Chapter 5 - Sensation And Perception

Question 1

What is transduction?
What are its four steps?

What is sensation and what is perception? Is there a correlation or causation between these?

Sensation involves the …..
Perception involves….

Answer 1

Transduction is the translation of physical stimulus into electrical energy in neurons and then into chemical energy due to the movement of charges, creating a neural stimulus.

More generally, turning external information into neural signals that the brain can interpret.

The four steps for transduction are:
1. Energy from the stimulus comes in
2. Receptors detect the stimulus and respond to it in the form of action potentials (neural impulses).
3. These signals are transmitted to the brain via certain neurons.
4. This is then received in the respective part of the brain that responds to these inputs.

Sensation is when this signal comes in and the neurons detect it, and perception is how the brain actually understands and responds to those signals. There is not a proven causation between these though, which is why it is still just an observed correlation.
Sensation is a physical process which has a causation effect, the stimulus is converted into electrical and chemical energy using neural impulses. But how we perceive this has not yet been proven.

Sensation involves the absorption of energy by sensory organs, and perception involves the organization and translation of sensory information into something meaningful.

Question 2

What are the physical properties of light and how does this relate to the perception of it? How do these properties also relate to the perception of sound? What is an acronym to understand this relation?

Answer 2

Light is both a wave and a particle, and this is why it is called a photon. And moving charges are an electric field which generates a magnetic field. This is electromagnetic radiation and based on its frequency will determine the colour of light that is perceived.

The wavelength of light relates to the hue or colour of the light, because this determines how much of the wavelength is absorbed by the specific pigments in the cones. The amplitude relates to the light’s brightness or intensity — meaning the taller the wave the more neurons it will stimulate at once, and hence the more signals that will be produced for that specific colour. This then makes it brighter — less of an absence of light. The purity of the light (whether it is mixed with other wavelengths or not) relates to its saturation.

Acronym:
W = wavelength H = hue (colour of light)
A = amplitude B = brightness (intensity — how many neurons are being hit at once with this light)
P = purity S = saturation (is it being mixed with other wavelengths)

Then for sound, the wavelength would correspond to the type of sound it is (high pitch = high frequency) the amplitudes would correspond to how loud it is, and the purity would correspond to timbre (or the type of instrument and how this differs between instruments to differentiate them even when playing the same note).

Question 3

How do you decrease the saturation of light in the additive model? What colour does this lead to? How do you decrease the value of light? What colour does this lead to? How do you change the hue of the light?

What does adding complimentary colours do in the additive colours model? What about subtracting in the subtractive colour model?

Answer 3

To decrease the saturation of light, add all colours together because white is essentially the combination of all colours. So the less pure the colour is (more colours mixed) the lighter and less saturated it becomes. So to do this set all colours to their maximum value.

To decrease the brightness or value of light, we need to remove all the colours and this leads to an absence of light which is black. This would be making all colours set to zero.

In the additive colour model, adding complimentary colours will bring them to white, which is why to decrease saturation just add the colour’s complimentary colour.

In the subtractive colour model, subtracting complimentary colours will bring them to black because a complimentary colours I just the mixture of the other two primary colours. So if you subtract all the primary colours from white light you get an absence of colour or black.

SO COMBINING COMPLIMENTARY COLOURS IN THE ADDITIVE COLOUR MODEL PRODUCES WHITE AND IN THE SUBTRACTIVE COLOUR MODEL PRODUCES BLACK, BECAUSE YOU ARE SUBTRACTING TO AN ABSENCE OF LIGHT.

Question 4

What is the additive colour model and subtractive colour model, and how can you use each of these to change brightness, saturation and hue?

Answer 4

The additive colour model starts from black (an absence of colour) and each pixel of colour adds to that to get closer to white. So when you combine complementary colours, this brings it to white because those wavelengths add to get max light. So adding colours together will bring the result to white, because you are building up from an absence of colour. This is how you desaturate something — you add more colours to it, bringing it to white. Then to decrease the brightness of a colour you add smaller amounts of that colour, as this means it’s closer to zero and hence the colour is darker.

The subtractive colour model starts from a background of white and removes wavelengths, resulting in whatever colours are left. So when you combine complimentary colours it brings it to black because you are subtracting those wavelengths from max light. To decrease the saturation of a colour here, you have to reduce the amount of pigment combined (not increase). This is because the origin is white, and so if you put less pigment you are subtracting less from max colouring and hence are further away from an absence of colour (black). The more colours you combine, the further away from white you get and the closer to black. So just start with not colours and you will have white, and slowly add some of that colour to saturate it. Because when you combine colours in this method you are subtracting their wavelengths and get closer to black, because when they are all zero you have white. So when you subtract complimentary colours you move towards an absence of colour. To decrease the brightness in the subtractive method, you just add more and more colours, which subtract wavelengths from white.

Question 5

What is timbre?

Answer 5

Timbre is the purity of sound, or the unique quality or tone colour of a sound, which allows us to distinguish between different sound sources even when they are playing the same note. This tone sets apart a piano from a flute, even when they play the same note.

This is because each instrument has a specific frequency.

Question 6

What happens when the eye views an image — how it it displayed on the retina?

Answer 6

When the eye views an image, it comes into the eye and flips so that the top of it is at the bottom of the retina and the bottom part is at the top. So light from the left visual field goes to the right corner of each eye, and light from the right visual field, goes to the left corner of each eye. Then all the chords from the left corners of the eyes go to the left hemisphere and all the cords from the right sides go to the right hemisphere. This is why the brain is able to understand the flipped image.

This flip is due to the way the cornea bends the light, and so it is up to the brain and the occipital lobe to correct that orientation.

Question 7

What is the blind spot and what causes it? Why are we not usually aware of the blind spot?

