(ScrolledUp) in ngx-infinite-scroll does not work

Question

i am using ngx-infinite-scroll in my angular app my problem is (scrolledUP) does not work but (scrolled) is working fine i do not why here is my code

html page :

     [infiniteScrollDistance]="2"
     [infiniteScrollThrottle]="50"
     [infiniteScrollUpDistance]="1.5"
     (scrolled)="getNextArticle()"
     (scrolledUp)="scrollUp()"

and in my ts component i already imported infinitscroll module and my code is :

scrollUp() {
console.log("scrolledUp");
}

so why scrolledup does not work ?