Comparing the effectiveness of graph neural networks and machine learning algorithms for fNIRS-based neuromarketing research

Functional near-infrared spectroscopy (fNIRS) has some advantages over other brain imaging methods in terms of cost and portability. For this reason, its use in neuromarketing is increasing. However, fNIRS brings some challenges along with its advantages. Due to features such as multichannel measurement and high temporal resolution, the nature of fNIRS data is complex and multidimensional [7]. Neuromarketing researchers have utilized machine learning algorithms to overcome these challenges. When these studies are analyzed, it is seen that successful results have emerged. Machine learning has influenced researchers working on graphs as well as neuromarketing researchers. Thus, graph neural networks have emerged, which allow the application of artificial neural networks to graph data structures. Thanks to the fact that the brain can be modeled as a graph structure using functional connections [14] and the high temporal resolution of fNIRS [7], there are neuroimaging studies using graph neural networks and fNIRS together. However, despite successful results, there is no neuromarketing research using this combination. Therefore, in this study, the performance of graph neural networks in fNIRS-based neuromarketing was analyzed and compared with machine learning algorithms that have been shown to yield successful results in this context. For the comparison, fNIRS measurements of a neuromarketing experiment conducted to determine perceptions toward brands were used. In the experiment, consumers were asked to decide (yes/no) whether the adjective shown with the brand logo was appropriate for the brand. The data set was obtained by cleaning the obtained measurements. First, a supervised machine learning approach was applied to this dataset. After the dataset went through several data preprocessing stages, various algorithms were trained on it. These were K-Nearest Neighbors, Support Vector Machines, Random Forest, Naive Bayes, and XGBoost algorithms. Then, two different voting classifiers, one for soft voting and one for hard voting, were created from the algorithms that were more successful than the others. After the machine learning approach was completed, the graph neural network approach was applied. The data obtained through fNIRS was transformed into a graph structure using functional connections in the brain. The Pearson correlation coefficient was used to calculate the functional connections. Since a graph was created for each trial of the participants and each graph had a label (yes/no), classification was performed at the graph level. For graph classification, the generated graphs were given as input to graph neural network architectures. The architectures used in the study consisted of Graph Convolutional Network, Graph Attention Network, and Graph Isomorphism Network. Finally, a soft voting classifier was created by combining these architectures. Test accuracy values of all methods were calculated and binomial confidence intervals were added to these values. The comparison results showed that machine learning algorithms generally outperform graph neural networks. Additionally, machine learning models based on ensemble learning have the best scores.