How are visual stimuli processed in the visual cortex?
(Essay plan notes)
Sanjay Manohar (Oxford 2015)
Intro
Localisation & identification: different kinds of problem
Muller's specific nerve energies; place-coding
Input from LGN: 6 layers;
1-2=magno -> layer IVc ->
3-6=parvo (M/L) -> layer IVc
konio=(S/ML) -> blobs layers 2/3
Lesion LGN: magno = motion; parvo = colour
V1
Primary V1 Area 17; Secondary V2-5 Area 18-19
Gordon Holmes - visual field defects
striate 4A/B/C - stellate cells 4C
Tootell 1991: 14C deoxyglucose autoradiography - retinotopy; calcarine fissure,
logarithmic (central 5 deg = 30%)
Allman Kaas 2000 - retinotopy of striate cortex in monkey single-cell
Wong-Riley 1979,
Blob cytochrome oxidase - from koniocellular = colour contrast, double opponent
interblob - parvocellular 4Cbeta, single-opponent, luminance responses
Ocular dominance: inject one eye with radiolabelled amino acid. Autoradiography.
hubel and wiesel - ocular dominance, anterograde radiolabelled proline
- ice-cube diagram
- monkey patched eye = critical window;
amblyopia and patch treatment
Livingstone and Hubel 1983 single neuron microelectrode, cat
Spatial frequency selectivity (graph)
Binocular disparity (graph, diagram)
- stereopsis - near/far cells Pollen 1981
- horopter, absolute vs relative
Simple cell RFs:
- H&W 1959 graphs of responses with orientation, motion, gabors
- static response to lines, location-specific
- spatial & temporal linearity - DeAngelis study, reverse correlation
- draw receptive field and possible wiring of
how orientation selectivity could arise
how and motion detection arise
H&W vertical penetration = similar orientation --> columns, pinwheel
Complex cell (H&W 1962)
- dynamic responses, location invariance, nonlinear, binocular
- LGN inputs -> simple cell RF; multiple simple cells -> complex RF
- hierarchical; feedforward models
End-stopped cells
V2 - more complex RFs, feature conjunctions, curves, 3d corners
V4 - location invariance
Tanaka studies: RF size increases
Moran & Desimone 1985 top down input
Extrastriate / Higher areas
dorsal stream ventral stream
-------------------------------------------------------------
Parietal lobe temporal lobe
V5, IPL, SPL V4, FFA, LOC, VWFA, grandmother
Ungerleider and Mishkin 1982 - monnkey landmark task vs pattern discrimination
where what
spatial cues, allocentric pattern detection, semantics
Dorsal stream
- MT/V5 Akinetopsia; active in imagined or illusory motion.
- Goodale and Milner 1992 - DF: post-box task - "vision for action"
- Salzman..Newsome 1992 microstim V5 -> altered report.
- Bisley Pasternak 2000 - MT in WM / comparison of directions
Ventral stream "what" V4 IT
- colour, achromatopsia;
- form, prosopagnosia; Tanaka 1996 IT;
- apperceptive agnosia - can copy but not recognise
- associative agnosia - identify but not semantically pair
- Fuster 1981 - IT in delayed response task
Both dorsal and ventral are polymodal
Weiskrantz 19174 blindsight - retinotectal / extrastriate
Anton Babinski syndrome confabulation
Big picture
Big picture:
divergence & feature extraction vs integration & binding
Gabor RFs as principal component analyis
hierarchical processing, predictive coding, multimodal
feedback as well as feedforward; attention, expectation
Why? Economical Olshausen and Field 1997 gabor
visual primitives
half cortex is "visual"
predictive coding
grandmother cell
Does the visual system integrate or segregate information
| Integration | Segregation |
| orientation = sum of ON-centre | different orientations in columns |
| colour (L/M; S/M+L) | two separate chroma channels |
| colour + form (double-opponent, edges) | blob vs interblob |
| disparity L-R | ocular dominance columns |
| larger RF = combines information | retinotopy, place-coded space |
| motion = T2-T1 | area MT |
| IT cells complex arrangements of shapes | dorsal vs ventral stream |
| top down input / expectation / polymodal | fusiform face area; visual word form area |