- Field of view is inspected through brief fixations over small regions of interest
- Central foveal vision lies between a visual angle of 1°-5° (this is the answer to the question in the previous post) => on a 21" monitor(distance ~60cm), the attention of the user is only on 3% of the picture
- Approx. 90% of viewing time is spent on fixations
2.1 The Eye
Often called the "world's worst camera", as it suffers from numerous optical imperfections
- spherical aberrations: prismatic effect of peripheral parts of the lens - HOWEVER: iris acts as a stop, limiting peripheral entry of light rays
- chromatic aberrations: shorter wavelengths (blue) refracted more than longer wavelengths (red) - HOWEVER: the eye is typically focused to produce sharp images of intermediate wavelengths
- curvature of the field: a planar object gives rise to a curved image - HOWEVER: the retina in curved compensating for this effect
- rear interior surface of the eye, which contains receptors sensitive to light (photoreceptors), which constitute the first stage of visual perception
- photoreceptors: convert light energy to electrical impulses
- photoreceptors are further classified into rods (dim and achromatic light: night vision) and cones (brighter chromatic light: daylight vision)
- Microsaccades!! If there were no such microsaccades, the image would fade within a second and the scene would go black
Hi Dan! Physiological facts alone eplain next to nothing. May I cite David Marr: "The key observation is that neurophysiology and psychophysics have as their business to *describe* the behavior of cells or of subjects but not to *explain* such behavior. [...] The best way of finding out the difficulties of doing something is to try to do it, so at this point I moved to the Artificial Intelligence Laboratory at MIT, [...] The first great revelation was that the problems are difficult. Of course, these days this fact is a commonplace. But in the 1960s almost no one realized that machine vision was difficult. [...] The reason for this misperception is that we humans are ourselves so good at vision." (Marr, pp 15-16)
ReplyDeleteMarr, D. (1982). Vision. A Computational Investigation into the Human Representation and Processing of Visual Information. W.H. Freeman and Company.
There is a nice 2010 reprint of this seminal book by MIT Press.
Cheers,
Walter Piechulla