L17 - L31 Summary Qs

Question 1

Physiological evidence for convergence between parallel pathways in the striate cortex

Answer 1

1) Orientation sel. varies across blob and interblob areas - with little difference in orientation tuning between blob and interblob areas (no r/ship b/w the degree of orientation sel. and colour sel)
2) No relationship between receptive field properties and cell’s location relative to cytochrome oxidase-rich regions
3) Single cell responses in V1 exhibit signatures of both M and P inputs

Question 2

What are the multiple input streams to Area MT?

Answer 2

V1 (4Calpha and 4C beta -> 4B) -> V2 Thick stripes -> V3 -> MT AND V2 Thick stripes -> MT directly
-Koniocellular region of LGN

Question 3

What is blindsight?

Answer 3

Damage to PVC (high metabolic demand) caused by hypoxia. Though perceptually blind in a part of the visual field, people perform above chance when forced to guess (forced-choice situation), say the location of a flash of light.

The reason they can still predict it is because the Dorsal Stream (Where) is also mediated by inputs to MT that bypass V1. It still receives input from the earlier stages of visual processing in the retina -> SC -> Pulv -> MT -> PPC AND LGN -> PPC

Question 4

Other functions of posterior parietal cortex

Answer 4

• Directing attention to spatial locations
• Helping bind different attributes of an object together
• Gating inputs into ventral stream
• Important for reading? (link to dyslexia)

Question 5

Area F5 in frontal cortex is unique as?

Answer 5

It responds when they see a particular action. When the subject does the action, the neurons also neurons. AKA mirror neurones aka Gandhi AKA empathy neurons - seeing someone sad makes you feel sad

Question 6

!Conjunctive vs Disjunctive eye movements

Answer 6

Conjunctive movements are eye movements that change the average direction of gaze of both eyes.

In disjunctive movements, the relative directions change, making them more convergent or more divergent, while leaving the direction of gaze unchanged.

Question 7

Saccades are fast BUT the muscles resist them - what is the major hindrance?

Answer 7

Viscosity of the EOMs e.g. the faster you try to move the honey, the more force you need as resistance is high. If you move slowly, there is less resistance

To get the muscles to move quickly, a BURST of innervation is needed. Antagonist forces must also be turned off. After the eyes get where they’re going, tonic innervation is needed to keep them in their new location

Question 8

Which extraocular muscle is in pons (where all the others are in midbrain)?

Answer 8

Lateral Horizontal Rectus (6th nerve)

Question 9

Which extraocular muscle does not originate at back of orbit

Answer 9

Inferior Oblique

Question 10

What cortical areas control: reflexive saccade, reflexive saccade inhibition, intentional saccade?

Answer 10

Reflexive saccade - PPC
Reflexive saccade INHIBITION - DLPFC
Intentional saccade - FEF

Question 11

Is gain higher or lower in the dark?

Answer 11

Lower ~0.6

Question 12

What is stimuli for vergence?

Answer 12

Disparity and blur (because you would try and focus on something that is not visualised well)

Question 13

Internuclear opthalmoplegia (INO)

Answer 13

Damage to the medial longitudinal fasciculus

If it is interrupted then the left eye can still abduct (look to the left) but the right eye cannot adduct (cannot look to the left).

Question 14

Medial longitudinal fasciculus location and what is it vulnerable to?

Answer 14

Runs from interneurones in the abducens (6th nerve) nucleus in the pons up to the oculomotor (3rd nerve) nucleus in the midbrain, crossing the midline as it goes to the other eye.

It is vulnerable to disease (MS in particular)

Question 15

Duane’s congenital retraction syndrome - what is it? How does one get it?

Answer 15

Benign condition where the hallmark is a unilateral or bilateral abducens palsy (limited abduction)- often, attempted adduction leads to a retraction of the affected eye into the orbit

Loss of 6th nerve - The 3rd nerve knows the lateral rectus is not innervated (when 6th nerve is absent) - 3rd nerve also innervates it, hence retracting eye back into the orbit

Question 16

Oscillopsia

Answer 16

Objects in the visual field appear to oscillate. The severity of the effect may range from a mild blurring to rapid and periodic jumping

Question 17

How does Alzheimer’s disease affect how we process novelty?

Answer 17

They fail to respond to novelty and have diminished visual curiosity - only looking at the kid but not the bipedal horse

Question 18

Ventral simultanagnosia

Answer 18

Able to see several objects at once, but their recognition of objects is piecemeal, or limited to one object at a time. Thus, individuals with ventral simultanagnosic symptoms are capable of navigating through a room without bumping into furniture.

• Colour vision is normal - can identify the colour plate but cannot integrate the information and identify the number
• Visual system could drive action e.g. gaze but without perception

Question 19

Dorsal simultanagnosia

Answer 19

Perception is limited to a single object without awareness of the presence of other stimuli. Thus, being able to see only one object at a time, a patient may collide with various objects in a room being unaware of them. Additionally, objects in motion appear more difficult to perceive

Question 20

Treisman’s feature integration theory

Answer 20

When perceiving a stimulus, features are “registered early, automatically, and in parallel, while objects are identified separately” and at a later stage in processing.
OR
Postulates an attentional spotlight (covert attention) acting on a visual area or areas early along the visual pathway that aids in early selection of visual field location for further processing

Question 21

How can selectivity of attention be demonstrated?