Answer 7

The blind spot is the gap in the retina on each eye where if an image falls on it we cannot perceive it. This is because this is where all the ganglia of neurons converge into the optic nerve which goes to the brain. So this is where all the information exits the eye, and therefore there are no receptor cells in this spot.

Each eye has this blind spot, which is below the fovea. We are not normally aware of this blind spot because each eye compensates for that blind part by taking in information and displaying an image where that would be. If you close one eye, your brain will essentially fill that area with whatever colours surround it to compensate for the image, but anything dark will be blocked out.

Question 8

What are the receptor cells in the eye called, and what are the two types of cells? Are receptor cells the innermost or outermost layer (if looking at the path that light takes to get to the eye?)

Answer 8

The receptor cells in the eye are photoreceptors because they take in photons and convert that to sensory information and neural impulses. Receptors are the innermost layer, meaning that all their supporting glial cells come before, causing a lot of light to be absorbed before it even reaches the receptors. The two types of receptor cells in the eye are rods and cones.

Question 9

What are rods? What type of synapses do they have to connect to ganglion? What are they mainly responsible for and what are their pros and cons?

Answer 9

Rods are the cylindrical rod shaped photoreceptor cells that are responsible for night vision and peripheral vision.
Pros: They are able to view things in an absence of light, because they can take in a lot of information and combine it into one image.
Cons: They cannot account for every detail because they are combining all this information and this results to less detailed and black and white vision.

Rods utilize convergent synapses, where multiple rod cells combine to send information to one post synaptic ganglion. This means that any little signals in each rod cell can combine together to create a large enough amount of neurotransmitters that the ganglion can be stimulated. So in low intensity light, this makes it easier to pick up signals, and hence night vision can occur. Because this is combining a ton of information together from different cells, the order in which the rods are stimulated does not matter. This is why details cannot be processed.

RODS PRODUCE BLACK AND WHITE IMAGES BECAUSE THEY ARE COMBINING SMALL SIGNALS FROM A BUNCH OF RODS AT CONVERGENT SYNAPSES, WHICH ADD TO PRODUCE WHITE LIGHT. THEN ANY DARK SPACES WILL BE ABSENCE OF LIGHT BECAUSE THERE IS NOT ENOUGH STIMULUS TO ADD UP AND PRODUCE AN ACTION POTENTIAL TO THE BIPOLAR CELL. SO ITS ESSENTIALLY LIGHT OR AN ABSENCE OF LIGHT, BUT ANY SMALL AMOUNTS OF LIGHT ARE MORE LIKELY TO BE SPOTTED THEN WITH CONES.

Question 10

What are cones? What type of synapses do they have to connect to ganglion? What are they mainly responsible for and what are their pros and cons?

Answer 10

Cones are cone shaped photoreceptors and are responsible for colour and daylight vision, as well as visual acuity (detailed vision).
Pros:
Images can be viewed with much more clarity and detail, helping in every day life.
Cons:
This means that small stimuli to each cone cell may not cause a response, and so in the dark where there is little stimuli, these will not work very well. Other cons are that you have to look directly at an object to have high visual acuity and colour vision, and this doesn’t account for the whole visual field.

Cones utilize individual synapses, meaning each cone cell is connected to exactly one cone cell, and hence only if the light is bright and intense enough will a signal occur. This is why bright light is required for this. However, because they are all individually connected, images can be processed much more accurately and in detail, producing colour as well.

Question 11

Where are rods and cones located within the retina? Are rods, cones, ganglion cells or bipolar cells most prevalent?

Answer 11

Rods are more located at the top and bottom of the retina, whereas cones are centralized on the fovea, which is where the clearest image can be produced if light hits here.
Rods however are everywhere along the retina because they far outnumber cones.
This is why peripheral vision is not coloured or in detail — it is rods that produce these images.
Rods are the most prevalent because cones have individual synapses so it would be impractical to have a synapse for a lot of different cone cells. Also all rods converge into bipolar cells which converge into ganglion cells, therefore rods have to be the largest abundance.

Question 12

How many pigments form the basis of colour vision? What is the difference between rods and cones in terms of the pigments used?

Answer 12

There are 4 pigments that form colour vision, one of which is the same for all rods, and the other three are distributed equally among the cones.
The three cones have pigments which absorb different wavelengths, and the absorption of these wavelengths in different proportions is analogous to mixing different colours.

Question 13

Where is visual information processed? What is processed where?

Answer 13

Visual info is processed in both the retina and in the brain.

In the retina:
Information is processed in the receptive field of a ganglion cells that the cones and rods attach to. The information processed here is more simple and initial processing, such as contrast to understand what the main image is that we are looking at, and simple geometric shapes.

In the brain:
Information is processed in the thalamus, occipital lobe (vision), parietal lobe (senses) and temporal (auditory and memory). This is where more details are processed, such as brightened, orientation, form, colour, motion and depth.

Question 14

Each ganglion cell has its own…
What is this responsible for?
Are these present for rods, cones or both?

Answer 14

Each ganglion cell has its own receptive field, meaning it produces a part of the image coming in from wavelengths of light from the group of rod cells that attach to its synapse. This group of rod cells can be very large due to large convergence.
These receptive fields are responsible for the seeing of light/dark contrast.
THESE RECEPTIVE FIELDS ARE ONLY FOR RODS BECAUSE THEY USE CONVERGENT SYNAPSES. Also this is processing the intensity and contrast of light, not the type of light (frequency) which cones process.

Question 15

What is the structure of a ganglion cell receptive field?

Answer 15

The receptive field of a ganglion cell is essentially all the rod cells that converge and send information to that specific ganglion cell.
The way that information is converged is this:
All the rods in the centre of that receptive field converge into one bipolar cell which takes information to the ganglion cell.
The rods surrounding this centre actually send information to horizontal cells, which then pass on information to the bipolar cell. So the information is sent indirectly to the bipolar cell, and converged before it gets there.

