So the idea here is to triangulate on the association
between event type A, some event type, and
a particular process by subtracting away multiple kinds of events.
And this helps us avoid some of the issues with pure insertion if
the different control conditions I'm subtracting off each have different kinds
of characteristics, and each of them is potentially
confusable with the process of interest in different ways.
So, a case study here is studies of the Fusiform Face Area, by Nancy Kanwisher et
al, and they did some really nice studies, and her's a slide from one of them,
in which faces are compared with many different kinds of things.
So they can pair faces with objects.
But of course, those differ in their different spatial frequencies.
So they can pair intact faces with scrambled faces,
where the basic spatial frequencies are preserved.
Faces with houses, faces with hands.
So maybe it's about body parts.
They can control for body parts.
Faces with animal faces,
faces with pictures of faces, drawings of faces, and other conditions.
So really across these multiple subtractions,
they are trying to triangulate on the idea that the FFA is activated when you see
a face, but not when you do other things.