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13 pages, 1062 KiB  
Article
Real-Time Computing Strategies for Automatic Detection of EEG Seizures in ICU
by Laura López-Viñas, Jose L. Ayala and Francisco Javier Pardo Moreno
Appl. Sci. 2024, 14(24), 11616; https://doi.org/10.3390/app142411616 - 12 Dec 2024
Viewed by 385
Abstract
Developing interfaces for seizure diagnosis, often challenging to detect visually, is rising. However, their effectiveness is constrained by the need for diverse and extensive databases. This study aimed to create a seizure detection methodology incorporating detailed information from each EEG channel and accounts [...] Read more.
Developing interfaces for seizure diagnosis, often challenging to detect visually, is rising. However, their effectiveness is constrained by the need for diverse and extensive databases. This study aimed to create a seizure detection methodology incorporating detailed information from each EEG channel and accounts for frequency band variations linked to the primary brain pathology leading to ICU admission, enhancing our ability to identify epilepsy onset. This study involved 460 video-electroencephalography recordings from 71 patients under monitoring. We applied signal preprocessing and conducted a numerical quantitative analysis in the frequency domain. Various machine learning algorithms were assessed for their efficacy. The k-nearest neighbours (KNN) model was the most effective in our overall sample, achieving an average F1 score of 0.76. For specific subgroups, different models showed superior performance: Decision Tree for ‘Epilepsy’ (average F1 score of 0.80) and ‘Craniencephalic Trauma’ (average F1 score of 0.84), Random Forest for ‘Cardiorespiratory Arrest’ (average F1 score of 0.89) and ‘Brain Haemorrhage’ (average F1 score of 0.84). In the categorisation of seizure types, Linear Discriminant Analysis was most effective for focal seizures (average F1 score of 0.87), KNN for generalised (average F1 score of 0.84) and convulsive seizures (average F1 score of 0.88), and logistic regression for non-convulsive seizures (average F1 score of 0.83). Our study demonstrates the potential of using classifier models based on quantified EEG data for diagnosing seizures in ICU patients. The performance of these models varies significantly depending on the underlying cause of the seizure, highlighting the importance of tailored approaches. The automation of these diagnostic tools could facilitate early seizure detection. Full article
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<p>Cohort distribution of recruited sample size.</p>
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<p>Noise reduction in mathematical transforms. On the left, we show the graphics corresponding to the mathematical transform Fourier applied to raw data. On the right, after using a biological 1.5 transform to the signal from the upper left, the power of the spectrum from the four main frequency bands can be shown, with an evident change related to a seizure. After applying a Wavelet transform, Daubechies 4, the spectrum potency for each frequency band can be demonstrated at a moment in which a seizure is happening.</p>
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<p>(<b>A</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from epilepsy and patients with a normal recording. It shows a sensitivity of 75% and a specificity of 78.8%. (<b>B</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from seizures who had epilepsy and patients with a normal recording. It shows a sensitivity of 85.7% and a specificity of 80%. (<b>C</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from seizures and patients with a normal recording, both from the subgroup Cranioencephalic Trauma. It shows a sensitivity of 100% and a specificity of 88.9%. (<b>D</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from seizures and patients with a normal recording, both from the subgroup Cardiorespiratory Arrest. It shows a sensitivity of 89.5% and a specificity of 100%. (<b>E</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from seizures and patients with a normal recording, both from the subgroup Brain haemorrhage. It shows a sensitivity of 100% and a specificity of 76.5%. (<b>F</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from focal seizures and patients with a normal recording. It shows a sensitivity of 100% and a specificity of 85.3%. (<b>G</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from generalised seizures and patients with a normal recording. It shows a sensitivity of 93.7% and a specificity of 100%. (<b>H</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from convulsive seizures and patients with a normal recording. It shows a sensitivity of 90.7% and a specificity of 100%. (<b>I</b>) Confusion matrix in the analysis of the performance in seizure detection between patients suffering from non-convulsive seizures and patients with a normal recording. It shows a sensitivity of 81.5% and a specificity of 100%.</p>
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30 pages, 11972 KiB  
Article
Identifying Infant Body Position from Inertial Sensors with Machine Learning: Which Parameters Matter?
by Joanna Duda-Goławska, Aleksander Rogowski, Zuzanna Laudańska, Jarosław Żygierewicz and Przemysław Tomalski
Sensors 2024, 24(23), 7809; https://doi.org/10.3390/s24237809 - 6 Dec 2024
Viewed by 463
Abstract
The efficient classification of body position is crucial for monitoring infants’ motor development. It may fast-track the early detection of developmental issues related not only to the acquisition of motor milestones but also to postural stability and movement patterns. In turn, this may [...] Read more.
The efficient classification of body position is crucial for monitoring infants’ motor development. It may fast-track the early detection of developmental issues related not only to the acquisition of motor milestones but also to postural stability and movement patterns. In turn, this may facilitate and enhance opportunities for early intervention that are crucial for promoting healthy growth and development. The manual classification of human body position based on video recordings is labour-intensive, leading to the adoption of Inertial Motion Unit (IMU) sensors. IMUs measure acceleration, angular velocity, and magnetic field intensity, enabling the automated classification of body position. Many research teams are currently employing supervised machine learning classifiers that utilise hand-crafted features for data segment classification. In this study, we used a longitudinal dataset of IMU recordings made in the lab in three different play activities of infants aged 4–12 months. The classification was conducted based on manually annotated video recordings. We found superior performance of the CatBoost Classifier over the Random Forest Classifier in the task of classifying five positions based on IMU sensor data from infants, yielding excellent classification accuracy of the Supine (97.7%), Sitting (93.5%), and Prone (89.9%) positions. Moreover, using data ablation experiments and analysing the SHAP (SHapley Additive exPlanations) values, the study assessed the importance of various groups of features from both the time and frequency domains. The results highlight that both accelerometer and magnetometer data, especially their statistical characteristics, are critical contributors to improving the accuracy of body position classification. Full article
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<p>Placement of all sensors on the infant and caregiver. The Developmental Neurocognition Laboratory Babylab provided the photos at the Institute of Psychology, Polish Academy of Sciences, with written consent from the caregiver for publication.</p>
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<p>Percentage of total visit duration spent in various positions for each infant at the 4-, 6-, 9-, and 12-month time points. Each coloured dot represents the contribution of an individual infant. The numbers in brackets at the bottom of each plot indicate the number of infants that did not show a given position at a given time point. These plots illustrate changes in the distribution of postural behaviours as infants develop their gross motor skills over time.</p>
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<p>Illustration of sensor readings from tri-axial accelerometer, gyroscope, and magnetometer positioned on the left leg of a 12-month-old infant. The data are displayed across three axes (X, Y, Z) for each sensor type, showing variations in movement patterns associated with different body positions.</p>
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<p>Sliding windows of 2 s with a 1-s overlap, showing assigned position fragments. Blue windows represent the Supine class, and teal windows indicate the Prone class. Windows where less than 75% of samples are consistently assigned the same position label were not assigned to any class.</p>