This structure has a property known as centre surround antagonism. This is called antagonism because if you stimulate the center of the receptive fields you produce a response, but if you stimulate the outside this prevents a response, or vice versa.

Which will occur depends on the type of bipolar cell that they are all converging to.

If the bipolar cell is an on centre cell, then light hitting the centre of the receptive field (centre rods) would activate that bipolar cell and cause a reaction in the ganglion. Then light hitting the surroundings will inhibit that bipolar cell and prevent reactions.

So summation of all these signals will be what results in a specific response.

If the bipolar cell is an off centre cell, light hitting the middle would inhibit the bipolar cell and produce no reaction. Light hitting the surroundings would produce a reaction.

Question 16

What are the 4 places that visual information goes after leaving the eyes? What is an acronym to remember this?

Answer 16

TPIP
After leaving the eyes, visual information goes to one or all of the following structures:
1. Thalamus = perception of brightness
2. Primary visual cortex in the occipital lobe = orientation
3. Inferior temporal lobe = perception of form and colour
4. Parietal lobe = perception of motion and depth.

Question 17

What does a cross section of the brain look like with nerves coming from the eyes to the occipital lobe?

Answer 17

Each eye has two groups of neurons, one coming from each side of the eye, processing each side of the visual field.

The lens flips incoming light, so that light from the left visual field goes to the right side of each eye, and light from right visual field goes to left side of each eye.

These groups then split from each eye, the left cords from the left and right eye going to the left visual area of the thalamus, and the right cords from both eyes going to the right visual area of the thalamus. This means that all information from the left visual field goes to the right hemisphere, and vice versa.

The crossing of the left cords from the right eye and right cords from left eye is called the optic chasm.
These neurons then all go to the visual cortex of the occipital lobe where orientation is perceived.

This crossing occurs so that

Remember the image is not actually flipped, the brain just interprets the neural impulses and forms and image based on it.

Question 18

Why do we have so much convergence for rod cells?

Answer 18

The degree of convergence drastically reduces the amount of processing required of the central nervous system, however it does produce low definition vision.
But because not every rod is analyzed, we don’t have to do as much processing, allowing the majority of photoreceptors to quickly produce an image.

Question 19

Why do we have the on and off cells?

Answer 19

The on and off cells help to enhance contrast, which is the main goal of the photoreceptors in the retina. They are supposed to analyze simple geometric shapes as well as contrast, so that the brain can more deeply break this down.
So by activating the centre, this allows an enhancement of contrast between light hitting those two areas, so that we can produce an image, focusing on the parts that have the highest contrast.

The on bipolar cells are activated by an increase in light in the main stimulus (not the background).

The off bipolar cells are activated by a decrease in light from the main stimulus, meaning the visual stimulus is darker then the background and so the peripheral rods are activated, turning this cell on.

Question 20

For four on centre cells, one with a tiny bit of light right at the centre, one with the size of the stimulus being the size of the centre of the circle, one with the centre of circle and some of surroundings being illuminated, and one being completely illuminated, which will have the largest and smallest responses?

Answer 20

The stimulus that illuminates the entire centre of the receptive field produces the highest frequency neural impulses and hence the largest response. This is because the entire centre is illuminated with no inhibition from the surroundings, and hence the image being looked at must have large contrast from its surroundings, making it the easiest and clearest to process.

The one with a tiny bit of light at the centre will have the second largest response, because even though it is just a small amount of light, it still has high contrast from its background.

The one with some in the periphery and all in the middle will have the third largest response, because there is still some light in the surroundings decreasing contrast and hence making a less defined response.

Lastly, the one which activates the middle and surroundings will have a very small response because there is little contrast, and the surrounding cells cancel out the middle one.

Question 21

What condition results from damage to the occipital lobe? What happens in this condition?

Answer 21

Blindsight. The occipital lobe is where the primary visual cortex is.

This is when people do not believe that they can see (they are cortical blind) however they are unconsciously processing the visual information and can identify things about it.

They can follow it with their eyes, they can sense an object in their visual field, and 78% of people can guess what is there, even though they actually can’t see it. This is because although the occipital lobe is what produces the image, there are other parts of the brain perceiving brightness, colour and motion and depth, and since these aren’t damaged this allows people to still identify that the object is there.

So since the occipital lobe, located at the back of the brain, is the primary visual processing center, responsible for receiving, interpreting, and processing visual information, including color, shape, and location, and connecting it to stored memories for object and face recognition, a lot of processing power is lost. However, other parts of the brain are still able to process, and this is why people are still aware of these objects.

Question 22

What was the cat experiment by Hubble and Wiesel? What were the results and the conclusion?

What did this experiment say about the role of the occipital lobe?

Answer 22

The cat experiment was trying to understand how orientation is perceived.

Essentially, a cat was shown a line in various orientations, and action potentials from very specific neurons was recorded by an oscilloscope.

For one specific neuron, a vertical line elicited a rapid firing rate, a horizontal line elicited no response, and a titled line created a moderate firing rate.

This appears that any vertical stimuli created a response in that neuron, but any horizontal components were ignored, because this was inhibiting that neurons response.

The conclusion that resulted from this was that neurons are very highly specialized, responding to very specific stimuli. So this neuron was specialized in analyzing only vertical stimuli.

This experiment showed that the occipital lobe processes the orientation of the stimulus, with each neuron specializing in a certain orientation.

Question 23

What does dorsal mean? Ventral?

Answer 23

Think of it alphabetically, dorsal is the top of the animal when on all fours, or the top of the brain. Then ventral is the bottom. So A —> Z from top of brain to bottom.

Dorsal: This means the back of the animal, so when on all fours, this would be the top, and hence this means the top of the brain.

Ventral: Front of the animal, meaning the stomach and so when on all fours this is the bottom. This is then the bottom of the brain.

