Lecture 11 Visual Processing Flashcards
(20 cards)
What is the main pathway responsible for conscious visual experience?
The retinogeniculate pathway (retina → LGN → V1).
What is the primary visual cortex also known as?
V1 or striate cortex.
What happens if there is a lesion in V1 on one side?
It causes hemianopia 偏盲—loss of vision in the contralateral visual field.
How is the visual field represented in V1?
Retinotopic organization—adjacent cells process adjacent parts of the retina.
What is cortical magnification?
More V1 cells are dedicated to the fovea than the periphery, enabling detailed central vision.
What do the upper and lower banks of the calcarine sulcus represent?
Upper bank = lower visual field; lower bank = upper visual field.
What are cortical columns in V1?
Modular units processing small parts of the visual field, arranged like a mosaic.
What are ‘blobs’ and ‘interblobs’ in V1?
Blobs: color-sensitive neurons; Interblobs: sensitive to orientation, motion, and depth.
What is orientation selectivity?
Simple cells in V1 respond best to bars of light in specific orientations.
How do V1 cells differ from LGN neurons?
V1 cells (simple cells) are orientation-selective; LGN neurons are not.
What is the role of area V4?
Processes colour; damage can cause achromatopsia (colour blindness).
What is the role of area MT (V5)?
Processes motion; neurons are direction-selective with large receptive fields.
What is MST responsible for?
Processes complex motion patterns like optic flow and biological motion.
What is akinetopsia?
Motion blindness due to bilateral MT damage; patients see ‘snapshots.’
What are the two streams in the two-stream hypothesis?
Dorsal stream (‘where’/’how’): spatial location and action; Ventral stream (‘what’): object recognition and form.
How does colour processing begin?
Begins in the retina with cone-opponent ganglion cells (R-G, B-Y).
Which LGN layers process colour info?
- Parvocellular: red-green;
- Koniocellular: blue-yellow.
Where does colour perception occur in the cortex?
Primarily in V4, with input from blobs in V1 and regions of V2.
What does the hierarchical feedforward model suggest?
Visual areas process information in increasing complexity (V1 → V2 → V4/MT).
What explains motion after-effects?
Adaptation of direction-selective neurons in MT.
