Study on the Cognitive Characteristics Induced by Changes in the Intensity, Frequency, and Duration of Vibratory Stimuli

doi:10.21203/rs.3.rs-2114888/v1

The purpose of this study is to analyze the cognitive characteristics that can be induced through vibration stimuli of two intensities, three frequencies, and five presentation periods. The experiment was conducted on 20 right-handed adult males and a subjective evaluation was performed using a questionnaire. Regression analysis was performed to observe the parameters affecting cognitive characteristics according to changes in intensity, frequency, and stimulation duration.

The regression analysis results showed that the cognitive characteristics affected by changes in intensity, frequency, and stimulation duration were 'heavy', 'bold’, 'thick', and 'light'. The cognitive characteristics affected by two-variable combinations were 'deep', 'clear', ‘vibrating’, 'dense', 'numb', 'blunt', 'shallow', 'fuzzy', and 'soft'. Cognitive characteristics affected by one of intensity, frequency, and stimulation duration were 'fast', 'pungent', ' skinny', 'thin', 'slow', 'ticklish', 'tingling', 'prickling', ‘tap', and 'rugged'. In this study, by observing the cognitive characteristics that can be induced through a combination of intensity, frequency, and stimulation duration, we confirmed that, in addition to intensity and frequency, the stimulation duration is an important factor that influences the induction of various cognitive characteristics. The results presented in the study can be used to enhance the utility of a hepatic surface for extended reality applications.

vibration

frequency

intensity

Stimulation duration

cognitive characteristics

The tactile sensations induced by a vibratory stimulus are reportedly influenced by the stimulus frequency, intensity, contact area, stimulation duration, and stimulation pattern¹. A majority of the studies focus on the frequency and intensity of a vibrating stimulus² because they have a significant effect on a user's perception of touch. In our previous study, to identify the cognitive characteristics of a vibration stimulus under various variables, we investigated stimuli under various frequencies and intensities and analyzed and reported the cognitive characteristics evoked under the stimuli ^3–5. However, a study on the cognitive characteristics that can appear under a combination of variables other than frequency and intensity has not yet been conducted. An additional variable that we investigated is the stimulation duration. On one hand, if the stimulation duration is too long, the user may adapt to the stimulus or, in some cases, suffers pain. On the other hand, if the stimulation duration is too short, the user cannot feel the touch. Empirical evidences demonstrate that subtle changes in touch perception appear with the changes in stimulation duration at the same frequency and intensity. To deliver more diverse and realistic tactile information for using a haptic interface, a quantitative study on the cognitive characteristics that can be induced by changes in stimulation duration, in addition to intensity and frequency, is needed. Further, securing the basic data on two or more variables, instead of one, that change at the same time and the type of cognitive characteristics they induce will not only contribute to the existing literature but also enhance the utility of a haptic interface.

In this study, we observed the changes in various cognitive characteristics according to the stimulation duration and, especially, the vibration intensity and frequency. We attempted to determine the relationship between the variables and cognitive characteristics. Based on the two intensities and three frequencies analyzed in our previous study, stimuli were applied to the first joint of the right index finger for five different durations. Our aim was to observe the various cognitive characteristics that can be induced through a combination of intensity, frequency, and stimulation duration.

The results of the regression analysis showed that the cognitive characteristics affected by the changes in intensity, frequency, and stimulation duration were 'heavy', ' bold ', 'thick', and 'light'. The regression formula obtained for each cognitive characteristic is shown in Table 1. Evidently, ‘heavy’, ‘bold,’ and ‘thick’ had a positive correlation with intensity and stimulation duration and a negative correlation with frequency. In contrast, 'light' showed a negative correlation with intensity and stimulation duration and a positive correlation with frequency.

Table 1 also lists the cognitive characteristics that were affected by any two variables among intensity, frequency, and stimulation duration. Cognitive characteristics that exhibited a positive correlation with intensity and stimulation duration were 'deep', 'clear', ‘vibrating’, 'dense', and 'numb', and the cognitive characteristics that exhibited a negative correlation with intensity and stimulation duration were 'shallow' and ‘fuzzy’. ‘Stubby’ showed a positive correlation with intensity and a negative correlation with frequency. Further, 'soft' showed a negative correlation with intensity and a positive correlation with stimulation duration.

