A rare condition that makes people unable to visualize images in their imagination could have further-reaching effects on the mind than we knew, scientists report.

Aphantasia, sometimes referred to as being 'blind in the mind', has been known about since the 19th century, but has only attracted significant scientific attention in recent years.

Those studies are telling us more about how aphantasia manifests in people, while also revealing new insights into how important mental imagery is as a component of other brain functions, such as memory.

In 2020, a team of researchers led by cognitive neuroscientist Alexei Dawes from the University of New South Wales (UNSW) in Australia found that people with aphantasia showed a reduced ability to remember the past and envision the future, in addition to recalling fewer dreams (and often with less detail).

Now, in a new study, some of the same scientists have discovered new evidence of aphantasia's impact on our memory and imaginations of the future.

"Episodic memory and future prospection are functionally similar," Dawes, now a researcher at the RIKEN Centre for Brain Science in Japan, explains in a Twitter thread about the new findings.

"Both are everyday cognitive processes involving the reconstructive simulation of events and scenes, typically accompanied by anecdotally vivid online sensory replay (or 'preplay') in the form of visual imagery."

While this inner visual imagery is something our minds conjure up on a continual basis, there's still a lot we don't know about how these images factor into our ability to actually recall episodes from the past.

To explore this, Dawes and fellow researchers conducted an experiment with about 60 participants, half of whom experienced aphantasia, with the other half being people without the condition, acting as a control group.

In the experiment, the participants completed an adapted version of the Autobiographical Interview, a test given to assess components of autobiographical memory in adults.

In the version conducted here, participants were asked to remember six life events (real memories) and imagine six hypothetical future events based on word cues, providing detailed written descriptions of each.

The results showed that aphantasic participants generated significantly fewer episodic details than participants in the control group, for both past and future events.

This included significantly weaker visual imagery, object imagery, and scene imagery, the researchers found, but noted that people with aphantasia did score similarly to the controls on spatial imagery ability.

"Most importantly, the current study provides the first robust behavioral evidence that visual imagery absence is associated with a significantly reduced capacity to simulate the past and construct the future," the researchers write.

"Aphantasic participants generated significantly fewer internal details than controls, irrespective of temporal direction, indicating that their event descriptions were less episodically rich and specific than participants with visual imagery."

Although we can't yet estimate the extent of the impact, the researchers say it's clear the ability to generate visual imagery is important for the mental construction of events, whether reconstructing real-life memories, or imagining scenarios that haven't taken place.

The fact that both past recollections and imaginary future anticipations are similarly affected could offer support for what's called the constructive episodic simulation hypothesis, which posits that future prospection is a cognitive process that assembles fragments of past memories to paint a picture of possible future events.

"By this account, internally 're-experiencing' and 'pre-experiencing' events should both involve the recombination of stored perceptual, spatiotemporal, and conceptual information, and thus rely on similar cognitive processes – including mental imagery," the researchers explain.

Of course, none of this means that people with aphantasia can't remember past events or imagine future ones, the researchers note.

But it does seem their ability to construct or reconstruct these internal scenes is diminished compared to people without the condition, whose ability to rely on a richer amount of mental visual imagery seems to give them an advantage in tapping into memories.

There's still so much we don't know about how this condition works, but studies like this one are helping to fill in the details – and not just on aphantasia, but on how memory and visual imagery intersect (or don't) inside all of our heads.

"The interactions between visual imagery, episodic event construction, and autobiographical memory are likely complex, and complicated further by the myriad individual differences that moderate each of these cognitive processes," the researchers write.

"However, aphantasia offers a unique model to begin exploring these interactions and building a wider taxonomy of cognitive simulation in the human brain."

The findings are reported in Cognition.