Smith has spent years studying the effects of sleep and sleep loss on memory and learning.
I think that the translation is inadequate given the missing word is “rendimento”. I don’t see that the sentence specifically identifies “learning”. Rendimento = yield and it could refer to learning performance, but we do not know that. Google translates: “Smith has been researching the effects of sleep for years and sleeping less causes memory loss and performance in studies.” Also the use of researching for pesquisando is better than studying.