How to distinguish scrolling by mouse from scrolling programmatically in JavaScript?

I am scrolling an overflowing DIV's content by changing the scrollLeft property in Javascript:

setInterval(function(){
  $('#scrollbox').scrollLeft($('#scrollbox').scrollLeft()+1);
}, 50);

However, I want to stop this as soon as the user scrolls the content themselves, using the mouse. I tried to detect this using the scroll event

$('#scrollbox').scroll(function(){...});

however, my automatic scrolling above also triggers that event. How can I distinguish this and only react to user-initiated scrolling? (or: how can I stop the above code from firing a scroll event? That would also do the trick)