In cognitive psychology, I've worked with a method known as "masked priming" [0], which is relatively well-known in the field to influence reaction times. Reaction time is a complex measure as it includes both "processing speed" as well as physical reaction times. The "prime" is considered subliminal, as one would not necessarily notice it being presented (although the mask definitely is noticeable). Interestingly, at short enough time scales, e.g. 16 ms duration times, the effect of the priming reverse, and it makes reaction times increase[1].

[0] http://www.u.arizona.edu/~kforster/priming/ [1] https://link.springer.com/article/10.3758%2FBF03196307

In 2006 I worked on analyzing data that showed this. The principal investigator was plagued by health problems and I didn't know how to connect what I was doing with the previous literature, so we didn't end up publishing anything. I felt like the idea was inevitable, but I don't know to what extent others believed this.

My model, which was basically guessed from common-sense principles (what would a flip-flop's output look like if there were no clock and the "update" signal were not discrete?), used equations that were similar to what would eventually become the GRU update equations. And the fit with the data was gorgeous: it took one parameter (a time constant that scaled how quickly sensory information was integrated with the current prediction) and the R^2 was north of 90%.

>I wonder how long it's existed as a theory in neuroscience.

Probably since a few minutes after the first time a neuroscientist saw a magician's act.