Finally, Table 1 lists the cognitive characteristics that were affected by one among the studied variables. The cognitive characteristics that had a positive correlation with intensity were 'fast' and 'pungent', whereas ' skinny and 'thin' showed a negative correlation with intensity. 'Slow', ‘ticklish’, 'tingling ', and ‘prickling’ showed a positive correlation with stimulation duration, and ‘tap’ showed a negative correlation with stimulation duration. Furthermore, ‘rugged’ exhibited a negative correlation with frequency.

The polarities (positive or negative) of the variables (intensity, frequency, stimulation duration) affecting each cognitive characteristic are summarized in Table 2.

In our previous studies ^3–5, we performed a systematic experiment to understand the changes in cognitive characteristics according to the changes in the various parameters of vibration stimulation. First, the cognitive characteristics under each of the nine frequencies (10, 50, 100, 150, 200, 225, 250, 275, and 300 Hz) were extracted at a fixed intensity ³. Starting from 150 ~ 200 Hz, the cognitive characteristics identified for low-frequency vibrotactile stimulations were 'slow', ‘protruding’ and ‘thick' and those derived for high-frequency vibrotactile stimulation were 'fast', 'shallow', and 'ticklish'. Second, stimuli under three intensities (Step 1: 0.25 G, Step 2: 0.38 G, Step 3: 1.3 G) and eight vibration frequencies (10, 50, 100, 150, 200, 225, 250, 300 Hz) were applied and the cognitive characteristics under each frequency and intensity were collected and reported ⁴. At all intensities, the only cognitive characteristic that appeared at the low frequencies (namely, 10 Hz and 50 Hz) was 'weak'. Above 100 Hz, the characteristic 'vibrating' appeared at most intensities. Between 100 to 150 Hz, different cognitive characteristics namely ‘thick’, ‘stubby’, and ‘heavy’ were observed depending on the intensity. Moreover, based on intensity, the characteristics ‘fast’, ‘shallow’, and ‘light’ appeared in the high-frequency vibration stimulation band of 200–300 Hz. Third, to extract the cognitive characteristics according to the intensity change for each of the eight vibration frequencies, three intensities were designated as variables and a curve estimation analysis regression analysis was performed ⁵. At 100 Hz and 225 Hz, as the intensity increased, the cognitive characteristic scores of 'strong' and 'heavy' increased, and the cognitive characteristic scores of 'weak' and 'light' decreased. They are opposite cognitive characteristics (‘weak’-‘strong,’ ‘light’-‘heavy’). At 10, 100, and 225 Hz, as the intensity increased, characteristics representing the sensation of a surface, such as 'blunt', were dominant, and at 100 Hz and 225 Hz, cognitive characteristics representing object shape (such as thick) and dynamic characteristics (such as push) appeared according to the intensity. Further, as the intensity decreased at 225 Hz, cognitive characteristics such as 'light' and 'shallow' were observed more. The cognitive characteristic 'fast' appeared only as the intensity increased at 300 Hz.

Chun et al. ⁶ tested stimuli under various vibration frequencies (25, 40, 50, 75, 85, 105, 120, 170, 220, 260, 290 Hz) and intensities (0.20, 0.45, 0.60, 0.80 V). They classified the words defining the stimuli based on whether they were easy to use or not. Words related to homogeneity (irregular, regular, etc.), height, depth (deep, low, shallow, etc.), stimulus range (bold, skinny, etc.), and rigidity (hard, curved, etc.) were not appropriate for characterizing vibratory stimuli. In contrast, words related to strength (strong, weak), degree of shaking (shaken, soft), thickness (bold, thick, skinny, thin), weight (heavy, light), and spacing (sparse, dense) were reportedly suitable for expressing the tactility of a simple vibration stimulus. Kim et al. ⁷ and Kyung et al. ⁸ reported that as the intensity of a vibration stimulation in the high-frequency band increased, the subjects experienced the surfaces more as coarse, rough, and less soft. Hwang & Hwang ⁹ reported that the human sensibility for fingertip vibrations might vary depending on the direction and frequency of vibration (20, 40, 80, 160, 320 Hz). Emotions corresponding to ‘light’, ‘sensitive’, ‘repulsive’, ‘ticklish’ and ‘exciting’ could be evoked. However, positive emotions such as 'satisfying', 'enjoyable', 'likable', and 'pleasing' were difficult to induce through fingertip vibration.