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<p>Composition of feature groups. Five distinct feature groups were extracted from each type of signal, including XYZ signals.</p>
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<p>Comparison of F1 scores for Random Forest and CatBoost models across three sensors and five postures. Parallel coordinate plots highlight the performance differences, with green indicating superior performance by CatBoost and red indicating better performance by Random Forest. Each line corresponds to one fold in the cross-validation. Boxplots provide a visual summary of F1 score distributions for each model and posture. Statistical significance is indicated using FDR-adjusted <span class="html-italic">p</span>-values (the asterisks indicate the significance level * <span class="html-italic">p</span> &lt; 0.05) derived from the Friedman test. The colour bar reflects the mean F1 scores for each posture, offering an overview of model performance across various conditions.</p>
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<p>A confusion matrix was obtained based on the predictions of CatBoost classifiers trained on the combined set of parameters for two pairs of sensors: Trunk and Legs. The percentage of actual classifications is displayed at the top, with average counts across the five folds and their standard error included in parentheses. The colour scale corresponds to the percentage of the actual position, providing a visual representation of classification accuracy.</p>
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<p>F1 score change for Catboost models using only one feature group at a time relative to models using all feature groups for two pairs of sensors: Trunk and Legs.</p>
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<p>F1 score change for models excluding one feature group at a time relative to the CatBoost model using all feature groups for two pairs of sensors: Trunk and Legs.</p>
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<p>The sum of |SHAP| values across five folds illustrates the features with the highest total impact on the model, categorised by different signals and features. This figure highlights the most influential features in the model’s predictions, with larger-sum |SHAP| values indicating a more significant impact.</p>
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<p>Mean |SHAP| values across five folds illustrate the features with the highest impact on the model, categorised by different signals and features. Presented values are multiplied by 1 × 10<sup>5</sup> for clarity. This figure highlights the most influential features in the model’s predictions, with elevated SHAP values indicating a more significant impact.</p>
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<p>Illustration of the correlation between the annotated (actual) and predicted time spent in five distinct positions across study sessions. The x-axis represents the real percentage of time spent in each position, while the y-axis shows the corresponding predicted percentage. Each point in the plot corresponds to a specific infant in a position during one study session, with a line of best fit illustrating the correlation between the real and predicted values. The closer the points align with the line, the more accurate the predictions. Based on the CatBoost model for two pairs of sensors, Trunk and Legs.</p>
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<p>Visual representation of train–test splitting and 5-fold cross-validation techniques for assessing model performance and optimising hyperparameters. Turquoise indicates the training set, and blue is the test set.</p>
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<p>F1 values averaged across five folds and corresponding standard error of mean, for pairs of sensors placed on the Trunk; Trunk and Legs; and Trunk, Legs, and Arms for CatBoost and Random Forest.</p>
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<p>Illustration of the correlation between the annotated (actual) and predicted time spent in five distinct positions across study sessions. The x-axis represents the real percentage of time spent in each position, while the y-axis shows the corresponding predicted percentage. Each point in the plot corresponds to a specific infant in a position during one study session, with a line of best fit illustrating the correlation between the real and predicted values. The closer the points align with the line, the more accurate the predictions. Based on the model for two pairs of sensors: Trunk and Legs.</p>
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21 pages, 3342 KiB  
Article
Integrating Remote Photoplethysmography and Machine Learning on Multimodal Dataset for Noninvasive Heart Rate Monitoring
by Rinaldi Anwar Buyung, Alhadi Bustamam and Muhammad Remzy Syah Ramazhan
Sensors 2024, 24(23), 7537; https://doi.org/10.3390/s24237537 - 26 Nov 2024
Viewed by 534
Abstract
Non-contact heart monitoring is crucial in advancing telemedicine, fitness tracking, and mass screening. Remote photoplethysmography (rPPG) is a non-contact technique to obtain information about heart pulse by analyzing the changes in the light intensity reflected or absorbed by the skin during the blood [...] Read more.
Non-contact heart monitoring is crucial in advancing telemedicine, fitness tracking, and mass screening. Remote photoplethysmography (rPPG) is a non-contact technique to obtain information about heart pulse by analyzing the changes in the light intensity reflected or absorbed by the skin during the blood circulation cycle. However, this technique is sensitive to environmental lightning and different skin pigmentation, resulting in unreliable results. This research presents a multimodal approach to non-contact heart rate estimation by combining facial video and physical attributes, including age, gender, weight, height, and body mass index (BMI). For this purpose, we collected local datasets from 60 individuals containing a 1 min facial video and physical attributes such as age, gender, weight, and height, and we derived the BMI variable from the weight and height. We compare the performance of two machine learning models, support vector regression (SVR) and random forest regression on the multimodal dataset. The experimental results demonstrate that incorporating a multimodal approach enhances model performance, with the random forest model achieving superior results, yielding a mean absolute error (MAE) of 3.057 bpm, a root mean squared error (RMSE) of 10.532 bpm, and a mean absolute percentage error (MAPE) of 4.2% that outperforms the state-of-the-art rPPG methods. These findings highlight the potential for interpretable, non-contact, real-time heart rate measurement systems to contribute effectively to applications in telemedicine and mass screening. Full article
(This article belongs to the Special Issue Innovative Sensors and IoT for AI-Enabled Smart Healthcare)
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<p>Illustration of remote photoplethysmography.</p>
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<p>Hyperplane problem of the SVR.</p>
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<p>Random Forest Regression model.</p>
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<p>Dataset used in this study. (<b>a</b>) Gender distribution; (<b>b</b>) Heart rate distribution by gender; (<b>c</b>) Heart rate distribution by category; (<b>d</b>) Height vs. Heart Rate by Gender; (<b>e</b>) Weight vs. heart rate by gender; (<b>f</b>) BMI vs. heart rate by gender.</p>
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<p>Region of interest used in this study.</p>
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<p>5-fold cross-validation.</p>
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<p>Workflow of the proposed method.</p>
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<p>Feature importance.</p>
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<p>Shapley additive explanations.</p>
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<p>Partial dependence plot for random forest model.</p>
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<p>Comparison with state-of-the-art methods.</p>
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28 pages, 1866 KiB  
Article
Human Operator Mental Fatigue Assessment Based on Video: ML-Driven Approach and Its Application to HFAVD Dataset
by Walaa Othman, Batol Hamoud, Nikolay Shilov and Alexey Kashevnik
Appl. Sci. 2024, 14(22), 10510; https://doi.org/10.3390/app142210510 - 14 Nov 2024
Viewed by 817
Abstract
The detection of the human mental fatigue state holds immense significance due to its direct impact on work efficiency, specifically in system operation control. Numerous approaches have been proposed to address the challenge of fatigue detection, aiming to identify signs of fatigue and [...] Read more.
