The impact of movement sonification on haptic perception changes with aging

Abstract

Combining multisensory sources is crucial to interact with our environment, especially for older people who are facing sensory declines. Here, we examined the influence of textured sounds on haptic exploration of artificial textures in healthy younger and older adults by combining a tactile device (ultrasonic display) with synthetized textured sounds. Participants had to discriminate simulated textures with their right index while they were distracted by three disturbing, more or less textured sounds. These sounds were presented as a real-time auditory feedback based on finger movement sonification and thus gave the sensation that the sounds were produced by the haptic exploration. Finger movement velocity increased across both groups in presence of textured sounds (Rubbing or Squeaking) compared to a non-textured (Neutral) sound. While young adults had the same discrimination threshold, regardless of the sound added, the older adults were more disturbed by the presence of the textured sounds with respect to the Neutral sound. Overall, these findings suggest that irrelevant auditory information was taken into account by all participants, but was appropriately segregated from tactile information by young adults. Older adults failed to segregate auditory information, supporting the hypothesis of general facilitation of multisensory integration with aging.

Figure 1

(A) Picture of the tactile device called ‘StimTac’. (B) Illustration of the StimTac’s vibration during the reference stimulation ΔAref = 750 nm consisting of a switching between two amplitudes of vibration: the highest amplitude (1500 nm) and an intermediate (750 nm). The two amplitudes were delivered alternately at 22 Hz. (C) Experimental set-up: seated participant explored the touchpad of the StimTac with their right index and wore headphones with synthesized sounds. An optical sensor recorded online the participant’s index displacements. (D) Experimental design: participants compared two different textures in presence of the same sound (that could be Rubbing, Squeaking or Neutral). During the experiment, all sound conditions were randomly presented.

Figure 2

Typical psychophysical curves from one young (A) and one older participant (B) reflecting the percentage of texture stimuli perceived rougher than the reference texture (ΔA = 750 nm) for each sound condition: Squeaking (pink), Rubbing (yellow) and Neutral (black). Symbols are the mean values obtained for 7 textures varying in roughness. JND: just noticeable difference; PSE: point of subjective equality. (C) Individual and mean JND values for the younger (dots) and older participants (triangles) in each sound condition: Squeaking (pink), Rubbing (yellow) and Neutral (black). Statistics are post hoc tests after Holm correction * (D) Individual and mean Gain indexes (%) (Squeaking in pink and Rubbing in yellow) for the younger (dots) and older (triangles) participants. The largest symbols are the mean of the groups and the horizontal bars are the median. Statistics are the main effect of the GLM (*) and t-tests different from zero ($). (E) Correlations between the two Gain indexes (Squeaking and Rubbing) within each group (Young: black dot line; Old: grey dash line). * or $ p < 0.05; **p < 0.01. Thr Threshold.

Figure 3

(A) Individual and mean point of subjective equality (PSE) values for the younger (dot symbols) and older participants (triangle symbols) in the Squeaking (pink), Rubbing (yellow) and Neutral (black) sound conditions. *p < 0.05, **p < 0.01 for post hoc tests with Holm correction; ^$p < 0.05, ^$$p < 0.01 for Wilcoxon tests different from zero. (B) Correlations between the PSE observed in the Squeaking and in the Rubbing conditions across the two groups (full line) and within each group (Young: black dot line; Old: grey dash line). Symbols are individual percentage of rougher responses compared to the reference texture for young (full dot symbols) and older (empty triangle symbols) participants.

Figure 4

(A) Mean finger movement velocity (cm/s) for younger (dot symbols) and older adults (triangle symbols) for each sound condition: Squeaking (pink), Rubbing (yellow) and Neutral (black). (B) Mean finger movement velocity (cm/s) for younger (dot symbols) and older adults (triangle symbols) depending on the various roughness textures explored by the participants. The statistics presented are the effects of the Sound conditions for the two groups confounded (A) and the main effect of the Groups for all the textures confounded (B). ns non-significant, *p < 0.05; ***p < 0.001.