Can I add a caption to a timeline block image?

Hi there,

I always add alt text to my images inside my timeline block.  My subject matter expert also asked if I could add a caption under the image like I do on the image blocks.  I said "sure" but I went in and I can't see a way to do it. There is no add caption option and I can't type below the media.  Anyone have a work around, or know why articulate wouldn't have a caption option under all images?

Thanks

Teresa