Objective: Active hyperthermia elicited by a heat stress trial (HST) was hypothesized to negatively impact higher-order cognitive ability. Design and Setting: A test-retest design with one within-subjects variable was utilized for this investigation. The independent variable was thermal condition (normothermic and hyperthermic) and the dependent variables were four factors of cognitive performance (working memory, attention, response speed, and processing speed) with associated subtests. Participants completed practice tests and returned at least 24 hr later to perform the tests before and after the HST. Subjects: Eight healthy adult males (age = 24.9+3.2 yr; height= 123.0+46.8 cm; body mass = 89.9+10.5 kg) volunteered. Measurements: We assessed cognitive performance via the Headminder ™ Cognitive Stability Index administered using a laptop computer online via a wireless secure internet browser in the normothermic and hyperthermic conditions. Core body temperature was measured via ingestion of a CorTemp ™ Ingestible Core Body Temperature Sensor (HT150002, HQ Inc., Palmetto, FL). Results: The memory factor revealed a significant (t7 = 4.675, p=.002) 12.22 % decrease in number correct for the hyperthermic (mean correct
