MIGX Restrictive Condition

I'd like to hide a MIGX field based on the value of another MIGX field. I don't expect it to be dynamic as the first field is already set.

Example:
- section_source can be section_text or section_image
- If section_source == section_image I want to show an image field

I've successfully used restrictive conditions before with snippets, but I can't figure out how to pass 'section_source' as a parameter. I guess it's not a placeholder in this context.

John