Normal or tingly? A story about hands and feet

Abstract

Aims

Spontaneous sensations (SPS) are sensations that are felt in the body in the absence of external stimulation. The literature on SPS has used explicit measures, such as questionnaires to explore SPS, while no studies to date have examined SPS on an implicit level. This study was conducted to collect representative stimuli that can be used to build such a task, for example, an Implicit Association Test.

Methods

An online survey was completed by 18 participants to identify the most frequent words used to describe our limbs in the presence or absence of SPS.

Results

Individuals who perceive and those who do not perceive SPS in their limbs describe their limbs as normal, while the most frequently described SPS were itching and tingling.

Conclusions

Thus, we use the same words/adjectives to describe how we perceive our limbs. However, the way we experience SPS varies as we experience more SPS in hands than feet.

Keywords:

• Spontaneous sensations
• hands
• feet
• body perception
• itching
• tingling
• normal

1. Introduction

When you are trying to relax, your attention might shift to various sensations across your limbs, such as tingling or itching to name a few. These spontaneous sensations (SPS) are usually perceived at periods of rest and almost everyone feels them across their body (Naveteur et al. 2005; Michael and Naveteur 2011). SPS has been of interest to researchers trying to understand how we perceive our body because of their relationship with conscious attention to bodily stimuli which contribute to the formation of our body image (Michael and Naveteur 2011) and with their relationship to disordered bodily awareness (Borg et al. 2015; Michael et al. 2015). While research has measured how the body feels in the presence of those sensations (Beaudoin and Michael 2014; Michael and Naveteur 2011; Michael et al. 2012, 2015, 2017, 2020; Naveteur et al. 2015; Salgues et al. 2021a, 2021b), a baseline measurement of how our body feels in the absence of those sensations is needed to develop an accurate understanding of our bodily perception. This is an important step as understanding bodily perception is crucial in our interactions with the environment and in building our sense of self (Harris et al. 2015; Michael et al. 2015).

The most common way to measure SPS is by using subjective methods. For instance, Naveteur et al. (2005) first examined SPS by asking participants to focus their attention for 10 s to the external side of the first metacarpus of either hand. Then, participants had to indicate whether they perceived any SPS and name the sensations. Half of the participants (51.7%) reported perceiving SPS including shaking, vibration, pricking, pulsations, changes in the temperature, muscular tension, pressure, or numbness. Michael and Naveteur (2011) replicated the results by Naveteur et al. (2005) for the whole hand, as participants focussed their attention for 10 s on their hands. Then, the list of SPS presented in the Naveteur et al. (2005) study was provided, and participants were asked to indicate which SPS they experienced during the rest. The SPS most frequently experienced were described by the words tingling (30%), numbness (20%), beat/pulse (19%), cooling (16%), warming (16%), muscle stiffness (15%), flutter (14%), and the words least frequently indicated were tickle (8%), vibration (7%), skin stretch (3%), and itch (2%). These findings have been replicated in follow-up work (Michael et al. 2012) and a functional magnetic resonance imaging (fMRI) study (Bauer et al. 2014). These authors used a Likert Scale ranging from weak to strong to measure attention towards SPS in their participants. To create the scale, the authors conducted a pilot study in which participants provided an unrestricted description of SPS from which the most frequent words used to describe SPS were then extracted and adopted in the scale. Similarly, to Naveteur et al. (2005), Michael and Naveteur (2011), and Michael et al. (2012), the most frequent SPS described in this pilot study were pulsation, vibration, enlargement, heat, cold, shrinkage, itching, stinging and numbness. Thus, there is an agreement in the SPS research on what adjectives are describing the SPS experience.

