"Long before it's in the papers"
January 27, 2015


Eyes betray numbers in our heads, study says

March 23, 2010
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.

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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 are thinking about. Participants in a University of Melbourne, Australia, study were asked to state a series of random numbers. By measuring their vertical and horizontal 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 select from a set of random numbers. Paced by an electronic metronome they named 40 numbers between one and 30 in a sequence as random as possible. For each number, the researchers measured the average eye position during the half-second before each numbers was declared.