Fig 1.
Stimuli were presented in a random and continuous stream of unimodal visual stimuli, unimodal auditory stimuli at four different frequencies and audiovisual stimuli. The auditory stimuli of 65 dB were presented through earphones. The visual target stimulus was a Gabor patch with horizontal gratings. Participants sat approximately 70 cm from the screen, and the subject’s task was to make a quick and accurate button response when the visual target stimulus was presented, regardless of whether an auditory stimulus was presented. A0.5, A1, A2.5 and A5: frequency of auditory stimuli of 0.5, 1, 2.5 and 5 kHz, respectively.
Fig 2.
EEG electrode placement and the 4 ROIs.
Table 1.
Behavioral mean data over all participants in the experiment.
Fig 3.
Waveforms of unimodal stimuli.
Unimodal visual (A) and auditory stimuli (B). 0.5, 1, 2.5, 5: frequency of unimodal auditory stimuli is 0.5, 1, 2.5, 5 kHz, respectively.
Fig 4.
Statistical significance of audiovisual integration.
The effects from point-wise running t-tests comparing AV to (A+V) for all participants when sound frequency is 0.5 kHz (A), 1 kHz (B), 2.5 kHz (C), 5 kHz (D), respectively. Time is plotted on the x-axis from 0 ms to 400 ms. Electrodes are plotted on the y-axis. Within a section the electrodes are arranged from the left lateral to the right lateral sites. Red points are the earliest start time of integration. Pink shades: integration effects at the late stage. F, frontal; F-C, fronto-central; C, central; C-P, centro-parietal; P, parietal; O, occipital.
Fig 5.
Topography of the significant spatio-temporal patterns of integration in the occipital area.
The time of onset of audiovisual integration was different when auditory stimuli were presented in the four conditions (A) 0.5 kHz, (B) 1 kHz, (C) 2.5 kHz, (D) 5 kHz. Right sides: Event-related potential of the sum of the unimodal stimuli (A+V) and bimodal (AV) stimuli at a subset of electrodes are shown from 100 ms before the stimulus to 400 ms after. The shade areas indicate the time periods when the bimodal response significantly differs from the sum of the unimodal responses (p < 0.05).
Fig 6.
Topography of the different significant spatio-temporal patterns of integration in the frontal and central areas.
An obvious pattern of integration effects was visible at 300–340 ms for sound frequencies of (A) 0.5 kHz, (B) 1 kHz and (C) 2.5 kHz at fronto-central and central areas; (D) No similar pattern of integration effects was observed for 5 kHz sound frequency at approximately 300–340 ms.