L17 - L31 Summary Qs Flashcards
Physiological evidence for convergence between parallel pathways in the striate cortex
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
What are the multiple input streams to Area MT?
V1 (4Calpha and 4C beta -> 4B) -> V2 Thick stripes -> V3 -> MT AND V2 Thick stripes -> MT directly
-Koniocellular region of LGN
What is blindsight?
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
Other functions of posterior parietal cortex
- Directing attention to spatial locations
- Helping bind different attributes of an object together
- Gating inputs into ventral stream
- Important for reading? (link to dyslexia)
Area F5 in frontal cortex is unique as?
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
!Conjunctive vs Disjunctive eye movements
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.
Saccades are fast BUT the muscles resist them - what is the major hindrance?
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
Which extraocular muscle is in pons (where all the others are in midbrain)?
Lateral Horizontal Rectus (6th nerve)
Which extraocular muscle does not originate at back of orbit
Inferior Oblique
What cortical areas control: reflexive saccade, reflexive saccade inhibition, intentional saccade?
Reflexive saccade - PPC
Reflexive saccade INHIBITION - DLPFC
Intentional saccade - FEF
Is gain higher or lower in the dark?
Lower ~0.6
What is stimuli for vergence?
Disparity and blur (because you would try and focus on something that is not visualised well)
Internuclear opthalmoplegia (INO)
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).
Medial longitudinal fasciculus location and what is it vulnerable to?
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)
Duane’s congenital retraction syndrome - what is it? How does one get it?
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
Oscillopsia
Objects in the visual field appear to oscillate. The severity of the effect may range from a mild blurring to rapid and periodic jumping
How does Alzheimer’s disease affect how we process novelty?
They fail to respond to novelty and have diminished visual curiosity - only looking at the kid but not the bipedal horse
Ventral simultanagnosia
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
Dorsal simultanagnosia
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
Treisman’s feature integration theory
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
How can selectivity of attention be demonstrated?
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
What is the binding problem in perception? How is the binding problem solved?
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.
What is the neural mechanism that underlie the attentional modulation in one brain region by another?
Neuronal oscillations and synchrony where enhanced response to stimulus leads LIP neurons to sync then drive MT neurons to fall in sync with them.
LTP
A persistent increase in synaptic strength following high-frequency stimulation of a chemical synapse.
