Stimulus illustrations, timing characteristics and subjective impressions of task difficulty.

(A) Top and bottom rows illustrate the visual information and auditory waveform for each stimulus, respectively. (BF) beep-flash stimulus, consisted of a single flash of a white dot on a black background and a single beep. (BFV) beep-flash-constant visual, was the same as (BF) except there was a smaller white dot, illustrated by the dashed circle, constantly on screen. (BFD) beep-flash-drumming, was the same as (BF) except there were 9 beep-flashes in each stimulus. (PLD) point-light-drumming, shown is a single movie frame and the waveform drumbeat. (FV) A single frame from the face-voice movie and the waveform representation of the word ‘tomorrow’. Note, the images are not to scale, the area of the point-light-drummer and the white flash dots (BF, BFV & BFD) approximately subtended the area of the mouth region in FV. (B) Illustration of timing characteristics (onset, offset and duration) for BF and BFV (left), BFD and PLD (middle) and FV (right). COA levels (ms), both audio- and video-leading, are displayed on the y-axis and the x-axis represents duration (ms) – note that x-axis scales are different across the 3 figures. For each COA level gray bars represent overall stimulus durations (see Stimuli section for details), while black bars represent relative timing characteristics between audio and video sequences. Top and bottom black bars can represent either the audio or video sequence. For example, the top black bar of the 67 COA condition for BF would represent the audio sequence for an audio-leading condition, while it would represent the video sequence for a video-leading condition. Vertical black bars in the middle figure (BFD &PLD) highlight that the duration of all COA stimuli was 3s and that the stimuli were cut from a larger audiovisual movie after separating the audio and video cues in time by each COA. (C) Separately for each stimulus type, pie charts represent the percentage of participants who found either SJ or TOJ the most difficult. Order of pie charts matches the order of the stimuli presented above in (A).