  Educators have developed an effective technique to get feedback after
in-person lectures, called "muddy card." Students are given time to reflect and
write the "muddiest" (least clear) point on an index card, to hand in as they
leave class. This practice of assigning end-of-lecture reflection tasks to
generate explicit student feedback is well suited for adaptation to the
challenge of supporting feedback in online video lectures. We describe the
design and evaluation of Mudslide, a prototype system that translates the
practice of muddy cards into the realm of online lecture videos. Based on an
in-lab study of students and teachers, we find that spatially contextualizing
students' muddy point feedback with respect to particular lecture slides is
advantageous to both students and teachers. We also reflect on further
opportunities for enhancing this feedback method based on teachers' and
students' experiences with our prototype.
