arXiv:2610.41645v1 Announce Type: new Abstract: Slides present information spatially, but narration unfolds linearly, leaving the viewer struggling to locate what the narration refers to. This split attention between audio and visual channels forces viewers to search the slide manually, imposing extraneous cognitive load and disrupting comprehension. The problem is especially acute on mobile devices, where dense layouts compressed onto small screens make visual search particularly effortful. In teacher-led settings, however, instructors naturally direct attention through pointing, pacing, and emphasis. Inspired by this, we present GuideSlide, a system that automatically generates Dynamic Visual Guidance for slide presentations, providing viewers with narration-synchronized visual cues that direct attention in real time. Given a PDF slide deck, GuideSlide automatically produces region-level zoom and time-aligned highlights without manual annotation. In a within-subjects study with 24 participants, GuideSlide substantially reduced perceived cognitive load and yielded higher immediate comprehension scores compared to static slides with identical narration. Participants strongly preferred the Dynamic Visual Guidance condition, reporting that it made narration easier to follow and reduced uncertainty about where to look. These findings suggest that narration-synchronized visual guidance is a valuable design strategy for slide-based presentations, with potential to extend to other instructional and presentation scenarios.