Here are some examples which show the human body sense negative ions directly and indirectly.
[Sense of sight]
Air ions are too small to see with the naked eye.
They are absorbed by dust floating in the air to form larger ions at or near the ground surface
and you can see the larger ions. In other words, you can sense the negative ions visually.
[Sense of taste]
It is not clear how they work but negative ions change taste.
For example, coffee and water change taste after negative ion irradiation.
You sense the negative ions indirectly.
The same goes with the senses of touch/smell/hearing.
However, you cannot sense directly except some examples.
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