In this study, by investigating the effect of stimulation duration in addition to frequency and intensity and based on the results of previous studies that observed tactile cognitive characteristics mainly according to frequency and intensity, we intended to analyze cognitive characteristics through a regression equation. Cognitive characteristics expressed under a combination of intensity (low intensity, high intensity), frequency (100, 225, 300 Hz), and stimulation duration (10 ms, 100 ms, 1000 ms, 2000 ms, 3000 ms) are summarized as follows.

First, among the subjective evaluation vocabularies presented in this study, the word pairs specified as antonyms in the standard Korean dictionary are 'heavy-light', 'deep-shallow', ' bold - skinny ', 'thick-thin', and 'fast-'slow'. 'Heavy' appeared as the stimulation duration increased under the high intensity and as the frequency decreased. The cognitive characteristic ‘‘light’ was induced as the stimulation duration decreased under the low intensity and the frequency increased. ‘Deep’ was expressed as the stimulation duration increased under the high intensity and ‘shallow’ appeared when the stimulus presentation time decreased under the low intensity. Evidently, ‘heavy-light’ (heaviness) and ‘deep-shallow’ (spatiality) were cognitive characteristics pairs for which the stimulus variables that evoked one (frequency, intensity, and stimulus presentation time) were the converse of that which evoked the other.

In a previous study ⁵, 'heavy-light', was reported to be a contradictory cognitive characteristics pair that appeared according to whether the intensity was high or low at frequencies 100 Hz and 225 Hz. In this study, the word pair 'heavy-light' appeared when the patterns of frequency and stimulation duration, in addition to that of intensity, were opposite. Chun et al. ⁶ reported that the words 'deep' and 'shallow', which indicate depth, were not suitable to express a vibration stimulation; however, the study produced limited results because the stimulation targeted only the frequency changes. Choi et al ⁵ showed that the cognitive characteristic score for 'shallow' increased as the intensity decreased at a frequency of 225 Hz. In this study, similarly to the results of previous studies, the appearance of 'shallow' was found to be unrelated to the changes in frequency but related to the stimulation duration and intensity. In addition, the characteristic pair 'deep-shallow' could be formed by controlling the intensity and duration of stimulation.

' Bold ' and 'thick', words for expressing the shape and thickness of an object, respectively, appeared as the stimulation duration increased and the frequency decreased under the high intensity. The opposite words ' skinny ' and 'thin' were found to appear only under the low intensity. A previous study ⁵, reported that the cognitive characteristic of 'thick' appeared predominantly as the intensity increased in the high-frequency band of 100– 225 Hz; however, the results on ' skinny ' and 'thin' were not reported. 'Fast-slow', a cognitive characteristic pair related to stimulus speed and temporality, did not appear with the opposite pattern of stimulus variables. In previous studies, 'fast' appeared as the intensity increased only at 300 Hz. In this study, 'fast' appeared at the high intensity and the antonym 'slow' appeared as the stimulation duration was increased.

Among the cognitive characteristics that express visual evaluation, ‘clear’ and ‘fuzzy’ can be considered as antonyms in meaning; however, they are not defined as antonyms in the Standard Korean Dictionary. 'Clear' appeared as the stimulation duration increased under the high intensity, whereas 'fuzzy' was a cognitive characteristic that was likely to be evoked as the stimulation duration decreased under the low intensity. Although the cognitive characteristics ‘clear’ and ‘fuzzy’ are not antonyms, they can be evoked using the converse combinations of intensity and stimulation duration.

