**Materials for the article "A Protracted Sensitive Period Regulates the Development of Crossmodal Sound-Shape Associations in Humans"**
**Format:** 3D objects (Stimulus pairs A and C) are in STL format. They can be viewed on OSF by clicking on the files, can be opened in most CAD software (a free and open-source CAD software is *FreeCAD*, available at [www.freecadweb.org][1]), or can be verified/viewed at a web STL viewer like [www.viewstl.com][2] (MIT-licensed). The authors used the software *Cura* and printed the stimuli with an *Ultimaker 2* 3D printer ([ultimaker.com/software/ultimaker-cura][3]).
2/2.5D forms (Stimulus pairs B and E) are in SVG and PDF formats which can be used with a compatible laser cutter/printer to produce the stimuli. For laser cutting, the authors used the *VisiCut* sotware ([visicut.org][4]).
**Funding:** European Research Council grant ERC-2009-AdG 249425-CriticalBrainChanges and DFG Ro 2625/10-1 to Brigitte Röder.
**Released under Creative Commons Attribution 4.0 International (CC BY 4.0): the materials can be used and modified freely given that there is attribution. Please cite the corresponding article!**
The authors assert that there are no competing interests. The materials are provided as-is and the authors cannot be held liable for any issues ensuing from the use of the materials.
**Design credit for stimulus pair A:** Arafat Hussain
**All presented stimuli laser cut/3D printed at the non-profit Fab Lab [Fabulous St Pauli][5], Hamburg**, with the kind help of Axel Sylvester.
[1]: http://www.freecadweb.org
[2]: http://www.viewstl.com
[3]: http://ultimaker.com/software/ultimaker-cura
[4]: http://visicut.org
[5]: http://www.fablab-hamburg.org/ "Fabulous St. Pauli"
