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Jigna J. Jadav, Dr.Uttam Chauhan RT&A, No 2 (78) STRESS DETECTION USING PHYSIOLOGICAL SIGNALS_Volume 19, June, 2024
ANALYSIS OF PERSONALIZED STRESS RECOGNITION IN THE OFFICE ENVIRONMENT
Jigna Jadav1, Dr. Uttam Chauhan2
1 Research Scholar, Computer Engineering, Gujarat Technological University, Ahmedabad, India.
Jigna_jadav@vgecg.acin
2 Assistant Professor, Computer Engineering department, Vishwakarma Government Engineering
College Chandkheda, Ahmedabad, India. ug_chauhan@gtu.edu.in
Abstract
In today's fast-paced lifestyle, pursuing holistic well-being has increased interest in monitoring and managing stress levels. Heart rate variability (HRV), a non-invasive measure of autonomic nervous system activity, has emerged as a valuable tool for assessing individual responses to stress. This study focuses on utilizing the capabilities of the Apple Watch to collect continuous HRV data in real-world contexts. A diverse dataset from individuals working in software companies was gathered, including HRV recordings during various stress-inducing scenarios. By employing HRV Time Domain, Frequency Domain, and Nonlinear features, the study uses Principal Component Analysis (PCA) to extract relevant features, considering the personalized nature of stress reactions. Addressing variations in stress responses among individuals, the study introduces an innovative approach using Long Short-Term Memory (LSTM) networks. A hybrid model, combining feature selection, dimensionality reduction, and ensemble techniques, is developed to predict stress levels based on individualized HRV patterns. Rigorous training and validation reached to an 88% accuracy rate. These findings demonstrate the effectiveness of the proposed methodology. The LSTM model accurately forecasts stress responses, highlighting the potential of Apple Watch-acquired HRV data for stress assessment. Beyond prediction, the study enhances understanding of the complex interplay between HRV dynamics and unique stress reactions. This novel approach, leveraging Apple Watch features and intelligent computing, offers a personalized method to predict stress levels using K-Means Clustering Algorithm. Through integrating K-means clustering and person-specific HRV analysis, the research endeavours to advance our comprehension of the intricate interplay between physiological responses and stressors. The study offers a novel perspective on stress response variations by delving into the distinct autonomic patterns characterizing each cluster. It sets the stage for developing targeted interventions and personalized stress management strategies.
Keywords: Stress Detection, Apple Watch Dataset, HRV, LSTM
I. Introduction
Nowadays, stress detection research has made strides with cutting-edge methods. Wearable tech captured heartbeat dynamics for stress prediction in college students [1]. Wearable sensors gathered diverse physiological signals, showcasing multi-dimensional stress responses [2]. Deep learning in 2022, with "Stress Detection Using Deep Convolutional Neural Networks," revealed patterns in physiological data [3]. "Stress Recognition Using Wearable Sensors and Mobile Phones" combined wearables and mobiles for accessible stress assessment [4]. Collectively, these studies illuminate stress's nuances via tech-driven insights. Wearables and deep learning enhance stress detection's precision, potentially personalizing interventions. This dynamic interdisciplinary progress ushers in more accurate, accessible strategies for stress assessment.
Many Datasets are publicly available for stress recognition. The novelty resides in the integration of HRV analysis. No prior study has generated a continuous 15-day dataset from working professionals in software companies using the Apple Watch. This dataset serves as a rich resource
for understanding stress over time. Furthermore, the study introduces personalized stress detection through clustering, recognizing the diversity of stress manifestations. As individuals navigate the challenges of modern work environments, their physiological responses to stress manifest in unique ways. The dataset is augmented with discrete emotion labels corresponding to their tasks, specifically Neutral, Stress, and Not Stress. This dataset provides a foundation for personalized stress assessment, acknowledging that stress responses are distinct for each individual.