Question 24

What happens once visual information is processed in the primary visual cortex of the occipital lobe?

Answer 24

Once processed in the occipital lobe, information is sent to two other areas of the cortex.

The ventral stream (bottom of the brain to the temporal lobe) processes the what of the object. Meaning the details — colour and form.

The dorsal steam (top of the brain to the parietal lobe) processes where the objects are and how to interact with these objects. Remember, parietal is for senses, so it makes sense that this would indicate where things are in space.

Question 25

What happens when the ventral stream is damaged?

Answer 25

When the ventral stream is damaged, (meaning the temporal lobe or nerves leading to it are damaged), this leads to AGNOSIA. AGNOSIA makes it difficult to recognize objects, people or sounds. There are 3 specific types of AGNOSIA: 1. Visual-form AGNOSIA, which is the inability to recognize visual forms or familiar objects. 2. Colour AGNOSIA: inability to recognize colours 3. Face AGNOSIA: inability to recognize faces. This makes sense because the temporal lobe processes details like colour, and also attaches to memory which is how one would recognize a familiar face.

Question 26

How does someone with agnosia draw an object when trying to copy it, and when drawing it from memory?

Answer 26

When trying to copy it, they are not able to draw the object because they cannot process the visual forms of the object or the colours, and hence are not able to picture in their mind what it should look like. They could not identify which lines were vertical and horizontal and could not identify the objects based on their forms and shapes. When drawing it from memory however, the hippocampus is still in tact, and so they can more or less accurately draw it. They still can’t process orientation or details very well, so the drawings will be quite messy. They also would not be able to recognize what they were drawing.

Question 27

How does someone with damage to the dorsal stream pick up an object with two hands? What about those with damage to the ventral stream? What does the differences between these people prove?

Answer 27

Someone with damage to the dorsal stream would not be able to understand where objects are and how to interact with them. Therefore, they would not understand where to put their two hands so that weight is distributed evenly and they can pick up the object. So they will chose very unstable grasp points not passing through the centre of the object. So although the what pathway is in tact — they can perceive the shape and colour of the object — the where and how pathway is damaged, preventing them from controlling their hand movements in relation to it. Those with damage to the ventral stream will not be able to see the form of the object but can somehow chose proper grasping points and pick up the object. They will also be able to draw the object from memory since their memory is still intact, even though they can’t process the form and colour just by looking at it. This clearly proves that these are separate pathways, because damaging each one individually will not effect the others abilities.

Question 28

What is colour? What are the two models of colour mixing?

Answer 28

Colour is the psychological representation of a mixture of lights in different wavelengths. It determines how we differentiate objects and perceive the world. Models of colour mixing: Additive colour mixing = using the primary colours Red Green and Blue, and building up from an absence of colour (black). This means that as you add colours you add wavelengths getting brighter colours and getting closer to white. Combining all colours in this model to the maximum produces white. Subtractive colour mixing = using the complimentary primary colours magenta cyan and yellow, going towards an absence of colour. So it starts with white and then as colours are added wavelengths are subtracted, darkening the colour until you get to an absence of colour. Combining all colours to the maximum in this model produces black.

Question 29

What happens when you mix the primary colours in additive colour mixing? What about mixing the primary colours in subtractive colour mixing?

Answer 29

When you mix the primary colours in additive colour mixing you get their complimentary colours. Red + blue = magenta Green + blue = cyan Red + green = yellow Clearly adding these gets closer to white because you are getting brighter colours. And then the combination of all three primary colours produces white. When you mix the secondary colours in subtractive colour mixing you get the primary colours, because you are subtracting wavelengths to move towards and absense of colour (or black). Yellow + cyan = green Yellow + magenta = red Magenta + cyan = blue Then all of them combined gives black, because you subtract all wavelengths to get an absense of colour. ADDITIVE = BLACK + COLOUR => BRIGHTER (TO WHITE) SUBTRACTIVE = WHITE - COLOUR => DARKER (TO BLACK)

Question 30

what things use additive and what use subtractive colour mixing?

Answer 30

Mixing pigments (paint and printers) use subtractive colour mixing because they start from white and then absorb certain wavelengths, which are not reflected back to the viewer and hence are essentially subtracted from the picture. So the perceived colour is a combination of all the colours that are reflected back (were not absorbed). Pixels on electronics use additive, and each pixel is composed of three sub pixels, each which emits a different wavelength, and that is the wavelength you see based on the proportions they are mixed in. SUBTRACTIVE: EACH FILTER ABSORBS CERTAIN WAVELENGTHS, AND WHATEVER IS NOT ABSORBED IS REFLECTED, GETTING CLOSER AND CLOSER TO AN ABSENCE OF WAVELENGTHS OR COLOUR. Max = black ADDITIVE: EACH CONSTITUENT CONTRIBUTES WAVELENGTHS, MOVING TOWARDS A BRIGHTER COLOUR. Max = white

Question 31

What colour will a filter of certain colour absorb? Why is this? How are these complimentary colours chosen?

Answer 31

Each filter of a certain colour will absorb its complimentary colour. Cyan absorbs red light Magenta absorbs green light Yellow absorbs blue light This is because that filter is only that colour because it is reflecting back the colours that it did not absorb. So if it is the perfect material to absorb red wavelengths of light, it will transmit and reflect back green and blue wavelengths, making the filter appear to be cyan. Remember, the complimentary colour is essentially the colour that results in mixing the other two primary colours not including the colour we are looking at. That is why when you absorb or remove the colour you are looking at, the two wavelengths remaining will combine to produce the complimentary colour. This then makes sense because any colour and its complimentary colour combined will produce black (additive) or white (subtractive). This is because the complimentary colour is made of the two other primary colours mixed together, and combining all of those primary colours will produce either black or white. ***Ex) additive colour mixing: *** Red and cyan are complimentary colours. Remove red by absorbing its wavelength, the two primary colours left are blue and green. When these are mixed this produces cyan, which is reds complimentary colour. It is complimentary because when you add blue and green to red, you are combining all primary colours, which produces white.

