Enhanced audio-tactile multisensory interaction in a peripersonal task after echolocation

Abstract

Peripersonal space (PPS) is created by a multisensory interaction between different sensory modalities and can be modified by experience. In this article, we investigated whether an auditory training, inside the peripersonal space area, can modify the PPS around the head in sighted participants. The auditory training was based on echolocation. We measured the participant's reaction times to a tactile stimulation on the neck, while task-irrelevant looming auditory stimuli were presented. Sounds more strongly affect tactile processing when located within a limited distance from the body. We measured spatially dependent audio-tactile interaction as a proxy of PPS representation before and after an echolocation training. We found a significant speeding effect on tactile RTs after echolocation, specifically when sounds where around the location where the echolocation task was performed. This effect could not be attributed to a task repetition effect nor to a shift of spatial attention, as no changes of PPS were found in two control groups of participants, who performed the PPS task after either a break or a temporal auditory task (with stimuli located at the same position of echolocation task). These findings show that echolocation affects multisensory processing inside PPS representation, likely to better represent the space where external stimuli, have to be localized.

Keywords: Audio-tactile; Echolocation; Multisensory; Peripersonal space.

Fig. 1

Experimental set-ups. a The set-up for the PPS task is shown. There were seven speakers generating sound sources at a different distance from the body. The first sound source was placed 17 cm apart from the left side of the head of each participant. The sound moved across the speakers as approaching the participant’s head (grey arrow). The vibro-tactile device was placed on the left side of the neck. The tactile stimulus was delivered when the sound was placed at one of the seven possible depicted distances (17, 34, 51, 68, 85, 102, 119). b The set-up for the echolocation detection task is shown. We used a bar located at 34 cm ahead the participant. The black the red arrows represent, respectively, the path of the self-generated click and the echo reflected by the bar. c The set-up of the temporal bisection task is shown

Fig. 2

The averaged bimodal RTs (normalized for the unimodal RTs) for each group is shown as a function of the seven distances sampled during the PPS task. Data for the ECHO group before (in blue) and after (in red) the echolocation training. Data for the TIME group before (in green) and after (in orange) the time bisection task. Data for the REST group before (in magenta) and after (in cyan) 15 min of break. *Significant difference with p < 0.05. ***Significant difference with p < 0.001. The error bars represent the standard error

Fig. 3

Bar plot represent the average RTs in the unimodal condition for each group before and after the auditory tasks in the Echo and Time group and for the first and second repetition in the Rest group. The error bars represent the standard error

Fig. 4

The bar plot on the left reports the average percentage of correct responses in the detection echolocation task and each empty symbols represent the result of a single participant. The plots on the right report the average of the precision and accuracy obtained in the time bisection task. The scatter plots represent the value for each participant. The error bars represent the standard error

Fig. 5

Estimate of sound distance in a scale from 1 to 100 as a function of point in space sampled for the seven-speaker set-up. Participants estimated sound distance for sounds originating from 119 cm in front (positive x value) and terminating at 17 cm at the head level. y-axis represents the average perceived value of the position of the sound on a scale from 1 to 100. The dashed line shows the equality line. The error bars represents the standard error