My question is two-fold.
First, I believe that metta is classified as a meditation object involving concentration. Yet, in this study, researchers suggest it is a mixture of focused attention (e.g. shamatha) and open monitoring (e.g. vipassana). Does Buddhism suggest in certain passages or teachings that compassion is dual in this way?
More so, from my experience, compassion meditations deepens insight. Theravada involves a mixture of shamatha and vipassana, and the Mahayana involves (more so) a union of compassion and wisdom recognizing sunyata. I feel the depth of metta might occur from its union of concentration and insight (as suggested in the previous paragraph) and from metta itself and the realization of sunyata (implied by their merging promoted by the Mahayana). I feel all these things occur with metta in my experience.
When talking about metta a researcher described the occurrence of gamma waves:
In Buddhism teachings and texts, is metta said to unite a variety of mental factors together?