II. Proposed Methodology
The physiological signal calculated by the time interval (R-R Interval) between consecutive heartbeats in milliseconds is known as heart rate variability. The supportive branch of the autonomic nervous system (ANS) controls the stress or reaction, preparing us to act, respond, and conduct in rebuttal to life's diverse needs. The time between heartbeats (R-R interval) varies from beat to beat, and this variation in HRV can reveal a lot about the body's physiological state. HRV should naturally rise during relaxing activities and fall during stressful situations when the body is able to take advantage of increased sympathetic action. Heart rate variability is higher when the heart beats slowly; when the heart rate increases, such as during stress or exercise, it decreases during relaxing activities. Heart rate and HRV are in the inverse relation. The Heart rate variability level intuitively varies daily depending on activity, anxiety, and work-related stress. The duration between heartbeats (R-R interval) fluctuates from beat to beat and can give information about the body's physiological reaction.
When investigated in a deeper context, stress is detrimental in workplace situations. According to The American Institute of Stress [5], 80% of workers feel stress on the job, so we have decided to detect stress in working employees. Here, we have mentioned different datasets available to see the stress conditions of persons using physiological Signals.
Authors [6] (Park & Kim, 2018) used an HRV signal to predict a daily mental stress level using a photoplethysmography (PPG) sensor in the wristband-type wearable device. They extracted low-frequency (0.04Hz - 0.15Hz) and high-frequency (0.15Hz - 0.4Hz) features of HRV using the autoregressive (AR) model. Eight university students' data was collected using a self-evaluation PSS scale for 30 seconds thrice daily for a week. Linear regression provided an accuracy of 86.35%, although additional machine learning algorithms and well-known PPG analytic tools can produce better outcomes. ten users wore the FITBIT device to detect stress and an online questionnaire. In addition, it measures different physical activities like sleeping patterns, BMI, and Heart rate variability[7].
The Heart rate (HR), galvanic skin response (GSR), and electrooculogram (EOG) signals are collected from 11 subjects. The participants were also given a mental arithmetic task and a challenging LEGO assembly without instructions to predict stress. They applied a k-means clustering algorithm for heart rate, EDA, and EOG and got an accuracy of 70.6 percent, 74.6 percent, and 63.7 percent, respectively[8].
To identify different physiological changes during a stressful task. The Trier Stress Test was used to prompt stress, with resting and stress phase ECGs, and the inter-second heart rate was recorded (using a FitBit). The study enlisted the participation of 30 student doctors and 30 general public. More investigation with a large sample of people with stratified anxiety scores based on the Depression Anxiety Stress Scale is required to further analyze the association with HRV [9]. The WESAD (Wearable Stress and Affect Detection) dataset [10] is a publicly available dataset used for research in affective computing and physiological signal analysis. It was developed to support developing and evaluating algorithms and models for stress and affect detection using wearable sensors. The dataset includes physiological sensor data collected from wearable devices, such as heart rate sensors and accelerometers, and self-assessment labels related to the participants' stress
levels and affective states. The data was collected from 15 participants in a controlled environment while they underwent different stress-inducing tasks and activities.
AMIGOS [11] was designed to collect participants' emotions in two social contexts: individual and group. AMIGOS was constructed in 2 experimental settings. First, 40 participants watched 16 short emotional videos. Then, they watched four long videos, including a mix of lone and group sessions. These emotions were annotated with self-assessment of affective levels and external assessment of valence and arousal through GSR and ECG signals.
The SWELL dataset [12] comprises heart rate variability (HRV) indices derived from the multimodal SWELL knowledge work (SWELL-KW) dataset, designed for research on stress and user modelling. This dataset was developed by researchers at the Institute for Computing and Information Sciences at Radboud University. The SWELL dataset was created through experiments involving 25 subjects engaged in typical office work activities, such as writing reports, making presentations, reading emails, and searching for information. The dataset captures various data modalities, including computer logging, facial expressions, body postures, ECG signals, and skin conductance. Each participant in the study underwent three different working conditions: stress, time pressure, and interruption.
