aguirreg

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
====== 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<sup>-1</sup> m<sup>-2</sup>)
  * Colorimetric units adjust radiometric units for visual wavelength sensitivity (e.g. luminance has units of cd m<sup>-2</sup>); 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<sup>-2</sup>)
    * starlight 10<sup>-3</sup>
    * moonlight 10<sup>-1</sup>
    * indoor lighting 10<sup>2</sup>
    * sunlight 10<sup>5</sup>
    * max intensity of common CRT monitors, 10<sup>2</sup>
  * One Troland (Td) of retinal illumination is produced on the retina when the eye looks at a surface of 1 cd / m<sup>2</sup> through a pupil of area 1 mm<sup>2</sup>.
  * 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 10<sup>6</sup>
  * Number of rods in each retina: 10<sup>8</sup>
  * 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 10<sup>5</sup> cones/mm<sup>2</sup>;
  * 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 10<sup>6</sup> 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 10<sup>5</sup> mm<sup>2</sup>; 1.7 mm thick
  * Total number of cortical neurons: 10<sup>10</sup>; density: 10<sup>5</sup> neurons / mm<sup>3</sup> 
  * Synapses: 5 x 10<sup>8</sup> synapses / mm<sup>3</sup> 4 x 10<sup>3</sup> synapses/neuron;
  * Axons: 3 kilometers / mm<sup>3</sup>
  * Number of corpus callosum fibers:  5 x 10<sup>8</sup>
  * 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<sup>-2</sup> (male), 10<sup>-4</sup> (female);
    * protanopia and deuteranopia, 10<sup>-2</sup> (male), 10<sup>-4</sup> (female);
    * tritanopia, 10<sup>-4</sup>; rod monochromacy, 10<sup>-4</sup>; cone monochromacy, 10<sup>-5</sup>
aguirreg

User Tools

Site Tools

Page Tools
