Capacitive sensors for detecting proximity and response.

We have implemented an inexpensive circuit that indicates when a subject is in close proximity to a specified area of arbitrary shape and size. The circuit can transform an easily created metal surface or a preexisting metal object into an experimental sensor. The subject need not make physical contact with the sensor to activate the mechanism, which enables the detection of subjects through nonconductive materials, such as wood and plastics. The technology is readily adapted to existing experimental setups. Applications of this technology, using pigeons, rats, and mice, demonstrate its flexibility: a nose-poke/peck sensor for response or choice detection; a subject location detector that can be placed on a floor, wall, or ceiling; and a perch that detects when a bird is present. This technology can also be applied to the study of behavior in primates and many other animal species.