The author was involved in curating a Social Media Status dataset highlighting three key emotions: happiness, sadness, and anger. This dataset was drawn from status updates contributed by seven distinct individuals and acquired from Kaggle. The dataset's core focus was emotions, with entries structured to include the status text and corresponding sentiment. Achieved an accuracy of around 79% using a CNN classifier [13].
I. Extraction of Heart Rate from Apple Watch
An optical heart sensor in the Apple Watch SE, as shown in Figure 1, measures your heart rate and heart rhythm. Utilize the Breath application to calculate your stress with maximum precision. The Apple Watch has numerous capabilities that can be used to track stress levels. For instance, it features a heart rate monitor that can detect variations in the wearer's heart rate and heart rate variability, which can signal stress levels. A breathing app for the Watch also leads users through breathing exercises to lower stress. The gadget also monitors sleep patterns, physical activity levels, and other health indicators that may assist in pinpointing stress origins and offer insights into general well-being. It's crucial to remember that these features shouldn't be used to diagnose or treat any medical conditions and aren't intended to replace expert medical advice.
Figure 1: Apple Watch SE
Gathering data in real-life contexts remains uncommon due to challenges such as limited context and reliance on self-reported information. Real-world data collection possesses both advantages and challenges. While it maintains ethical constraints and context awareness, it lacks a clear ground truth and introduces noisy data. HRV in real-world scenarios and highlighted its small relationship with stress compared to controlled lab settings[14]. This underscores the importance and complexity of real-world data collection, offering insights that can be challenging to deduce.
Figure 2: Extraction Process of Heart Rate Using Apple Watch
Figure 2 shows the process of extracting heart rate using The Apple Watch and the Health application on your paired iPhone. It can accurately measure your heart rate.
• Ensure your Apple Watch is correctly worn on your wrist.
• Tap the Heart Rate app on your Apple Watch.
• Begin measuring your heart rate within the app.
• Wait a few seconds for your heart rate to display on the Watch.
• The data is automatically synced to the Health app on your paired iPhone.
• Open the Health app on your iPhone to see heart rate data trends.
• Download Export.XML file
• Extract Heart Rate Data from that XML file.
Heart Rate Signal - Subid 8
16400 16600 16800 17000 17200
Time
Figure 3: Heart Rate Signals of Subjects
Figure 3 shows individual plots for the subject's heart rate signal, showcasing the variations in their heart rate over time. The exact appearance of the plots and the specific data details depend on the content of the CSV file. This t would be useful for visualizing and analyzing heart rate variability among different subjects in the dataset.
Jigna J. Jadav, Dr.Uttam Chauhan RT&A, No 2 (78) STRESS DETECTION USING PHYSIOLOGICAL SIGNALS_Volume 19 June, 2024
II. File Preprocessing
Figure 4 explains the heart rate variability (HRV) data analysis derived from XML files, particularly focusing on data collected through Apple Watch devices. The script's main objective is to calculate a diverse array of HRV features encompassing both time domain and frequency domain metrics, subsequently organizing and storing these features within a CSV (Comma-Separated Values) file. Several critical libraries for XML parsing, HRV analysis, numerical computations, CSV handling, file searches, and operating system interactions are imported to initiate this processed. By defining a designated time frame using start and end dates, the script specifies the period for data extraction and evaluation.
Figure 4: Process of File Generation
Utilizing the glob function, the script locates the relevant XML files containing heart rate data. The CSV file that will house the calculated HRV features is opened, and its initial row is allocated for labels describing the different metrics that will be computed and saved.
III. Features Calculations & Selection
The core functionality of the script involves iterating through the identified XML files. 'Record' elements are examined within each file to determine pertinent heart rate data. Valid heart rate measurements are isolated by cross-referencing the data's time stamps with the designated time frame. Subsequently, the script calculates RR intervals, the temporal gaps between consecutive heartbeats, from the heart rate values. It forms the basis for HRV analysis, then employs the HRV analysis library to address missing values, perform frequency domain analysis and compute time domain. Here is the summarized description of HRV analysis. The data is obtained from an Apple Health export file and is parsed using the xml.etree Element Tree module. We define a specific date range to query the data for analysis.
