Field of view

The field of view is the extent of the observable world that is seen at any given moment. In case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.

In the context of human vision, the term "field of view" is typically used in the sense of a restriction to what is visible by external apparatus, like spectacles or virtual reality goggles. Note that eye movements do not change the field of view.

If the analogy of the eye's retina working as a sensor is drawn upon, the corresponding concept in human (and much of animal vision) is the visual field. It is defined as “the number of degrees of visual angle during stable fixation of the eyes”. Note that eye movements are excluded in the definition. Different animals have different visual fields, depending, among others, on the placement of the eyes. Humans have an almost 180-degree forward-facing horizontal diameter of their visual field, while some birds have a complete or nearly complete 180-degree visual field. The vertical range of the visual field in humans is typically around 135 degrees.

The range of visual abilities is not uniform across the visual field, and varies from animal to animal. For example, binocular vision, which is the basis for stereopsis and is important for depth perception, covers 114 degrees (horizontally) of the visual field in humans; the remaining peripheral 60–70 degrees have no binocular vision (because only one eye can see those parts of the visual field). Some birds have a scant 10 or 20 degrees of binocular vision.

Similarly, color vision and the ability to perceive shape and motion vary across the visual field; in humans the former is concentrated in the center of the visual field, while the latter tends to be much stronger in the periphery. The physiological basis for that is the much higher concentration of color-sensitive cone cells and color-sensitive parvocellular retinal ganglion cells in the fovea – the central region of the retina – in comparison to the higher concentration of color-insensitive rod cells and motion-sensitive magnocellular retinal ganglion cells in the visual periphery. Since cone cells require considerably brighter light sources to be activated, the result of this distribution is further that peripheral vision is much more sensitive at night relative to foveal vision.

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