Peripersonal space in the front, rear, left and right directions for audio-tactile multisensory integration

Abstract

Peripersonal space (PPS) is important for humans to perform body-environment interactions. However, many previous studies only focused on the specific direction of the PPS, such as the front space, despite suggesting that there were PPSs in all directions. We aimed to measure and compare the peri-trunk PPS in four directions (front, rear, left, and right). To measure the PPS, we used a tactile and an audio stimulus because auditory information is available at any time in all directions. We used the approaching and receding task-irrelevant sounds in the experiment. Observers were asked to respond as quickly as possible when a tactile stimulus was applied to a vibrator on their chest. We found that peri-trunk PPS representations exist with an approaching sound, irrespective of the direction.

Figure 1

The schematic of the experiment. A virtual audio source was presented. The audio motion was presented toward the participant (approaching sound) or away from the participant (receding sound) in four body-relative directions (front, rear, left, and right). Participants were asked to detect a tactile stimulus presented on the chest as quickly as possible, irrespective of the sound stimulus. Timings of the tactile stimulus and the sound motion were systematically varied.

Figure 2

The results of the Experiment RTs (ms) as a function of the temporal delays (ms). Circular and triangular symbols indicate the approaching and receding sounds, respectively. The gray area indicates the timing of the pink-noise emission. Error bars represent standard errors.

Figure 3

The results of the Experiment RTs (ms) as a function of the temporal delays (ms). The four direction conditions (front, rear, left, and right) were merged. The description of the figure is the same as in Fig. 2. The error bars represent standard errors. Asterisks represent significant differences (p < .05) between the RTs for the approaching sound and the receding sounds as a result of multiple comparisons (Shaffer's modified sequentially rejective Bonferroni procedure).

Figure 4

The number of observers (N) of all 20 participants (N/20) and its percentage (%) with R² (coefficient of determination for the sigmoidal function) higher than 0.5 for each body-relative direction for the approaching sound condition. The results of Table 1 and these results, taken together, imply that the PPS in the front and left directions might be stronger while the PPS of the rear might be weaker.

Figure 5

Experimental design. (a) Layout of the loudspeakers and observers. (b) Direction to the loudspeakers.