cortical column

column, cortical

In the visual cortex, neurons with similar properties are arranged in columns (about 2 mm high) perpendicular to the surface of the cortex. The columns traverse the six cortical layers until they reach the white matter. Neurons throughout a column respond either to stimuli oriented at the same angle (orientation column) or to the inputs from the same eye (ocular dominance column, ocular dominance slab). A neighbouring column will then have neurons responding to a slightly different orientation from the one next to it and perhaps the same eye or the other eye. Neurons in layer 4 represent an exception, as they may respond to any orientation or to one eye only. Strabismus in early childhood disrupts the development of ocular dominance columns, thus preventing the development of depth perception. See visual area; blobs; hypercolumn.

Table C5 Approximate colour temperature (in K) of some light sources
clear blue sky	12000-26000
overcast sky	6600
sun	5000-6000
electronic flash	about 5600
moonlight	4000
tungsten-halogen lamp	3000
tungsten filament lamp	2600
candle flame	2000

Table C6 Prevalence (%) and classification of colour vision defects
	anomalous trichromats
	deuteranomal		protanomal	tritanomal
male	4.6%		1%	0.0001%
female	0.35%		0.03%	unknown
colour response	slight green deficiency		red deficiency	blue deficiency
	dichromats
	deuteranope		protanope	tritanope
male	1%		1.1%	0.005%
female	0.01%		0.01%	0.003%
colour response	green deficiency	insensitive to red		blue deficiency
neutral point	498 nm	493 nm		570 nm
	monochromats
	cone monochromat		rod monochromat
	unknown		0.003%