The detection of the human mental fatigue state holds immense significance due to its direct impact on work efficiency, specifically in system operation control. Numerous approaches have been proposed to address the challenge of fatigue detection, aiming to identify signs of fatigue and alert the individual. This paper introduces an approach to human mental fatigue assessment based on the application of machine learning techniques to the video of a working operator. For validation purposes, the approach was applied to a dataset, “Human Fatigue Assessment Based on Video Data” (HFAVD) integrating video data with features computed by using our computer vision deep learning models. The incorporated features encompass head movements represented by Euler angles (roll, pitch, and yaw), vital signs (blood pressure, heart rate, oxygen saturation, and respiratory rate), and eye and mouth states (blinking and yawning). The integration of these features eliminates the need for the manual calculation or detection of these parameters, and it obviates the requirement for sensors and external devices, which are commonly employed in existing datasets. The main objective of our work is to advance research in fatigue detection, particularly in work and academic settings. For this reason, we conducted a series of experiments by utilizing machine learning techniques to analyze the dataset and assess the fatigue state based on the features predicted by our models. The results reveal that the random forest technique consistently achieved the highest accuracy and F1-score across all experiments, predominantly exceeding 90%. These findings suggest that random forest is a highly promising technique for this task and prove the strong connection and association among the predicted features used to annotate the videos and the state of fatigue. Full article
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<p>Timeline of each session.</p>
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<p>Models used to label the videos.</p>
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<p>The overall scheme used for detecting the fatigue state.</p>
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<p>The relationship between the mental performance and the inverse of fatigue (red dotted line denotes an example threshold value separating fatigued and not fatigued states).</p>
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<p>The relationship between the threshold and the F1-score.</p>
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26 pages, 4018 KiB  
Article
A MediaPipe Holistic Behavior Classification Model as a Potential Model for Predicting Aggressive Behavior in Individuals with Dementia
by Ioannis Galanakis, Rigas Filippos Soldatos, Nikitas Karanikolas, Athanasios Voulodimos, Ioannis Voyiatzis and Maria Samarakou
Appl. Sci. 2024, 14(22), 10266; https://doi.org/10.3390/app142210266 - 7 Nov 2024
Viewed by 853
Abstract
This paper introduces a classification model that detects and classifies argumentative behaviors between two individuals by utilizing a machine learning application, based on the MediaPipe Holistic model. The approach involves the distinction between two different classes based on the behavior of two individuals, [...] Read more.
This paper introduces a classification model that detects and classifies argumentative behaviors between two individuals by utilizing a machine learning application, based on the MediaPipe Holistic model. The approach involves the distinction between two different classes based on the behavior of two individuals, argumentative and non-argumentative behaviors, corresponding to verbal argumentative behavior. By using a dataset extracted from video frames of hand gestures, body stance and facial expression, and by using their corresponding landmarks, three different classification models were trained and evaluated. The results indicate that Random Forest Classifier outperformed the other two by classifying argumentative behaviors with 68.07% accuracy and non-argumentative behaviors with 94.18% accuracy, correspondingly. Thus, there is future scope for advancing this classification model to a prediction model, with the aim of predicting aggressive behavior in patients suffering with dementia before their onset. Full article
(This article belongs to the Special Issue Application of Artificial Intelligence in Image Processing)
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<p>Argumentative image dataset sample.</p>
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<p>Non-argumentative image dataset sample.</p>
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<p>Cross-validation metrics for the three models.</p>
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<p>AUC scores of the three trained models. A model that makes random guesses (practically a model with no discriminative power), is represented by the diagonal dashed blue line that extends from the bottom left (0, 0) to the top right (1, 1). The ROC curve for any model that outperforms the random one will be above this diagonal line.</p>
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<p>Confusion matrix of Random Forest Classifier after training.</p>
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<p>Confusion matrix of Gradient Boosting after training.</p>
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<p>Confusion matrix of Ridge Classifier after training.</p>
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<p>Learning curve of Random Forest Classifier after training.</p>
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<p>Learning curve for Gradient Boosting after training.</p>
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<p>Learning curve of Ridge Classifier after training.</p>
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<p>Paired <span class="html-italic">t</span>-test statistic results across all models and metrics.</p>
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<p>Confusion Matrix of Random Forest Classifier after testing.</p>
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<p>ROC AUC score of Random Forest Classifier after testing.</p>
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<p>Final model evaluation metrics.</p>
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<p>Probability range/count of correct argumentative and non-argumentative predictions per 0.1 accuracy range, with 1.0 being the perfect accuracy score.</p>
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19 pages, 3429 KiB  
Article
A Machine Learning Framework for Classroom EEG Recording Classification: Unveiling Learning-Style Patterns
by Rajamanickam Yuvaraj, Shivam Chadha, A. Amalin Prince, M. Murugappan, Md. Sakib Bin Islam, Md. Shaheenur Islam Sumon and Muhammad E. H. Chowdhury
Algorithms 2024, 17(11), 503; https://doi.org/10.3390/a17110503 - 4 Nov 2024
Viewed by 671
Abstract
Classroom EEG recordings classification has the capacity to significantly enhance comprehension and learning by revealing complex neural patterns linked to various cognitive processes. Electroencephalography (EEG) in academic settings allows researchers to study brain activity while students are in class, revealing learning preferences. The [...] Read more.
