If there is anything keeping people from having solid visualizations throughout the day, it's not sleeping enough. It's a night-and day difference in mental imagery. None of these studies control for anything like that or sleep, which really just shows you how hard they are fishing for something which isn't there. A lot of sleep issues are totally incurable without switching to back sleeping, getting rid of lint (people refuse to do this), and eliminating a sedentary lifestyle. Now if you tried to do studies on people like that you wouldn't be able to find any. But I can tell you I've experienced "aphantasia" and it's cured by getting a good night's sleep. A lot of people never get a good night's sleep ever.