Many speed-reading methods involve making sure that new words are always in just the right place for the fovea to recognise. The people behind a new app called Spritz realised that the easiest way to do that is by flashing the words up, one after another, in the same small box. By focusing on that box, the reader can identify each new word without having to shift their gaze. For no extra effort, reading becomes much faster.

Try Spritz for yourself, and you might agree with the company’s claims. But Sally Andrews, a professor of cognitive psychology at the University of Sydney, says that effective speed-reading isn’t quite that simple. In an analysis published after Spritz hit the headlines this year, she said that it’s the time it takes to comprehend words that can slow us down. Unfamiliar and long words, in particular, take more time to recognise and understand.

Spritz is asking us to process the written word at a similar pace to how we do speech, Andrews told BBC Future. But if we fail to catch a word in speech we can use other cues such as intonation or the speaker’s hand gestures to fill in the gap and work out what’s being said. These cues are missing from the written words presented by Spritz, which might make comprehension trickier.

But comprehension is not necessarily impossible, as fans of Spritz might argue. This may be because Spritz readers are subconsciously relying on their prior knowledge or experience to fill in any words they miss. Providing the style of writing is familiar, a Spritz reader’s brain might still have some ability to guess any missing words and work out the meaning of a text. “I would argue that what people are doing is not actually understanding what the author has written but picking up words and phrases,” says Andrews. “The more they know already, the greater the degree of that fragmentary information they’ll pick up.”