English is my native language, but I'll confess I'm not 100% clear on this particular detail. Which of the two following sentence fragments, in your opinion, is correct?
Option 1. "What I've experienced is slowly developing sensations..."
Option 2. "What I've experienced are slowly developing sensations..."
I mostly want to go with option two, but I thought I remembered some rule learned long ago about "what" being considered to be in the singular and the verb therefore having to agree with it. Can anyone set me straight on this?
Both sound perfectly correct to me.
I think the confusion comes from "What" being potentially plural or singular (e.g., What are these? What is this?). If we replace "what" with terms that are marked for being plural, we can see the difference. Here, I'll replace "what" with "thing":
Singular: [The thing] I've experienced is slowly developing sensations...
Plural: [The things] I've experienced are slowly developing sensations...
Now, both of those sound perfectly correct. Some might be tempted to object that in the first sentence, the sentence equates a singular thing--the thing--with a plural thing--sensations. But there's nothing wrong with that: consider the sentence "The team is eleven people," which does the same thing.
The difference between the two, if there is any difference, is the subject of the first--the thing--stresses the singularity of the experience. You're talking about one thing, one singular state, a state of slowly developing sensations. With the latter, you're talking about the individual sensations.
Bottom line: if these are the type of issues you're dealing with in English, then you're fluent. Use either construction and be happy.