First, we iterate over the XML file to extract heart rate values recorded within the specified date range. We filter out the relevant data based on the sample type, explicitly focusing on heart rate measurements ('HKQuantityTypeIdentifierHeartRate'). The extracted heart rate values are stored in a list called heart rates. Next, we calculate the RR intervals from the extracted heart rate values, representing the time between successive heartbeats. We utilize a formula to estimate the RR intervals from the heart rate values, considering the average duration between successive heartbeats. Additionally, we apply the Malik rule, which was implemented through the hrvanalysis.remove_ectopic_beats function to identify and remove ectopic beats from the RR
interval data.
Time domain features quantify RR interval variability, revealing insights into heart rate fluctuations over specific time spans. The Mean NN Interval (Mean NNI) portrays the average duration between successive normal heartbeats [15]. The Standard Deviation of NN Intervals (SDNN) characterizes overall RR interval variability, indicative of autonomic modulation. The Root Mean Square of Successive Differences (RMSSD) reflects short-term variability with parasympathetic sensitivity [16]. The Percentage of NN50 Intervals (pNN50) gauges parasympathetic influence by identifying RR intervals differing by over 50 ms [17].
Frequency domain analysis dissects HRV into frequency bands. Low Frequency (LF) power signifies both sympathetic and parasympathetic activity, whereas High Frequency (HF) power primarily denotes parasympathetic modulation [17]. The LF/HF ratio quantifies sympathetic-parasympathetic balance [18].
The nonlinear analysis captures intricate patterns. Sample Entropy (SampEn) gauges HRV complexity based on pattern repetition. Poincare plots visually explore RR interval relationships, providing insights into autonomic dynamics [19].
Additional PhysioBank, PhysioToolkit, and PhysioNet furnish resources for physiological signal access and analysis. Advanced HRV analysis methods are exhaustively covered, offering insights into diverse techniques [20].
To organize and store the accumulated HRV features, the script combines these metrics with the corresponding heart rate values and unique subject identifiers. This composite data is structured into arrays and consistently added as new rows within the previously opened CSV file. As the script concludes the analysis for each subject, it echoes the calculated HRV feature arrays to the console. This Python script provides an automated and systematic approach to parsing, analyzing, and storing HRV data from Apple Watch-generated XML files. It facilitates an in-depth exploration and understanding of physiological monitoring and health analysis within heart rate variability.
Figure 5: Feature Importance vs. Explained Variance Ratio
Figure 5 indicates the most influential features by examining the explained variance ratios associated with each principal component. These ratios indicate the proportion of total variance
Figure 6: K-Fold Stratified Sampling and Accuracy
in each component's dataset. The indices of the most impactful features are identified by sorting these ratios in descending order. The actual feature names are then extracted from the original dataset columns. We Have Used the stratified cross-validation method to evaluate the performance of a machine learning model in a way that ensures the distribution of target classes within each fold of the cross-validation is representative of the overall distribution in the dataset. This is particularly important when dealing with imbalanced datasets where certain classes might be underrepresented. The goal is to prevent any particular class from being disproportionately overrepresented or underrepresented in any fold, which could lead to biased model evaluation. StratifiedKFold is used to split the data into training and testing sets while preserving the class distribution as defined in Figure 6. The model is trained and evaluated on each cross-validation fold, and the results are stored in the fold_results list. In our work, six fold results are achieved.
