Michele Sinico,  The Influence of Directionality on the Giovanelli Illusion.   journal   = {International Journal of Psychological and Behavioral Sciences}, [online]. World Academy of Science, Engineering and Technology.
    November 2018, vol. 144(12). 1632 - 1635
    [viewed 29 November 2021]. Available from: https://publications.waset.org/pdf/10009863.