In computers, encoding is the process of putting a sequence of characters (letters, numbers, punctuation, and certain symbols) into a specialized format for efficient transmission or storage. Decoding is the opposite process -- the conversion of an encoded format back into the original sequence of characters. Encoding and decoding are used in data communications, networking, and storage. The term is especially applicable to radio (wireless) communications systems. Visual encoding uses images and neuronal encoding uses sounds. You do not use meanings or acronyms while coding. So that leaves you with your two answers of images and sounds and based on what I have stated here, we can infer that visual encoding uses images, so that is your answer:)
