New Scientist - USA (2021-02-27)

27 February 2021 | New Scientist | 55

Tom Gauld

for New Scientist

Answers

Another thing that an animal
can do to discern fine detail is to
move closer to objects of interest.
This is because visual acuity is
distance-dependent: the closer
you are to something, the better
you will be able to perceive it.
Some reef fish are famous for
their complex colour patterns.
It turns out that these probably
aren’t visible to other reef fish
from far away and so, in fact, may
function as camouflage when
viewed from a distance. From
close up, however, these patterns
are perceivable and so can serve
as signals to nearby viewers.
The animal with the sharpest
eyesight is the wedge-tailed eagle,
with an acuity of 140 cycles per
degree, which is more than double
that of humans. However, we
actually have some of the sharpest
vision in the animal kingdom, so it
is easy for us to make assumptions
about what animals can see based
on our own perceptual experience,
which may not be accurate.
Next time you are walking
your dog or bird-watching, give
some thought to the fact that the

animals around you probably

don’t perceive the visual scenes

in the same way you do.

Colour confusion

I see the shoes (pictured) as mint

green and grey, but a friend sees

pink and white. Does this mean we

continually see different versions of

the colours around us? (continued)

Peter Calver

Stansted, Essex, UK

I looked at the picture before I

went to bed and saw a grey shoe

with mint-green trim. Nothing

I did would allow me to perceive

any other colours. I put the

magazine next to the bed to show

my wife the next day, but in the

morning, the shoe had changed

to pink with greyish-white trim.

Even looking at it from 3 metres

away, it still seemed pink. Yet to

my wife, it was grey and green.

A few hours later, I glanced at

the photograph and the shoe

had gone back to grey and green!

While the lighting was different

on all three occasions, once

my eyes perceived one colour

or the other, changing the lighting

didn’t seem to affect what I saw.

Paul Douglas

Wellington, New Zealand

I hate to throw a spanner in the

works, but I can see both mint

green and grey, and pink and

white - sometimes even at the

same time, but mainly in different

strengths of light.

If I am outside and in normal

daylight, I see a pink shoe and

white laces. But if I am in my tent

(I am homeless) where it is darker,

I see the same picture as a grey

shoe with mint-green laces.

You can try it yourself. Take

a picture using a digital camera

in low light and I think you will

find that the pink turns grey,

even in normal daylight.  ❚

Quick quiz #90

Answer

1 The bowhead whale. Its

mouth can be almost 5 metres

long, 4 metres high and

2.5 metres wide

2 Clavius

3 Amylopectin

4 The bathysphere submersible

5 63

Cryptic Crossword

#51 Answers

ACROSS 1 Sate, 3 Neap tide,

8 Numb, 9 Emergent,

11 Proportional, 13 Timing,

15 Cicada, 17 Interglacial,

20 Abomasum, 21 Marl,

22 Sinusoid, 23 Post

DOWN 1 Sunspots, 2 Tempo,

4 Enmity, 5 Periodical, 6 Ikebana,

7 Eats, 10 Roundelays, 12 Fall

flat, 14 Monsoon, 16 Agouti,

18 Imago, 19 Laps

#101 Red triangle^

Solution

The red and blue triangles in

the illustration have the same

length of base and height, so

have the same area. By the same

argument, the blue triangle and

triangle ABC have the same area.

But ABC is half

the area of

square ABCD,

and ABCD is

four times the

area of the

small square,

which is 8.

So the area

of the red

triangle is 16.

A B

D C

E F

@D

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