Many who commented on this article took the instinctive, overly narrow approach, namely what events unique to the 1990s caused this specific decline in creative thinking? The correct way to solve these problems is to first gather as many similar examples and then see what they have in common. It's not as though this is the first time in human history that creativity has declined. Rising and falling violence rates have been present throughout history, and it looks like they correspond to flowering artistic creativity (rising) or downplaying the arts and focusing on reason, science, and enlightenment (falling).
The high point of violence rates in Western Europe over the past 800 years seems to have been the period from about 1580 to 1630. That's using homicide rates, but there was an unusual amount of political intrigue and bloodshed as well -- not to mention the peak intensity of the Early Modern European trials of witches and werewolves. At least since the post-Roman Dark Ages, if any generation had reason to suspect that the world was going to blow up, it was these guys. And of course they produced some of the greatest works of literature, especially in England.
I wonder how English people circa 1600 would have scored on a psychologist's creativity test? Obviously we cannot go back in time and give them one, but they have left plenty of fossil evidence to look at for clues. As I've delved into the plays and poetry of this period, one thing that's struck me is how the footnotes always mention that in Early Modern English a plural subject would often -- though not necessarily -- be paired with a singular verb, if the subject was to be construed as a whole. This footnote appears as a general warning in every single play I've read so far, it is that common. Here's an example from Marlowe's Doctor Faustus (1.3.80-81), along with the note in my copy:
O Faustus, leave these frivolous demands
Which strikes* a terror to my fainting soul!
* (it is not unusual to have a plural subject -- especially when it has a collective force -- take a verb ending in -s)
Linguists distinguish between "mass nouns" for wholes vs. "count nouns" for pieces. To tell which one a certain noun is, just ask if you cut it in half, would you still call each of them the same as you called the original? For example, if I have water and split it into two sections, each one is still called water. But if I have an apple and cut it in half, you would look at me weird if I gave you one of the pieces and said, "Here's an apple for you."
But there is no objective distinction between what is a count noun or a mass noun; it depends on how the speaker construes things. You know those pictures that look either like two faces pointed at each other or a chalice, depending on how you twist your mind? That's what we have here. To use a blacker example that's famous among linguists, typically "cat" is a count noun -- if I cut one in half, each of the pieces is not a cat. However, it's fine to say that "When Jayden hurried away in his car, he accidentally ran over Fluffy, and there was cat all over the driveway." In this way of conceiving cats, they're not individual beings but instead a big blobby mass of cat-like stuff, much like water or hay or mud. So sure, if you cut a portion of it in half, you still have cat here and cat there.
I see it as the mark of a more flexible mind's eye that the Early Moderns were happy to sometimes use a singular verb and sometimes a plural verb with a plural subject, depending on whether they construed the subject as a whole or as separate pieces. Here we don't have to guess what they were thinking -- if there was a singular verb, one ending in -s, we know they construed it as a collective.
By the way, this is one of those things that Westerners are supposed to be worse at than East Asians, if we believe the evidence in Nisbett's book The Geography of Thought. Westerners are supposed to be more analytical, slicing things up and looking at the separate pieces, while Easterners are supposed to be more holistic, stepping back and seeing the relationships among the pieces as creating a single network or whole. Maybe this observation is true only for modern Westerners -- English people around 1600 seemed right at home switching from part to whole for a far broader range of things than they do today.
The most recent article I could quickly find on this topic was written in 1934, but that should be good enough. His overview is that from the Old English period up through the 17th C., it was totally acceptable to pair a plural noun with a singular verb if the noun was to be construed as a whole. This came under "logical" attack during the 18th C -- no surprise there, that century was ground zero for Aspie dorks taking things too literally -- and was largely gone by the end of the 19th C. (Examples can still be found; they're just far less frequent than in pre-modern times.)
Are these the linguistic fossils of the change in people's basic traits that Greg Clark documents in A Farewell to Alms? As they moved from an economy based on some mix of farming and herding (or even hunting and gathering) to a more market / capitalist economy, people sure seemed to become a lot more like Ned Flanders in their basic personality. We see this in the context of language with all the grammar Nazis out there today, although again much of those clueless complaints go back to the 19th or 18th C. ancestors of today's language mavens. ("Maven, schmaven!" as Steven Pinker says.) In Shakespeare's day, either there were hardly any grammar Nazis around or their targets had enough sense to tell them to get a life, mellow out, and not over-analyze everything, that it makes sense if you just step back and look at it the right way.
Worse, people actually get a kick out of lecturing us about how, for instance, we can't start a sentence with "hopefully" because it DOES.... NOT.... COMPUTE... People try to show off their lack of cognitive flexibility these days. This flabbiness at a fairly early stage in the culture creation process -- how you look at things -- goes a long way to explain why most modern stuff doesn't seem anywhere near as compelling as what came before. Adaptation to market-based economies required minds that were better at specialization than generalism, and that would guide their bearers to be good cogs in the economic machine. We certainly have this to thank for the dramatic increase in our material standard of living, but we seem to have traded this off against a more creative way of thinking.