Millions of Australians who spent months in lockdown may look back at the past 12 months as a bloated mass of time that never seemed to end.
But some people always visualise time as a 3D form — pandemic year or not.
While it varies between individuals, the phenomenon has a name: time-space synaesthesia.
Some see days and weeks arranged around them.
For as long as she can remember, Liz, who lives in Central Victoria, has perceived months of the year as a roundish but intangible form.
"It's almost like being on a road," she says.
She pictures January 1 at the 6 o'clock position, then travels anti-clockwise as she moves through the months.
"It goes uphill, and then plateaus out a bit at winter, and then starts going downhill again towards the end of the year," Liz says.
She also associates specific chunks of the year with shades of light and dark.
For instance, this time of year is always dark and squashed up.
"I don't know whether that's just because there's a lot of stuff happening and that's how I feel — that time is compressed," she says.
"And then winter seems to always be a grey shade."
What is time-space synaesthesia?
Time-space synaesthesia is one of dozens of different types of synaesthesia, where the stimulation of one sense elicits another.
For instance, some people have "coloured hearing", where voices or music produce distinctive hues.
Others have what's called grapheme-colour synaesthesia, where colours are associated with letters and numbers.
For it to be considered synaesthesia, the link must be consistent and automatic, says Anina Rich, who leads the Synaesthesia Research Group at Macquarie University.
But there is some debate about where time-space synaesthesia sits in relation to other kinds of synaesthesia.
It's not as black and white as, say, coloured hearing, where either you have it, or you don't.
But everyone, to some extent, has an internal mental number line — a representation, in our mind, of where numbers sit in space.
Many people, especially those who read left to right, will subconsciously organise numbers with the smallest to the left and the biggest on the right.
Experiments starting in the 1990s objectively measured this so-called spatial-numerical association of response codes, or SNARC effect.
"If I put a number on a computer screen and ask you to tap a key with your left hand if it's less than five, or with your right hand if it's greater than five, you will be faster to respond than if it's the opposite orientation," Professor Rich said.
This holds true regardless of whether you visualise sequences or not.
So it could be that time-space synaesthesia isn't an either/or phenomenon, but exists on a continuum.
On one end are people who have no visual representation of time and space.
"And then as you're going along, there might be people who kind of get a sense of where the week is around them," Professor Rich said.
Like Liz. She also has a visual representation across decades that looks a little like a piece of string that loops around and travels through a 3D space.
The 1800s start high up in space to the left, then as the decades roll on, the line drops vertically.
It starts to level out in the 1970s and 80s, then heads up again during the 90s, before plateauing again around the turn of the millennium.
Around the present day, the line gets a little fuzzy.
"When I start thinking about 2030, it starts to go up, diagonally. After about 2040, it goes almost vertically until I get to 2100," Liz says.
"Then, for some reason, it starts going back off to the left into the distance again."
So why do some people report seeing time in space?
No-one really knows for sure.
Professor Rich says there are two main theories for how synaesthesia in general arises.
The first is that synaesthetes have extra hardwired connections between senses in their brain that the rest of us don't have.
"That's categorical," she says.
"That's saying synaesthetes are physically different from non-synasethetes.
"And then there's the more dimensional approach that says we've all got connections between the senses — our brains are massively interconnected — but it might be that synaesthetes have more co-activation [of those brain regions]."
In other words, synaesthetes are aware of that link between senses, but for the rest of us, it stays under our conscious radar.
While there have been relatively few studies of time-space synaesthetes, they do seem similar in some respects.
For instance, most tend to report a year as an oval or ellipsoid shape — which makes sense, as the year is a cycle.
Liz thinks that how she feels about each part of the year probably affects its "uphillness" or "downhillness".
"It's a bit like having hump day in a week," she says.
"You feel like you're travelling up, you get to the top, and then you're going downhill again."
Does this affect day-to-day life?
Time-space synaesthesia could be one of the more common forms of synaesthesia.
Depending on how it's defined, estimates range from 2.2 per cent of the population to 20 per cent.
And there are potential benefits to a mental calendar. You may be less likely to double-book yourself, Professor Rich says, because you "see" that space blocked out.
"Anecdotally, people report these sorts of things, but in terms of objective evidence, the literature's still very young."
Other studies suggest time-space synaesthetes have an excellent visual memory for — unsurprisingly — dates, something Liz experiences.
Her earliest memory goes back to when she was 2 or 3 years old, and verified by her mum.
"I have a lot of fairly detailed memories of early life … and my memories are very strong visually," Liz says.
"I think I've got more of a head for dates and details for when we go travelling. I can remember where and when we did things."
But what she has in visual recollection is lost when it comes to listening to information.
"I'm so bad at processing auditory information," Liz says.
"I never found there was much point in sitting there and listening unless I could write or draw something."
If this sounds like you, or you're just interested in finding out if you have a different form of synaesthesia, Professor Rich's research team could help bring to light any synaesthetic qualities.
On the whole, she says, there are only very rare cases where any kind of synaesthesia is thought to interfere with day-to-day functioning in any way.
"Often we talk about it as having an unusual gift. But for most people, it's just their way of perceiving the world."