Among the words suggested for subjective evaluation, 'prickling' and ‘pungent’ and the kinesthetic words 'tingling' and 'numbness' express the sensation of pain. The cognitive characteristics 'prickling' and 'tingling' were induced as the stimulation duration increased, and 'numbness' was induced as the stimulation duration increased under the high intensity. ‘Pungent’ appeared only at the high intensity. The cognitive characteristics related to nociception and myesthesia could be induced by increasing the intensity and stimulation duration and were not significantly related to the change in frequency.

In previous studies, as the intensity increased at 225 Hz and 250 Hz, the intrinsic property of vibrational stimulation, 'vibrating', became dominant ⁵. In this study, the cognitive trait was induced not only by the high intensity but also by increasing the stimulation duration. Among the words expressing tactility, 'dense', a cognitive characteristic that can express gaps, was also found to be induced by increasing the stimulation duration under the high intensity. The word expressing surface tactility, ‘soft,’ was generated when the stimulation duration was increased under the low intensity. ‘Soft’ was a cognitive characteristic that did not appear when the variables were frequency and intensity, as was the case in our previous studies. In this study, we found that ‘soft’ could only be induced by the combination of stimulation duration and intensity.

Choi et al. ^{3, 4} reported that the cognitive characteristic of ‘ticklish’ appeared predominantly at high frequencies in the range of 200–300 Hz. In this study, the word ’ticklish’ was found to be uncorrelated to frequency; however, when combined with the results of previous studies, we found that 'ticklish' could be induced by increasing the stimulation duration with a high-frequency vibration stimulus. “Tap”, the dynamic cognitive characteristic most frequently experienced by most subjects, showed significant changes only with the stimulation duration and appeared only with shorter stimulation duration.

The cognitive characteristic ‘stubby’, which represents the sense of a surface, was expressed when the frequency was decreased to 10, 100, and 250 Hz under the high intensity, similarly to the results of this study and previous studies ⁵. Further, the cognitive characteristic 'rough' showed a negative correlation with frequency; it was expressed as the frequency decreased.

Previous studies reported only the results of observing the intensity according to frequency, cognitive characteristics according to the changes in frequency and intensity, or the suitability of the words for expressing the stimulus. Reports on the cognitive characteristics that appear under a combination of variables other than frequency and intensity are relatively scarce. In this study, the cognitive characteristics that could be induced by a combination of three variables, frequency, intensity, and stimulation duration, were analyzed. In addition to vibration frequency and intensity, stimulation duration was also found to be an important factor that influences the induction of various cognitive characteristics. The results of this study also showed that a wider range of tactile sensations could be presented with the combination of the three variables. The various cognitive characteristics that can be evoked through the combination of frequency, intensity, and stimulation duration can be used to improve the utility of a haptic interface. Therefore, for all extended reality platforms using a haptic interface (virtual reality, augmented reality, mixed reality, substitutional reality), the results of this study may be utilized to match parameters that allow users to experience various and realistic tactile sensations.

The investigation of stimulation duration pursued in the study facilitated the observation of cognitive characteristics that were not produced in previous results. However, the study was conducted with only three high-frequency components and two intensities, which is a limitation. Moreover, the study was conducted only on young adult males. Further studies are needed to rectify this problem.

4.1. Preliminary Experiment for Selecting Stimulation Duration

Based on the results of our previous research ⁵, among three intensities (1st stage: 0.25 G, 2nd stage: 0.38 G, 3rd stage: 1.3 G) and eight vibration frequencies (10, 50, 100, 150, 200, 225, 250, 300 Hz), two intensities (low intensity: 0.25 G, high intensity: 1.3 G) and three frequencies (100 Hz, 225 Hz, 300 Hz) that produced a distinct difference in cognitive characteristics were first selected.

To select the range of stimulation duration, which is the main parameter analyzed in this experiment, a preliminary experiment was conducted on eleven adult males (23.4 ± 1.3 years).