Classroom EEG recordings classification has the capacity to significantly enhance comprehension and learning by revealing complex neural patterns linked to various cognitive processes. Electroencephalography (EEG) in academic settings allows researchers to study brain activity while students are in class, revealing learning preferences. The purpose of this study was to develop a machine learning framework to automatically classify different learning-style EEG patterns in real classroom environments. Method: In this study, a set of EEG features was investigated, including statistical features, fractal dimension, higher-order spectra, entropy, and a combination of all sets. Three different machine learning classifiers, random forest (RF), K-nearest neighbor (KNN), and multilayer perceptron (MLP), were used to evaluate the performance. The proposed framework was evaluated on the real classroom EEG dataset, involving EEG recordings featuring different teaching blocks: reading, discussion, lecture, and video. Results: The findings revealed that statistical features are the most sensitive feature metric in distinguishing learning patterns from EEG. The statistical features and RF classifier method tested in this study achieved an overall best average accuracy of 78.45% when estimated by fivefold cross-validation. Conclusions: Our results suggest that EEG time domain statistics have a substantial role and are more reliable for internal state classification. This study might be used to highlight the importance of using EEG signals in the education context, opening the path for educational automation research and development. Full article
(This article belongs to the Special Issue Supervised and Unsupervised Classification Algorithms (2nd Edition))
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<p>Flowchart of the proposed machine learning framework to classify classroom EEG recordings.</p>
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<p>(<b>A</b>) Students’ brain waves can be measured using EEG in a high school classroom from Dikker et al. [<a href="#B20-algorithms-17-00503" class="html-bibr">20</a>] and (<b>B</b>) the brain waves of students can exhibit rapid synchronization with those of their peers, a phenomenon observed in more engaged students (<b>left</b>). A lack of synchronicity with their peers (<b>right</b>) was observed among less engaged students.</p>
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<p>Figure from Dikker et al. [<a href="#B20-algorithms-17-00503" class="html-bibr">20</a>], explaining the setup of the data collection process. Data for the four methods are taken for this study, which includes ’teacher reads aloud’, ’video’, teacher lectures’, and ’group discussion’. The respective session time for each method is also mentioned in the figure.</p>
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<p>F-values bar plot for each significant feature from ANOVA. Green color bar denotes the lowest F-value.</p>
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<p>Comparison of classification performance with various features (in terms of accuracy). <a href="#algorithms-17-00503-f005" class="html-fig">Figure 5</a> shows the classification performance, reflecting the performance of the statistical features using RF, KNN, and MLP classifiers, illustrating the time-domain statistical characteristics of EEG signals that can effectively discriminate reading, discussion, lecture, and video learning-style patterns. The confusion matrix, which is illustrated in <a href="#algorithms-17-00503-f006" class="html-fig">Figure 6</a>a, provided further insights into the performance results in accurately categorizing instances. Significantly, accurate classifications were made for 341 occurrences of discussion, 384 occurrences of lecture, 347 occurrences of reading, and 375 occurrences of video. Nevertheless, the model demonstrated its shortcomings through the misclassification of instances in diverse contexts. For example, 72 occurrences of discussion were incorrectly classified as lecture, which suggests areas that could be enhanced.</p>
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<p>Confusion matrix of a fold using statistical features obtained from (<b>a</b>) RF, (<b>b</b>) KNN, and (<b>c</b>) MLP. The diagonal elements are the correctly recognized samples.</p>
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<p>Topographical maps of different learning styles. (<b>a</b>) Reading, (<b>b</b>) video, (<b>c</b>) lecture, (<b>d</b>) discussion.</p>
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<p>Statistical results of two-tailed paired <span class="html-italic">t</span>-test. * denotes <span class="html-italic">p</span> &lt; 0.0001.</p>
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16 pages, 12159 KiB  
Article
LGNMNet-RF: Micro-Expression Detection Using Motion History Images
by Matthew Kit Khinn Teng, Haibo Zhang and Takeshi Saitoh
Algorithms 2024, 17(11), 491; https://doi.org/10.3390/a17110491 - 1 Nov 2024
Viewed by 546
Abstract
Micro-expressions are very brief, involuntary facial expressions that reveal hidden emotions, lasting less than a second, while macro-expressions are more prolonged facial expressions that align with a person’s conscious emotions, typically lasting several seconds. Micro-expressions are difficult to detect in lengthy videos because [...] Read more.
Micro-expressions are very brief, involuntary facial expressions that reveal hidden emotions, lasting less than a second, while macro-expressions are more prolonged facial expressions that align with a person’s conscious emotions, typically lasting several seconds. Micro-expressions are difficult to detect in lengthy videos because they have tiny amplitudes, short durations, and frequently coexist alongside macro-expressions. Nevertheless, micro- and macro-expression analysis has sparked interest in researchers. Existing methods use optical flow features to capture the temporal differences. However, these optical flow features are limited to two successive images only. To address this limitation, this paper proposes LGNMNet-RF, which integrates a Lite General Network with MagFace CNN and a Random Forest classifier to predict micro-expression intervals. Our approach leverages Motion History Images (MHI) to capture temporal patterns across multiple frames, offering a more comprehensive representation of facial dynamics than optical flow-based methods, which are restricted to two successive frames. The novelty of our approach lies in the combination of MHI with MagFace CNN, which improves the discriminative power of facial micro-expression detection, and the use of a Random Forest classifier to enhance interval prediction accuracy. The evaluation results show that this method outperforms baseline techniques, achieving micro-expression F1-scores of 0.3019 on CAS(ME)2 and 0.3604 on SAMM-LV. The results of our experiment indicate that MHI offers a viable alternative to optical flow-based methods for micro-expression detection. Full article
(This article belongs to the Special Issue Supervised and Unsupervised Classification Algorithms (2nd Edition))
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<p>Illustration of LGNMNet-RF Overall Architecture.</p>
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<p>Illustration of Detailed LGNMNet-RF Architecture.</p>
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<p>Examples of facial edge features detected using XDoG filter.</p>
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<p>Examples of MHI generated from XDoG edge detected images.</p>
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<p>Illustration of <math display="inline"><semantics> <msup> <mi mathvariant="script">R</mi> <mo>′</mo> </msup> </semantics></math> pseudo-labelling with temporal extension of <span class="html-italic">k</span> = 6.</p>
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24 pages, 2431 KiB  
Article
Identifying Tampered Radio-Frequency Transmissions in LoRa Networks Using Machine Learning
by Nurettin Selcuk Senol, Amar Rasheed, Mohamed Baza and Maazen Alsabaan
Sensors 2024, 24(20), 6611; https://doi.org/10.3390/s24206611 - 14 Oct 2024
Cited by 1 | Viewed by 894
Abstract
Long-range networks, renowned for their long-range, low-power communication capabilities, form the backbone of many Internet of Things systems, enabling efficient and reliable data transmission. However, detecting tampered frequency signals poses a considerable challenge due to the vulnerability of LoRa devices to radio-frequency interference [...] Read more.
