There's no studies. It's like asking for a study about how people tend to smile when they're happy. Do you really need a study for something so obvious? Do you go around the world thinking nothing is true or real unless someone spent money on some sort of quantitative analysis?
If you read the rest of my post you'll see that what I stated follows from logic. When we have a series of tasks we want written down, we automatically write it down via a list of imperative procedures. This is done automatically. We haven't taken any TODO list writing lessons or anything before hand we just do it procedurally meaning we're born to do it this way. It's innate.
This is the obvious default. And thus as a result any programming language similar to that default will be more intuitive.
As for your wife, who's to say procedural programming is not easier? She may have found racket easy but that doesn't mean she wouldn't find imperative languages far more intuitive.
Are there some studies that back that up? My wife took the How to Code course on edX, and the use of Racket was a non-issue. The use of it was quite literally transparent.
The issue is that humans react to something foreign with huge amounts of bias. So if I person has any introduction at all to some form of a C-type of language, it seems to shut down all forms of curiosity, generally speaking. I honestly wonder if that has been studied.
I was first taught C, Python, and Java, and was totally uninterested in programming. Once I found functional-first and visual dataflow languages, I was hooked.
I'm generally curious what C and Python people think when they learn something like Prolog? Do they exclaim "this isn't hard enough?".