2.3. Phase Tracking
Participants with naturally occurring menstrual cycles (not on hormonal birth control) tracked their menstrual cycle by recording daily basal body temperature and menstrual symptoms into a tracking app (FertilityFriend) accessible to both the participant and researcher. This data was used to indicate cycle start date, cycle length, and ovulation date, and was used to confirm status prior to testing sessions. Salivary estrogen was also used to determine the cycle phase. Estrogen levels were determined from a 2.5 mL passive drool salvia sample analyzed by an ELISA assay (Salivary 17 β-Estradiol Enzyme Immunoassay Kit, Salimetrics, LLC, State College, PA, USA). 