The visual function

Like other human sensory systems, the visual system comprises a peripheral organ, the eye, responsible for image formation and transduction in the form of signals that can be transmitted along nerve pathways, followed by a cortical analysis apparatus whose complexity has yet to be fully deciphered.

We won't go into the first part of the eye, made up of transparent tissues (cornea and crystalline lens separated by a liquid similar in composition to salt water) whose role is to form a clear image on the retina, a very thin neuronal tissue covering the back of the eye. It should be noted, however, that short focal length optics (around 25 mm between the anterior and posterior poles of the eye) projecting an image onto a concave hemispherical surface cannot achieve constant image quality. Image quality is at its best in the axis of vision (the direction of the fovea, as we'll see below), then deteriorates very rapidly in lateral vision, leading to a concomitant drop in visual acuity. The performance of our retinal tissue will also depend on this characteristic.

Beyond this, the cortical analysis organ is extremely diversified, but here too, it cannot cope with the processing of the various types of information that flow into it via the sensory pathways with the same power. Our visual brain, for example, favors spatial localization over frequency analysis, as we shall see later.

All this will enable us to better understand and appreciate human visual behavior under specific experimental conditions. This is the field of psychophysics, where we'll look in more detail at the establishment of visual units, the function of contrast sensitivity and color vision.