Before I got involved and did any scientology training or processing (at about age 30) I had a sometimes-functioning photographic memory. It worked when I needed it. Lost it after scientology training and processing.
before scientology training and processing, I read rapidly and tested with very high retention rate. after scientology training and processing, reading was a laborious process and for years i stopped reading for pleasure because it was just too much trouble! Never retested the retention rate.
Now, after 30 years free of scientology, I can read for pleasure at a fairly rapid rate, but with both pleasure-reading and reading to learn something, I often find myself going over and over and over small segments of material without "getting" it. this did not happen before scientology.
I'm past 60 so it's likely there are other factors affecting my cognitive ability. But I first noticed these unpleasant effects in my mid and late 30s, right after scientology.
A friend, in when I was, now also "out," commented to me years ago that she had lost her short-term memory as a result of scientology. She didn't read much for learning new skills, but she also read a lot, rapidly, for pleasure, and also lost that ability. Haven't asked her recently if it ever came back. At the time, I was still enthralled and didn't want to believe her. I do believe her now.
Make of this what you wish.