Question

imperceptibly has the same or almost the same meaning as:
unfailingly
unnoticeably
involuntarily
implausibly

Explanation:

• "Imperceptibly" means in a way that is not perceptible or noticeable.
• "Unnoticeably" also means in a way that is not noticed.
• "Unfailingly" means always or without fail.
• "Involuntarily" means not done voluntarily or without choice.
• "Implausibly" means in a way that is not plausible or believable.

Answer:

unnoticeably