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An interesting study on the recognition of pictures of
individual faces by chimpanzees was carried out by
Bauer and Philip [3]. The authors found that three
chimpanzees initially trained to match photographs of
faces of the same individuals were able to later match
different vocalisations to facial portraits of the familiar
individuals.
Experiments on cross-modal perception can also
provide us with useful indications concerning the ques-
tion of picture recognition in nonhuman primates. For
example, Davenport and Rogers [16] trained three apes,
one orang-utan and two chimpanzees, who were unfa-
miliar with photographs, to match a visual sample (the
real object) to an haptically presented object. When the
visual sample was a photograph, subjects’ responses
were clearly above chance (80% or more) from the
beginning. Further, there was little difference in accu-
racy between colour and black-and-white photographs,
and no difference between real objects and their colour
photographs. Thus, it seems that apes are able, even
without any familiarity with photographs, to recognise
them and treat them like real objects. In another exper-
iment [17], five chimpanzees trained only in a haptic to
visual cross-modal experiment with real objects were
submitted to the same sort of problems with photo-
graphs or drawings; four of the subjects performed
significantly above chance with full-size colour photo-
graphs, with full-size or half-size black-and-white pho-
tographs and with full-size line drawings. However,
cross modal-perception was better with photographs
than with line drawings.
An experiment of cross-modal matching of objects
with their photographs was conducted by Malone et al.
[66] with two adolescent male rhesus monkeys. One of
the monkeys was trained on visual to haptic matching
to sample, and the other on haptic to visual matching
to sample (the visual stimuli were full-sized colour
photographs of the haptic objects). While both mon-
keys succeeded on the task, they needed prior training
to do so and the authors highlighted that it was unclear
whether training was necessary because subjects had
difficulty mastering the matching-to-sample procedure,
or if they had to learn first the equivalence between
photographs and objects. In a subsequent experiment
[97], the same subjects were required to perform the
same task but with black-and-white photographs, sil-
houette photographs, and outlines drawings of the ob-
jects, that is, forms of stimuli with which they had had
no prior training; the monkeys were still able to per-
form the task when visual stimuli were black-and-white
photographs and silhouette photographs, but not with
outline drawings.
Zimmermann and Hochberg [114] trained infant rhe-
sus monkeys (5-150 days of age) to discriminate be-
tween flat and solid objects (e.g. squares and cubes) and
then tested the transfer to photographs and outlines
figures of these objects. The results showed that these
subjects were able to make consistent responses to
pictorial representations of the stimuli (photographs or
drawings) and that while the presence of shadow facili-
tated transfer, this feature was not necessary.
Dasser [14] showed that two Java monkeys were able
after a few trials, to identify novel views (full face or
full animal) of a familiar conspecific presented on
slides, and that another subject could match different
body parts of the same familiar group members. In a
subsequent experiment, Dasser [15] showed that two
adult female Java monkeys, first familiarised with slides
of their conspecifics, were able to identify mother - off-
spring pairs or to match views of offspring to their
mother, a task which requires the recognition of group
members on the slides.
In a recent study by our group [5], olive baboons
were trained on the natural category of food versus
non-food with real objects. After categorical transfer
with novel items, subjects were trained again with one
pair of cut-out pictures each of which belonged to the
two previously learned categories; after this limited
training, categorical transfer was high in both baboons
for cut-out photos of the food and non-food objects.
Results of the experiment and of additional control
situations involving various modes of picture presenta-
tions further demonstrated the abilities of the baboons
to relate real objects to their pictorial representations.
A consideration of studies using nonprimates reveals
that most of these experiments have been conducted
with birds, especially pigeons, but studies with other
zoological groups will be considered subsequently. One
of the first studies concerned with the question of
picture recognition in animals addressed the ability of
pigeons to recognise a conspecific shown in a picture
[62]. The authors used three pigeons with experimental
histories of attacking a mirror target, but not pictures,
and submitted them to an intermittent schedule of
reinforcement for key pecking; they found comparable
results for both temporal pattern and locus of attacks
(the head region) to that reported in studies with live,
taxidermally stuffed pigeons or mirror targets. Subse-
quent experiments demonstrated that an upright silhou-
ette, white-on-black silhouette of a pigeon, with or
without eye, was more effective in controlling attack
than an inverted silhouette, an outline of a pigeon, or a
piece of coloured paper.
A study of transfer of discrimination from solid
objects to pictures by pigeons was carried out by Cabe
[10]. The pigeons, which were naive with respect to
pictorial stimuli, were first trained to discriminate two
objects, and then four groups of four pigeons were
tested in reinforcement reversal with objects, black-and-
white photographs, silhouettes or line drawings of those
objects; negative transfer was expected in all cases if the
pigeons recognised the pictures. In fact, negative trans-