III. Experimental Results and Discussion
We Have used the architecture of the LSTM model [21] using the Keras API provided by TensorFlow [22]. The model consists of an LSTM layer with 64 units, a fully connected (Dense) layer with three output units (matching the number of classes) and a softmax activation function. The model is compiled with the Adam optimizer and categorical cross-entropy loss function, which is suitable for multiclass classification. We referenced the existing models with the proposed ones. In the base paper, the author [23] observed the root-mean-square error (RMSE) and Mean absolute error (MAE) without calibration samples. The accuracy of the classification models on the SWELL Dataset for HRV signals was 61.6%. After adding 100 calibration samples, accuracy increased to 93.9%. Machine learning algorithms, such as supervised and unsupervised, are used on the SWELL-KW Dataset. From that, decision tree induction has the highest accuracy, with 75 % accuracy [24]. In our experimental setup, we get an overall 88% accuracy by applying the LSTM model and considering the time series property. However, neither author used the time-series property to obtain the result. The epoch-wise accuracy and loss plot visualizes the training process, showcasing the evolution of accuracy and loss over the training epochs, as shown in Figure 7.
Epoch vs Accuracy Epoch vs Loes
Epoch Epoch
Figure 7: Epochwise Accuracy and Loss Plot 0 12
J_I_L
36509 326 983
719 41059 32S
202 40 403 55
Predicted label
Figure 8: Confusion Matrix for Different Stress Conditions
Figure 8 illustrates the Confusion Matrix, delineating each row as representing the actual stress level observed in the dataset, while each column represents the predicted stress level generated by the model.
By analyzing the values within the confusion matrix, we can assess the model's ability to classify instances into their respective stress categories correctly. For instance, the diagonal elements of the confusion matrix represent the instances where the predicted stress level aligns with the actual stress level, indicating accurate predictions by the model. On the other hand, off-diagonal elements highlight instances where the model misclassifies the stress level, providing insights into the types of errors made by the model. It defines various stress conditions observed in the study. Stress levels are stratified into three distinct categories: 0, 1, and 2, each conveying specific contextual nuances. Stress level 0 denotes a neutral state, indicative of an absence of significant stressors and a generally favourable condition. Conversely, stress level 1 signifies the experience of stress triggered by particular circumstances such as meetings, presentations, or looming project deadlines, reflecting stress responses associated with task-related pressures. In contrast, stress level 2 delineates stress stemming from routine work responsibilities within the organizational setting, highlighting stress manifestations arising from day-to-day job demands and obligations. This categorization provides a nuanced understanding of stress dynamics, encompassing varying stressors in professional environments.
Figure 9: The flow of Stress Detection Figure 9 illustrates the overall flow of stress detection systems,
• The stress detection process begins by gathering data through smartwatches worn by 15 employees. These smartwatches collect various physiological information that could indicate stress levels.
• A dataset is constructed with the collected data. This dataset includes information in terms of frequency, time, and nonlinear domains. These aspects provide a comprehensive view of the physiological signals related to stress.
• Preprocessing techniques are applied to enhance the quality of the dataset. This involves cleaning and refining the data to eliminate noise, inconsistencies, or irrelevant information.
• The dataset identifies 22 features derived from Heart Rate Variability (HRV).
• A subset of 8 features are selected using Principal Component Analysis (PCA) to streamline the analysis. This reduces the complexity of the data while retaining its essential patterns.
• The process of model evaluation involves using k-fold stratified sampling. This technique ensures that the dataset is divided into subsets while maintaining the distribution of stress levels in each subset. Subsequently, a Long Short-Term Memory (LSTM) model is employed, a type of neural network well-suited for sequence data. This model utilizes the selected features to predict and categorize stress levels in subjects.
IV. Personalized Model
As different users have relatively different responses to stress conditions, examining the individuals' heart rate variability ranges, the dataset and machine learning model should be designed carefully. So we have applied the clustering algorithm after applying LSTM Model on 15 Individuals and after applying K-means Clustering Algorithm.
Authors investigated stress response patterns through the application of K-means clustering. The authors utilize K-means clustering to analyze and group stress response data from individuals. By applying this technique, they aim to identify distinct. This study contributes to the field of stress
research by utilizing a data-driven approach to understand and categorize stress response behaviours [25].Research was conducted to investigate stress response clusters using K-means analysis. The authors explore distinct clusters within stress response data by employing the K-means clustering algorithm. The study aims to identify and characterize patterns in how individuals respond to stress factors [26].
