Project Summary-Brij Saxena And Kuntal Das

EYE – A Window to the soul


Visible indication of mental work has always been a promising topic in the field of research for the psychologists. In an article in Scientific American, the psychologist Eckhard Hess has described the pupil of the eye as the window to the soul. In his article, Hess has described that how the variations in the size of pupil give indication of the mental work that the person is doing.

Pupils react not only to the changes of intensity of the light (pupillary light reflex) but also in reaction to arousal or emotions. For example Hess and Polt (1960) presented pictures of semi-naked adults and babies to adults (four men and two women). Pupils of both sexes dilated after seeing pictures of people of the opposite sex, but in females the difference in pupillary sizes occurred also after seeing pictures of babies, as well as mothers with babies. The scope of research in this topic has given rise to the subject of “cognitive pupillometry”.


How Variation In The Size Of Pupil Gives Indication Of Mental Work:

Pupils are sensitive indicators of mental effort. They dilate substantially when people do mental work like multiply two digit numbers, and they dilate more if the problems are hard than if they are easy.

With changing demands of the task, the size of the pupil varies second by second. The effort builds as our focus increases on the task, reaches its peak value and gradually decreases when we complete the task or we give up. Corresponding to this the size of the pupil gives an inverted ‘V’ graph. It shows that with increasing mental work the size of the pupil goes on increasing and it gradually shrinks when the task is over.

Different tasks require different level of mental work-

  • The mundane conversation demands little or no effort. The pupil remains small and do not noticeably dilate.

  • During the tasks which require high level of mental work such as multiplying a three digit number to a two digit number the size of the pupil can increase as much as 50% of the normal size.

  • When the given task is too tough for the person to perform, the size of the pupil shrinks as the mind decides to give up.


  • We performed our experiment on three people.

  • We took snapshots of their eye which depicted the variation in the size of their pupil during the course of the experiment.

  • The task given to the subject was that we gave them four digit numbers at intervals of 6 seconds. The subject has to answer after incrementing each digit of that number by 3, before the new number is announced.

  • Another task that was given was to mentally calculate the product of two two-digit numbers.


During the course of the experiment we observed remarkable variations in the pupil size. When the subjects were performing the tasks, the size of their pupil increased gradually, though there were many variations in the size. When the given task was over and the subjects were asked to relax, the size of their pupil gradually reduced to the normal size. Although the experiment was not performed in perfectly ideal setup but from the analysis of the collected data we can safely conclude that variations in the size of pupil indicate the level of mental work


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