Complex perceptions like voice recognition or discrimination of similar sound sequences need experience and can generally be trained.Complex perceptions are often multi-sensory perceptions.The example of multi-sensory perceptions: To distinguish between a real apple and fake the subject needs to touch or to smell it, because visual inspection may be insufficient. The basic principles of perception training are similar to problem solving.The perception of a simple stimulus (like a sound of a given intensity) can normally not be trained to function below its .