Cognitive performance in a modified version of the Stroop task 2 h after intake of either a low- or high-flavanol dietary intervention. Inverse efficiency score (IES) is described as reaction time/accuracy (expressed in seconds) during cognitive performance across four different conditions representing progressively harder cognitive demands (a). The Double-Stroop condition induces the slowest cognitive processing (higher IES) compared to the other conditions (word, colour and Stroop). The benefit of the high-flavanol intervention (lower IES) in only apparent in the Double Stroop condition, when the level of conflict is higher. The cognitive benefit of high-flavanol cocoa in the Double Stroop over and above the other cognitive tasks is significantly higher in comparison to the low-flavanol intervention (*p = 0.045) (b). Two sub-groups of volunteers, (i): N = 13 and (ii): N = 4, revealed distinct oxy-haemoglobin benefits from flavanols during hypercapnia (c); with only the sub-group (i) showing benefits from flavanols during both the hypercapnia challenge and the cognitive task (d). The data is presented as Mean ± SEM.