These studies show the most common words used to describe SPS. However, these SPS are ‘violations’ of a baseline, as ∼12% of participants do not experience SPS in more than half of the tested conditions (Michael et al. 2012), and in the study by Naveteur et al. (2005) almost half of the participants (48.3%) did not experience SPS. Those participants were excluded from the analyses as the authors were interested in measuring the presence of the SPS experience and not the absence of them. How do we describe our sensations in absence of SPS? To date, measuring SPS on an explicit level, using subjective reports, such as questionnaires has been the common practice. However, cognition operates under two separate systems of processing: the automatic, unconscious, quick, and implicit system and the controlled, conscious, slow and explicit system (Velkoff and Smith 2020). Therefore, explicit and conscious measures, such as self-reports might not be accurate reflections of an individual’s perceptions and attitudes (Carey and Preston 2019). For example, results obtained using explicit measures might be influenced by expectation bias (Gallagher et al. 2021) or response bias, as participants might be unwilling to express their own attitudes or unable to accurately perceive their own cognitions due to poor insight (Velkoff and Smith 2020). Furthermore, measures and tasks in body representation research might differ in terms of the level of awareness required to perform the task, such as more implicit vs. more explicit (Brusa et al. 2021; Scarpina et al. 2019), and dissociations have been reported between implicit and explicit measures (Gallagher et al. 2021). No studies to date have examined SPS on an implicit level (unconscious and automatic). Understanding SPS on an implicit level is important as implicit measures are often good predictors of behaviours. They are free of expectation or response biases and, if used in combination with subjective reports, they can provide a more holistic insight into one’s cognition (Carey and Preston 2019; Gumble and Carels 2012).

The most commonly used task to explore implicit cognitions is the Implicit Association Test (IAT; Greenwald et al. 1998). The IAT assesses beliefs, attitudes, and cognitions on an unconscious and implicit level. Using a computer-based reaction task, the IAT allows to the measurement of the strength of associations between two concepts (e.g., flower vs. insects) and an attribute (e.g., pleasant vs. unpleasant). Participants are presented with a series of target words in the centre of the screen (e.g., bees) and they are asked to categorize the words based on two categories displayed on the left (e.g., flower and pleasant) and on the right (e.g., insects and unpleasant) of the screen. Participants usually pair target words (e.g., bees) faster with the category that matches their own beliefs (e.g., insects and unpleasant) as the process is automatic.

The IAT is an excellent candidate to explore implicit components of SPS and fill a gap in SPS research. An IAT tailored to SPS has yet to be empirically tested, and it is not straightforward to establish which target words would be appropriate to use. If one follows the IAT classic structure an SPS-IAT would consist of two concepts (presence of SPS vs. absence of SPS) and an attribute in relation to the self (self vs. other; Carey and Preston 2019; Preston and Ehrsson 2018). The presence of the SPS concept is straightforward, as the previous research provides plenty of words to build this category. However, words that perfectly match the category absence of SPS are lacking. These words are essential and must be precise, as randomly established words could lead to the reduced construct validity of the IAT and hence unreliable results (Nosek et al. 2005).

The present study aims to provide an initial understanding of how participants perceive and describe their hands and feet, both in the presence of SPS and the absence of SPS. This will build the necessary knowledge to tackle implicit components of SPS via tasks, such as the IAT. We included feet as well as hands, as our experience of SPS might not be the same across our limbs due to the sensory differences among them. Hands have a higher representation in the somatosensory cortex (Penfield and Rasmussen 1950), are twice as thermosensitive than the feet (Ackerley et al. 2014). In addition, touch receptor density is higher in fingertips and tactile sensitivity varies across the body with the most sensitive to be the forehead and the palm, while the thigh and the shin are the least sensitive (Ackerley et al. 2014). Therefore, the experience of SPS might be different across our limbs and this might be reflected in the descriptions of SPS for those limbs.

2. Materials and methods

A Qualtrics survey was launched from December 2020 until January 2021. Ethical approval was granted by the Ethics Committee at Heriot-Watt University (0924). The study was conducted in concordance with the Declaration of Helsinki (Association 2013).

2.1. Participants

For exploratory and survey pilot studies, a sample size between 10 and 30 participants is deemed to be sufficient (Hertzog 2008). Participants were recruited using a convenience sampling method. Advertisements were placed on the Student Research Participation System (STREP) at Heriot-Watt University in which psychology students had the opportunity to take part to gain credit which is part of a course requirement. Online advertisements were published in the professional and personal network of the authors and social media (Facebook, Twitter, and LinkedIn) were also used.