Answer 21

1) Inattentional blindness
Paying attention to A so you do not notice B

2) Change blindness
Perceptual phenomenon that occurs when a change in a visual stimulus is introduced and the observer does not notice it. For example, observers often fail to notice major differences introduced into an image while it flickers off and on again.

3) Attentional Blink
The phenomenon that the second of two targets cannot be detected or identified when it appears close in time to the first.

E.g. When you a presented a series of letters and suddenly a number, then more letters and a number, you will only see both numbers if the time between the numbers are at least 500 msec apart, otherwise you miss it

Question 22

What is the binding problem in perception? How is the binding problem solved?

Answer 22

Receptive field sizes progressively increase along the ventral stream as different stimulus attributes are processed in different cortical areas. How do you bind all this info together?

However, position invariance is an important property of any system of object recognition - which means certain neurons responds to specific things e.g. faces

The spotlight of attention acting on an early visual area aids in the selection of a visual field location for further processing. Thus binding errors do happen in PPC lesions.
OR
Synchronisation between neurons that code for features that belong to the same object.

Question 23

What is the neural mechanism that underlie the attentional modulation in one brain region by another?

Answer 23

Neuronal oscillations and synchrony where enhanced response to stimulus leads LIP neurons to sync then drive MT neurons to fall in sync with them.

Question 24

LTP

Answer 24

A persistent increase in synaptic strength following high-frequency stimulation of a chemical synapse.

Question 25

LTD

Answer 25

Activity-dependent reduction in the efficacy of neuronal synapses lasting hours or longer following a long patterned stimulus.

Question 26

Surround suppression

Answer 26

An effect seen when neurons do not respond as much when the stimulus is enlarged.

Question 27

Hebbs hypothesis

Answer 27

Simultaneous activation of cells leads to pronounced increases in synaptic strength between those cells that play a role in memory and learning. Presynaptic activity needs to occur first, then postsynaptic activity at the same synapse for LTP to occur.

An example would be axon of cell A excites cell B and repeatedly takes part in firing it, some growth process/metabolic change takes place in one or both cells so increasing A’s efficiency as one of the cells firing B

Question 28

Optical flow

Answer 28

The pattern of apparent motion of objects, surfaces, and edges in a visual scene caused by the relative motion between an observer (an eye or a camera) and the scene.

Question 29

What is biological motion?

Answer 29

Act of perceiving the fluid unique motion of a biological agent.

Question 30

Borders provide a cue about occlusion which can tell us something is in front or behind without using the depth cue. What do random dot stereograms demonstrate?

Answer 30

That depth can be seen without borders/edge cues

Question 31

MST not only tuned to direction, optic flow but also?

Answer 31

Disparity - providing info about parallax, depth cues for self-motion

Question 32

When does binocular rivalry occur?

Answer 32

When dissimilar images are presented to corresponding retinal locations in the two eyes, the two stimuli compete for perceptual dominance (you don’t see a fused image, you see a few moments of image from the right, then the left)

Question 33

Neuronal mechanisms underpinning binocular rivalry

Answer 33

• Incompletely understood
• Evidence for early stage encoding of monocular info (LGN/V1)
• Evidence for residual encoding of the suppressed visual signal from brain imaging studies: not sufficient to generate a visual percept

Question 34

Parallax

Answer 34

Objects move at different speeds on the retina depending on the distance from the observer (assuming a static environment) - the objects in the distance appear to move more slowly than the objects close to the camera.

Question 35

Kinetic depth effect

Answer 35

Person is stationary but the object is moving (e.g. rotating). The retinal velocities depend on the distance of each feature from the observer.
*Motion cues providing info about depth as they are moving at different speeds

Question 36

What happens when you suture BOTH eyes shut - binocular deprivation?

Answer 36

Fewer binocular cells, but there are cells driven by either contra or ipsilateral eye (where else in monocular deprivation, only one area, ipsi or contra, has cells). Receptive fields are not very abnormal.

If both eyes are shut, they segregate because there is no competition between them

Question 37

3 Types of Amblyopia

Answer 37

1) `Occlusion
When one eye is occluded by a congenital cataract or a lid ptosis (droopy lid)

2) Anisometropic
When the two eyes have very different refractive errors (e.g. myopic, hyperopic)

3) Strabismic
When one eye is deviated (eye turn, squint)

Question 38

There is strong post-saccadic enhancement of reflexive ocular following

Answer 38

If you are looking at a fixation spot with a textured screen and you suddenly move the textured screen, there is a delay and your eye chases the moving image. If we suddenly move an image after a saccade, there is an increase in tracking speed (compared to when there isn’t a saccade)