Transduction

Transduction (trans- + -duc- + -tion, "leading through or across") can refer to:

Transduction (machine learning)

In logic, statistical inference, and supervised learning, transduction or transductive inference is reasoning from observed, specific (training) cases to specific (test) cases. In contrast, induction is reasoning from observed training cases to general rules, which are then applied to the test cases. The distinction is most interesting in cases where the predictions of the transductive model are not achievable by any inductive model. Note that this is caused by transductive inference on different test sets producing mutually inconsistent predictions.

Transduction was introduced by Vladimir Vapnik in the 1990s, motivated by his view that transduction is preferable to induction since, according to him, induction requires solving a more general problem (inferring a function) before solving a more specific problem (computing outputs for new cases): "When solving a problem of interest, do not solve a more general problem as an intermediate step. Try to get the answer that you really need but not a more general one." A similar observation had been made earlier by Bertrand Russell: "we shall reach the conclusion that Socrates is mortal with a greater approach to certainty if we make our argument purely inductive than if we go by way of 'all men are mortal' and then use deduction" (Russell 1912, chap VII).

Transduction (physiology)

In physiology, sensory transduction is the conversion of a sensory stimulus from one form to another.

Transduction in the nervous system typically refers to stimulus alerting events wherein a physical stimulus is converted into an action potential, which is transmitted along axons towards the central nervous system where it is integrated.

A receptor cell converts the energy in a stimulus into a change in the electrical potential across its membrane. It causes the depolarization of the membrane to allow the action potential to be transduced to the brain for integration.

Transduction and the senses

The visual system

In the visual system, sensory cells called rod and cone cells in the retina convert the physical energy of light signals into electrical impulses that travel to the brain. The light causes a conformational change in a protein called rhodopsin. This conformational change sets in motion a series of molecular events that result in a reduction of the electrochemical gradient of the photoreceptor. The decrease in the electrochemical gradient causes a reduction in the electrical signals going to the brain. Thus, in this example, more light hitting the photoreceptor results in the transduction of a signal into fewer electrical impulses, effectively communicating that stimulus to the brain. A change in neurotransmitter release is mediated through a second messenger system. Note that the change in neurotransmitter release is by rods. Because of the change, a change in light intensity causes the response of the rods to be much slower than expected (for a process associated with the nervous system).