A thread:

1 GOs don't require the use of images. From my reading, DCT is about the use of images paired with words, to aid retrieval. And as @olivcav has pointed out, Pavio worked with simple ideas and concepts.

2 Most of the research into GOs appears to be unhelpful. Hattie lumped all visual strategies together and reported his finding under the heading, concept maps.

3 Fiorella and Mayer, in LaGA, report that mapping, while having a medium-to-high effect size, also take a long time to complete and are difficult to construct.

4 Both studies appear to concentrate on concept maps and in doing so, omit 30+ other GOs. All of which, I argue, are less complicated to read and construct. Skipping over all GOs, to begin with concept maps, is like a ballerina being introduced to pirouettes before a plie.

5 In my opinion, Fiorella and Mayer’s boundary conditions of time and difficulty to construct, are nonsense.