Eyes betray numbers in our heads

Courtesy of the
University of Melbourne
and World Science staff
It may be harder to lie about your age, or your pok­er hand, af­ter new re­search has found that our eye po­si­tion be­trays the num­bers we’re think­ing about.

Par­ti­ci­pants in a Uni­vers­ity of Mel­bourne, Aus­tral­ia, study were asked to state a se­ries of ran­dom num­bers. By meas­ur­ing their eye po­si­tion, re­search­ers said they could re­liably pre­dict the next cho­sen num­ber—be­fore it was spo­ken.

A left­ward and down­ward change in eye po­si­tion an­nounced that the next num­ber would be smaller than the last, the sci­en­tists said. Cor­re­spond­ingly, up­ward and right­ward fore­cast a larg­er num­ber than the last. The de­gree of eye move­ment re­flected the size of the nu­mer­i­cal shift.

The pa­per was pub­lished March 23 on­line in the re­search jour­nal Cur­rent Bi­ol­o­gy.

“When we think of num­bers we au­to­mat­ic­ally code them in space, with smaller num­ber fall­ing to the left and larg­er num­bers to the right. That is, we think of them along a left-to-right ori­ented men­tal num­ber line—often with­out even no­tic­ing this num­ber-space as­socia­t­ion our­selves,” said re­searcher To­bi­as Loetscher of the uni­vers­ity, an au­thor of the stu­dy.

“This study shows that shifts along the men­tal num­ber line are ac­com­pa­nied by sys­tem­at­ic eye move­ments. We sug­gest that when we nav­i­gate through men­tal rep­re­senta­t­ions—as for ex­am­ple num­bers—we re-use brain pro­cesses that pri­marily evolved for in­ter­act­ing and nav­i­gat­ing in the out­side world.”

“This study will hope­fully pro­vide a tem­plate to in­ves­t­i­gate how the hu­man mind works via a con­nec­tion with the space and world around us,” added co-au­thor Mi­chael Nicholls.

The study in­volved ask­ing twelve right-hand­ed men to name 40 num­bers be­tween one and 30 in a se­quence as ran­dom as pos­si­ble, paced by a met­ro­nome. For each num­ber, the re­search­ers meas­ured the av­er­age eye po­si­tion dur­ing the half-sec­ond be­fore each num­bers was de­clared.