Images are used to compare and contrast conceptual information. People think about their experiences with these unconscious images and thoughts. A concept could be a summary or example of a certain type of experience, and using images would probably create more detail for the concept. Words obviously trigger and direct conceptual thinking, however the content of conceptual thinking comes from feelings or visualizations. Visualizations might be tied in with fast thinking or slow, emotional thinking. Doing math doesn't require emotional processes but would require complex visual processes but not necessarily complex conceptual thought - since most advanced thought is actually emotionally based and might or might not use emotional processes when thinking.
The question then would be when is an emotional process used in thinking. I mentioned that math doesn't require emotional processes and was just visual. Many concepts are just visual even if they are emotional concepts, however - so this could be difficult to figure out.