14 May 2022 | New Scientist | 21AS MANY as 3.9 per cent of
people have aphantasia, the
inability to picture images
in their head. But formally
diagnosing the condition is
difficult. A simple physiological
test involving a webcam could
one day offer a solution.
We have known since the
19th century that some people
lack a mind’s eye, but interest
in the phenomenon grew only
about 10 years ago.
Now, Rebecca Keogh at
Macquarie University in
Australia and her colleagues
have studied the effectiveness
of a test they have developed
for aphantasia by recruiting
56 people without the
condition and 18 people
who said they have it.
The test is based on changes
to pupil size. Looking at a bright
object causes a person’s pupils
to constrict in order to reduce
the amount of light hitting
the retina. Dim objects, on the
other hand, cause the pupils to
dilate to boost the amount of
light reaching the retina. The
researchers speculated that a
similar effect could be observed
if people were told to imagine
a bright or dark object.“My favourite theory is that
when you imagine a mental
image, you recruit brain areas
involved in perception... and
these areas are connected
to parts of the brain that are
controlling the size of the pupil,”
says Thomas Andrillon at theParis Brain Institute, who
worked on the study.
In their tests, the researchers
tracked each person’s pupil
size using an infrared camera.
They showed a participant a
bright image of an object on a
screen for 5 seconds, and told
them to memorise it. After
the image disappeared and
the participant’s pupils had
returned to their original size,
they were asked to imagine the
object in their heads. This task
was repeated until they had
looked at 16 bright images
and 16 dark images.
The pupils of all participants
changed in response to seeing
bright and dark images on the
screen. About 90 per cent ofthose without aphantasia also
showed pupil size changes
when told to imagine those
images. However, the same was
true of just 39 per cent of people
who said they had aphantasia
(eLife, doi.org/hsxm).
Andrillon suggests the test
could one day be used to check
if someone has aphantasia.
The current method, called the
binocular rivalry task, requires
mirrors and can’t easily be
carried out at home, he says.
But Keogh says the test still
needs to be refined before it
can be used widely. “We cannot
run this study without access
to infrared glasses that can
measure pupil size,” she says.
This is because the pupil size
changes seen in those without
aphantasia are still very small –
a change in diameter of about
0.2 to 0.4 millimetres.
The team wants to gather
more data with larger sample
sizes and hopes to develop a
test that can be done at home
via a laptop webcam.
Andrillon says such a test
would be important because
many people only discover they
have aphantasia later in life.
“We’re not always necessarily
experiencing things the
same way other people are
experiencing things,” he says.
“It is a promising step for the
field to have a more objective
way to measure visual imagery
ability, especially for researchers
who are interested in visual
imagery extremes like
aphantasia,” says Zoë Pounder
at the University of Oxford.
However, she says the study
needs to be replicated with
larger sample sizes. ❚Some people are
unable to visualise
objects in their headNeuroscienceJason Arunn MurugesuJASPE
R^ JAMES/GET
TY
IMAGESWebcam test could show
whether you lack a mind’s eye
THERE are only 10 vaquitas left
in the world, but a genetic analysis
suggests the small porpoises aren’t
necessarily doomed to extinction –
so long as they stop getting
ensnared in fishing nets.
Marine biologists estimate
that even at their most populous,
vaquitas (Phocoena sinus) never
numbered more than a few
thousand individuals in the
Gulf of Mexico.
By the 1990s, there were just
hundreds left. Vaquitas’ naturally
small population size reduced
their genetic diversity, which
researchers worried could lead
to offspring that are less healthy
than their parents. “But our study
is showing that reality is more
nuanced than that,” says Jacqueline
Robinson at the University of
California, San Francisco.
Robinson and her colleagues
analysed 20 vaquita genomes,
which came mostly from animals
that died between 1985 and 2017.
They used the genetic data to
model the species’ future. When
vaquita by-catch deaths were
reduced by 80 per cent, the species
went extinct in more than half of
the simulations, they found. But
when such deaths were halted,
the species recovered in more
than 90 per cent of the simulations
(Science, doi.org/gp32s3).
“I was pleasantly surprised,”
says Robinson. “I didn’t expect
[the results] to be that optimistic.” ❚WildlifeCorryn WetzelVaquitas could breed
their way back from
brink of extinction“ It is a promising step to
have a more objective
way to measure visual
imagery ability”The vaquita lives near
the northern end of
the Gulf of MexicoPA
UL
A^ O
LS
ON
/NO
AA