Long-range networks, renowned for their long-range, low-power communication capabilities, form the backbone of many Internet of Things systems, enabling efficient and reliable data transmission. However, detecting tampered frequency signals poses a considerable challenge due to the vulnerability of LoRa devices to radio-frequency interference and signal manipulation, which can undermine both data integrity and security. This paper presents an innovative method for identifying tampered radio frequency transmissions by employing five sophisticated anomaly detection algorithms—Local Outlier Factor, Isolation Forest, Variational Autoencoder, traditional Autoencoder, and Principal Component Analysis within the framework of a LoRa-based Internet of Things network structure. The novelty of this work lies in applying image-based tampered frequency techniques with these algorithms, offering a new perspective on securing LoRa transmissions. We generated a dataset of over 26,000 images derived from real-world experiments with both normal and manipulated frequency signals by splitting video recordings of LoRa transmissions into frames to thoroughly assess the performance of each algorithm. Our results demonstrate that Local Outlier Factor achieved the highest accuracy of 97.78%, followed by Variational Autoencoder, traditional Autoencoder and Principal Component Analysis at 97.27%, and Isolation Forest at 84.49%. These findings highlight the effectiveness of these methods in detecting tampered frequencies, underscoring their potential for enhancing the reliability and security of LoRa networks. Full article
(This article belongs to the Special Issue AI-Driven Cybersecurity in IoT-Based Systems)
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<p>The number of active connections for both Internet of Things and non-IoT devices worldwide from 2010 to 2025 is measured in billions [<a href="#B3-sensors-24-06611" class="html-bibr">3</a>].</p>
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<p>Experimental setup for data collection using HackRF for frequency manipulation. The system consists of two MKRWAN 1310 devices for wireless signal transmission and reception, interfaced with computers for monitoring and control [<a href="#B23-sensors-24-06611" class="html-bibr">23</a>].</p>
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<p>HackRf have been utilized for manipulation of the system in <a href="#sensors-24-06611-f002" class="html-fig">Figure 2</a>. A software-defined radio (SDR) device, the HackRF, can send and receive radio signals in the 1 MHz to 6 GHz frequency range.</p>
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<p>Flowchart depicting the methodology for image-based anomaly detection using multiple machine learning models.</p>
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<p>Anomaly scores distribution for isolation forest.</p>
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<p>Block diagram of a jamming signal generation flowgraph in GNU Radio.</p>
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<p>Interface of the jamming signal generator.</p>
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<p>Anomaly scores distribution for LOF.</p>
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<p>Confusion matrices showing the performance of five anomaly detection algorithms—(<b>a</b>) Autoencoder, (<b>b</b>) Isolation Forest, (<b>c</b>) Variational Autoencoder, (<b>d</b>) LOF, and (<b>e</b>) Principal Component Analysis (PCA)—in classifying normal and anomalous data. Darker shades represent correct classifications (true positives and true negatives), while lighter shades show misclassifications (false positives and false negatives).</p>
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<p>ROC curves for traditional (<b>a</b>) autoencoder, (<b>b</b>) isolation forest and (<b>c</b>) variational autoencoder.</p>
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<p>ROC curves for (<b>a</b>) LOF and (<b>b</b>) Principal Component Analysis (PCA).</p>
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24 pages, 1208 KiB  
Article
Text Analytics on YouTube Comments for Food Products
by Maria Tsiourlini, Katerina Tzafilkou, Dimitrios Karapiperis and Christos Tjortjis
Information 2024, 15(10), 599; https://doi.org/10.3390/info15100599 - 30 Sep 2024
Viewed by 1249
Abstract
YouTube is a popular social media platform in the contemporary digital landscape. The primary focus of this study is to explore the underlying sentiment in user comments about food-related videos on YouTube, specifically within two pivotal food categories: plant-based and hedonic product. We [...] Read more.
YouTube is a popular social media platform in the contemporary digital landscape. The primary focus of this study is to explore the underlying sentiment in user comments about food-related videos on YouTube, specifically within two pivotal food categories: plant-based and hedonic product. We labeled comments using sentiment lexicons such as TextBlob, VADER, and Google’s Sentiment Analysis (GSA) engine. Comment sentiment was classified using advanced Machine-Learning (ML) algorithms, namely Support Vector Machines (SVM), Multinomial Naive Bayes, Random Forest, Logistic Regression, and XGBoost. The evaluation of these models encompassed key macro average metrics, including accuracy, precision, recall, and F1 score. The results from GSA showed a high accuracy level, with SVM achieving 93% accuracy in the plant-based dataset and 96% in the hedonic dataset. In addition to sentiment analysis, we delved into user interactions within the two datasets, measuring crucial metrics, such as views, likes, comments, and engagement rate. The findings illuminate significantly higher levels of views, likes, and comments in the hedonic food dataset, but the plant-based dataset maintains a superior overall engagement rate. Full article
(This article belongs to the Special Issue 2nd Edition of Information Retrieval and Social Media Mining)
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<p>Comparison of TextBlob, VADER and GSA on Plant-Based Dataset.</p>
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<p>Comparison of TextBlob, VADER, and GSA on hedonic dataset.</p>
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<p>Comparison of TextBlob, VADER, and GSA using the samples from the plant-based dataset.</p>
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<p>Comparison of TextBlob, VADER, and GSA using the samples from the hedonic dataset.</p>
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<p>Confusion matrices of Support Vector Machine and Logistic Regression in hedonic dataset.</p>
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<p>Correlations between comment length and likes, and also between comment length and reply count in both plant-based (<b>a</b>) and hedonic (<b>b</b>) datasets.</p>
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<p>User Activity for comments in plant-based (<b>a</b>) and hedonic (<b>b</b>) datasets. Note, 0 = Monday, 1 = Tuesday, 2 = Wednesday, 3 = Thursday, 4 = Friday, 5 = Saturday, 6 = Sunday, while in the right visualizations 0 = midnight, 1 = 1:00 a.m., etc.</p>
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22 pages, 1476 KiB  
Article
An Optimal Feature Selection Method for Human Activity Recognition Using Multimodal Sensory Data
by Tazeem Haider, Muhammad Hassan Khan and Muhammad Shahid Farid
Information 2024, 15(10), 593; https://doi.org/10.3390/info15100593 - 29 Sep 2024
Viewed by 892
Abstract
Recently, the research community has taken great interest in human activity recognition (HAR) due to its wide range of applications in different fields of life, including medicine, security, and gaming. The use of sensory data for HAR systems is most common because the [...] Read more.