Question 32

What happens when light is shone through a cyan filter, then a magenta filter, then a yellow one? What about magenta, then yellow, then cyan? What about yellow, then cyan, then magenta?

Answer 32

Cyan > magenta > yellow: The cyan filter means that green and blue light is being reflected. So that means that red wavelengths were absorbed. This leaves green and blue to be transmitted. A magenta filter indicates that red and blue lights are being reflected, and green is absorbed. But since only blue and green are incident, green will be absorbed like normal and blue will be transmitted. Then yellow is normally a combo of red and green, so this material is built to absorb blue light. So if only blue light is incident, then it will be absorbed and no light will pass through. So essentially the colour of the filter indicates what colours are reflected and transmitted (the colours that mix to produce that filter colour) and what colour is absorbed due to that material (the complimentary colour to the filter). Even if not all white light is incident, whichever colours are normal absorbed will be, and this is how light is filtered out. For magenta > yellow > cyan: Magenta is made of red and blue combining. So these are the wavelengths which pass through, and the green is what is absorbed due to that material. Then after this we only have red and blue light, and yellow is made of red and green. So blue is complimentary and absorbed, and only red will pass through. Lastly we have a cyan filter which is made of blue and green light being reflected, so red will be absorbed and no light will pass through at the end. Yellow > cyan > magenta: Yellow is made of red and green adding together, and so blue is absorbed by this material. Then the cyan filter absorbs red, so only green passes through. Magenta is blue and red so green is absorbed, and no light remains. CLEARLY, USING THE THREE PRIMARY SUBTRACTIVE COLOUR FILTERS IN SUCCESSION WILL COMPLETELY FILTER OUT ALL LIGHT DUE TO PIGMENT ABSORPTION, UNTIL YOU GET TO BLACK BY MIXING ALL PIGMENTS TO AN ABSENCE OF COLOUR.

Question 33

What type of light comes out of each initial filter (combining the primary colours that are transmitted)? How does this explain the colour of something behind a filter?

Answer 33

For a cyan filter, the colours reflected or absorbed are the colours which mix to produce cyan (blue and green). Therefore, the light that comes out will be cyan in colour! This makes sense why the light reaching your eyes from an object behind the filter will appear the same colour as your filter! Yellow: red and green will come through, which mixes to produce yellow light, making objects appear yellow. Magenta: blue and red will come through, mixing to produce magenta which makes objects appear magenta.

Question 34

A colour absorbs its ___________ colour.

Answer 34

A colour absorbs its complimentary colour.

Question 35

As we have mentioned before, what happens when you desaturate (make less pure) a hue for additive and subtractive colour mixing? What about when you decrease the value of a hue (make it less concentrated) for both? Due to this, how do you darken a colour for each, and how do you brighten a colour?

Answer 35

When you desaturate a hue: Additive: when you add colours together in additive, you are moving away from black and hence to desaturate you make the colour a lighter version of itself (towards white). Subtractive: when you combine colours you subtract from white light, which removes wavelengths are brings it close to an absence of colour, darkening the colour and bringing it closer to black. When you decrease the value of a hue: Additive: if you decrease the value of each hue numerically, this will make the hue darker because you are adding less light so it’s closer to black. Subtractive: if you decrease the value combined, you are subtracting less from white (or from the combination of all wavelengths) and so you are making the hue brighter or closer to white. To darken a colour: Additive: just add less of each colour and hence there is less light total. Subtractive: combining more of each colour removes more and brings it closer to black. To brighten a colour: Additive: add more of each colour to bring it closer to white. Subtractive: combine less of each colour to keep it closer to a maximum value (white).

Question 36

Pigments use __________ colour mixing and light uses __________ colour mixing.

Answer 36

Pigments use subtractive colour mixing (start from white and then absorb certain wavelengths to reflect the complimentary colour), and light uses additive colour mixing. So if you have yellow paint, this paint is actually absorbing yellow’s complimentary colour blue light, and reflecting back red and green which combine to make yellow. So this is removing a wavelength from white light to produce a darker colour. If you have red paint, then blue and green (cyan) light would be absorbed, leaving this red colour.

Question 37

What are the two theories of colour vision? Give a brief overview of both…

Answer 37

Trichromatic theory: (3 colours!) The human eye has three types of receptors with differing sensitivities to different light wavelengths. So each type of cone is stimulated in different ways by the wavelengths. So one cone more strongly reacts to red light, one to green light, and so on. Remember whatever is reflected by the object is the colour that we see and hence is the colour that reflects back into our eye. The ratio of the activity of these different receptive types is what creates our impression of different colours. Opponent process theory: There are three pairs of colours (including complimentary colours which are a mixture of the other two primary colours in a given set) and these pairs have antagonistic responses. So if a certain colour stimulates a cone it reacts, but if the complimentary colour hits it then it’s inhibited.

Question 38

What does a graph of three differnt wavelengths of light look like in representing trichromatic theory?

Answer 38

This graph has wavelength of light coming in on the x axis and the normalized absorbance of the light by receptors on the y axis. There are then three curves, one is blue which peaks at 420 nm (shortest wavelength) then green which peaks at 534nm, and then red peaking at 564 nm. There are then three cones, one which absorbs blue light, one absorbing red and one absorbing green (based on their pigments). So the curve for each colour represents how much light is absorbed by each specified cone. At 500nm, we are near the bottom of the blue curve, near the top of green and in the middle of red. Therefore, blue receptors are stimulated to 20% of their maximum, red stimulated to 55% and green stimulated to 75%.

Question 39

What is colourblindness and what causes it?

