Senses are the physiological methods of perception. The senses and their operation, classification, and theory are overlapping topics studied by a variety of fields, most notably neuroscience, cognitive psychology (or cognitive science), and philosophy of perception.

Definition of "sense"

There is no firm agreement among neurologists as to exactly how many senses there are, because of differing definitions of a sense. In general, one can say that a "sense" is a faculty by which outside stimuli are perceived. In other words, senses are transducers from matter to mind. School children are routinely taught that there are five senses (sight, hearing, touch, smell, taste; a classification devised by ancient peoples). It is generally agreed that there are at least seven different senses in humans, and a minimum of two more observed in other organisms.

A broadly acceptable definition of a sense would be "a system that consists of a sensory cell type (or group of cell types) that responds to a specific kind of physical phenomenon, and that correspond to a defined region (or group of regions) within the brain where the signals are received and interpreted." Where disputes arise is with regard to the exact classification of the various cell types and their mapping to regions of the brain.

Five classical senses

 Sight

Sight or vision describes the ability of the brain and eye detecting electromagnetic waves within the visible range (light) interpreting the image as "sight." There is disagreement as to whether this constitutes one, two or even three distinct senses. Neuroanatomists generally regard it as two senses, given that different receptors are responsible for the perception of colour (the frequency of photons of light) and brightness (amplitude/intensity - number of photons of light). Some argue that stereopsis, the perception of depth, also constitutes a sense, but it is generally regarded that this is really a cognitive (that is, post-sensory) function of brain to interpret sensory input to derive new information. This "third" sense has recently been thought by some scientists to be associated with the time dimension, although no concrete proof has yet been recorded to validate this theory. The inability to see is called blindness.