Proof of concept study: Testing human volatile organic compounds as tools for age classification of films

Humans emit numerous volatile organic compounds (VOCs) through breath and skin. The nature and rate of these emissions are affected by various factors including emotional state. Previous measurements of VOCs and CO2 in a cinema have shown that certain chemicals are reproducibly emitted by audiences reacting to events in a particular film. Using data from films with various age classifications, we have studied the relationship between the emission of multiple VOCs and CO2 and the age classifier (0, 6, 12, and 16) with a view to developing a new chemically based and objective film classification method. We apply a random forest model built with time independent features extracted from the time series of every measured compound, and test predictive capability on subsets of all data. It was found that most compounds were not able to predict all age classifiers reliably, likely reflecting the fact that current classification is based on perceived sensibilities to many factors (e.g. incidences of violence, sex, antisocial behaviour, drug use, and bad language) rather than the visceral biological responses expressed in the data. However, promising results were found for isoprene which reliably predicted 0, 6 and 12 age classifiers for a variety of film genres and audience age groups. Therefore, isoprene emission per person might in future be a valuable aid to national classification boards, or even offer an alternative, objective, metric for rating films based on the reactions of large groups of people.

人类通过呼吸与皮肤排放大量挥发性有机化合物（Volatile Organic Compounds，VOCs）。此类排放的组分与速率受多种因素影响，其中包括情绪状态。此前针对影院内挥发性有机化合物与二氧化碳的监测研究表明，观众因特定影片中的情节产生情绪反应时，会规律性地排放特定化学物质。本研究借助不同年龄分级的影片数据，分析了多种挥发性有机化合物与二氧化碳的排放量与影片年龄分级（0、6、12、16级）之间的关联，旨在开发一种基于化学特征的客观影片分级方法。本研究构建了基于所有被测化合物时间序列提取的时间无关特征的随机森林（Random Forest）模型，并在全量数据的子集上测试了模型的预测性能。研究发现，多数化学物质无法可靠地预测所有年龄分级，这大概率反映了当前影片分级体系的现状：现行分级基于观众对多种因素（如暴力情节、性内容、反社会行为、毒品使用与粗俗语言）的感知敏感度，而非数据中所体现的本能生理反应。但研究在异戊二烯（Isoprene）上取得了颇具前景的结果：该物质可在多种影片类型与观众年龄组中，可靠地预测0、6、12级年龄分级。因此，未来人均异戊二烯排放量或许可成为各国影片分级委员会的有力辅助工具，甚至能基于大规模观众的群体反应，提供一种客观的影片评级替代指标。