“But I’m not sure whether I’m just imagining it” is something I often hear from people who are starting to be able to tune into the felt sense of metta.
At a certain point, the metta practice becomes less about generating the felt sense, and more about listening to it, with sensitivity and appreciation, in such a way that one can begin to become more easily absorbed into it.
And it’s natural, when we’re listening for something, to want to hear what’s really there; if we’re anticipating a guest, many other things can begin to sound like a knock at the door, and we can become prone to false positives.
Practitioners who are smart, meta-cognitive, and have a healthy wariness of the power of confirmation bias don’t want to accidentally fool themselves into thinking that they’re experiencing metta, when they really aren’t. So it can seem like a good idea, good epistemological hygiene, to try to get rid of one’s expectations and preconceptions, and to approach the sensations in the body with as neutral a state of mind as possible.
As sensible as this view may seem, it can actually be a stance that hinders the development of metta at this point. Being confronted with the limitations of this view of looking for what’s “really real” in our experience is also what makes this junction such a fertile place to begin to develop some insight into the nature of perception.
There’s no test you can do to detect ‘deliciousness’ in a food, no matter how precise and accurate your equipment is. Deliciousness depends on how the food you have interacts with what tastebuds you have. Different animals have very different compositions of tastebuds; for instance, cats cannot taste sweetness at all; they lack the receptor entirely. And of course experience - even just of taste - is determined by more than just the state of your tastebuds; it’s also constructed by your history, expectations, beliefs, conditioning, attention, view, and yes - imagination. We have a lot of control over some of these, and we can develop flexibility and range in our ways of experiencing as a skill by playing creatively with them.
This skill in playing with perception in meditation really isn't that far from learning to experience more deliciousness in food. Actually there is a lot we can do to impact the experience of eating the same food - presentation, expectation, setting, taking the time to savour it, etc. etc. But to make the thought experiment neater and more compelling, let's imagine that you could just learn to modify your own tastebuds at will. If you could do that, it would become clear why this question "but I'm not sure whether I'm just imagining the deliciousness" is a category error.
Deliciousness was never something in the food in the first place; no matter how much skill you develop in altering your tastebuds, it wouldn’t get you any closer to accurately perceiving which foods are really and truly delicious. There’s not any objective truth there could be about that. And everything that’s ever in your direct experience is like this; it’s a product of interaction, not an objective representation of some real property.*
In a similar way, the skill we’re developing in service of samadhi is more like learning how to experience deliciousness - more like savouring - than like perceiving with dry accuracy what sensations are really there. It’s not like there’s a perfectly formed, defined, discrete sensation or emotion hanging around somewhere “in the body” (or “in the brain”) waiting to be perceived, just as there was no deliciousness waiting to be perceived “in the food”.
If you’re starting to feel something that might be metta, and you try to establish whether that feeling is “real” or not by adopting more of a probing, close attention to moment-to-moment local sensory experience (because that feels more objective), you probably will find that the experience changes or even goes away - but that doesn’t mean that it was made up! That close, probing, moment-to-moment attention to local sensory experience is just one way of looking, and it’s very useful and appropriate for some things, but not others.
If the sensations that you're noticing in metta practice feel like they might be influenced by the fact that you're expecting them to arise, or you're looking in a certain way, well that's also true for all other sensations! It's just that the ways of looking that inform our ordinary experience are so habitual and agreed upon that they go unquestioned.
This course is for samadhi rather than insight, but they overlap inevitably, and this is the link to insight practice. Part of what insight is is learning to notice how perceptions are constructed, and the constructedness of experience gets clearer and clearer the more skill you develop in playing with perception in these ways, and the more readily you’re able to loosen your more habitual ways of looking.