Cognitive Science 42 (2018) 664–677
Copyright © 2017 The Authors. Cognitive Science published by Wiley Periodicals, Inc. on behalf of
Cognitive Science Society.
All rights reserved.
ISSN: 0364-0213 print / 1551-6709 online
Spontaneous Emergence of Legibility in Writing Systems:
The Case of Orientation Anisotropy
Minds and Tradition Research Group, Max Planck Institute for the Science of Human History
Received 29 May 2014; received in revised form 8 July 2017; accepted 14 August 2017
Cultural forms are constrained by cognitive biases, and writing is thought to have evolved to ﬁt
basic visual preferences, but little is known about the history and mechanisms of that evolution.
Cognitive constraints have been documented for the topology of script features, but not for their
orientation. Orientation anisotropy in human vision, as revealed by the oblique effect, suggests that
cardinal (vertical and horizontal) orientations, being easier to process, should be overrepresented
in letters. As this study of 116 scripts shows, the orientation of strokes inside written characters
massively favors cardinal directions, and it is organized in such a way as to make letter recogni-
tion easier: Cardinal and oblique strokes tend not to mix, and mirror symmetry is anisotropic,
favoring vertical over horizontal symmetry. Phylogenetic analyses and recently invented scripts
show that cultural evolution over the last three millennia cannot be the sole cause of these effects.
Keywords: Orientation anisotropy; Oblique effect; Symmetry; Cultural evolution; Neural recycling
Written signs are created by human brains to be read by human brains. Their shape
can instruct us about two issues central to the ﬁeld of cultural evolution: the inﬂuence of
cognitive constraints on cultural forms (Sperber & Hirschfeld, 2004) and the origins of
functional complexity in culture (Tennie, Call, & Tomasello, 2009). The visual appear-
ance of most scripts ﬁts basic constraints of the human visual system (Changizi &
Correspondence should be sent to Olivier Morin, Max Planck Institute for the Science of Human History,
Jena, Germany. E-mail: firstname.lastname@example.org
This is an open access article under the terms of the Creative Commons Attribution License, which
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