PowerPoint and other digital slide presentations are now commonplace in the conference room, but there remains little research into their impact on the challenging cognitive process of simultaneous interpreting. This thesis replicates a previous study exploring the impact of the lexical density (the proportion of words in a text with lexical properties) and visual clarity of visual input on simultaneous interpreters' fluency. Student interpreters work with varying PowerPoint presentations and their output is evaluated by counting prosodic disfluencies. On average, the interpretations of speeches accompanied by less lexically dense and less visually clear presentations (where the same information was displayed in more words) are found to be more fluent, confirming the counterintuitive results of the original study. This suggests visually displayed keywords are more difficult to process than full sentences during simultaneous interpretation; there is growing evidence that simultaneous interpreters interact with slide presentations very differently to audiences