VISUAL PERCEPTION

Question 1

What is Vision for?

Answer 1

Survival. - we need our vision to find desirable things and to avoid dangerous things.

Question 2

What types of eyes do certain species have and what’s the main distinction?

Answer 2

Humans and animals such as dogs and cats have frontal eyes as we are predators. Animals such as rabbits and deers have side eyes as they are prey.

Question 3

What is the evolution perspective of frontal eyes and side-eyes? And what are the key details?

Answer 3

Side eyes (as seen on a rabbit) are to help with an expanded visual field for spotting predators. They have a 330-degree visual span. They have a slim overlapping area of both eyes which is important for depth information.

Frontal eyes (as seen on a human) are to help with an accurate target on prey. Our visual field is larger but slightly smaller - a span of 190 degrees. We have a huge overlapping space, which provides us with binocular information: a cue for distance information. This helps to know the exact location of the prey. Great depth perception.

Question 4

What is Perception as a Constructive Process? What is our brain doing in this process?

Answer 4

The idea is that perception is not just about detecting stimuli, but also involves interpreting and organising information to create a coherent understanding of our environment. Our brain actively constructs our perception of the world rather than passively receiving sensory input.
- Our brain is constantly making unconscious inferences.

eg: Our perception of an object’s colour will change depending on the light colour in the room. i.e. if the room is red then the green hoodie will look different due to the illumination.

• our mind will consider the colour of the walls, floor, and ceiling when judging an object’s colour
• If our mind is familiar with the room colour, we will readjust its perception of a particular object’s colour to what it truely is, despite the red illumination. This is called Light Constancy: when the colour of an object is perceived as being the same under different lighting conditions.

Question 5

Why is perception constructiveness important?

Answer 5

-To predict the future, using prior knowledge and experience
-To classify/arrange objects, to identify them and categorise them
-To process information selectively - delegating our attention to relevant sensory input, and filtering out irrelevant information
-To reduce processing load by simplifying sensory info - chunking information by grouping them into meaningful units

Question 6

What is the anatomy of the human eye and the basic processes for seeing?

Answer 6

General: we have overlap and binocular information to tell us the distance between things

Seeing: the target object reflects light onto our eyes - we process the light rather than the actual object

The eye:
SCLERA: tough protective covering outside our eyes
CORNEA: Transparent part, the light enters through our eye here
IRIS: at the back of the Cornea is the iris muscle (colour part) which holds the pupil in the middle
PUPIL: can be large or small based on the intensity of light - i.e small pupil allows less light in when too bright
LENS: The lens can change shape to help with specific ranges of focus
RETINA: at the backside of our eye. We have lots of cells in our retina. Photoreceptors on our retina are the most important: they receive light and then convert it into electrical signals which is transmitted through the optic nerve to the brain.
BLIND SPOT: An area in our eye where the retina connects to the optic nerve, here there are no photoreceptors.
IMAGE: The image is projected upside down in our brain, but our brain turns it back around.

Question 7

Explain how we focus light by the lens.

Answer 7

Our lens will vary in shape depending on the distance of the target stimuli.

For distant objects, the lens shape must be thin to project the object onto our retina. The closer by objects are focused behind the retina to ignore them

For Nearby objects we need a thick lens, they are required to project onto the retina

Question 8

What are the normal and abnormal lens processes/conditions

Answer 8

Normal: the lens has great elasticity, and flexibility and can adjust and change in shape easily - allowing short and long vision.

Nearsighted/ Myopic: Caused by thick lens (or eyeball is too long), which cant be flattened enough to see far away. The projected image is projected infront of the retina therefore its vague and isnt being percieved well.

Farsighted/Hyperopic: Lens is too thin, couldn’t be thivkened enough to see close up images. Images are projected to behind the Retina and we can’t see behind our retina ofc/ it’s unclear

Presbyopia: same as farsightedness but the cause is due to aging. Our lens become rigid/ loss of elasticity

Question 9

What are the types of Photoreceptors?

Answer 9

We have 2 types, they differ in size, shape, sensitivity and function

Rods: 100-200 million.
- they detect light, very sensitive, IN dark rooms our visions rely on rod cells. Location are in peripheral locations except for the fovea and blind spot.

Cones: We have three types of cones S,M,L. Each one is sensitive to different wavelengths/ colours.
We can perceive different colours because we have different cone cells.
Mainly concentrate Fovea, daylight vision relies on cone cells - sensitive to light, must have light to determine colours.

Question 10

Explain what happens with Dark Adaptation.

Answer 10

At the first moment of turning off lights, we can’t see anything - our cone cells have no light source to reflect info to us anymore.

At first, our eyes haven’t adapted. After time, our rod cells begin to make out shapes in the room - we have adapted/ adjusted.

Question 11

Explain Cone Adaptation.

Answer 11

Is the process by which the cone cells in our eyes adjust to different levels of light so that we can still see colours accurately in various lighting conditions.

Question 12

Explain Rod Adaptation.

Answer 12

The process by which the rod cells in our eyes adjust to different levels of light, particularly in low-light conditions, to help us see in the dark. i.e dark adaptation

Question 13

Explain Lateral Inhibition

Answer 13

The contrast relates to a boarder: the boarder for one object is the end of one object and the start of another.

Lateral inhibition is a process in the retina where light-detecting cells are influenced by their neighbours, enhancing contrast and making edges and details in our vision clearer.

• when a photoreceptor detects light, it not only sends a signal to the brain but also sends inhibitory signals to neighbouring photoreceptors - reducing the activity of its neighbours.

eg: if neuron A is stimulated it will be a lot. If neuron B (next to A) is stimulated, it will reduce the amount of stimulation for A.

Question 14

What is the Chevreul Illusion?

