I've seen studies like this, but there are some caveats.

if you only try to imagine how wonderful it will be when you finish, I don't imagine you'd need much research to know this is not likely to be effective when you hit a snag.

Also, if the imagining is done in a purely emotional way, it's likely to be as variable and evanescent as most emotions.

The integrated research I've seen suggests this combination:

1. Have a clear idea as well as visceral image (grounded in clear, calm emotion as well as physical sensations) of the end goal.

2. Have just as clear - if not more clear - well thought through idea of what the most likely obstacles will be to achieving your goal.

3. Set a clear deadline if an external one is not available.

EXAMPLE

I used to procrastinate for hours in finishing my psychological evaluations. The only external deadline was about 1 to 2 weeks after conducting the evaluation. Since I did 2 or 3 reports a week, averaging 20 pages, that means in the course of 2 weeks I could have as much as 120 pages accumulate of unwritten reports.

1. DEADLINE: So I worked on setting a deadline. I discovered if fully focused, I could write a report in 2 hours (it often took me all day if I was procrastinating, doing it on and off)

2. SMALL CHUNKS: I divided the report into 9 sections. I also prioritized them from easiest to hardest, and ALWAYS started with the easiest (that meant NO procrastinating at the beginning).

3. REWARDS AND/OR BREAKS. I'd give myself permission to take a breather after each section - generally, something pleasant (getting up and dancing, playing my keyboard, etc) NO CHECKING EMAIL OR SOCIAL MEDIA!!

4. I went from an average of 9 hours per report to 2 hours, and that remained for the next 3 years.

These techniques help!