Image copyright Getty Images

"Ghosts are invisible to most people, but visible to a few."

Susan Hiller said this in 2005 at a gallery in London where one of her video installations was being shown.

For the piece, J-Street Project, she had spent three years filming clips of different street names in Germany that referred to a lost Jewish presence, such as "Judenstrasse" and "Judenweg".

She then put them together in a quiet montage, punctured only by the occasional oblivious honk from a passing van, or a glimpse of a pedestrian walking idly by.

"These street names are ghosts of the past, haunting the present," she said of the piece. "The street signs in my images explicitly name what's missing from all these places."

Ghosts were visible to Hiller. Not in a literal sense, of course, but she could see the histories that others had collectively forgotten - and through her art, whether it revived neglected memorial plaques or documented dying languages, she gave the rest of us a glimpse of these ghosts too.

Following a short illness, Hiller died on Monday 28 January at the age of 78.

'Connection, empathy, identification'

Hiller was born in Tallahassee, Florida, in March 1940 and grew up there and in Cleveland, Ohio.

As a teenager she had dreamed of being an artist. She noticed things that others didn't, and was curious about everything she came across.

But this inquisitiveness led her down a different path - and after doing undergraduate degrees in film and photography, and then archaeology and linguistics, in New York, she was awarded a fellowship to do postgraduate work in anthropology in New Orleans.

She was at the start of a potentially successful career in the 1960s, carrying out fieldwork in Guatemala, Mexico and Belize - but it didn't take long for her to realise that, while she loved exploring new cultures and ideas, something about anthropology didn't really sit right with her.

Image copyright Carla Borel Image caption Susan Hiller, pictured in 2014, originally trained as an anthropologist

What bothered her about anthropology, she would explain decades later, was the discipline's claim to be objective. It was during a lecture on African art that she had a revelation.

"In contrast [to anthropology], I felt art was, above all, irrational, mysterious, numinous," she wrote in the foreword to a book she edited, The Myth of Primitivism. She realised she wanted to "relinquish factuality for fantasy".

"Words 'about' the peoples represented by the marvellous sculpture seemed redundant; the more facts, analyses and theories I had learned, the further away I felt from any real connection with them, and what I wanted was connection, empathy, identification."

And so, with that, she abandoned her doctoral thesis to become an artist.

There's no denying that her love of travelling and her ability to read cultures was informed by her work as an anthropologist, too - although her son Gabriel Coxhead tells BBC News that constant references to her postgraduate training annoyed her.

"At the beginning of her career, some people felt that the sorts of overlooked or unusual phenomena she was investigating weren't suitable subjects for art," he says. "So sometimes her history as an anthropologist would get trotted out. I suppose it was meant to give her art legitimacy. But she knew her work didn't need justifying in this way."

Crashing waves

Hiller and her husband David then spent almost a decade living in different countries across the world - Morocco, India and France, to name a few - and even after moving to London in the early 1970s, they continued to travel and periodically live abroad.

On her first trip to the UK, visiting the seaside town of Weston-super-Mare, Hiller noticed something in all of the shops: postcards showing stormy waves crashing against various parts of the English coastline.

Image copyright Jack Hems Image caption Susan Hiller spent years collecting seaside postcards of rough seas in England

Similar cards, she later noticed, were being sold in seaside towns all over England. None of the postcards named the photographers - but the images, she felt, said something profound about how the country was presenting itself to the rest of the world at that time. She spent the next four years buying the cards in every seaside shop she saw them.

Together, they became her first major artwork: Dedicated to the Unknown Artists.

Image copyright Getty Images Image caption People watch The Last Silent Movie, which revives extinct languages

About a decade later, she photographed a series of 41 memorial plaques dedicated to people who had died carrying out acts of heroism. A teenage girl who died saving a child from a stampeding horse, for example.

"What struck me was that [people] had sat in front of these perfectly visible objects for years and years," she is quoted as saying in a 2011 exhibition catalogue. "The objects had been, literally, invisible."

Years later, when Hiller was living in Germany in 2002, she noticed a street sign with the word "Jude" - Jewish - in it. For most people it blended into the background, but in that sign Hiller saw the lost memories of a community that had been tragically driven out of its home. So she spent three years documenting 303 of them for J-Street Project.

And in 2007, her video The Last Silent Movie resurrected haunting archive footage of the last speakers of languages that are now extinct.

These were the ghosts that only a few people could see.

'A different kind of truth'

Hiller started off working firmly in the conceptualist tradition in the early 1970s, with performance pieces that included - among other things - getting a bunch of her friends to spend three nights sleeping in "fairy rings" in an English meadow and map out the dreams they'd had.

Later, though, she would become a pioneer of so-called "new media" work, experimenting with film and audio recordings in a way that was well ahead of her time.

Through using this media to look at alien abductions, life-after-death, religion and dreams, Hiller became known as an artist of the paranormal - or as she called it, "paraconceptual".

Image copyright Getty Images Image caption In Psi Girls, Hiller compiles clips showing paranormal activity and 'witchcraft' in popular culture

But really it was her insatiable curiosity that meant that she was simply fascinated by the experiences of outsiders - the things that people try to tell the world, but that fall on deaf ears.

Take Witness, a work she made in 2000 - around 400 small speakers dangle from the ceiling, each one playing a different person's account of being abducted by aliens. They spoke numerous different languages, but their conviction and belief were the same.

In another work, Channels, multiple TV screens show people talking about having life-after-death experiences after being legally declared dead. And a series of photos from 2008, Homage to Marcel Duchamp: Auras, is a collection of portraits which people believe show their auras.

Image copyright Getty Images Image caption Susan Hiller's Homage to Marcel Duchamp, 2008 - a collection of 'aura photographs'

Did Hiller really believe people were abducted by aliens or had out-of-body experiences after dying, or that you could genuinely see someone's aura in a photo?

Some thought so, but this would be taking her work at face-value.

"For her, it wasn't about believing or not believing in aliens,", Mr Coxhead says. "What she was interested in was the fact that people believed they were abducted by aliens."

"It's a social fact of the world that there are reports of aliens, reports of out-of-body experiences... whether or not the reports are true is another thing, but the reports themselves are what she was exploring, and what that says about people."

She saw people's visions of aliens as no different to people's religious visions - which is also why, from 1969 until she died, she collected holy water from sacred sites from Wales to the Ganges.

These other-worldly experiences weren't factual truths, strictly speaking. But for Hiller, they represented a different kind of truth.