D. Bo6et, J. Vauclair/Beha6ioural Brain Research 109 (2000) 143-165
145
was not totally devoid of pictorial representations (it is
impossible in the USA!), as he accidentally saw repre-
sentations of objects, for example, billboards on the
highway.
Even very early in life, infants are already able to
discriminate between 2-D and 3-D stimuli. Thus, Pipp
and Haith [76] observed that 4-week-old infants differ-
entiated 3-D from 2-D forms, with the 2-D forms
invoking shorter fixation times. This experiment was
repeated with 8-week-old infants who also processed a
3-D form in a different manner than a 2-D form, not in
terms of overall fixation time but in the visual scan
patterns elicited; there were more eye movements in
response to 3-D forms. An experiment carried out by
Appel and Campos [1] may offer some insight into how
infants differentiate 2-D and 3-D stimuli; results
showed that 8-week-old infants could discriminate be-
tween stimuli differing only in terms of binocular dis-
parity, that is, when they were habituated to
stereograms without retinal disparity and then pre-
sented with the same stereogram with retinal disparity,
heart rate increased indicating that they dishabituated.
Bower [6] studied the reaction of neonates when a
real ball or its colour photograph was presented at such
a distance that the ball could only be touched but no
grasped. The real object was frequently contacted but
the photograph not at all (it did not even elicit hand
raising) although the infants attentively stared at it. In
contrast, very young infants (under 23 days of age)
were shown to perform a similar amount of reaching in
the presence of either a three-dimensional ‘graspable’
object (an orange textured sphere) or a two-dimen-
sional picture of it [32]. Slater et al. [91] showed that
new-borns (mean age: 2 days and 21 h) could discrimi-
nate real objects from their photographs; all partici-
pants looked longer at the real objects, even with
monocular viewing, leading the authors to suggest that
motion parallax was a salient cue for this discrimina-
tion. Interestingly, there was no evidence that the new-
borns were able to recognise stimulus similarity across
dimensions, thus, for these new-borns, differences be-
tween objects and their two-dimensional representa-
tions seemed to be more detectable or salient than their
similarities.
Other investigations indicate that human babies are
not only able, with very little or no experience with
photographs, to discriminate these from real objects,
but also to recognise what they represent. In an experi-
ment carried out by Rose [81], 6-month-old infants
presented with various geometric stimuli were not only
able, in an habituation and visual preference test, to
discriminate 2-D from 3-D stimuli, but also to transfer
habituation from 2-D to similar 3-D stimuli, or in-
versely from 3-D to similar 2-D objects. This apparent
ease of processing objects and pictures in a similar way
is not, however, a consistently reported result. For
example, some authors found that very young children
(less than 30 months of age) did not interpret the
pictures as representing current reality; when the loca-
tion of a hidden toy was demonstrated using photo-
graphic stimuli, 24-month-olds did not use this
information to retrieve the toy, a task which 30-month-
olds readily performed [23].
Dirks and Gibson [30] have shown that 5-month-old
infants, without any experience of photographs, who
had previously been habituated to an unfamiliar, live
face, showed no change in fixation time when presented
with a slide of the same person, but dishabituated when
presented with a slide of a novel person who differed in
sex, hair colour, and hairstyle from the familiar face.
However, if the novel person was of the same sex, and
had the same hair colour and hairstyle as the familiar
face, no difference in fixation time was observed, sug-
gesting that these infants could see the similarity be-
tween a live person and their photograph using rather
gross physiognomic features. Similar findings are re-
ported in a study by Barrera and Maurer [2] who found
that 3-month-old babies who had never seen photo-
graphs looked longer at their mother’s photograph than
at a stranger’s one. Related evidence of an early sensi-
tivity of infants to pictures of conspecifics comes from
the study of the phenomenon of gaze following; for
example, Hood et al. [46] showed that 3-month-olds
could detect another individual’s gaze shifts even when
presented as digitised pictures of adult faces.
Cross-modal experiments can also be valuable in the
study of transfer from objects to pictures or the reverse.
Rose et al. [82] showed that such a transfer was possible
with 12-month-old infants, but that it depended on
familiarisation time: with a familiarisation time of 30 s,
infants were only able to perform a cross-modal trans-
fer from touch to vision (real objects), and to transfer
in a visual-visual task from real objects to both their
outline drawings and coloured silhouettes. With an
increased familiarisation time of 45 s, subjects were able
to cross-modally transfer from touch to real objects, to
their outline drawings and to their coloured silhouettes.
However, with a familiarisation time of 15 s, infants
were no longer able to transfer in a visual - visual task
from real objects to their outline drawings, or coloured
silhouettes.
Streri and Molina [92] conducted another experiment
on cross-modal transfer with infants of only 2 months
of age. Somewhat paradoxically, these authors found
that pictures were more easily recognised than real
objects in a transfer from vision to touch: transfer
occurred between felt objects and their 2-D visual sil-
houettes, but not between felt objects and their visual
counterparts. The authors hypothesised that this rela-
tive ease could be explained by the fact that infants take
more information from seeing stimuli than from touch-
ing them. Thus, the use of pictures could have sim-