When I see a question in an Aphantasic questionnaire it makes me laugh internally because the poor Phantasics probably have to visually see a real horse or video) before they can draw it. What comes to my mind when I an asked such a question is not an image of a particular horse, in fact I don't see any images at all, but what I get is a sort of database of related instantly-recallable facts such as: a horse is an animal, an equine animal, it has 4 legs and a tail, it was used as a 'power source' in earlier time, but nowadays is mostly used for sport or recreation, etc etc, some particular horses, especially race horses had names, which might be remembered etc etc. From the data I could improvise a generic picture of a horse, but it would no be a specific horse. So asking me that question would be a waste of time and would no doubt be misinterpreted by a Phantasic researcher. Other responders in here have described the creation of a drawing, bit by bit, function by function; that's exactly what I would do, even in drawing something simple like a house.

Hey James, great question! Wilma Bainbridge offers an interesting perspective on how we can use drawings to uncover what's inside the memory of people with aphantasia in this research presentation here.

I wonder if "sighted" people draw what they see although that is impossible for me to imagine? I have to construct the bicycle bit by bit - wheel, spokes, tyres, derailleur if its geared (of course now I'll need to do a cage and the jockey wheels), cassette, chain oh forgot the brakes etc. I expect I would be able to get the details right because I construct it from a list of parts? 

i have Aphantasia and my picture of a bike would be conceptual. two wheels and a frame, very much stick person. so i think you are probably on the wrong track. now if you asked people to draw a picture of their own bike you might see a difference. in my case it would be almost the same.