I'm geeking out on Square One Research on The Human Eye and Sight. It is the best explanation of perception I've seen with frequent explanations of relevance to design -- environmmental, software, architecture, and even lighting.

My favorite facts so far:

• The persistence of vision of cones is much longer than that of rods, around 1/20th of a second. This is why flicker is much easier to detect out of the corners of the eye rather than directly in front.

  (Cones are sensitive to different frequencies of light, whereas rods are sensitive to light levels. Rods are concentrated away from the macular, the central focus point of the eye.)



• Comfort and visibility are dependent upon the luminance patterns within the visual field. Comfort is dependent on the variation in luminances in the visual field (luminance ratios)...Clutter can create an overload of the visual system due to excessive luminance ratios.

  Luminance is the amount of light reflected off of an object and into the eye. I hadn't thought about the discomfort caused by clutter, since my concern over clutter is dominted by the difficulties cluttered design pose for visual search (predictability to help scanning as well as to make it easier to draw attention by breaking the pattern).



• The highest visibility occurs when the object is brighter than the background (white print on black paper).

  How the history of paper, ink, and computer interfaces has flown in the face of perception science. Lament!



• As the level of background luminance increases, the time required to interpret details will decrease. Just as the camera requires a longer exposure time in dim light than in bright light, so does the eye. The eye can distinguish and discriminate details at low luminance levels if given enough time.

  Kinda useless to me, unless I try to design watermarks that only emerge if stared at or some such, but still cool.

All this was prompted by me wanting to review the human eye's discrimination of detail in terms of degrees, since I interviewed a HCI-cog psych PhD the other day and he geeked too quickly for me to keep up when talking about details. I found that on the Square one page too, under "Visual Acuity," all the way at the bottom. :P The journey was long and geeky, but worth it.