Answer 39

Colour blind individuals are born with only one or two cone receptors. The colour the person is unable to create depends on the cone that is missing. Whatever is missing is the wavelength that cannot be absorbed and therefore cannot stimulate any pathways which represent that colour in the mind. If missing two receptors, no colour can be seen. Missing one, then the variety of secondary colours that can be seen is smaller.

Question 40

What is one weakness of the trichromatic theory? What does the opponent process theory do to combat this?

Answer 40

One weakness of the trichromatic theory is that it fails to explain why we see complimentary colours when we look away from an image. Remember, complimentary colours are the colours produced by mixing the two other primary colours not including the one we are looking at. The opponent process theory says that a stimulus will trigger an excitatory reaction for that colour in one cone cell, and an inhibitory reaction in the others which produce the complimentary colour (so the two others). Then when that cell stops being stimulated, this releases the inhibition on the other cell, and so there is a small burst in activity as it goes from nothing to slight stimulation. This is why you see a faint afterimage of the complimentary colours. It’s not excited, its just not inhibited and so its slightly more active then it was before.

Question 41

What happens when you stare long enough at something due to the opponent process theory? What is an example of this phenomenon in practice?

Answer 41

Once you stare long enough the neurons being activated fatigue and release their inhibition on the antagonist neurons, and so the opposite image will appear in our minds. This is because both the excitatory and inhibitory reactions weaken. An example would be the spinning woman that can be interpreted in different ways. One neuron interprets her as spinning clockwise, inhibiting neurons that would process it as counterclockwise. If you stare long enough that neuron fatigues and you see the women as spinning counterclockwise because the other neuron all of a sudden stops being inhibited. Also the water fall, if you look at it for a long time and then look at a still waterfall, it will be moving slowly upwards due to the inhibited neuron now having some activity.

Question 43

What is psychophysics?

Answer 43

Psychophysics is the study of how physical stimuli are related or translated into psychological experience. How does a change in physical stimulus correlate with the change in the psychological experience of it?

Question 44

Can the relationship between physical stimuli and psychological experience be modelled with a mathematical equation? Is it a 1:1 ratio?

Answer 44

Yes it can, and this relationship can be described by Weber’s ;aw and Fechner’s law. This is not a linear 1:1 ratio between x (the intensity of the physical stimulus) and y ( the psychological ability to detect change).

Question 45

What are the two basic concepts of psychophysics, and what is each one called?

Answer 45

The two basic concepts are the absolute threshold and just noticeable difference (JND).

Question 46

What is absolute threshold? What is a simple example describing it? What specific point was found by researchers in terms of stimulus intensity? Whose law is this?

Answer 46

Absolute threshold is the minimum amount of physical stimulation required for a psychological response to occur — for someone to detect the change. An example representing this is slowly adding light to lightbulbs: As you slowly add light, as soon as it is bright enough to notice, this is the absolute threshold, where an actual psychological perception of the physical stimulus occurs. However, researchers found that there is no single stimulus intensity at which the subject jumps from no detection to completely accurate detection, because it varies based on surroundings and other stimuli. So in each trial, this absolute threshold differed.

Question 47

What is the operational definition of absolute threshold? (Remember a specific measurable definition)…

Answer 47

Absolute threshold is the intensity level at which the probability of detection by people is 50% (because again, this differs from person to person, trial to trial, and based on many other incoming stimuli).

Question 48

What does a graph of proportion of yes responses vs the stimulus intensity look like?

Answer 48

This graph is a curved s line, where at small stimulus intensity it grows exponentially, with more and more people noticing the change. Then the steepest slope is where the rate of yes responses per unit of stimulus intensity increase is the largest, and this is where absolute threshold is. Because the most people are just beginning to say yes, so most people are crossing the threshold from seeing nothing to seeing the stimulus. Then after that it looks like a log graph, as most people see it now and slowly almost 100% of people begin to see the stimulus.

Question 49

What is signal detection theory? What are the two main points?

Answer 49

Signal detection theory: This theory indicates what determines ones detection of the stimulus occurring. So what will make them more likely to notice the stimulus? There are different factors because people’s ability to notice the differences is based on their individual brains. The two main points are: 1. The intensity of the stimulus: if the intensity is low or ambiguous (it is hard to distinguish from the background noises), then ones ability to notice the stimulus depends on other factors. So the consistency of decision making is much lower if the stimulus is ambiguous because their ability to notice the stimulus amongst background is lower. 2. The psychological state of the individual, and the context of the situation. The two processes that determine this are their sensory processing ability and their decision making process abilities.

Question 50

What is an analogy to how context and consequences of a decision determine ones response to that decision..

Answer 50

For a doctor trying to make a diagnosis, the consequences of missing the diagnosis can be very high, and so making the decision to have lab tests is the safe option. There is also very low risk in making the decision to do the tests, and therefore there is a bias in this decision making do to context influence.

Question 51

What are the 4 possible decision outcomes when saying if the stimulus is there or not? What is each one called?

Answer 51

1. Hit: The stimulus is present and the perceiver says that they see it. 2. Miss: The stimulus is present and the perceiver says that they don’t see it. 3. False alarm: The stimulus is absent and the perceiver says that they see it. 4. Correct rejection: The stimulus is absent and the person says they don’t see it.

Question 52

What do unbiased responses to indicating if a stimulus is there or not look like, in terms of the percent in hit, miss, false alarm and correct no?

Answer 52

For unbiased responses, the decision is made only based on sensory information, so they are truly indicating whether or not they saw the stimulus and this would be based on its intensity. Therefore, the hit rate and correct no rates should be the same because they are correct in their identification the same proportions no matter if the answer is yes or no. Then the miss rate and false alarm rate should also b e the same. If the stimulus is very salient, then responses will be mostly accurate, with small errors due to one’s lack of ability to notice the stimulus (just based on differences in brain chemistry). If not very salient, it would be 50 50 for all, where hit and correct no are similar, as this would be unbiased. So the hit rate and correct rejection rate will both be the same = 95%. Then the false alarm rate and miss rate will be the same = 5%. This is all because the decision is based on sensory information only.

