I'm currently working on a study and incidentally found that reaction timings were slower for vocal responses compared to manual responses (i.e. 600ms for the manual response vs. 700ms for the vocal response).
Study: Participants saw a small figure and had to indicate whether this figure is identical to a set of figures that they had to memorize beforehand (either by pressing a button or be saying "green"). Reaction timing of the vocal response were set to the moment in which a first sound was detected (i.e. immediately when the word onset started).
Although it is intuitive that vocal onsets might take longer, I asked myself whether there are neuronal correlates that account for this?