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plified and reduced visual information, consequently
rendering the object more easily identifiable for the
infant who had only tactile experience of the object.
Subsequent experiments performed by the same authors
using the habituation procedure provided some evi-
dence that 2-month-old babies were able to perceive
both the commonalties and the differences of 3-D ob-
jects and their 2-D representations.
Experiments measuring event-related potentials have
reached the same conclusion as most of the experiments
presented above. Recordings of ERPs in 7-month-old
babies while they were watching pictures of faces
showed that the active components differentiated be-
tween a happy face and a fearful face but not between
an angry face and a fearful face [71], suggesting that the
infants recognised what was presented on the pictures.
Perhaps the most impressive demonstration of young
infants’ abilities in interpreting pictorial representations
can be found in a study on intermodal transfer between
oral exploration of objects and visual matching. In
effect, in two experiments, Kaye and Bower [52]
showed that new-borns as young as 12 h old were able
to match tactile shapes (pacifiers) with visual represen-
tations of the pacifiers’ shafts displayed as digitised
coloured or black-and-white images on a computer
screen.
In summary, cross-cultural studies have demon-
strated that adults who have never seen any two-dimen-
sional representations may experience difficulties
recognising pictures; these participants need some ex-
planation and some experience with a photograph (or a
drawing) before being able to perceive what it repre-
sents. However, developmental studies reveal that the
ability to recognise significant information in pictures
such as photographs is evident even in very early
infancy (demonstrated at 3 months or even younger).
This apparent paradox between adult and infant perfor-
mance will be discussed in the conclusion of this article.
Human babies are also able to discriminate real objects
from their pictorial representations; this precocious
ability does not, however, preclude infants and even
toddlers from confusing an object and its referents. The
methods, populations and main results of the studies
discussed above are summarised in Table 1.
3. Studies with animals: convincing demonstrations
3.1. Spontaneous responses to pictures
In this section, studies that provide rather unambigu-
ous evidence of spontaneous responses to pictures as if
they were real objects are considered; studies using
static and motion pictures will be presented in turn.
3.1.1. Responses to still pictures
The perception of still pictures can elicit adapted
responses by monkeys. Thus, von Heusser [43] reported
that a tamed marmoset displayed grabbing responses in
front of photographs representing different prey (e.g.
ants, butterflies) but displayed fear reactions when
shown a picture of a cobra. In a similar vein, Rosenfeld
and van Hoesen [83] related that naive rhesus monkeys
reacted with hasty retreat, threat responses and vocali-
sations to the first presentation of slides of rhesus
monkeys’ faces. These monkeys also displayed abortive
approach-retreat before touching the stimuli (i.e. the
slide projector), this behaviour did not persist, however,
because the subjects quickly realised that the stimuli
were only pictures (i.e. unresponsive, immobile stimuli).
Comparable findings were obtained with cynomolgus
macaques by Kyes et al. [60], namely, that dominant
monkeys produced threatening gestures when shown,
for example, pictures of gorillas or humans, while sub-
ordinates gave submissive responses to these same
stimuli.
Sackett [87,88] presented real-life-size coloured slides
of various social stimuli to rhesus monkeys; subjects
exhibited different responses to the various stimuli,
many of these responses being appropriate to the situa-
tion. Moreover, the level of responses to a given slide
varied according to age and rearing conditions: subjects
reared in isolation showed more exploration of non-
monkey pictures and pictures without any social com-
munication content than with socially relevant pictures.
Results of another experiment [59] with hamadryas
baboons suggest that these monkeys were able to recog-
nise slides of conspecifics. Subjects were given control
over slide selection and viewing time, with some slides
depicting individual troop members and others depict-
ing various facial areas of a troop member; the baboons
were highly reliable in their choices, with dominance
status seemingly a primary factor in troop member
preference and slides of full faces being consistently
chosen and the eye region attracting the greatest
attention.
Overman and Doty [72] have investigated hemi-
spheric specialisation for face processing in pigtail
macaques. Prior to testing, the authors examined if
their subjects would react in a similar manner to real
models and pictures of humans and monkeys; various
emotional reactions were measured (e.g. vocalisations,
lip-smacking, etc.) at the first presentation of different
categories of slides and results showed that pictures of
humans and monkeys were clearly differentiated from
other classes of stimuli such as flowers, insects or
landscapes.
The available neurophysiological evidence supports
the view that nonhuman primates establish some corre-
spondence between photographs and the individual
monkeys they represent. For instance, studies with