Transduction has to occur in every sense because the nervous system can only carry:

1. The world supplies energy in many different physical forms. 2. Neurons, however, communicate in only one currency. 3. The conversion from sensory stimulus energy to action potential is known as transduction. 4. So light, sound and pressure must each be converted into that common signal. 5. Without transduction the brain would receive nothing it could read. _Source: OpenStax Psychology 2e (CC BY 4.0), Ch 5 'Sensation and Perception', sections 5.1-5.6_