2.2. Measures

Participants completed a short online survey titled ‘How do you feel your hands and feet?’ composed of four questionnaires: Screening Questionnaire, General Questionnaire, Limb Laterality Preference Questionnaire, Spontaneous Sensations Questionnaire. See Appendix for the full survey.

2.2.1. Screening questionnaire

Participants were eligible to take part if they did not have a history of neurological, medical, and mental health conditions and use of psychotropic or psychoactive medications as those factors can affect the experience of bodily sensations (Michael et al. 2012). To ensure our eligibility requirements were met, a screening questionnaire was used to determine: the presence of a neurological condition (e.g., epilepsy, Parkinson’s disease, and stroke), presence of a medical condition (e.g., heart condition, diabetes, and arthritis), presence of a mental health condition (e.g., depression, anxiety, and drug/alcohol addiction) diagnosed from a healthcare professional and use of psychotropic or psychoactive medication within the past 3 months. Additionally, we required that participants are English native speakers, as we aimed to collect representative words in English, which describe the experience of spontaneous and normal sensations.

2.2.2. General questionnaire

A general questionnaire was devised to collect demographic information (e.g., age, biological sex, and gender). An open question regarding biological sex and gender was used to be inclusive for all genders and sexes (Cameron and Stinson 2019). Information on factors that might influence the experience of bodily sensations (exercise, caffeine consumption, smoking, and alcohol consumption) was asked (Borg et al. 2015; Michael et al. 2012, 2015; Michael and Naveteur 2011). Additionally, a single question about the presence of restless leg syndrome was asked as spontaneous sensations are often a symptom of this condition (Karroum et al. 2012) as well as the presence of a skin condition, such as psoriasis as it might impact the SPS experience. Finally, the education level of the individuals was asked as it might impact how participants describe their bodily sensations using words.

2.2.3. Limb laterality preference

Handedness and footedness were measured using eight items from the Lateral Preference Inventory by Coren (1993). Four items measure handedness related to writing, throwing a ball, using a knife, using a hammer, and four items measure footedness related to kicking a ball, picking up a pebble, stepping on a beetle, and stepping up on a chair. Participants indicated their preference with left (−4), either (0), or right (4) as options. The average of scores in each item indicates the laterality preference, while scores between −3 and −1 indicate a moderate left preference, scores between 3 and 1 indicate a moderate right preference, scores at 0 indicate no preference, 4 scores indicate right sidedness, and −4 scores indicate left sidedness.

2.2.4. Spontaneous sensations questionnaire

A Spontaneous Sensations (SPS) questionnaire was devised to identify words that we use to describe our hands and feet, in the presence and absence of SPS. We provided participants with a definition of what SPS is (Spontaneous sensations are sensations that you feel on your body when you are not moving and even when you are not touched), without providing specific examples, to ensure consistency of understanding but at the same time avoiding a bias in the words used (1. Definition of SPS). Participants were then asked to indicate whether they generally experience SPS in their limbs and if yes, they were asked to indicate the location of SPS and to describe them using up to five words (2. Presence of SPS; 3. Location of SPS). Finally, participants described how their limbs feel in the absence of SPS using up to five words (4. Absence of SPS) (see Figure 1). The reasoning of structuring our task in terms of asking first about the Presence of SPS and then about the Absence of SPS is to ensure that participants understand how their limbs feel like when they experience SPS as this reflection will, in turn, aid them in understanding how their limbs will feel like in absence of those sensations. If it were the opposite order, participants might have confused what SPS is and thus described sensations that belong to the presence of the SPS category (e.g., tickling sensations; Michael et al. 2012) as the absence of SPS.

Figure 1. Spontaneous sensations questionnaire flow. SPS: spontaneous sensations. Arrows indicate the flow of the questionnaire.

2.3. Procedure

All measures were administered online using Qualtrics. Informed consent was obtained by all participants, and the debriefing procedure was followed upon the completion of the survey. Participants first completed the screening questionnaire to ensure whether our eligibility requirements were met, followed by the general questionnaire and the lateral preference inventory. Then participants completed the SPS questionnaire for hands and feet. The study took up to 15 min to complete.

