Carlson lecs

Question 1

The LGN has 6 layers, how many a magno and how many are parvo?

Answer 1

The 2 innermost layers are magnocellular and the 4 outermost are parvocellular

Question 2

Define amplitude, frequency and phase of waves.

Answer 2

Amplitude represents the ‘size’ of the waves (peaks and troughs), frequency is the number of times they occur in a given time frame, and phase is whether or not they are ‘in’ phase (occurring at the same time) or ‘out of phase’, one may be staggered a little behind the other.

Question 3

What would be the result of a Fourier transform on a complex sound wave?

Answer 3

Fourier transform is taking complex wave forms and breaking them apart into these components - a constituent set of sine waves

Question 4

What are the advantages and disadvantages of EEG and MEG?

Answer 4

EEG is a lot cheaper than MEG;

Question 5

Our friend the medulla oblongata (the lower part of the brainstem) is responsible for heart rate frequency. How is this controlled?

Answer 5

The medulla oblongata monitors the amount of carbon dioxide and oxygen levels in the blood stream. If there is not enough oxygen (too much carbon dioxide), it sends a signal to the heart and heart rate is increased as well as breathing, allowing more oxygen in.

Question 6

Delta, theta, alpha, beta and gamma waves. Which mental states do these represent?

Answer 6

Delta & theta = sleep
Alpha, beta and gamma = awake

Delta waves represent deep dreamless sleep, theta waves REM sleep as well as deep relaxation/ meditation. Alpha waves are awake whilst calm and relaxed, beta waves are for cognitive processing, gamma waves for ‘higher processes’ such as perception, problem solving and consciousness.

Question 7

Alpha brain waves, a relaxed yet alert state, are in what common range which varies between people?

Answer 7

Alpha waves oscillate between 8-12 Hz, which is 8-12 cycles per second

Question 8

Name a problem with using the BOLD proxy in fMRI to deduce areas of brain activity

Answer 8

One problem with the BOLD proxy is that some parts of the brain receiving oxygen are only ‘en route’ to the functional areas. It’s not possible to deduce with 100% certainty that those areas using oxygenated blood are those necessary for the experimental task.

Question 9

Delta and theta waves are present in which states? What are their features?

Answer 9

Delta waves are present in deep dreamless sleep whilst we have no body awareness.

Theta waves are present during transition to sleep, REM and deep meditative/ relaxed states whilst awake.

Question 10

What are the features of alpha, beta and gamma waves?

Answer 10

Alpha waves are present whilst awake but relaxed.

Beta waves are what happens when we’re active and processing cognitive information.

Gamma waves represent higher mental activity such as perception, problem solving and ‘consciousness.’

Question 11

How does the medulla oblongata monitor heart-rate?

How do pearl divers take advantage of this system?

Answer 11

The medulla oblongata monitors how much C02 and oxygen I have in my blood stream. If there is too much carbon dioxide and not enough oxygen, it sends messages to increase heart-rate and breathing so that I can access more oxygen.

Pearl divers hyperventilate for 30-40 seconds to increase the oxygen levels to their hearts, and can then dive with no oxygen tank for up to 2 minutes.

Question 12

What is the binding problem, and how does the brain solve it? Use the woman and dog as an example.

Answer 12

The binding problem represents the problem of how the brain combines sensory information to make sense of the world. This is solved rhymically.

A visual example of this is when I look at a woman with a dog on her lap, i have some neurons firing in synchrony representing the woman and others in their own synchrony representing the dog. Therefore I am able to perceive the woman an dog as 2 seperate entities.

Question 13

Using single cell recording, what kind of coherence was found between an IT (higher order visual) neuron and 2 V4 (lower order) neurons which had receptive fields tuned for different orientations?

Answer 13

They found that the IT neuron fired in synchrony with whichever V4 neuron was responding to the attended orientation. The IT neuron was coherent with the attended neuron’s AP rhythm.

Question 14

When are our hormones most active?

Answer 14

Our hormones are most active during sleep.

Question 15

How does adenosine effect blood flow, and how does this relate to sleep?

Answer 15

Build-up of adenosine increases blood flow, which increases activity in the vlPOA promoting sleep.

Question 16

How does caffeine interact with adenosine receptors?

