# Towards Detection of Interest Using Physiological Sensors
## 2 Methodological Choices and Research Questions
### The Levels of Interest  
The vast majority of research on interest based on the psychological point of view suggests that there are two types of interest: individual and situational interest [11; 27; 44; 45]. Individual interest is reflective of the preferences of an individual regarding a particular subject or activity and their contributions to cognitive performance. In contrast, situational interest comprises interest caused by environmental factors in most individuals, regardless of their individual differences [14]. Nevertheless, it is still early to come to a conclusion regarding the types or levels of interest from a physiological point of view. This may be due to the smaller number of the physiological studies on \"interest\" compared to psychological studies and the lack of adequate measures due to high cost, problems with temporal resolution, long computation time, etc. Here we highlight the numerous methods used to quantify interest. [PERSON] et al. [37] proposed using facial expressions to define levels of interest based on the intensity and weight of emotion. The intensity of interest was computed by considering the number of relative facial expression images for an emotion. The weight of interest was computed using a three-dimensional effect space (arousal, stance, and valence) discussed in [46]. Positive values of arousal, valence, and stance were associated with positive expressions, while negative values of arousal, valence, and stance were associated with negative expressions. This suggests that positive and negative values for interest are reflective of high and low interest, respectively. However, it is not clear whether interest can be initiated in the presence of negative affect. Interestingly, [PERSON] [6] has stated that interest can also operate in affectively negative situations, although it is suggested that affective states associated with interest tend to be positive. Nevertheless, negative affective states have been reported to be associated with interest on rare occasions [47]. Using the interactive system (iTourist) created by [PERSON] and [PERSON] [38], the authors studied eye gaze patterns to assess the subject's interest. They measured the likelihood that a user was interested in an object based on the object's arousal level and eye-gaze intensity. Eye-gaze intensity is modified by other eye-gaze factors, such as frequency of gaze and relative size to baseline, which either inhibit or increase the object's excitability. [PERSON] and [PERSON] [35] studied postures to assess the learner's interest. They classified interest as high, medium, or low. However, the performance of the classifier in the above study was poor in identifying medium interest. In addition, the classifier often had problems differentiating between high and low interest. As a result, interest levels were only classified as \"low interest\", \"high interest\", or \"taking a break\" in the final report. Studies of brain activity that use EEG utilized different approaches to assess interest. The study by [PERSON] et al. [48] used 8 EEG channels and classified interest into high situational interest and low situational interest. This study classified situational interest (SI) into high SI and low SI with high classification accuracy. [PERSON] and [PERSON] [49] used a one-channel EEG device. In order to analyze the data, the authors used a commercial analyzer that assigned percentage values to five emotional states, including \"interest\" (0%: low degree, to 100%: high degree). Interest has also been assessed by combining data of multiple modalities from three different channels: face, posture, and game information [36]. The authors classified interest level as high interest, low interest, or refreshing (they defined refreshing as a state associated with a short break in the task to restore concentration). The above study extended [PERSON]'s work [35], which studied postures to determine the level of interest. This explains the similarity between the reported interest levels in the two studies.