3. Results

3.1. Sample characteristics

Eighteen healthy individuals completed the survey (age M = 32.72, SD = 13.64). In terms of sample characteristics, 56% (n = 10) indicated female biological sex, and 44% (n = 10) identified as females in terms of gender, 33% (n = 7) as males, and 6% (n = 1) as gender-fluid.

Participants were educated for an average of 17.17 years (SD = 3.05). The majority of the participants exercised weekly (78%, n = 14) for 5 h on average (SD = 2.88). Moreover, 78% (n = 14) of the participants consumed caffeine within the past 24 h, and 28% (n = 5) consumed alcohol within the past 24 h. All participants were non-smokers (100%, n = 18). One participant (6%) reported restless leg syndrome in both legs. Skin conditions were reported by 22% (n = 4), with two participants reporting feet as the body parts affected, one participant reported the right hand and both feet, and one participant reported only the hands to be affected.

In terms of hand laterality preferences, 78% (n = 14) reported right preference, 11% (n = 2) reported moderate right preference, 6% (n = 1) reported moderate left preference, and 6% (n = 1) reported left preference. With regards to foot laterality preferences, 83% (n = 15) indicated a moderate right preference, 11% (n = 2) indicated a right preference, and 6% (n = 1) indicated moderate left preference.

3.2. Presence of spontaneous sensations descriptions

The majority of participants (67%, n = 12) indicated that they do not generally experience SPS in their limbs, named Group_NO-SPS. Six participants (33%) indicated that they generally experience SPS, named Group_SPS.

In the Group_SPS (n = 6), all participants experienced sensations in one or both hands, while four participants (67%) experienced SPS in their feet too. Specifically, three participants (50%) reported SPS on all limbs, two participants (33%) reported SPS on both hands and one participant (17%) reported SPS on both feet, and on the left hand. Overall, 53% of SPS were present on the left side of the body and 47% of SPS on the right side of the body.

3.2.1. Hands

Of the participants who experienced SPS in hands (n = 6), most of them (67%, n = 4) used two adjectives to describe their hands in the presence of SPS, while one participant (17%) used three adjectives and one participant (17%) used four adjectives. The most common descriptions for hands with SPS were tingly/tingling (33%, n = 5), followed by itchy/itching (20%, n = 3) and temperature-related words, such as cold (13%, n = 2) and warm (7%, n = 1). Numb was also reported by two participants (13%, n = 2) while stiff and prodded were used once (7%).

3.2.2. Feet

Of the participants who experienced SPS in feet (n = 4), two participants (50%) used four adjectives to describe their feet in the presence of SPS, one participant (25%) used one adjective and one participant (25%) used three adjectives. The most common descriptions were itchy/itching (25%, n = 3) and tingly/tingling (25%, n = 3), followed by numb (17%, n = 2). Cold, warm, tightness, and a bit painful were reported once (8%).

3.3. Absence of spontaneous sensations descriptions

Overall, most participants (67%, n = 12) used one adjective to describe their hands in the absence of spontaneous sensations (SPS), three participants (17%) used two adjectives, one participant (5%) used three adjectives, one participant (5%) used four adjectives and one participant (5%) used five adjectives. See Figure 2 for words used to describe the absence of spontaneous sensations (SPS) in hands.

Figure 2. The percentages (frequencies) of adjectives used to describe hands in absence of spontaneous sensations (SPS) in the sample (N = 18).

Overall, most participants (67%, n = 12) used one adjective to describe their feet in the absence of SPS, while five participants (28%) used two adjectives and one participant (5%) used four adjectives (Figure 3, words used to describe absence of sensations in feet).

Figure 3. The percentages (frequencies) of adjectives used to describe feet in absence of spontaneous sensations (SPS) in the sample (N = 18).

To ensure that all participants, regardless of whether they experience SPS (Group_SPS) or not (Group_NO-SPS), similarly describe their limbs, that is, they use representative words of the absence of SPS experience, a breakdown of the limb descriptions in absence of SPS per group (Group_SPS and Group_NO-SPS) is provided below:

3.3.1. Absence of spontaneous sensations descriptions, Group_SPS

The frequency of the adjectives used to describe hands and feet by participants who generally experienced SPS in hands (n = 6; Group_SPS) and feet (n = 4; Group_SPS) is described below.