Select features of an individuals accoding to response of stress condtions
Divides a subjects into groups whose having similar kind of response to conditions using K-means ALgorithm
Figure 10: The flow of Personalized Stress Detection
Figure 11: Clusters According to Stress Response of Individuals
Performing K-means clustering on individuals based on their response to stress conditions. K-means clustering is a popular unsupervised machine-learning technique used for grouping similar data points into clusters. In your case, the data points would represent individuals, and the features could be the responses of those individuals to stress conditions. Calculating the average heart rate and condition for each subject creates a data frame that is subsequently sorted by condition values in Figure 10. Employing the K-Means algorithm with three clusters, the script performs clustering on the data and assigns cluster labels to each subject. These cluster labels are then mapped to stress response labels, and the resulting categorical stress levels are incorporated into the data frame. The data visualization aspect involves generating a 3D scatter plot using Plotly Express, wherein cluster labels, subject IDs, and stress response labels are represented along the x, y, and z axes, respectively, as shown in Figure 11. Customizations to the plot are applied, including axis labels, hover data, and legend formatting. Overall, it serves to analyze and visualize stress response patterns in relation to different subjects.
V. Discussion
Our study delves into stress assessment and management, leveraging the unobtrusive and non-invasive capabilities of wearable technology, specifically the Apple Watch. The overarching goal is to develop a methodology that enables the continuous and accurate detection of stress over extended periods, aligning with the growing emphasis on holistic well-being and stress management in today's fast-paced world. Our study aimed to utilize Apple Watch-acquired HRV data for personalized stress assessment, employing a robust methodology involving feature extraction, model development, and validation. Through rigorous analysis, we achieved an impressive 88% accuracy rate in predicting stress levels using an LSTM model, highlighting the efficacy of our approach. These findings underscore the potential of wearable technology in monitoring and managing stress effectively. While promising, our study acknowledges limitations such as the small sample size and the need for further validation.
Additionally, it's worth noting that other models beyond LSTM, such as Random Forest or Support Vector Machines, could also be explored for stress prediction. Recommendations include validation across diverse populations and settings, comparative analysis with existing methods, and exploration of long-term intervention effects. Overall, our study contributes to advancing stress assessment methodologies and offers practical solutions for personalized stress management in real-world contexts. Lastly, the use of wearable devices for stress assessment raises ethical considerations related to data privacy, informed consent, and potential stigmatization. It is essential to address these ethical concerns and ensure responsible use of personal health data in stress management interventions.
VI. Conclusion and Future Work
Based on our experimental findings, it was evident that applying suitable preprocessing techniques led to a notable enhancement in classifier efficiency, improving results by approximately 4-5%. We are achieving 88% accuracy using LSTM. This study offers a meticulously designed blueprint for stress detection. It underscores the potential of smartwatch-derived physiological data and advanced machine learning techniques in comprehensively addressing the complex challenge of stress assessment. This research's outcomes contribute to our understanding of stress dynamics and the development of reliable tools for stress monitoring, holding significant implications for individual well-being and workplace productivity. As this research advances stress detection using physiological data and LSTM analysis, several avenues for future work emerge. One significant direction is the exploration of a more extensive and diverse dataset to validate the model's performance across different demographic and environmental factors. Incorporating physiological signals beyond HRV, such as skin conductance and body temperature, could enrich the model's accuracy. Personalized features can be added to detect stress in individuals. Researchers could consider exploring more advanced clustering techniques that can capture variations within clusters
more effectively or combining clustering with other analysis methods to provide a more comprehensive understanding of stress response patterns at both the group and individual levels. This paper is a strong foundation for further research in stress analysis and physiological responses, potentially contributing to both scientific understanding and practical applications in health and wellness for individuals.
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