The different information channels that keep the human body in contact with the environment are traditionally grouped into five senses: taste, smell, touch, hearing, and sight. Taste and smell are mediated by chemical reactions at the nose and mouth; touch includes all the data gathered at diverse skin receptors: texture, temperature, pressure, humidity; hearing results from a mechanical process in the tympanum; and sight involves the interaction of light with the eye. However mediated through independent physical phenomena, human senses are not completely isolated from each other. They contribute to perception as an active team led by the brain to furnish every person with their own notion of what lies ahead.

In front of a coffee cup, senses complement, influence, and even compete with each other, to offer a full and personal impression of the coffee-drinking experience. Taste and smell lead to the flavor appreciation under a mutual influence. Touch and hearing may eventually supply conclusive details about the porcelain, complementing the visual inspection of the cup, which, in turn, exerts a non-negligible dominance on taste. Further connections, in every way more mysterious, are revealed by the synesthetic condition of some hypothetical individuals to whom the coffee's aroma might sound like an Elgar march.

Synesthesia is a peculiarity in perception that occurs when a stimulus over one sensorial channel triggers the perception of a different sense. It grounds the basis of some artificial approaches to sensing, since it implies the possibility of deliberately causing a sensorial impression without a direct stimulus. Certain sensorial impairments, like color-blindness, may be partially overcome by means of an implanted device that transduces the frequency of light corresponding to each color into a different sound frequency. As a result, colors, the notes of light, can be distinctively heard.

A beam of light has physical properties other than its color; like intensity, direction of propagation, or polarization. These properties may be affected in the interaction of light with different objects, revealing in the process diverse characteristics of such objects.