What is "dual coding," and why does it strengthen memory?

Dual coding pairs a VERBAL representation (words) with a VISUAL one (diagram, timeline, labelled sketch) so a single idea is encoded through two complementary channels.

Encode an idea only in words and you have one route back to it. Encode it in words and a meaningful image and you have two — if one path fails at test, the other can still deliver. The channels are complementary, not redundant: a diagram captures structure and relationships that prose states only linearly.

It rates MODERATE in the evidence — a real, worthwhile boost, not a magic bullet. The key is that the two codes reinforce the same concept from different angles.