@article{ref1,
title="Systems of spatial reference and their interactions in preschool children. I. Degree of constraint in perceptive data",
journal="Année psychologique",
year="1973",
author="Berthoud, M.",
volume="73",
number="1",
pages="23-36",
abstract="<p>[Abstract unavailable]</p><p>Language: fr</p>",
language="fr",
issn="0003-5033",
doi="",
url="http://dx.doi.org/"
}