Question 53

What are the two types of biased responses, and what do the 4 rates look like for each?

Answer 53

The two types of biased responses are NAY-sayers and YEA-sayers. YEA-sayers want to say yes that they saw the stimulus because the consequences of not seeing it are very high, and the risk of saying they see it is low (false alarm has no damage). Therefore, the hit rate and false alarm rate will be quite high, whereas the correct rejection rate and miss rate will be quite low. YEA sayers are trying to minimize the miss rate because that has high consequences. An example of this is ordering lab tests for a diagnosis, missing a diagnosis has very high consequences so most will say yes to ordering the diagnosis. NAY-sayers have very high consequences for a false alarm, and so they will try to minimize the false alarm rate, leaving it at the random 5%. They will more often say no because the risk of saying no is not as high as saying yes and having the stimulus not actually being there. So here the false alarm rate will be minimized, and the miss rate will be high, with the hit rate being relatively low, because they are reluctant to say yes. So just look at the false alarm rate and miss rate because these two are 5% in unbiased responses, but in biased responses these will differ depending on the type of unbiased response. An example of this is identifying a murderer, a false alarm would have high consequences due to death sentences, so this is minimized.

Question 54

What is the just noticeable difference?

Answer 54

JND is the smallest difference in the amount of stimulation that a specific sense can detect. So as stimulus increases in stimulation, what is the difference in intensity that someone will be able to notice?

Question 55

What was noticed about increasing the intensity of the stimulus and ones ability to notice a difference? What is an example of this?

Answer 55

As the stimulus is increased, ones ability to notice a difference in intensity lowers. Meaning once a stimulus is already quite strong, a small difference in intensity is not easily noticeable. However when the stimulus is very small, small changes in intensity will be seen. For a lightbulb, when very dim, once it becomes bright enough to see, you will be able to easily notice its brightening. But once it is quite bright, changing its intensity will not be noticeable. If a bunch of lights are on, turning one off will not really be noticeable.

Question 56

Each JND fraction is a _______ _______.

Answer 56

Each JND unit is a constant increment. It is measured as a ratio, and so although the numerator and denominator change, the fraction as a whole should stay constant.

Question 57

What is the Weber law?

Answer 57

Weber’s law states that the just noticeable difference of a stimulus will be constant throughout, and at each point it is a function of the magnitude of the initial stimulus. The overall formula is the intensity of the final stimulus in that increment of change, minus the initial stimulus strength, divided by the initial stimulus strength. So: (I n-1 — I n) / (I n) = K = JND So remember n is just whatever number of intensity it is in the scale of intensity, starting from zero intensity.

Question 58

Assuming that you are just able to detect the difference between 300g and 310g. If the initial weight is 600g, what will be the just noticeable difference? (From 600g, how much do you have to add to notice a difference in mass at this starting intensity?)

Answer 58

So remember, JND is the the smallest difference in the amount of stimulation that a specific sense can detect. Since we are no starting with a larger stimulus intensity, the difference in mass to notice a change will be larger. Then because it says you are JUST able to detect the difference between 300g and 310g, that means that this is the change in the intensity of stimulus starting at 300g that you will be able to detect a change in mass using touch receptors. Anything below that you will not be able to notice. So since JND is constant for a certain stimulus type, and K = (I2 - I1) / I1 = (310 - 300) / 300 = 0.0333 (the proportion of the original stimulus that will cause one to notice a change). Then we can use this to calculate what JND would be for 600g starting = K * 600 = 20g. This makes sense, at a larger mass the change in mass that will stimulate a noticeable difference will also have to be larger. Could also do it this way: K = (310 - 300) / 300 = X / 600 = 10 / 300 So x or JND = 20g. Now remember, JND is a constant proportion of the size of the initial stimulus. So you have to divide it by the initial stimulus to get this proportion. But the actual JND for a specific mass is the numerator of that CONSTANT K VALUE. Then to get JND at a specific stimulus intensity if you have K, just multiply that mass by K! Change in I / I will also remain constant.

Question 59

What is Fechner’s law? How does this relate to what we already talked about for Fechner?

Answer 59

Fechner’s law describes how people perceive a stimulus, and he was the one who looked into absolute threshold — the strength at which one would first notice the stimulus. He also looked at what factors influenced one’s ability to detect the stimulus, and this was their psychological state and the context of the situation, as well as the intensity of the stimulus. This mathematical law looks at the less ambiguous case (psychological state varies greatly from person to person) and instead looks at how the intensity of the stimulus effects their subjective sensation of the stimulus (how they perceive it). It’s not looking directly at absolute threshold anymore. This law says that one’s subjective sensation of a stimulus is proportional to the logarithm of the intensity of the stimulus. S = K log R Where: S = sensation (measured in JND, or in other words each increment occurs each time they notice a new stimulus) K = constant R = Reiz (stimulus amount) Then remember as we saw with the JND ratio K, the larger the initial stimulus, the larger the JND is going to be because it takes more stimulus to notice a change in the already large intensity. So that means as the stimulus increases, one’s perception of that stimulus does not continue to increase at the same rate, it slows down — leading to a larger change in the value in order to produce a subjective understanding of change. This is why it is log, because the growth of the y-axis (subjective sensation) is much smaller then the x axis, causing much larger increases in units of the stimulus to produce one JND unit increase. So as y increases in constant units, x increases drastically. This is because as the stimulus gets larger, you have to increase it by larger and larger amounts to get the same JND.

Question 60

What is the main implication of Fechner’s law?

