Zener cards

[7] In his book, The New Apocrypha, John Sladek expressed incredulity at the tests, stating, "It's astonishing that playing cards should have been chosen for ESP research at all.

[8] Terence Hines has written of the original experiments: The methods the Rhines used to prevent subjects from gaining hints and clues as to the design on the cards were far from adequate.

Methodological problems with his experiments eventually came to light, and as a result, parapsychologists no longer run card-guessing studies and rarely even refer to Rhine’s work.

"[10] The chemist Irving Langmuir called Rhine's experiments an example of pathological science–"the science of things that aren't so," as he described it–and criticized its practitioners not as dishonest people but as ones that have sufficiently fooled themselves.

[12] In 2016, Massimo Polidoro tested an Italian mother and daughter who were claiming a 90% and above success rate of psychic transmission using Zener cards.

The women were cognizant of the fact that they required visual contact to achieve transmission of the symbols, saying, "This kind of understanding is so natural to us, all this attention to us is also very surprising.