Answer 14

An example of Lateral Inhibition. Where we perceive exaggerated contrasts at the edges of different shades of grey. Panels of grey (Mach band)- we perceive a line that borders these different shades apart.

Question 15

What is light?

Answer 15

A form of electromagnetic radiation

Question 16

How do we perceive colour? And what is in our visible range?

Answer 16

We need light, which is a form of electromagnetic radiation containing a wide range of wavelengths.

Our 3 types of cone cells help to recognise different colours.

For humans, our visible range of light is from 400-700 nanometers.
This excludes a lot of what’s available out there: UV light can damage our visual system. We perceive infrared light as heat.

Lightbulbs/ the sun emits light, but we can see a table because it reflects light.

Question 17

What is the relationship between the colours of objects and the wavelengths that are reflected?

Answer 17

Different physical properties will reflect different wavelengths within the 400-700 nanometer spectrum.

Blue paint: perceptually it is blue because it reflects a lot of short wavelengths of light, 500 and below ish.

Green paint: it reflects the middle wavelengths 500-550 the most, perceptually that’s green.

Tomato: perceived as red because it reflects mostly 650-700 wavelengths.

White paper: it reflects a high percentage of all colours, i.e it reflects a large amount of light (80-90%)

Black pepper: has low reflective properties - it absorbs most of the light rather than reflecting. Low-level reflectance on all of the colours within our WL spectrum. Therefore, every colour absorbed results in the perception of black

Question 18

What are the 3 types of Cone Cells and what do deficiencies result in?

Answer 18

The three types are S, M, and L, representing short, medium, and long wavelengths.

S-cone around 419 WL range
M-cone around 531 WL range
L-cone around 559 WL range

Rods: around 496

We have three different types of colour deficiencies:

• If we don’t have all cone cells, then we are subject to colour blindness

Protanope: No L cones
Deuteranope: No M cones
Tritanope: No S cones

Another type of colour blindness is when you only have 1 type of cone cells present, due to there being no colours to contrast to, we perceive black and white only.

Another type is where we have NO cones, you only have rods - we perceive no colours. This can be uncomfortable and we become very sensitive to light

Question 19

What is the Trichromatic Theory/Helmholtz Theory of colour?

Answer 19

Addresses our ability to distinguish between different wavelengths. We use our 3 cones to respond to the nanometers - but the activation won’t be as strong as the preferred cone of that range. The activation level is all different across the 3 cones. - This helps to mix and perceive combined/different colours.

Each colour we perceive corresponds to a unique pattern of activation among the three types of cones.

We can’t distinguish colours with only one type of cone cell because colour vision relies on comparing signals from multiple types of cone cells. - Perceived colour is based on the relative amount of activity - the pattern of activity.

Question 20

What is Opponent Process Theory? (Hering 1878)

Answer 20

The idea is that colour vision is caused by opposing responses generated by blue + yellow, black + white, and red + green. i.e colour perception is controlled by 3 colour pairs.
- Within each pair, the activation of one colour inhibits the activation of the other colour

we can’t have red and green activate at the same time.

Question 21

At what stages do the Trichromatic Theory and the Opponent Process Theory work?

Answer 21

The TT works at the very beginning; when the light reaches our eyes we have different activation

The OPT refers to the connection between the processing in the cone cells and the transmission to our brains/ process of the retina

Question 22

Perceiving size and depth on the Retina

Answer 22

Perceived size is determined by the retinal image size.
The image of an object on the retina gets smaller as the object gets farther away, and vice versa.

Perceived size is also influenced by the perceived depth and our knowledge of the world. - We gather information from the environment to determine whether the image is actually big or small. - when we don’t have a depth cue, then our measurements rely on our retina sizing

The Ponso illusion: 2 parallel lines eventually converge perceptually

Question 23

What are our cues to infer depth?

Answer 23

a) Linear perspective. Our eyes perceive parallel lines to converge the farther away they get - illusion of depth and distance

b) Texture Gradient. objects that we are closer to are perceived to have more texture and detail

c) Interposition/Occlusion - when an object overlaps another, the overlapping object appears closer, giving an idea of depth

d) Relative height. Objects lower in the visual field appear smaller/closer, and objects taller appear farther away

Question 24

What does the binocular disparity cue for depth entail?

Answer 24

The image in our left and right eye are similar but have differences, which is how we interpret the distance of objects:

This difference is called binocular disparity. Both eyes perceive the position of objects differently which results in an accurate depiction of where they are.

Question 25

Explain how we organise sensory experiences using the Gestalt approach. Explain it’s elements.

Answer 25

“Perception of the whole is more than simply the sum of the individual parts”

• rather than seeing things individually we create a collective picture.

Proximity: Things that are closer together tend to be grouped together

Similarity: similar elements tend to be grouped together/ stimulus with the same features

Pragnanz (good figure, simplicity):
where every stimulus is seen as simply as possible

Good continuation: Regions that appear to follow in the same contours are grouped together

Common Fate: Things that move together are perceived as belonging together

Question 26

What are the two cortical streams?

Answer 26

Dorsal: ‘Where and How’ Involved in the perception of movement, location and how to move to respond to or interact with an object. Is sent to the parietal lobe.

Ventral: ‘What and what’ Involved in the perception of colour and form, this info is sent to the temporal lobe. Processes features.

what: Object discrimination
where: landmark discrimination
how: how can we interact with said thing

Question 26

Visual Pathways explanation

Answer 26

The object reflects light onto the Retina, info will be transmitted through the Optic Nerve, then sent to the Optic Chiasm, then there’s a crossover- info goes into the Optic Tract, 90% of the Optic Tract is sent to the LGN (Lateral Geniculate Nucleus) - then sent to the V1(primary visual cortex) - the rest is sent to the superior colliculus (the region of eye movement to see more of it)