With reference to the stimulation duration of 100 ms used in our previous study ^3–5, vibration stimuli of two intensities and three frequencies were selected prior to their application on the first joint of a subject's right index finger for seven different durations (10 ms, 100 ms, 1000 ms, 2000 ms, 3000 ms, 4000 ms, 5000 ms). The presence or absence of pain and the time for which the presented stimulus was felt were checked for each stimulation duration. The residual time of a stimulus was more than 15 seconds when the stimulus was presented for 4000 ms and 5000 ms, and the subject felt frequent pain. Therefore, to exclude pain and residual effects as much as possible, the following five stimulation durations were selected for the experiment: 10 ms, 100 ms, 1000 ms, 2000 ms, and 3000 ms. With these stimulation times, the residual time of the stimulus was less than approximately 10 seconds.

4.2 Preliminary Experiment for Creating a Subjective Evaluation Questionnaire

A subjective evaluation questionnaire was prepared to analyze the changes in cognitive characteristics according to intensity, frequency, and stimulation duration. Responses related to tactile, temperature, pain and kinesthetic senses were collected based on the subjective evaluation questionnaire used in our previous study ^3–5. In addition, the meaning of each word was examined using the standard Korean dictionary published by the National Institute of the Korean Language (http://stdweb2.korean.go.kr/). After removing words having overlapping meanings, 46 words were collected and a preliminary experiment was conducted to create a subjective evaluation questionnaire.

Vibration stimuli with different intensities, frequencies, and stimulus presentation times were randomly applied to the first joint of the index finger of the right hand of 11 males (23.4 ± 1.3 years) once at a time. All the words describing the senses felt were collected. The words used in the subjective evaluation experiment were selected based on the words expressed by more than 20% of the subjects. The 24 selected words were ‘skinny,’ ‘light,’ ‘ticklish,’ ‘bold,’ ‘deep,’ ‘slow,’ ‘thick,’ ‘heavy,’ ‘stubby,’ ‘soft,’ ‘vibrating,’ ‘clear,’ ‘fast,’ ‘dense,’ ‘acrid,’ ‘pungent,’ ‘thin,’ ‘shallow,’ ‘prickling,’ ‘rugged,’ ‘numb,’ ‘tingling,’ ‘tap,’ and ‘fuzzy.’ Each word was assessed on a 5-point scale (1 point: no feeling, 5 point: strong feeling) to mark the subjective evaluation questionnaire (Fig. 1).

4.3. The Experiment

The experiment was conducted on 20 right-handed adult males (24.4 ± 1.7 years) having normal cognitive function. This study was approved by the Institutional Bioethics Committee of Konkuk University (IRB project number: 7001355-202011-HR-408) and complied with the regulations of the Helsinki Declaration. Prior to the experiment, participants were informed about the study and provided written informed consent.

One trial of the experiment consisted of a stimulation phase (10 ms, 100 ms, 1000 ms, 2000 ms, 3000 ms), during which a stimulus was applied, and a rest phase (15 s), during which no stimuli were applied (Fig. 2.). A total of 30 stimulation parameters was created using the combinations of 2 intensities, 3 frequencies, and 5 stimulation times selected in the preliminary experiment, and one among the 30 parameters was randomly selected for a trial. The stimulus under each parameter was applied twice and a subjective evaluation was performed. To prevent the subject from adapting to the stimulus, the interval between the applications of two different types of stimuli was 5 minutes.

Regression analysis (PASW Statics 26) was performed to observe the parameters that affect the cognitive characteristics according to changes in intensity, frequency, and stimulation duration.

Acknowledgments

This work was supported by a Mid-career Researcher Program Grant through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (MOE) (No. NRF- 2021R1A2C2009136). This work was also supported by the National Research Foundation of Korea (NRF) funded by the Korean government (MSIT). (No. 2020R1A2C1100349)

Conflicts of Interests

The authors declare that there are no conflicts of interests.

Data Availability Statement

The datasets generated during this study are available from the corresponding author on reasonable request.

