On the Physical Origins of Inverted Optic Images

Abstract

In the behavioral sciences, discussions of vision often carry an implicit assumption that the formation of inverted optic images is a result of human technology (i.e., cameras) or biological mechanisms (i.e., the chambered eye). If this assumption were true, then inverted images would be—in effect—an invention of living things, which, in turn, would have important consequences for our understanding of the evolution and psychology of vision. In this article, I briefly review the history of ideas relating vision and optics to the formation of inverted optic images. I then evaluate the necessary and sufficient conditions for the formation of inverted images. I demonstrate that inverted optic images (including inverted optic flow) can and do form in the absence of any biology and that sufficient conditions for inverted image formation predate the origins of life. Inverted images are not an invention of biological systems; rather, biological systems and human technologies exploit preexisting facts of physical optics. This conclusion is consistent with the ecological premise that life is coherent with physical law.

Notes

¹In the history of science the meaning of image has changed qualitatively. When I refer to inverted optic images I am using the modern, or contemporary, meaning of image, which is illustrated in Figure 1. In a later section I review the contrast between this use of the term and earlier uses.

²The ancient Greeks knew about the magnifying powers of glass, as evidenced by their use of the “burning glass,” in which a spherical glass container filled with water could be used to heat objects that were placed on the side of the sphere opposite the sun. However, there is no record of any Greek philosopher suggesting any relation between the burning glass and any facet of optics or vision.

³Very large cameras obscura have been built as astronomical instruments, principally in the 17th century. Known as astronomical gnomons (Heilbron, 2001), their purpose was to create an image of the light source (the sun) rather than of the illuminated environment. Several astronomical gnomons still exist. An accessible example is in the church of Saint Sulpice in Paris.

⁴A separate cause for doubt about lenses was more concrete, although it was often given a supernatural interpretation. Early lenses were of poor quality, with variable curvature. The resulting visual distortions, which tended to be wavering and unpredictable, were often attributed to the Devil. Such fears are vividly expressed in The Name of the Rose (Eco, 1983), a novel about monastic life in 1327 CE. The fictional protagonist, William of Baskerville, owned a pair of spectacles but often refrained from wearing them in public, fearing that they (and, by implication, he) would be thought to be diabolical.

⁵Photography was invented in 1839. Since then the “eye as camera” analogy typically has been assumed to refer to the photographic camera (e.g., Wade & Finger, 2001). However, the previous discussion makes clear the analogy actually predates photography by at least 400 years.

⁶Skeptical readers might point out that sunlight passing through foliage is not an instance of purely physical image formation, given that the foliage is biological. However, the same principles operate in situations that precede any biology. For example, sunlight can pass through gaps between pebbles, fractures in rock, or erosional features, such as natural bridges.

⁷Although these images do not require animate agency they can be relevant to purposeful behavior. For example, as part of an “inverted image, thinking animal” system, images of the sun under foliage afford awe and insight about ecological optics (cf. Stoffregen, 2000, 2004).

⁸The invention of the shutter is related to the sensitivity of emulsions used to record photographic images. Cameras used by Daguerre did not have shutters because the relatively insensitive photographic emulsion required long exposures, often several minutes. Shutters were mandated by more sensitive emulsions that were developed in the 1870s (Newhall, 1982; Tubbs, 1975).