Answer 60

This relates psychological reality with physical reality, in other words: psychophysical parallelism. S = physical psycho = KlogR This also resulted in the brith of experimental psychology, where the researcher can control one variable (physical) and measure the psychological response.

Question 61

Again, what is the difference between sensation and perception (2 for each)

Answer 61

Sensation: -The stimulation of sense organs -involves the absorption of energy in the form of light and sound waves, by sensory organs -this is not yet understanding the information, just bringing it in. Perception: -The selection, organization and interpretation of sensory information -involves organization and translation of sensory information into something meaningful that determines how we perceive the world around us.

Question 62

What are some factors which affect the outcome of perception? (7)

Answer 62

Clarity of the stimulus • Context in which the stimulus appears • Way of presentation • Viewing perspective • Background knowledge of the viewer • Focus of attention • Schema (And many other factors)

Question 63

What is the word superiority effect? Does it apply to other stimuli as well?

Answer 63

The word superiority effect is that people can better recognize letters within words compared to isolated letters or letters presented in non-word strings. This does apply to other stimuli as well, because the brain can more easily understand something ambiguous when with other stimuli, as it groups it together to make sense of the image as a whole. Therefore, context has a huge effect on visual images.

Question 64

What is bottom up processing? For visual processing, what is the output question? For decision making, how does this affect your response?

Answer 64

Bottom up processing is when you don’t have an initial expectation for what you are going to see, so you analyze the image from its basics and then break it down and interpret it. You take in sensory information and then assemble and integrate it to create a response. For visual processing, the output question is what am I seeing? For decision making, your response is affected by the expectation you have for an output. If the stimulus is barely reaching absolute threshold, it might be half and half whether you detect it or whether you make the right decision. But if you already know where to look then it will be much easier to detect even if it’s JND. Bottom up is more data driven rather then comparing to previous knowledge, because you are trying to take in data and understand what you are seeing.

Question 65

What is top down processing? What is the main question coming out of top down processing for visual?

Answer 65

Top down processing is when you already have an expectation for what you are going to see, because you have been shown what to look for before. So you comprehend that source, processes it, and then look to the stimulus and process its features to see if it matches with what you were expecting. It is much easier to notice something when you know what to look for. Top down processing uses models, ideas and expectation to interpret sensory information. The main question coming out of top down processing for visual is, is that something I’ve seen before — comparing to information you already know. Essentially, this is pre-existing concept driven processing.

Question 66

What is another name for bottom up and top down processing? What are a few examples for each?

Answer 66

Bottom up: also known as DATA DRIVEN PROCESSING. Perception is based on the physical features of the stimulus. Ex) identifying letters isolated from words or words isolated from sentences. Completing the stroop task without being effected by the meanings of the words — meaning you don’t have previous knowledge that you connect to those words, and so you can process the physical information completely seperately. This means there is NO stroop effect. Top down: also known as CONCEPT DRIVEN PROCESSING. The interpretation of sensory information based on knowledge, expectations and past experience. Ex) context effect — the context around the stimulus effects how you process it. word-superiority effect — easier to understand letters within their word because you know what letter to expect. stroop effect — you processing of the physical stimuli is effected by your background understanding of the word’s context.

Question 67

What is structuralism? What is a method for measuring this? Is this more similar to bottom up or top down processing?

Answer 67

Structuralism is one system of thought for explaining how we perceive things, and says that we break down a whole into its parts, or a compound into its elements, and then build that up into a new image in our mind, and this is how we compare it to pre-existing knowledge to understand the meaning. To see how we do this, the stimulus is systematically varied and the subject’s subjective feelings about the change are measured. For example, breaking down ones skin tone into elementary colours to understand it. The printer can do this very quickly but humans cannot. So this is definitely how computers process. This is more similar to bottom up processing, because the stimulus is taken in and broken up into elementary components to try to understand what is being seen. So it allows us to look at the parts individually and understand how they form the whole.

Question 68

What is gestalt psychology?

Answer 68

Gestalt psychology is the opposite of structuralism, saying that the whole is more than the sum of its parts. Or in other words, the human brain likes to see the whole picture and compare the whole to other known patterns. This is more similar to top down processing, because you are comparing a whole image in your mind . The brain tends to complete similar patterns or incomplete figures, and elements forming a line or a curve are perceived as belonging together. This kind of explains the word superiority effect, when combined together into words letters are much easier to understand because the whole is greater and makes more sense then the sum of its parts.

Question 69

What is an issue with top down processing and what is an example that shows this?

Answer 69

An issue with top down processing is that it can hinder normal processing and problem solving skills by bringing in pre-existing knowledge that biases your ability to see possibilities for solving. For example, the candle-mounting problem, you are given a box with nails in it, hooks and the candle, and you are supposed to hang the candle so the wax doesn’t drip. Because of top down processing, your brain looks at the whole and only sees the box as a holder for the nails. However, if bottom up processing is allowed, (or structuralism) the whole is broken into its components to try to understand what is seen, and so the box can be seen as something that could hold the candle. Those presented with an empty box were twice as likely to solve the problem as those with a box full of nails, due to the hindrance of top down processing (look at it all as a whole). So because the whole is not the same as the sum of its parts, top down processing (building all the parts into one image) is not always accurate.

Question 70

What distinguishes a human from a robot?

Answer 70

Robots are very good at bottom up processing (combining parts into an overall picture, however they cannot as easily see those individual parts if they are in a separate image). This is because they don’t have pre-existing knowledge like humans to know what to look for if told. Therefore, asking robots to look for something in an image is impossible, because they cannot do top down processing like humans can.

Question 71

Another example of top down processing that only humans can do:

Answer 71

The faces in the nature image, if told what to look for we can find the faces. But computers analyze all the pieces and put it into a whole, and hence only see a nature scene, and cannot find the faces. Because they don’t have the pre-existing knowledge for what the faces look like.