seeing a tiled image of the world.

Question 20

Importance of light in the ganglion cells?

Answer 20

Depending on where light is in the receptive field can increase different levels of excitation and inhibition.

Input is excitatory when there is direct light in receptive field centre.

Output is inhibitory when there is a decrease in light, from the periphery.

Question 21

Importance of light in the ganglion cells?

Answer 21

Depending on where light is in the receptive field they can create different levels of excitation and inhibition.

Input may be excitatory when there is direct light in receptive field centre.

Output may be inhibitory when there is a decrease in light, from the periphery.

Question 22

What are two distinct characteristic of the receptive field?

Answer 22

On centre off surround, and

Off centre on surround.

Question 23

What is the on centre off surround receptive field?

Answer 23

This is where ganglion cells fire at maximum (on-centre) when it sees a bright spot in a dark background.

Question 24

What is the off centre on surround receptive field?

Answer 24

This is where ganglion are inhibited by wanting to see a dark spot in a light background. Inhibition in the centre, excitation all around.

Question 25

How do the receptive fields work together?

Answer 25

Edge detectors

Integrate patterns of light over an area and indicate if patterns are different to an adjacent area.

Question 26

What is the ciliary muscle?

Answer 26

It works as a lens that is variable in shape to do with focus. It can be stretched out, pushing focus further away or can be squished in pushing the focus closer.

Question 27

What is the fovea?

Answer 27

It is the exact centre of the visual field, where light rays enter the eye straight along the axis of the eye.

Question 28

What are the two photoreceptors that accentuate the middle of the visual field?

Answer 28

Cones and Rods

Question 29

What are cones?

Answer 29

They are densely packed, highly acute photoreceptors responsible for colour vision.

There are three kinds, Red, Blue and Green which receive different waves of light. They work primarily in photopic (daylight) vision.

Question 30

What happens to cones in the transition from photopic to mesopic to scotopic vision?

Answer 30

They slowly die without the light in photopic conditions. They perceive colours in an abnormal way in mesopic vision (dusk) until dying in complete dark (scotopic) after 30 minutes. If you see colour in complete dark it is due to your brain remembering the colour of the object.

Question 31

What are rods?

Answer 31

Cells in the retina and peripheral visual fields responsible for black and white vision, seeing every shade of grey.

They have more acuity in detecting luminance as they work at night.

Question 32

What is the optic nerve?

Answer 32

It is the long nerve that travels from the back of the eye to the thalamus and other hindbrain structures.

Question 33

What is the characteristics of the eyes ipsilateral arrangement?

Answer 33

Because light travels in a straight direction, if it is coming from the right visual field it will hit the left side of both eyes. Vis a vis for the left visual field.

Left visual field information is then stored in the right brain, and right visual field information is stored in the right brain.

Question 34

What is the optic chiasm?

Answer 34

This is where the two bundles of nerves from the left and right cerebral hemispheres cross over one another until they reach the thalamus

Question 35

What is the lateral geniculate nucleus?

Answer 35

It is a part of the Thalamus that processing information, receives projections then sends it to the occipital lobe

Question 36

What are the two synaptic connections in the transference of visual information?

Answer 36

1. From Basal Ganglion cells to the Thalamus

2. Thalamus to the occipital lobe.

Question 37

What are the two pathways in which visual informations flows or processed?

Answer 37

The ‘what’ and ‘where’ pathway’s.

Question 38

What is the ‘what’ pathway?

Answer 38

A pathway that runs from the striate (visual) cortex through to the lower temporal lobe determining what an object is. Objects in the striate cortex such as lines evolve into more complex shapes like cones or squares eventually processing colour and texture at different points along the pathway. All processes occur simultaneously, shape information processed in a shape module, colour information processed in a colour module etc.

Question 39

What is the ‘where’ pathway?

Answer 39

Involved in locating objects in space, following its movement, and guiding movement towards it. This pathway moves from the striate cortex through the middle and upper regions of the temporal lobes and up into the parietal lobes.

Question 40

Huber and Weasel discovered the intelligent filters in the Primary Visual Cortex, known as V1. What are these cells called and how do they work to understand objects, relative to their complexity?

Answer 40

Simple cells
They respond to an edge at a particular orientation in a specific part of the visual field.

Complex cells
Respond to an edge at a particular orientation falling anywhere within a wider field. May also respond to motion.

Hypercomplex cells
Respond to a line which ends within the receptive field ‘end stopping’

Question 41

How to higher level intelligent filters work?

Answer 41

These are filters that are primarily at work in the temporal lobe. They detect combinations of lines/edges (squares or cone shapes) as well as colour and orientation combinations.

Question 42

What is an implication to our visual processing filters if there is a lesion in the temporal lobe?

Answer 42

Generally there is an agnosia of some kind, being the inability to recognise objects. Some regions specific in identifying faces can cause prosopagnosia, with the ability to identify others things, just not faces.

Question 43

What is an implication of damage to the parietal lobe in terms of visual processing?

Answer 43

This can cause problems of spatial awareness, creating visual neglect.

This can result in hemineglect, where one whole side of the visual field is lost.

Question 44

How does hemineglect manifest?

Answer 44

As various levels of denial about the the world, as if the missing parts in the world don’t exist. This is how the brain copes.

Question 45

What is some key information about visual maps?

Answer 45

We are constantly building, developing and adding onto our visual maps, creating multiple parallel visual maps. This is a product of evolution where some systems are still imprinted in us however have become redundant.

These maps are creating retinotopically meaning that what we see in our visual field is mapped onto the retina, specifically centred-weighted in the fovea.

Question 46

What is blindsight?

Answer 46

Where individuals are unaware of their ability to see. They cannot visualise the environment but unconsciously interact with objects presented to them. Speculating, that visual processing happening in the superior colliculus as well as the lateral geniculate nucleus apparently leads to visual responses that can guide behaviour outside of awareness.

Question 47

If you had a robot and wanted to build a visual system what are all the basic fundamentals it will need to process information?

Answer 47

A system for detecting light.

A system for focusing on important stuff, a lens, ciliary muscle, fovea, cones, rods.

System for detecting edges (ganglion and simple cells)

Higher system for identifying objects from the edges and patterns (temporal lobe and filters for patterns)

Higher system for identifying where objects are (Parietal lobe system)