====== Wandell's Useful Vision Values ======
Brian Wandell compiled and made available a list of values and relationships that are useful in vision science. We have added a couple of items to his list below.
The original was taken from [[http://white.stanford.edu/~brian/numbers/|Brian A. Wandell's site]]
===== Units =====
* Radiometric units represent physical energy (e.g., radiance has units of watts sr-1 m-2)
* Colorimetric units adjust radiometric units for visual wavelength sensitivity (e.g. luminance has units of cd m-2); scotopic units are proportional to rod absorptions; photopic luminance units are proportional to a weighted sum of the L and M cone absorptions
* Typical ambient luminance levels (in cd m-2)
* starlight 10-3
* moonlight 10-1
* indoor lighting 102
* sunlight 105
* max intensity of common CRT monitors, 102
* One Troland (Td) of retinal illumination is produced on the retina when the eye looks at a surface of 1 cd / m2 through a pupil of area 1 mm2.
* Lens focal length: f (meters); lens power = 1/f (diopters)
* Conversion of linear units (X) to decibels: Y = 20 log10(X); a change of 0.3 log10 units is a factor of 2, or 6 dB
===== Image Formation =====
* The eyes are 6 cm apart and half-way down the head
* Visual angle of the sun or moon = 0.5 deg
* At arm's length: thumbnail = 1.5 deg; thumb joint= 2.0 deg; fist = 8-10 deg
* Monocular visual field measured from central fixation: 160 deg (w) x 175 deg (h)
* Binocular visual field measured from central fixation: 200 deg (w) x 135 deg (h)
* Region of binocular overlap: 120 deg (w) x 135 deg (h)
* Range of pupil diameters: 2mm -8mm.
* Refractive indices: air 1.000; glass 1.520; water 1.333; cornea 1.376
* Optical power (diopters): cornea, 43; lens, 20 (relaxed); whole eye, 60
* Change in power due to accommodation, 8 diopters
* Axial chromatic aberration over the visible spectrum: 2 diopters
===== Retina =====
* Retinal size: 5 cm x 5 cm; 0.4 mm thick
* One degree of visual angle = 0.3 mm on the retina
* Number of cones in each retina: 5 x 106
* Number of rods in each retina: 108
* Diameter of the fovea: 1.5 mm (5.2 deg);
* rod-free fovea: 0.5 mm (1.7 deg);
* foveola (rod-free, capillary-free fovea): 0.3 mm (1 deg);
* size of the optic nerve head: 1.5 mm x 2.1 mm (5 deg (w) x 7 deg (h))
* location of the optic nerve head: 15 deg nasal
* Peak cone density: 1.6 x 105 cones/mm2;
* Foveal cone size: 1-4 mu (diameter) x 50-80 mu (length);
* extrafoveal cone size: 4-10 mu (diameter) x 40 mu (length)
* Size of rods near fovea: 1 mu (diameter) x 60 mu (length)
* S cone spacing (foveal): 10 arc min
* L and M cone spacing (foveal): 0.5 arc min
* Number of (L + M) cones / Number of S cones = 14 (though the ratio may be higher in the foveola)
* 1.5 106 optic nerve fibers/retina; ratio of receptors to ganglion cell in fovea 1:3; ratio of receptors to ganglion cells for whole retina, 125:1
===== Cortex =====
* Area of entire cortex: 1.3 x 105 mm2; 1.7 mm thick
* Total number of cortical neurons: 1010; density: 105 neurons / mm3
* Synapses: 5 x 108 synapses / mm3 4 x 103 synapses/neuron;
* Axons: 3 kilometers / mm3
* Number of corpus callosum fibers: 5 x 108
* Number of macaque visual areas: 30
* Size of each area V1: 3cm by 8 cm
* Half of area V1 represents the central 10 deg (2% of the visual field)
* Width of a human ocular dominance column 0.5-1.0 mm; width of a macaque ocular dominance column 0.3 mm">.
===== Sensitivity =====
* Minimum number of absorptions for: scotopic detection 1-5
* detectable electrical excitation of a rod 1
* photopic detection 10-15
* The number of photoisomerisations per rod (per sec?) required to saturate the retinal rod circuit.
* Following exposure to a sunny day, dark adaptation to a moonless night involves
* 10 minutes (photopic)
* 40 minutes (scotopic)
* change in visual sensitivity 6 log10 units
* Highest detectable spatial frequency at high ambient light levels, 50-60 cpd
* low ambient light levels, 20-30 cpd
* The contrast threshold (Delta L / L) for a static edge at photopic luminances is 1%.
* Highest detectable temporal frequency: high ambient large field, 80 Hz; low ambient, large field 40 Hz.
* Typical localization threshold: 6 arc sec (0.5 mu on the retina)
* Minimum temporal separation needed to discriminate two small, brief light pulses from a single equal-energy pulse: 15-20 ms
* Stereoscopic depth discrimination: step threshold, 3 arc sec
* point threshold, 30 arc sec
===== Color =====
* Visible spectrum: 370-730 nm
* Peak wavelength sensitivity: 507nm (scotopic) and 555 nm (photopic)
* Spectral equilibrium hues: 475 nm (blue)
* 500 nm (green)
* 575 nm (yellow)
* no spectral equilibrium red
* Number of basic English color names: 11
* Incidence of
* anomalous trichromacy, 10-2 (male), 10-4 (female);
* protanopia and deuteranopia, 10-2 (male), 10-4 (female);
* tritanopia, 10-4; rod monochromacy, 10-4; cone monochromacy, 10-5