Lecture 8 Flashcards
How is the visual field mapped in the occipital lobe?
Upper visual field is mapped below the calcarine sulcus
Lower visual field above the calcarine sulcus
Not peripheral regions of the retina are represented in progressively more anterior parts of the striate cortex
What are the 6 layers in the V1 cortex?
What are the 3 sub layers in layer IV?
What is layer IVC divided into?
6 layers: I, II, III, IV, V, VI
Layer IV: A, B, C
Layer IVC: IVCα and IVCβ
Magnocellular LGN neurons project to layer IVCα
Parvocellular LGN neurons project to layer IVCβ
Slide 2
What is ocular dominance?
Neurons with similar ocular preference
Left eye and right eye inputs to layer IV are laid out as a series of alternating bands
Rather than randomly mixing, neurons connected to the left and right eyes are as distinct in layer IV as they are in the IGN
Slide 3-4
Where does info from the right and left eye start to mix?
Layer IVC stellate cells project axons radially up mainly to layers IVB and III where info from left and right eye begins to mix
All IVC neurons receive input from one eye
Most neurons in layers II, III, V, VI receive some amount of input from each eye
At layer IV neurons have received info and begin talking to eachother
Slide 5
What is binocularity?
Signals from the 2 eyes are combined at the cellular level in the striate cortex
This provides basis for stereopsis (sensation of depth)
What is binocular disparity?
What 2 cells respond to disparities?
Disparity between the 2 eye cues of objects nearer or father than the fixation point is interpreted as depth
Cortical far cells discharge to disparities beyond the plane of fixation
Near cells respond to disparities in front of the plane of fixation
Slide 6
What are orientation-selective neurons?
Prefer a certain orientation
Some cortical neurons respond vigorously to light dark bars or edges only if the bars are presented at a particular range of orientations within the cells receptive field
The orientation to which a cell is most responsive is referred to as the neurons preferred orientation
Orientation-selective neurons are thought time be specialized for the analysis of object shape
Slides 7-12
What is dorsal stream?
Spatial aspects of vision
Analysis of motion
Positional relationships between objects in the visual scene
Many direction selective neurons (selective damage -> akinetopsia)
Slide 13
What is ventral stream?
High resolution form vision and object recognition
Selective damage -> prosopagnosia
Slide 13
How do neurons encode visual percepts?
2 hypothesis’
- Schemes that rely on an implicit representation over a very broad and distributed population of neurons
- Schemes based on the explicit representations by highly selective grandmother neurons
- brain has a separate neuron to detect and represent every object (including ones grandmother)
What is invariant neural representation?
Different views of the same person or object evoke identical activity patterns
Slide 15
What is non-invariant neural representation?
Different views evoke different activity patterns
Slide 15