3.3.1.1. Hands

Of the participants who experienced SPS in their hands (n = 6), when asked to describe their hands in absence of SPS, most participants (83%, n = 5) used one adjective and one participant (17%) used two adjectives. The most common adjectives used to describe hands in the absence of SPS in this sample, were normal (43%, n = 3), followed by being aware (29%, n = 2). The adjectives fuzzy and cold were reported once (14%, n = 1).

3.3.1.2. Feet

Of the participants who experienced SPS in their feet (n = 4), when asked to describe their feet in absence of SPS, most participants (75%, n = 3) used one adjective and one participant (25%) used two adjectives. The most common words used to describe feet in the absence of SPS in this sample, were normal (50%, n = 2), followed by being aware (25%, n = 1), fuzzy (16%, n = 1), and cold (16%, n = 1).

3.3.2. Absence of spontaneous sensations descriptions, Group_NO-SPS

The frequency of the adjectives used to describe hands and feet by participants who did not generally experience SPS in hands (n = 12; Group_NO-SPS) and in feet (n = 14; Group_NO-SPS) is described below.

3.3.2.1. Hands

Of the participants who did not experience SPS in their hands (n = 12), when asked to describe their hand, most participants (59%, n = 7) used one adjective, two participants (17%) used two adjectives, one participant (8%) used three adjectives, one participant (8%) used four adjectives, and one participant (8%) used five adjectives. The most common adjectives used to describe hands in the absence of SPS in this sample, were normal (26%, n = 6), followed by cold (18%, n = 4), and warm (9%, n = 2). The following adjectives were reported once (4%): comfortable, bendy, solid, no sensation, pain free, fine, natural, rough, still, smooth, and dry.

3.3.2.2. Feet

Of the participants who did not experience SPS in their feet (n = 14), when asked to describe their feet, most participants (64%, n = 9) used one adjective, four participants (29%) used two adjectives and one participant (7%) used four adjectives. The most common adjectives used to describe feet in the absence of SPS in this sample, were normal (33%, n = 7), followed by cold (9%, n = 2). The following adjectives were reported once (5%): warm, comfortable, bendy, solid, no sensation, pain free, fine, relaxed, unnoticed temperature, whatever it is touching, achy, light.

4. Discussion

This study aimed to understand how participants perceive their hands and feet, in the absence and the presence of spontaneous sensations (SPS). The most frequent adjectives to describe how limbs feel like in the presence of SPS were tingly, itchy, temperature-related SPS (cold and warm), and numb; most participants used more than two adjectives to describe their limbs, and hands reported more SPS than feet. The most frequent adjectives to describe how limbs feel in the absence of SPS were normal and temperature-related SPS (cold and warm), while most participants used one adjective to describe their limbs.

4.1. Presence of spontaneous sensations descriptions

The descriptions of SPS provided by participants in this study support the SPS results of the research on hands and extend this to include feet. The most frequent descriptions of SPS were tingly, temperature-related (cold, warm), and numb (Michael and Naveteur 2011; Michael et al. 2012); itchy was also frequently reported (Bauer et al. 2014). Therefore, participants still report experiencing the most frequent descriptions of SPS even when they are not provided with a list of words to choose from. This was true for both hands and feet. Hence, our study’s methodology reduces the possibility of bias by not providing the list of possible SPS, and it also replicates previous studies of SPS in hands and extends those findings in feet.

All participants in the Group_SPS experienced sensations in one or both hands, while four participants experienced SPS in their feet. This might suggest differences in how we perceive bodily sensations across our limbs. For instance, hands are more sensitive to temperature changes than feet, the fingers have higher touch receptor density than the feet and the palm is one of the most tactile sensitive areas of the body (Ackerley et al. 2014). Hence, there might be differences in the location and intensity of SPS presented in hands and feet. To further support this suggestion, temperature-related SPS (cold and warm) were more frequent in hands than feet. Therefore, how the way we experience SPS in our hands and feet might differ.