Recently, the research community has taken great interest in human activity recognition (HAR) due to its wide range of applications in different fields of life, including medicine, security, and gaming. The use of sensory data for HAR systems is most common because the sensory data are collected from a person’s wearable device sensors, thus overcoming the privacy issues being faced in data collection through video cameras. Numerous systems have been proposed to recognize some common activities of daily living (ADLs) using different machine learning, image processing, and deep learning techniques. However, the existing techniques are computationally expensive, limited to recognizing short-term activities, or require large datasets for training purposes. Since an ADL is made up of a sequence of smaller actions, recognizing them directly from raw sensory data is challenging. In this paper, we present a computationally efficient two-level hierarchical framework for recognizing long-term (composite) activities, which does not require a very large dataset for training purposes. First, the short-term (atomic) activities are recognized from raw sensory data, and the probabilistic atomic score of each atomic activity is calculated relative to the composite activities. In the second step, the optimal features are selected based on atomic scores for each composite activity and passed to the two classification algorithms: random forest (RF) and support vector machine (SVM) due to their well-documented effectiveness for human activity recognition. The proposed method was evaluated on the publicly available CogAge dataset that contains 890 instances of 7 composite and 9700 instances of 61 atomic activities. The data were collected from eight sensors of three wearable devices: a smartphone, a smartwatch, and smart glasses. The proposed method achieved the accuracy of 96.61% and 94.1% by random forest and SVM classifiers, respectively, which shows a remarkable increase in the classification accuracy of existing HAR systems for this dataset. Full article
(This article belongs to the Section Artificial Intelligence)
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Graphical abstract

Graphical abstract
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<p>Standard sequence of steps for human activity recognition from raw sensory data: The first two boxes in the figure depict the sensory signals, where the <span class="html-italic">x</span>-axis represents the time and the <span class="html-italic">y</span>-axis represents the information provided by the respective sensor, e.g., accelerometers measure a changing acceleration (in meters) on the sensor, gyroscopes measure changing angular motion, etc.</p>
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<p>Classification of existing features encoding techniques for HAR systems.</p>
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<p>The proposed method works in a two-level hierarchical manner: First, the atomic activities are recognized directly from raw sensory data and the atomic score of each atomic activity is calculated. In the second step, the optimal features are selected on the basis of atomic score percentage and fed to the classifiers for composite activities recognition. The first box in the figure depicts the sensory signals, where the <span class="html-italic">x</span>-axis represents the time and the <span class="html-italic">y</span>-axis represents the information provided by the respective sensor, e.g., accelerometers measure a changing acceleration (in meters) on the sensor, gyroscopes measure changing angular motion, etc.</p>
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<p>An illustration of decomposition of time series data into sequences and subsequences. The first two boxes in the figure depict the sensory signals, where the <span class="html-italic">x</span>-axis represents the time and the <span class="html-italic">y</span>-axis represents the information provided by the respective sensor, e.g., accelerometers measure a changing acceleration (in meters) on the sensor, gyroscopes measure changing angular motion, etc.</p>
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<p>Codebook-based feature computation process. The codebook is constructed by grouping similar subsequences using a k-means algorithm. The center of each codebook is a codeword. The features are computed by assigning each subsequence to the most similar codeword. The first two boxes in the figure depict the sensory signals, where the <span class="html-italic">x</span>-axis represents the time and the <span class="html-italic">y</span>-axis represents the information provided by the respective sensor, e.g., accelerometers measure a changing acceleration (in meters) on the sensor, gyroscopes measure changing angular motion, etc.</p>
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<p>Results of one-vs.-all classification of composite activities. The performance of the proposed method is measured using two matrices, namely, accuracy and <math display="inline"><semantics> <msub> <mi>F</mi> <mn>1</mn> </msub> </semantics></math> score.</p>
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<p>The performance comparison of proposed one-vs.-all classification with the results computed in [<a href="#B6-information-15-00593" class="html-bibr">6</a>]. The proposed model consistently performed better for each composite activity recognition.</p>
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<p>Accuracy of SVM and RF classifiers for composite activities recognition on different percentages of atomic score. The graph shows that both the classifiers performed best for 90% atomic score as their input features.</p>
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<p>An illustration of training and testing loss of both classifiers used in this study: (<b>a</b>) SVM loss curve, (<b>b</b>) random forest loss curve.</p>
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18 pages, 5642 KiB  
Article
Well-Being and Sustainable Utilization of Forest Environment with Diverse Vegetation Distributions
by Yu Gao, Yingna Zhang, Weikang Zhang, Huan Meng, Zhi Zhang and Tong Zhang
Sustainability 2024, 16(19), 8469; https://doi.org/10.3390/su16198469 - 29 Sep 2024
Viewed by 699
Abstract
Forest landscape space is the basic unit of forest landscape resources. Healthy forest landscape resources can not only improve the sustainable cycle of forest ecological service function, but also have a positive impact on human health and well-being. Evidence supports the view that [...] Read more.
Forest landscape space is the basic unit of forest landscape resources. Healthy forest landscape resources can not only improve the sustainable cycle of forest ecological service function, but also have a positive impact on human health and well-being. Evidence supports the view that the forest environment is beneficial to people’s health, and further discussion of the dose response between environmental attributes and physical and mental recovery has been widely carried out by scholars. As an important component of environmental attributes, it is necessary to clarify the relationship between vegetation distribution and users’ health in order to better plan, design, and utilize forest environmental resources. This study mainly used the virtual immersive forest environment video in VR, and used the difference test in SPSS 23.0 to clarify whether the distribution of vegetation in the forest environment will affect the physiological and psychological recovery effect of users. The main results are as follows: (1) Experiencing the forest environment can promote users’ physiological and psychological health, and its recovery effect is significantly better than the indoor environment (p < 0.05). (2) The distribution of vegetation in the forest environment will affect users’ physiological and psychological recovery effect. Among them, in the cluster and randomly distributed forest environments, the relaxation and concentration of users can be improved mainly by alleviating their negative emotions. In the evenly distributed forest environment, users mainly achieve the purpose of relaxation by improving their vitality and positive emotions. These results show that the distribution of vegetation is one of the factors for the restoration of forest environment. In the future design and management of the forest environment, the health and well-being of users can be effectively enhanced by getting involved with the vegetation distribution in the site, aiming to provide a scientific basis for the promotion of the rehabilitation function of forest landscape space and its sustainable utilization, thus promoting the sustainable development of forest resources and improving people’s quality of life. Full article
(This article belongs to the Section Health, Well-Being and Sustainability)
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<p>Study areas and study materials, created by Yu Gao (Shenyang Agricultural University). Note: the forest environment in this study mainly refers to the plant space composed of trees, which has beautiful scenery visually and can provide visitors with entertainment, viewing, learning, rest, and other activities functionally. (<b>A</b>): study areas. (<b>B</b>): Survey drawings and field survey photos. (<b>C</b>): study materials.</p>
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<p>Experimental flow chart and experimental photos, created by Yu Gao (Shenyang Agricultural University).</p>
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<p>Differences of users’ physiological and psychological indices between baseline and pre-test. Note: *: <span class="html-italic">p</span> &lt; 0.05; **: <span class="html-italic">p</span> &lt; 0.01.</p>
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<p>Restoration effects and differences between indoor environment and forest environment. Note: *: <span class="html-italic">p</span> &lt; 0.05; **: <span class="html-italic">p</span> &lt; 0.01.</p>
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<p>Restoration effect and difference of users in forest environment with different vegetation distribution. Note: *: <span class="html-italic">p</span> &lt; 0.05; **: <span class="html-italic">p</span> &lt; 0.01.</p>
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13 pages, 3143 KiB  
Article
Ensemble Techniques for Robust Fake News Detection: Integrating Transformers, Natural Language Processing, and Machine Learning
by Mohammed Al-alshaqi, Danda B. Rawat and Chunmei Liu
Sensors 2024, 24(18), 6062; https://doi.org/10.3390/s24186062 - 19 Sep 2024
Cited by 1 | Viewed by 2632
Abstract
The proliferation of fake news across multiple modalities has emerged as a critical challenge in the modern information landscape, necessitating advanced detection methods. This study proposes a comprehensive framework for fake news detection integrating text, images, and videos using machine learning and deep [...] Read more.
