# EEG Investigation on the Tactile Perceptual Performance of a Pneumatic Wearable Display of Softness

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## Abstract

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## 1. Introduction

## 2. Materials and Methods

#### 2.1. Wearable Pneumatic Tactile Display of Softness

#### 2.2. Experimental Setup and Tactile Stimulation Protocol

#### 2.3. EEG Signals Recording

#### 2.4. EEG Signals Processing and SEP Peaks Identification

#### 2.5. Statistical Analysis

## 3. Results

#### 3.1. SEP Waveforms

#### 3.2. SEP Latencies and Amplitudes as Functions of Tactile Pressure Intensity

#### 3.3. SEP Latencies and Amplitudes as Functions of the Number of Simultaneously Stimulated Fingers

## 4. Discussion

#### 4.1. Effect of Signal Recording from the Contralateral Cerebral Hemisphere

#### 4.2. Effect of the Tactile Pressure Intensity

#### 4.3. Effect of the Simultaneous Stimulation of Multiple Fingers

#### 4.4. Possible Influence of the Experimental Conditions and Methodological Choices

## 5. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**The wearable pneumatic tactile display of softness: (

**a**) Images of a prototype sample, showing the deformation of the membrane upon pressurization; (

**b**) schematic drawings of the principle of operation, showing that upon pressurisation the membrane indents the fingertip’s skin and increase its contact area, so as to provide two essential tactile stimuli for the perception of softness; (

**c**) image of the complete system, where three tactile displays are independently controlled by an electropneumatic unit; (

**d**) tactile pressure rise as a function of time, following the onset of the pressure stimulus (‘pressure ON’), at 10, 20 and 30 kPa.

**Figure 2.**Experimental setup for the tactile stimulations of the right-hand fingers and EEG recordings from the somatosensory cortex: (

**a**) schematic representation, showing the arrangement of the subject and the location of the ipsilateral electrodes (Fc2, Fc4, C2, C4) and contralateral electrodes (Fc1, Fc3, C1, C3) used in the experiments; (

**b**) picture of a subject during a test.

**Figure 3.**Grand-average SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations of the right-hand thumb at a pressure of 10, 20 and 30 kPa. The amplitudes of the main signal components are indicated with segments for the contralateral recordings, as they typically provided the largest amplitudes.

**Figure 4.**Grand-average SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations of the right-hand thumb and index finger at a pressure of 10, 20 and 30 kPa. The amplitudes of the main signal components are indicated with segments for the contralateral recordings, as they typically provided the largest amplitudes.

**Figure 5.**Grand-average SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations of the right-hand thumb, index and middle finger at a pressure of 10, 20 and 30 kPa. The amplitudes of the main signal components are indicated with segments for the contralateral recordings, as they typically provided the largest amplitudes.

**Figure 6.**Latency values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations of the right-hand thumb at a pressure of 10, 20 and 30 kPa. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 7.**Amplitude values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations of the right-hand thumb at a pressure of 10, 20 and 30 kPa. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05.

**Figure 8.**Latency values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations of the right-hand thumb and index finger simultaneously at a pressure of 10, 20 and 30 kPa. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 9.**Amplitude values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations of the right-hand thumb and index finger simultaneously at a pressure of 10, 20 and 30 kPa. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 10.**Latency values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations of the right-hand thumb, index and middle finger simultaneously at a pressure of 10, 20 and 30 kPa. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 11.**Amplitude values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations of the right-hand thumb, index and middle finger simultaneously at a pressure of 10, 20 and 30 kPa. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 12.**Latency values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes, in response to tactile stimulations at a pressure of 10 kPa of either only the thumb, the thumb and index simultaneously, or the thumb, index and middle finger simultaneously. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 13.**Amplitude values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations at a pressure of 10 kPa of either only the thumb, the thumb and index simultaneously, or the thumb, index and middle finger simultaneously. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 14.**Latency values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations at a pressure of 20 kPa of either only the thumb, the thumb and index simultaneously, or the thumb, index and middle finger simultaneously. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 15.**Amplitude values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations at a pressure of 20 kPa of either only the thumb, the thumb and index simultaneously, or the thumb, index and middle finger simultaneously. The error bars represent the standard deviation among the ten subjects.

**Figure 16.**Latency values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations at a pressure of 30 kPa of either only the thumb, the thumb and index simultaneously, or the thumb, index and middle finger simultaneously. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05, or two asterisks for a p-value < 0.01.

**Figure 17.**Amplitude values of the various components of the SEP waveforms recorded via contralateral and ipsilateral electrodes in response to tactile stimulations at a pressure of 30 kPa of either only the thumb, the thumb and index simultaneously, or the thumb, index and middle finger simultaneously. The error bars represent the standard deviation among the ten subjects. Data with statistically significant differences are connected by arrows, with associated asterisks that indicate the significance level: one asterisk for a p-value < 0.05.

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## Share and Cite

**MDPI and ACS Style**

Carpi, F.; Valles, M.C.; Frediani, G.; Toci, T.; Grippo, A.
EEG Investigation on the Tactile Perceptual Performance of a Pneumatic Wearable Display of Softness. *Actuators* **2023**, *12*, 431.
https://doi.org/10.3390/act12120431

**AMA Style**

Carpi F, Valles MC, Frediani G, Toci T, Grippo A.
EEG Investigation on the Tactile Perceptual Performance of a Pneumatic Wearable Display of Softness. *Actuators*. 2023; 12(12):431.
https://doi.org/10.3390/act12120431

**Chicago/Turabian Style**

Carpi, Federico, Michele C. Valles, Gabriele Frediani, Tanita Toci, and Antonello Grippo.
2023. "EEG Investigation on the Tactile Perceptual Performance of a Pneumatic Wearable Display of Softness" *Actuators* 12, no. 12: 431.
https://doi.org/10.3390/act12120431