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Social recognition experiments which used pictorial
stimuli with hens, failed to indicate any transfer of
discrimination from live birds to photographs [19]: hens
preferred flock-mates rather than unfamiliar conspe-
cifics (even when they saw only their heads and necks)
when presented with live stimuli, but they failed to
show any preference with photographic stimuli. Similar
findings were observed in a study of hens shown video
sequences [21]: hens neither took longer to eat near
unfamiliar conspecifics than near flockmates, nor near
high-ranking flockmates than near low-ranking flock-
mates, as they usually did when they saw live stimuli
behind a clear screen. Pigeons also failed to exhibit any
natural social response when they were presented with
life-size moving video images of conspecifics [86].
5.2. Acquired responses
5.2.1. Reactions to still pictures
Winner and Ettlinger [110] trained two chimpanzees
with no prior experience with photographs in a match-
ing-to-sample task. First, the subjects had to match real
objects to real objects and subsequently had to match
objects with their photographs. Initially, they were un-
able to perform the task successfully with performance
remaining at chance levels for the first 4 days and then
rising moderately, but not consistently, above chance.
The second experiment of Winner and Ettlinger at-
tempted to replicate the results obtained by Davenport
et al. [17] (see above); in their experiment, two chim-
panzees with no prior experience with photographs
were required to transfer a discrimination between pairs
of objects that were felt but not seen to their photo-
graphic representations or vice versa. The new subjects
responded significantly above chance when tested only
with objects and at chance level when required to
transfer a learned response from a felt object to a
photograph or from a photograph to a felt object. The
authors suggest that in Davenport et al.’s experiment
the objects were not paired by size: consequently, sub-
jects might have succeeded by choosing the bigger one.
Jitsumori [50] has also demonstrated that picture
recognition is difficult for untrained animals. The task
consisted of training four monkeys (two of them had
prior experience with discrimination problems between
pictures containing or not containing monkeys) and
four experimentally naive pigeons to discriminate be-
tween normally oriented displays and top-bottom re-
versals. If the monkeys saw meaningful objects in these
slides, then transfer was supposed to occur with various
novel slides; subjects were trained with a go/no-go
discrimination task with colour pictures of full humans,
and then tested with other pictures of humans, mon-
keys, birds, mammals and man-made objects. Both
monkeys and pigeons showed good transfer to novel
human pictures but when tested with other pictures,
levels of performance revealed considerable interindi-
vidual variation, namely, in pigeons and in nonexperi-
enced monkeys transfer was relatively good for some
pictures but not for others. Thus, the overall perfor-
mance was inconsistent and successful transfer might be
explained by perceptual similarities among the slides
presented in a fixed orientation. In this study, only one
of the experienced monkeys produced results suggestive
of the perception of meaningful objects in pictures.
Another experiment [19] attempted to establish
whether or not transfer between geographical locations
and photographs of those locations occurred in homing
pigeons. Eight pigeons were trained to discriminate
photographs of two geographical locations, having
been given visual experience of a real geographical
location beforehand. Half of the birds were transported
to one of the two locations that appeared in the photo-
graphs, while the remaining subjects were transported
to a third, ‘irrelevant’ location. Although there was no
significant difference in acquisition or transfer to novel
stimuli between the two groups, the authors suggest
that this might be due to their methods (inadequate
amount of experience outside or lack of immediate
reward for learning about the environment), but also to
differences between human and bird vision (see above).
Moreover, it is possible that the pigeons were process-
ing the far-distance views and the near-distance views in
different manners.
A study with laying hens by Bradshaw and Dawkins
[7] attempted to replicate the experiment performed by
Dasser [14] (see above) with macaques. Hens were
trained to discriminate between slides of either familiar
or unfamiliar conspecifics and were then presented with
novel views of these birds; during training, the right-
hand side of a hen’s head was presented, whereas the
novel stimulus set was composed of pictures of left-
hand side of the corresponding hen’s head, a frontal
view, or a view of the tail or feet. The birds failed to
generalise discrimination from training slides (both fa-
miliar and unfamiliar) to novel view categories and the
authors concluded that their study provided no evi-
dence that the hens perceived the slides presented as
representations of their group members. Ryan and Lea
[86] obtained somewhat comparable results in a study
in which pigeons and chickens were trained to discrimi-
nate between slides of two individuals (two pigeons or
two chickens). For both species, the chicken slides were
learned faster and better than the pigeon slides, with
the pigeons’ performances being much worse than
chickens’ on both chicken and pigeon stimuli. More-
over, only one pigeon out of six was able to discrimi-
nate slides of pigeons, and none learned to discriminate
between two different stuffed pigeons, even though a
subsequent experiment proved that they readily dis-
criminated individual live pigeons.