For some people, hearing certain sounds may activate color-sensitive regions of the cortex so as to trigger a sensation of color. This phenomenon is called

Answer: Synaesthesia

Explanation:

Synaesthesia is disorder state in which senses of the body get linked with each other that was not connected previously. This condition produces automatic response in another sense organ when simulation takes place in a particular sense organ.

This neurological disorder can occur in a person through inheritance at time of birth or early stage of childhood. Example of synaesthesia are individual feeling sensation on body while smelling certain fragrance or odor, seeing sounds etc.