Neurofeedback (NF) has the potential to enhance cognitive functioning through learned regulation of brainwave activity. However, NF for optimizing performance in healthy people is still in its infancy and currently not fully explored. Here, we present an experiment where 12 subjects undergo 10 sessions of a novel NF protocol with eyes-closed bidirectional theta coherence training. This protocol was selected based on several ideas: contemporary neuroscience suggests that neural coherence support neuronal communication, and high task-related coherence is often observed with higher performance. At the same time, brain s theta waves have been shown to be particularly involved in attentional processes. In addition, it can be argued that neural flexibility should encompass the ability to regulate up and down in accordance with the cognitive demands of the environment. In order to evaluate the success of the NF training in the experimental group, a multiple object tracking (MOT) task was administered both pre- and post-training while both electroencephalogram (EEG) and pupillometry were recorded simultaneously. A passive control group performed the test twice for comparisons, with the same time lag. The results indicate that NF training was successful in enhancing attentional processes, since behavioural improvements were found in both accuracy and response time (RT) during MOT, and only in the NF group. In addition, lower task-related pupil dilations suggested that less mental effort was deployed during post-training MOT by the experimental group compared to the control group. The baselines of resting EEG recorded before each NF session were compared to the initial baseline and revealed widespread increases in coherence in all frequency bands. Analysis of task-related EEG indicated higher levels of longitudinal coherence in the experimental group during the post-training MOT. However, we cannot exclude that confounding variables related to changes in motivational factors could make comparisons between the control group and experimental group problematic. We can only tentatively conclude that the novel NF protocol employed in the current experiment shows promising support for beneficial effects of bidirectional theta NF on cognition.