## 2 Method
### Experimental Procedure  
The study compared the effects of three cognition-enhancing hot beverages (two types of tea and one type of coffee) to a comparable (control) traditional hot beverage (herbal tea and Columbian coffee). The experiment was performed over two one-hour sessions with a minimum of one week between testing sessions. Using a within-subjects repeated measures design, participants completed a series of three cognitive tasks over three blocks and consumed either a cognition-enhancing hot beverage (coffee or tea) or a traditional hot beverage. The traditional hot beverage (coffee or tea) acted as a control. Prior to the start of the study, participants expressed their preference for hot tea or coffee and were assigned to their preferred beverage category for product consumption in the study. Participants expressing preference for tea were randomly assigned to either the blue tea or yellow tea (40 per group). Both these teas were enhanced teas albeit with a slight difference in composition. These teas were lemongrass hibiscus herbal infusions with turmeric, ginseng, and ginkgo. The difference between the teas was that the yellow tea contained caffeine (40-50 mg) while the blue tea did not. The traditional (control) hot tea was a lemon herbal tea containing no caffeine. Similarly, the enhanced coffee was a ground arabica coffee with added cocoa flavanols, while the traditional (control) hot coffee contained a medium Colombian coffee blend. Both coffee types (traditional and enhanced) contained approximately 90-100 mg of caffeine. After giving consent, participants were fitted with sensor devices as described in the next section. Participants consumed a different beverage in each session (day 1 and 2), but the same beverage (enhanced or traditional) was used for all blocks in a single session. Participants were instructed not to consume any hot beverages for at least two hours before partaking in the study. A task battery was designed to simulate tasks that participants would complete during a workday. The first task was a mental arithmetic task. Addition and multiplication were performed at varying difficulty levels. For the simple task, participants were given single-digit integers (3 + 5 or 4 \(\times\) 6). For the challenging task, participants were given double-digit integers (14 + 62 or 12 \(\times\) 15) to increase task difficulty. The challenging task requires more effort, concentration, and focus than the simple task. Participants were given up to 10 seconds to respond to each question with a five second inter-stimulus period. The task lasted a total of three minutes. The next task was a sustained attention task, rapid visual processing (RVP). Participants were asked to identify a given target in a series of numbers where digits were presented serially one at a time. Target sequences were either a single-digit (2) or a triple-digit sequence (2-4-6) in order to increase difficulty. Participants were instructed to press ENTER on the last number of the sequence when it appeared in order. The digits, from 1 to 9, appeared in pseudo-random order on a screen at a rate of 100 digits per minute. This task requires sustained attention and focus to be able to perform well. Participants were given a total of 4 target sequences to identify, two simple and two challenging. The task lasted a total of three minutes. The final task was a conflict resolution task, Stroop task. In this task, there are again two levels of difficulty, simple (congruent) and challenging (incongruent). Participants were asked to look at color words (i.e., red or blue) under two different conditions: _congruent_, where the word was displayed in the color that its name denoted (e.g., \"blue\" displayed in blue font) and _incongruent_, where the word was displayed in a different color font than its name denoted (e.g., \"blue\" displayed in yellow font). For this task, participants are required to keep multiple things in memory in order to perform well. Participants completed a total of four blocks, two congruent and two incongruent.