Greg Detre
25/11/99
sub-cortical visual pathways
centre surround � mutually antagonistic � insensitive to whole cell illumination
spatial contrast rather than luminance
p- and m-retinal cells (parasol and midget)��������� size of dendritic field
analysign the world at a different spatial scale
P-cells in fovea � fine-grained, convert to single cone
little overlap � important principle of retinal sampling = spatially efficient
tile the retina doubly (on + off-centre cells)
M-cell 3 times the diameter of P-cell � also tile
M-cell 3 times the diameter of P-cell � also tile
density P:M 9:1���������� 10% specialised, project � non-thalamic
can vary the spatial contrast (the difference between illumination + background)
m-cells quite sensitive respond lots over different contrast ranges
detect fine scale contrast/reflectances in the external world
chromatic selectivity
LGN:
parvo-cellular layers (P-cells project) 4 layers
magno-cellular layers (M-cells)
the physiology = exactly same as retina
segregation of input according to ocularity
the further from the fovea, the bigger the receptive fields
eccentricity � 1/resolution
90% retina � LGN
10% � superior colliculus (convergent input from somatosensory + auditory as well)
sit on top of motor neurons
sensorimotor integration awaiting resopnses eye/head
protection � pupil light response
suprahiasmatic(???) nucleus � close to hypothalamus + pituitary)
set biological clock���� registration with daylight
why don't we see double?
cortical map represents density of retinal ganglion cells in the fovea
visual cortex neurons in area 17 are selective to bars (orientation)
orientation tuning curve
simple:
bar detectors based on a line of receptive field
H&W predict optical stimulus for receptive field (other way round???)
spatially separate mutually antagonistic sub-fields
complex:
spatially paired on & off responses
same range of timing � just as orientation-selective
less selective of position � not selective of locality
complex � converging lots of simple cells
hyper-complex
continuum of tuning for length
(as well as bar orientation and width)
used for occlusion + termination
and possibly also curvature
cortical cells = binocular = get information from both eyes
parasol + midget vs parvo + magno???
single cone/triplet?