Mackay, C. K., Brazendale, A. H., & Wilson, L. F. (1972). Concepts of horizontal and vertical: A methodological note. Developmental Psychology, 7(3), 232-237.
http://dx.doi.org/10.1037/h0033344
Presented 4 tasks involving the representation of horizontal or vertical lines to 81 7-9 yr. olds. The tasks had been intuitively judged by the Es as either simple or complex. Results confirm these judgments and indicate that difficulties arise in the interpretation of children's performance on such tasks. Children may be seen as developing 1 concept prior to the other, depending on the tests selected. A further finding is that the Ss in this study did not reach a level in the development of these concepts expected by Piaget of 9 yr. olds. (PsycINFO Database Record (c) 2016 APA, all rights reserved)