The proliferation of fake news across multiple modalities has emerged as a critical challenge in the modern information landscape, necessitating advanced detection methods. This study proposes a comprehensive framework for fake news detection integrating text, images, and videos using machine learning and deep learning techniques. The research employs a dual-phased methodology, first analyzing textual data using various classifiers, then developing a multimodal approach combining BERT for text analysis and a modified CNN for visual data. Experiments on the ISOT fake news dataset and MediaEval 2016 image verification corpus demonstrate the effectiveness of the proposed models. For textual data, the Random Forest classifier achieved 99% accuracy, outperforming other algorithms. The multimodal approach showed superior performance compared to baseline models, with a 3.1% accuracy improvement over existing multimodal techniques. This research contributes to the ongoing efforts to combat misinformation by providing a robust, adaptable framework for detecting fake news across different media formats, addressing the complexities of modern information dissemination and manipulation. Full article
(This article belongs to the Section Internet of Things)
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<p>Example images data from MediaEval 2016 dataset.</p>
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<p>Samples from a multi-modal dataset.</p>
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<p>Stepwise architecture of unimodal methodology.</p>
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<p>Proposed BERT-based CNN model.</p>
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<p>Architecture diagram for multi-modal methodology (proposed model).</p>
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<p>Accuracy of proposed model.</p>
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<p>Loss of proposed model.</p>
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18 pages, 7463 KiB  
Article
Comparison of Three Indoor Viewing Models and On-Site Experiences to Assess Visual Landscape Perception in Urban Forests
by Jinyu Zhang, Xiuli Diao, Zhe Zhang, Jin Wang, Zijing Lu, Yu Wang, Yanxia Mu and Wenyue Lin
Forests 2024, 15(9), 1566; https://doi.org/10.3390/f15091566 - 6 Sep 2024
Viewed by 884
Abstract
Contacting forests in different ways and conducting public perception evaluations of forests are important ways to evaluate forest construction. In order to explore the differences between on-site and manual post-collection indoor evaluations in forest landscape surveys, we combined subjective evaluation and objective indicator [...] Read more.
Contacting forests in different ways and conducting public perception evaluations of forests are important ways to evaluate forest construction. In order to explore the differences between on-site and manual post-collection indoor evaluations in forest landscape surveys, we combined subjective evaluation and objective indicator monitoring (eye movement characteristics, physiological indicators) based on different forest observation scales. We compared and analyzed the suitability of the following four visual approaches: on-site observation, manual collection, followed by indoor viewing normal photos (NP), videos (VD), and virtual reality panoramas (VR), in terms of public preference, perception, and psychological emotion. The results showed the following: (1) Compared with the on-site evaluation, the three indoor visual approaches (NP, VD, and VR) showed no significant difference in “landscape beauty” and “spatial perception”. VD also showed no significant difference in “landscape perception”, “seeing”, and “plant color preference” and had the strongest substitution for site evaluation. (2) With the exception of small-scale landscapes, in which on-site evaluation showed no substitutability, for the rest of the landscape scales, each of the three indoor visual approaches showed substitutability for on-site evaluation to varying degrees. (3) When conducting physiological and psychological surveys, watching videos and VR are more ideal. In terms of eye tracking, VR is closest to on-site observation. Practice shows that video was closer to on-site observation in most landscape preferences and perceptions. VR was suitable for presenting public visual behavioral characteristics, and NP showed some advantages in landscape beauty and spatial perceptions. The findings of the study can provide a scientific basis for the selection of visual approaches in future landscape evaluation. Full article
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<p>Location of the research site.</p>
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<p>Panoramic photos of each vista used as experimental samples at four different landscape (viewing distance) scales. (Scale 1: mega-scale, ≥200 m; Scale 2: large-scale, 200–100 m; Scale 3: mid-scale, 100–50 m; Scale 4: small-scale, ≤50 m).</p>
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<p>Procedure. Notes. (<b>a</b>) Tobii Pro VR eye-tracking device (VR group), (<b>b</b>) ErgoLAB V3.0 smart wearable human factors physiological recorder; (<b>c</b>) Tobii Pro Fusion virtual reality eye-tracking device (VD group, NP group); (<b>d</b>) ErgoLAB V3.0 human-computer environment synchronization platform; (<b>e</b>) Flowchart of experimental design; (<b>f</b>) Experimental Groups. OS: On-site group, VR: Virtual reality panorama group, VD: Video group, NP: Normal photo group. (<b>g</b>) Experimental monitoring index.</p>
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<p>Means of questionnaires for different public preferences and perceptions. Notes. *: <span class="html-italic">p</span> &lt; 0.05; **: <span class="html-italic">p</span> &lt; 0.01.</p>
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<p>Means of questionnaires for different landscape scales.</p>
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<p>Heat map for different landscape scales. Notes. Since ordinary photos cover a smaller angle than other methods, the image size ratio is not guaranteed to be the same, and gray is used to fill in the unfilmed areas.</p>
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14 pages, 2866 KiB  
Article
Effect of Exposure to 2D Video of Forest Environment with Natural Forest Sound on Psychological Well-Being of Healthy Young Adults
by Emilia Janeczko, Małgorzata Woźnicka, Wojciech Kędziora, Krzysztof Janeczko, Katarzyna Śmietańska, Piotr Podziewski and Jarosław Górski
Forests 2024, 15(9), 1549; https://doi.org/10.3390/f15091549 - 2 Sep 2024
Viewed by 1212
Abstract
Background and Objectives: In recent years, there has been a significant increase in interest in the health benefits of contact with nature. The theoretical and practical aspects of this issue are constantly being investigated. It is worth noting, however, that there is a [...] Read more.
