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or of an empty room were presented to the subjects,
they showed much shorter, or no, display. Finally, the
duration of the display was longer when video images
were in motion rather than still and when only the head
region was visible rather then when only the body
region was visible.
An experiment carried out by McQuoid and Galef
[67] with juvenile Burmese fowls provides evidence that
observing feeding among conspecifics via video tapes
has similar effects as observing live conspecifics on
subsequent feeding behaviour (i.e. preferences for food
dishes); thus, the sight of a video of a conspecific
feeding before testing, even without sound, reduced the
latency of the first peck. Further, a videotape of a fowl
actually feeding on a food dish was more effective in
reducing the latency of the first peck and in enhancing
preference for that type of food dish than a videotape
simply representing a fowl (either active or immobile)
near a food dish.
Jenssen [49] studied the recognition of motion pic-
tures by lizards. In this study, female lizards could
choose between two films, one with males displaying
the normal courtship behaviour and the other with
males presenting altered displays; in most cases, the
females chose the normal displays. This experiment
suggests that female lizards could recognise male lizards
in the film and that they could be sensitive to their
behaviour. When video sequences displaying aggressive
displays of their own species were shown to male
lizards, these animals responded with the appropriate
responses (e.g. head-bobbing, crest erection) which they
would exhibit in front of live opponents. Moreover,
such behaviours were inhibited when video-recorded
sequences of heterospecific lizards were presented [65].
Some experiments have reported evidence of image
recognition in fishes, at least when video images (imply-
ing motion) were used. Thus, Rowland [85] showed that
male and female sticklebacks reacted to video images of
a zigzag dancing male played at a normal or slightly
faster tempo in a similar way as they would react to a
live male; when the tempo was slower or much faster
than the normal tempo, the animals were less attracted.
In guppies, consistency of mate preference was studied
by presenting females with males under three experi-
mental procedures: live males behind clear glass, live
males behind one-way glass and images of males on
videotapes. Females spent significantly more time in
proximity to males behind clear glass than in video and
one-way glass presentations, but they spent equal time
with males behind one-way glass and videotaped males
[58]. In all three experiments, females responded to
stimuli by displaying sexually oriented behaviours and
the results show that when interaction was not possible,
a videotaped male was as attractive as a real male.
Some studies suggest that even invertebrates can
recognise video images. For example, Clark and Uetz
[11] carried out an experiment with jumping spiders and
found that in a V-maze choice, spiders preferentially
chose a videotape with moving prey to a videotape
without prey. In addition, the spiders did not discrimi-
nate between a live prey and its simultaneously pre-
sented video image and they behaved in a manner
comparable to their reactions with life stimuli when
they were presented with televised images of prey in-
sects (attack), conspecifics (courtship) and heterospe-
cific spider species (retreat).
3.2. Acquired responses in picture recognition
We will now turn to a consideration of studies that
have attempted to test the abilities of different animal
species using pictures (still and in motion) as stimuli.
Although most of the experiments summarised below
were aimed at investigating picture recognition, we
have also considered experiments for which the explicit
goal was not picture recognition as these studies also
present findings relevant to this topic.
3.2.1. Reactions to still pictures
Hayes and Hayes [39] reared a female chimpanzee,
Vicki, in their home, almost like a human child. While
they did not specifically train her in picture perception,
they did test her ability to recognise pictures depicted in
books and other materials and to imitate actions illus-
trated in films, photographs, and line drawings. Vicki
was able to recognise most of the pictures she saw, even
when the pictures were presented as black-and-white
drawings. Nevertheless, those authors reported that
Vicki did not confuse photographs with real objects;
Vicki did not try to grasp 2-D objects and when she
pointed for example to pictures of beverages, she said
‘cup’, and let the person who was with her go to the
kitchen and get a drink. Gardner and Gardner [38]
showed that four chimpanzees that had been famil-
iarised with pictures could also recognise and name in
American Sign Language various objects represented
on new slides.
Sarah, an adult chimpanzee experienced with films
and photographs was shown videotaped scenes of a
human actor struggling with one of eight problems and
then presented with two photographs that could consti-
tute a solution to the problem [78]. Sarah chose the
correct photograph on seven of the eight problems
suggesting that she recognised both what happened in
the films and the objects as depicted in photographs
and as films. Furthermore, Savage-Rumbaugh et al.
[89] trained chimpanzees to categorise various objects
into the two categories ‘tools’ or ‘foods’; when the
objects were replaced by photographs (the subjects were
already familiarised with pictures), the two chimpanzees
tested were still able to categorise (and thus to recog-
nise) them.