Author’s contribution

- Conceptualization, methodology, formal analysis, data curation, and writing-original draft preparation: CMH, KHS, and CSC

- Investigation: KKB, KYJ, and KJS

- All authors have read and agreed to the published version of the manuscript.

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Table 1

Results of Regression Analysis of Cognitive Characteristic Scores for Three Variables: Intensity, Frequency, and Stimulation Duration

Variable combinations	Cognitive characteristics	The regression formula
Three-variable combinations	Heavy	y=0.761+0.56intensity-0.248frequency+0.106*time (intensity: p<.001, frequency: p<.001, time: p=.001)
	Bold	y=0.664+0.540intensity-0.12frequency+0.064*time (intensity: p<.001, frequency: p=.033, time: p=.048)
	Thick	y=0.578+0.613intensity-0.155frequency+0.078*time (intensity: p<.001, frequency: p=.005, time: p=.013)
	Light	y=2.088-0.427intensity+0.12frequency-0.078*time (intensity: p<.001, frequency: p=.044, time: p=.023)
Two-variable combinations	Deep	y=0.625+0.213intensity+0.062time (intensity: p<.001, time: p=.006)
	Clear	y=0.963intensity+0.273time (intensity: p<.001, time: p<.001)
	Vibrating	y=0.587intensity+0.624time (intensity: p<.001, time: p<.001)
	Dense	y=0.616+0.177intensity+0.108time (intensity: p=.008, time: p<.001)
	Numb	y=0.778+0.160intensity+0.067time (intensity: p=.032, time: p=.012)
	Stubby	y=1.109+0.397intensity-0.125frequency (intensity: p<.001, frequency: p=.014)
	Shallow	y=2.225-0.4intensity-0.07time (intensity: p<.001, time: p=.038)
	Fuzzy	y=2.330-0.327intensity-0.142time (intensity: p<.001, time: p<.001)
	Soft	y=1.433-0.320intensity+0.106time (intensity: p<.001, time: p<.001)
One-variable	Fast	y=1.310+0.363*intensity (p=.006)
	Pungent	y=0.821+0.113*intensity (p=.003)
	Skinny	y=1.617-0.333*intensity (p<.001)
	Thin	y=1.973-0.333*intensity (p<.001)
	Slow	y=1.053+0.064*time (p<.001)
	Ticklish	y=0.943+0.128*time (p<.001)
	Tingling	y=0.910+0.068*time (p=.001)
	Prickling	y=0.688+0.078*time (p<.001)
	Tap	y=2.321-0.313*time (p<.001)
	Rugged	y=1.142-0.09*frequency (p=.034)

Table 2

Polarity of Variables (Intensity, Frequency, Stimulation Duration) Affecting the Cognitive Characteristics

	Constant	Intensity	Frequency	Stimulation duration
Heavy	0.761	+	ㅡ	+
Bold	0.664	+	ㅡ	+
Thick	0.578	+	ㅡ	+
Light	2.088	ㅡ	+	ㅡ
Deep	0.625	+		+
Clear		+		+
Vibrating		+		+
Dense	0.616	+		+
Numb	0.778	+		+
Stubby	1.109	+	ㅡ
Shallow	2.225	ㅡ		ㅡ
Fuzzy	2.330	ㅡ		ㅡ
Soft	1.433	ㅡ		+
Fast	1.310	+
Pungent	0.821	+
Skinny	1.617	ㅡ
Thin	1.973	ㅡ
Slow	1.053			+
Ticklish	0.943			+
Tingling	0.910			+
Prickling	0.688			+
Tap	2.321			ㅡ
Rugged	1.142		ㅡ

No competing interests reported.

Study on the Cognitive Characteristics Induced by Changes in the Intensity, Frequency, and Duration of Vibratory Stimuli

Status:

Version 1

Abstract

Figures

1. Introduction

2. Results

3. Discussion And Conclusion

4. Research Methods

4.1. Preliminary Experiment for Selecting Stimulation Duration

4.2 Preliminary Experiment for Creating a Subjective Evaluation Questionnaire

4.3. The Experiment

Declarations

References

Tables

Additional Declarations

Status:

Version 1