Background and Objectives: In recent years, there has been a significant increase in interest in the health benefits of contact with nature. The theoretical and practical aspects of this issue are constantly being investigated. It is worth noting, however, that there is a large group of people for whom the only available form of contact with nature can only be through images (the view outside the window, photos and films about nature), recorded sounds of nature or descriptions of nature. Research indicating how much exposure to nature in the dimension of virtual reality achieves improvements in well-being, mood and vitality is therefore urgently needed. Material and Methods: The main goal of the experiment was to examine whether watching a 20-min 2D video of forest environment or reading a textbook on forest knowledge for 20 min would bring any psychological benefits. The order of both exposures was intentionally changed (reversed) for every second participant in this study to reduce the order effect. A group of 16 volunteers, students of Warsaw University of Life Sciences, took part in the experiment. The psychological tests before and after each of the two parts of the experiment (viewing a picture with sound and reading a book) were established using five questionnaires: Profile of Mood State (POMS); Positive and Negative Affect Scale (PANAS); Restorative Outcome Scale (ROS); Subjective Vitality Scale (SVS) and State-Trait Anxiety Inventory (STAI). Results: As a result of the analyses, a 20-min viewing of a 2D video of a forest with natural sounds of nature was shown to have a positive effect on the psychological relaxation of the subjects in the form of an increase in restorativeness and vitality in the participants of the experiment, as well as a greater decrease in negative feelings, tension and anger than when reading a forest-themed book. Watching a video of a landscape can reduce tension and anger levels significantly, which can be an important guideline in relation to the interior design of public spaces and the protection of employees from the adverse effects of psychosocial working conditions, as well as the desire to stabilize anger and maintain emotional stability in everyday life. Full article
(This article belongs to the Special Issue Soundscape in Urban Forests - 2nd Edition)
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<p>Excerpt from the video used in the experiment.</p>
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<p>The simplified diagram of the experiment’s process, which ignores the fact that the order of both exposures (“Forest Self-Education” and “Virtual Forest Exposure”) was intentionally changed (reversed) for every second participant in this study to reduce the order effect.</p>
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<p>Favorable changes in positive (ΔPA) and negative (ΔNA) affect.</p>
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<p>Favorable changes in subjective restorativeness (ΔROS) and subjective vitality (ΔSVS).</p>
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<p>Favorable changes in following dimensions of mood: Tension (ΔT), Anger (ΔA), Fatigue (ΔF), Depression (ΔD), Confusion (ΔC) and Vigor (ΔV).</p>
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<p>Favorable changes in state anxiety (ΔSTAI).</p>
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19 pages, 2275 KiB  
Article
Evaluating Thermal Infrared Drone Flight Parameters on Spider Monkey Detection in Tropical Forests
by Eduardo José Pinel-Ramos, Filippo Aureli, Serge Wich, Steven Longmore and Denise Spaan
Sensors 2024, 24(17), 5659; https://doi.org/10.3390/s24175659 - 30 Aug 2024
Cited by 1 | Viewed by 1019
Abstract
Geoffroy’s spider monkeys, an endangered, fast-moving arboreal primate species with a large home range and a high degree of fission–fusion dynamics, are challenging to survey in their natural habitats. Our objective was to evaluate how different flight parameters affect the detectability of spider [...] Read more.
Geoffroy’s spider monkeys, an endangered, fast-moving arboreal primate species with a large home range and a high degree of fission–fusion dynamics, are challenging to survey in their natural habitats. Our objective was to evaluate how different flight parameters affect the detectability of spider monkeys in videos recorded by a drone equipped with a thermal infrared camera and examine the level of agreement between coders. We used generalized linear mixed models to evaluate the impact of flight speed (2, 4, 6 m/s), flight height (40, 50 m above ground level), and camera angle (−45°, −90°) on spider monkey counts in a closed-canopy forest in the Yucatan Peninsula, Mexico. Our results indicate that none of the three flight parameters affected the number of detected spider monkeys. Agreement between coders was “substantial” (Fleiss’ kappa coefficient = 0.61–0.80) in most cases for high thermal-contrast zones. Our study contributes to the development of standardized flight protocols, which are essential to obtain accurate data on the presence and abundance of wild populations. Based on our results, we recommend performing drone surveys for spider monkeys and other medium-sized arboreal mammals with a small commercial drone at a 4 m/s speed, 15 m above canopy height, and with a −90° camera angle. However, these recommendations may vary depending on the size and noise level produced by the drone model. Full article
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<p>Map of Los Arboles Tulum, Tulum, Mexico, with 2 ha lots (white lines) showing the drone take-off and landing points (white dots with a black center) and flight routes (yellow lines) over five spider monkey sleeping sites (red squares) where we tested the effect of three flight parameters on spider monkey detectability.</p>
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<p>(<b>a</b>) Drone at height H with camera pointing directly down (−90°). The value <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>D</mi> </mrow> <mrow> <mn>90</mn> </mrow> </msub> </mrow> </semantics></math> is the distance on the ground subtended by a camera with an angular field of view <span class="html-italic">θ</span>. (<b>b</b>) Side-on view of drone at height H facing toward the right, with the center of the camera field of view pointing an angle of <span class="html-italic">ϕ</span>. <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>D</mi> </mrow> <mrow> <mi>N</mi> </mrow> </msub> </mrow> </semantics></math> is the distance on the ground from directly below the drone to the nearest point of the drone’s field of view. <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>D</mi> </mrow> <mrow> <mi>N</mi> </mrow> <mrow> <mi>G</mi> </mrow> </msubsup> </mrow> </semantics></math> is the distance from the drone to this point, with G being ground. <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>D</mi> </mrow> <mrow> <mi>M</mi> </mrow> </msub> </mrow> </semantics></math> and <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>D</mi> </mrow> <mrow> <mi>F</mi> </mrow> </msub> </mrow> </semantics></math> are the distances on the ground from directly below the drone to the middle (<math display="inline"><semantics> <mrow> <msub> <mrow> <mi>D</mi> </mrow> <mrow> <mi>M</mi> </mrow> </msub> </mrow> </semantics></math>) and farthest (<math display="inline"><semantics> <mrow> <msub> <mrow> <mi>D</mi> </mrow> <mrow> <mi>F</mi> </mrow> </msub> </mrow> </semantics></math>) point on the drone’s field of view. The angle <span class="html-italic">χ</span> is an arbitrary angle between zero and <span class="html-italic">θ</span> to generalize the mathematical expressions. (<b>c</b>) Reprojected view of (<b>b</b>), rotated to show the width (W) of the field of view on the ground at the point nearest to the drone, <math display="inline"><semantics> <mrow> <msubsup> <mrow> <mi>D</mi> </mrow> <mrow> <mi>N</mi> </mrow> <mrow> <mi>W</mi> </mrow> </msubsup> </mrow> </semantics></math>.</p>
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<p>Examples of (<b>a</b>) high thermal contrast zones and (<b>b</b>) low thermal contrast zones, and how the spider monkeys appear in the videos (inside the white circle).</p>
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<p>Spider monkeys (within white circles) in TIR drone footage under different combinations of flight height and camera angle: (<b>a</b>) 50 m and −90°, (<b>b</b>) 40 m and −90°, (<b>c</b>) 50 m and −45°, and (<b>d</b>) 40 m and −45°.</p>
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<p>Level of agreement between coders for different flight parameter combinations for high (blue points) and low (orange point) thermal contrast zones. Gray points indicate that both contrast zones had the same level of agreement. The categories of level of agreement between coders on the <span class="html-italic">y</span>-axis are as follows: SL (slight), F (fair), M (moderate), SU (substantial), AP (almost perfect). The values of the flight parameter combinations on the <span class="html-italic">x</span>-axis are presented in the following order: flight speed (m/s), flight height (m a.g.l.), and camera angle (°).</p>
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