We use a tense that is appropriate for the message we wish to convey." Researchers have found that individuals who have been blind , and who thus have never seen anyone gesture , nevertheless make hand motions just as frequently as sighted people do ."
In the above sentence , (" have been blind " is past perfect continuous (isn't it? ) No. It is present perfect and " have never seen anyone gesture " is past perfect ) No. It is present perfect ... What I am asking is : Is this change allowed ? Should it not be " never been seeing anyone gesture " ? No. that is not acceptable English
In a nutshell , when should we change tenses ?