Answer 16

Caffeine is an adenosine antagonist; it blocks adenosine receptors so that we’re no longer sensitive to adenosine.

Question 17

The SCN is akin to our internal clock, governing circadian rhythm. Why do neurons within the SCN fire as a phase show, all running on slightly different cycles?

Answer 17

It’s thought that neurons in the SCN are responsible for governing different structures of the brain which each operate on different cycles. They are firing in synchrony with those structures (on a 24 hour cycle).

Question 18

What does optical imaging measure and how?

What kinds of experiments is it used for?

Answer 18

Optical imaging measures oxygenation of the blood. A camera is placed at the surface of the brain and then the ratio of blue to red light is measured. When oxygen is used by the brain, the amount of blue light increases as blood is returned to the heart.

Optical imaging is used for orientation column tests, because when the monkey views a visual stimulus with a certain orientation blood will rush to cells with that receptive field and that area will appear blue as the oxygen is used.

Question 19

What is entropy, a concept introduced by Claude Shannon, and how does it relate to disorder?

Answer 19

Entropy is the amount of disorder. The more disorder, the more entropy eg image of a crowded street compared to a beach scene; since the beach scene has big chunks of similar colour, encoding can create a smaller file size than if every pixel was a different colour.

Question 20

Explain the Bayesian theory conceptually, using the Dalmatian image as an example, followed by the craters/ bumps example.

Answer 20

Bayesian theory proposes that to perceive the Dalmatian in the image, we combine both the visual stimulus and top -down processes; prior knowledge of Dalmatians.

In the craters/bumps example, our prior experience tells us that light comes from above. Therefore when the craters photo is turned upside down we see bumps.

Question 21

Marr’s framework (1982), which was extremely influential in computer science, provided 3 levels of explanation; the computational theory, representational algorithm and hardware implementation. Detail each level.

Answer 21

1. The computational theory; what is the goal? Eg why do we need to recognise faces?
2. Representational algorithm; how is the information encoded? eg light hits the retina, we receive facial information. Needs to be coded from V1 to higher order areas; this code is the algorithm.
3. Hardware implementation eg how are we going to solve this problem, with what mechanical or biological system?

Question 22

What did Shepard and Metzler (1971) find when they had subjects judge whether an object was the same (but rotated) or mirrored?

Answer 22

Shepard and Metzler found that the time it took respondents to decipher this was the same amount of time it would take them to mentally rotate the object, showing that there is a specific process (algorithm) involved with performing this task.

Question 23

The fovea is only able to perceive about 10 degrees (5 thumbnails) of imagery. What is being deduced from this 10 degrees that is not being perceived by other retinal ganglion cells?

What are rods more sensitive to in the periphery?

Answer 23

The fovea is the only part of our eyes which perceives colour, since the highly sensitive cones are clustered around the fovea.

Rods are detecting movement in the periphery.

Question 24

Retinal ganglion signals are compressed immediately in the fovea. We have 5 million cones and 120 million rods, yet only 1.1 million axons leave via the optic nerve in the retina. How is this 100% compression possible?

Answer 24

This level of compression is possible because some receptors are convergent. For example, neuron B might have 7 receptors converging on it, meaning that if a light stimulates any of these 7 photoreceptors, neuron B will fire. However, if a light large enough to stimulate all 7 neurons is seen, B will fire more frequently.

Sensitivity is decreased in that if B fires, we don’t know exactly where the stimulus is; however we gain sensitivity in that B responds to a larger area than a 1:1 receptor : neuron relationship.

Question 25

Give an example of a stimulus which we can’t look at directly to perceive

Answer 25

We can’t look directly at a dim star because it’s not bright enough to stimulate photoreceptors in our fovea with a 1:1 relationship. However, with convergent rod photoreceptors we can spread the stimulus across enough receptive fields to see it in the periphery.

Question 26

Explain how the healing grid illusion works using Bayesian priors

Answer 26

In the case of the healing grid, the Bayesian prior is that our brains know that the signals from our periphery are blurry. Therefore when fixating at the centre of the grid, the sides (which are actually misaligned) begin to ‘heal’ as our brain uses its prior knowledge (top down process) to perceive an all-over grid.