The SPS were represented equally to both sides of the body. This is different from research showing that SPS were more frequent in the left side of the body (Michael and Naveteur 2011; Michael et al. 2012; Naveteur et al. 2015). However, that research focussed on right-handed participants and hands only, while our research complements and enhances the SPS literature by exploring both hands and feet and by including hand and foot preferences for right, left, and mixed laterality.

4.2. Absence of spontaneous sensations descriptions

In terms of limb descriptions in the absence of SPS, the words normal and temperature-related words, such as cold and warm were the most frequent. By dividing the sample into two groups, those who do not generally experience SPS (Group_NO-SPS) and those who do (Group_SPS), a slightly different pattern appears. The most frequently used words to describe limbs in the absence of SPS in the Group_NO-SPS were normal and temperature-related words (cold, warm). Whereas, the most frequently used words to describe limbs in absence of SPS in the Group_SPS were normal and aware. This might be related to the fact that no examples of SPS were provided to the participants to reduce the bias of reporting, and as such, participants might not have had expectations on what SPS might appear. Therefore, sensations, such as cold and warm, which are SPS and they have been repeatedly reported by SPS research (Michael and Naveteur 2011; Michael et al. 2012), might have been categorized to the absence of SPS adjectives by the Group_NO-SPS due to the lack of examples that we did not provide. Furthermore, the adjective aware was used to describe limbs in the absence of SPS by the Group_SPS. This adjective was not used by the Group_NO-SPS. It might be that conscious attention to somatic stimuli allows us to construct our body image by providing us with information about the spatial frontiers of our body and by becoming more aware of them (Michael and Naveteur 2011). Hence, individuals with reduced bodily awareness of bodily sensations might then perceive SPS differently. In other words, those who pay more attention to their body might be more aware of it and thus they are more likely to experience SPS (Michael et al. 2015).

The adjective normal was the most frequently used word to describe hands and feet in the absence of SPS in both groups. It should be noted that words provided least frequently, such as natural, comfortable, and fine might also be categorized under the normal term. Three out of six participants of the Group_SPS also used the adjective normal, to describe their limbs without SPS experience. Hence, the adjective normal describes how limbs feel, irrespective of whether an individual experiences SPS or not.

Most participants indicated that they do not experience SPS generally in their limbs. This is not surprising, and it is partly in line with Naveteur et al. (2005) who showed that ∼48% of their sample did not experience SPS. However, our study included a short question which aimed to capture the general experience of SPS, without providing examples of SPS and this is different from other studies in the SPS literature (Naveteur et al. 2005, 2015; Michael and Naveteur 2011; Michael et al. 2012, 2015, 2017). In addition, experimental studies in the literature asked participants to pay attention to their hands for any SPS at that moment. Therefore, participants in this study might have underreported their SPS experience due to the lack of SPS examples or not remembering any of their past SPS experiences.

4.3. Conclusions

This study showed that the most frequently used words to describe limbs in the absence of SPS is normal, irrespective of whether the individual generally experiences SPS or not. For people who generally experience SPS, descriptions of itchy, and tingly were the most frequent in both hands and feet. This study also shows that more participants perceived SPS in their hands than their feet. Hence the way we experience SPS varies across our limbs. However, we use the same words to describe how our limbs feel, irrespective if we are talking about hands or feet. The words identified in this study can be used to explore SPS on an implicit and automatic level using an Implicit Association Test (IAT; Greenwald et al. 1998). The most frequent words used to describe the experience in the presence/absence of SPS can be included in the IAT as validly representative stimuli for those categories (Nosek et al. 2005). In this way, the research community can further understand what SPS are using explicit and implicit methods, and how we pay attention to them.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The dataset is fully available here: Efstathiou M., Delicato L., Sedda A. 2021. Normal or Tingly? A story about Hands & Feet. Open Science Framework. https://doi.org/10.17605/OSF.IO/2QZFD.

Additional information

Funding

The work was supported by a PhD Scholarship from the Centre for Applied Behavioural Sciences at Heriot-Watt University.

Appendix

Survey: How do you feel your hands and feet?

Screening Questionnaire:

Before you start the experiment, we ask all prospective participants to read the following statements for the following reasons: (1) the way we designed this specific research and (2) the tasks that you will be asked to carry out.

