While sculptures of Nelson Mandela and Princess Diana were suggested by the British public in a recent poll, people will now choose from entries ranging from a skyscraper to a car covered in white paint representing pigeon droppings.
"Nelson might have briefly shut his other eye in astonishment," The Daily Telegraph said on Friday.
A one-eyed sculpture of Britain's most famous naval commander, Lord Horatio Nelson, who defeated Napoleon at the Battle of Trafalgar in 1805, occupies the neighbouring plinth.
Working models of the six structures competing for a seat next to Nelson will be exhibited at the National Gallery until 8 February.
The Fourth plinth
The Fourth Plinth Commissioning Group will take comments from the public before selecting one piece which will be displayed for a year to 18 months before another piece of art is selected.
Equestrian statues of British Empire heroes occupy the three other corners of London's most famous square, one of Nelson, one of another 19th century general and another of King George IV.
But the fourth has stood empty since King William IV died in
1837, without leaving enough funds to have his own statue erected.
Sculptures under consideration to fill the void include a
skyscraper by American Chris Burden, and two oak missiles from Britain's Stefan Gec.
Fellow British sculptor Marc Quinn was the creator of an entry
depicting a disabled pregnant woman, while two other submissions were inspired by the square's winged inhabitants, the pigeons.
One of these is a a car covered in white paint and its creator,
British artist Sarah Lucas, hopes the pigeons will contribute to the mess if it wins.
The other, by German artist Thomas Schutte is entitled Hotel
for the Birds and is made out of Perspex.
The final entry, from Nigerian-born Sokari Douglas Camp, is a
stainless steel sculpture of marching people waving "No War" posters inspired by the recent anti-war demonstrations in London, many of which centred on Trafalgar Square.