Hello, Naruepron. No, the meaning of base in this sentence does not mean improve. It means to use something as a foundation for something else. So, this sentence means: John Wada used his research on people with language problems as a foundation for his findings. Hope that helps!

Literally, a 'base' is something you build something on, like the base of a statue, or the foundations of a building. Here, basing your findings on something means that your study started from that, or that the findings came from investigation of the information it was 'based on'. So - the studies were very important to the findings, they didn't just improve them. Remember to be careful with your plurals in English. You should have used FindingS and problemS in your sentence. Also, he improveD, and names like Wada start with a capital.