The following statements are aimed at understanding if you are eligible to take part in our study. If any of the following statements apply to you, unfortunately, you are not eligible to take part at the present time. If you are in doubt, please contact us at [email protected]

We thank you for your time and of your interest in our study.

Do any of the following statements apply to you?

• Are you a non-native English speaker?

• Do you have a diagnosed neurological condition, such as epilepsy, Parkinson’s disease, multiple sclerosis, or others?

• Have you ever had a stroke or a traumatic brain injury?

• Do you have a heart condition (e.g., angina, history of heart attack)?

• Do you have diabetes?

• Do you suffer from arthritis?

• Do you have problems with moving your hands and/or feet?

• Do you have a diagnosis of a mental health condition (e.g., depression, anxiety, drug, or alcohol addiction) from a healthcare professional (e.g., psychiatrist or psychologist)?

• Within the past 3 months, have you taken any medication for mood (e.g., antidepressants, antipsychotics, anxiolytics, and mood stabilizers)?

• Within the past 3 months, have you taken any substance that can affect your thoughts, moods, and behaviour (e.g., cannabis, hashish, ecstasy, cocaine, heroin, and amphetamines)?

Yes/No

General Questionnaire:

Now we will ask you a series of questions about your profile, your habits, and health. Some questions might seem strange: please bear with us, we will explain their aim at the end of the study.

• What is your age? Open question

• I identify my biological sex as: Open question

• I identify my gender as: Open question

• How many years of education do you have?

• Do you exercise (e.g., meditation, yoga, weightlifting, and running)? Yes/No If yes, how many hours per week to you spend exercising?

• Did you have a caffeinated drink (e.g., red bull, coffee, tea, and soft drinks) within the last 24 h? Yes/No

• Did you have an alcoholic drink (e.g., wine, whisky, and beer) within the last 24 h? Yes/No

• Do you smoke (e.g., cigarettes and cigar)? Yes/No

• Do you suffer from restless leg syndrome? For more information about restless leg syndrome can be found here: https://www.nhs.uk/conditions/restless-legs-syndrome/. . ? Yes/No If yes, which body parts are affected?

• Do you suffer from a skin condition (e.g., eczema and psoriasis) in your hands and/or feet? Yes/No If yes, which body parts are affected?

• Do you use a QWERTY keyboard? Yes/No If no, please describe the type of keyboard that you use Open question

Lateral Preference Inventory by Coren (1993):

The following questions are aimed to measure your hand and foot preference. Please read each question below. Decide which hand or foot you use for each activity and check one box (left, either, right) that best describes your behaviour in each case.

Which hand…

• Do you use to draw? (1) Left Either Right

• Do you use to throw a ball to hit a target? (2) Left Either Right

• Do you use to hold an eraser on paper? (3) Left Either Right

• Do you use to remove the top card when dealing from a deck? (4) Left Either Right

Which foot…

• Do you use to kick a ball to hit a target? (1) Left Either Right

• Would you use to pick up a pebble with your toes? (2) Left Either Right

• Would you use to step on a bug? (3) Left Either Right

• Do you place on a chair first to step on it? (4) Left Either Right

Spontaneous Sensations Questionnaire:

Spontaneous sensations are sensations that you feel on your body when you are not moving and even when you are not touched.

Now we ask you to think about your own experience of spontaneous sensations in your hands and feet.

• Do you generally feel spontaneous sensations in your hands and feet? Yes/No

If Yes: Please select the areas that you generally feel spontaneous sensations: Right Hand Right Foot Left Hand Left Foot

If they select Right Hand/Left Hand: How does your hand(s) feel when you are experiencing any spontaneous sensations? Please use up to 5 words to describe the feelings.

If they select Right Foot/Left Foot: How does your foot/feet feel when you are experiencing any spontaneous sensations? Please use up to 5 words to describe the feelings.

Now we ask you to think about your hands and feet, without the spontaneous sensations.

• How does your hand/hands feel when you are not experiencing any spontaneous sensations? Please use up to 5 words to describe the feelings.

• How does your foot/feet feel when you are not experiencing any spontaneous sensations? Please use up to 5 words to describe the feelings.