FoundationalConceptsNeuroscience

group), that possess structures, called pit organs, that detect infrared
radiation in a way similar to how eyes detect visible light. The pit
organs are positioned below the eyes and near the nostrils, and en-
able the snake to accurately locate prey animals even in complete
darkness.
There are some technological gadgets used by humans to facilitate
vision in the dark. These night vision devices are used by military and
law enforcement personnel to see under conditions of very low light
or even in complete darkness. One kind of device, called an image in-
tensifier, amplifies very low intensities of visible light. Even on a very
dark night there is still a low level of visible light—from the moon
and stars, for example. A second kind of gadget is called an infrared or
thermal imager. Like the rattlesnake’s pit organ, it detects infrared ra-
diation, to which the human visual system is insensitive. The gadget
converts the infrared image to signals in the visible region of the spec-
trum, allowing things to be seen even in complete darkness—as long
as they emit infrared radiation, as any person or other warm-blooded
animal would.
Another property of electromagnetic radiation is something called
polarization, which can be thought of as vibration of the electromag-
netic field aligned along specific angles in relation to the direction of
propagation. Light from the sun, radiating through space, is vibrating
in all possible angles of polarization. However, when sunlight inter-
acts with the molecules of air in Earth’s atmosphere, it scatters so as
to generate a variation in polarization across the vault of the sky (Fig.
11.6). That is, the angle of polarization, and the extent to which the
light is polarized, varies depending upon where in the sky one looks
relative to the sun.
This can be demonstrated by looking through a polarizing filter
(such as the lens in polarizing sunglasses) at different regions of the