The Eyes have it…and then not

22 Sep


I remember past readings from different sources about body language and face reading, that pupil responses can reveal much about the listener during dialogue.  I remember also from my training in medicine, how the pupil is innervated by nerve systems which categorically exists in two separate camps.  One is the sympathetic circuit, which seems to follow a particular concert of arousal activities.  During this state, there is a preparation for action e.g. physical  aggression.  The heart races, there is a movement of blood flow to central core survival pathways, the blood pressure increases and any mechanism for restorative functions are placed on hold (such as urination and digestion).  The parasympathetic circuit runs almost antagonistic to the sympathetic circuit,  It is most evident in slowing the heart rate, restorative and allows for eliminations and digestion.  This all made possible by the way organ systems respond to similar chemical messages.  How efficient this is!

Allow me to elaborate.  Epinephrine (adrenaline) is like sliding a long finger across three receptor buttons, each with different intensity



 This arrangement of buttons have a particular effect, as is consistent with epinephrine.  However, Dopamine, which is a precursor to epinephrine, has a structure similar, but not the same as epinephrine.  At low doses it acts on the same buttons (a1, a2 ,b1).  However, when the dose of dopamine is increased it begins to push a different set of buttons (a2, b1, b2).  Now instead of increasing the blood pressure, it begins to open up blood flow in regions consistent with a parasympathetic circuit, leading to decreased pressure and relaxing the bladder.  Such actions are common for many drugs, in that a change of dosing can have a significant change in effect.  This point helps people suffering from asthma may find some medicines are contraindicated for heart problems.  Beta 2 buttons open the airway, but beta 1 medicines cause hypertension and tend toward bronchioconstriction.

Now considering this sympathetic and parasympathetic matter, there seems to be an emotional interplay with pupil dilatation. When on is in love (infatuation), and the pupil dilates as when the sympathetic system kicks in.  The mouth gets dry, the hands sweat and the heart races.  This tells you that the pupil response is somehow tied directly into the limbic system,  or the emotional brain. Now if emotions seemed to fluctuate based on interest, it would be reasonable to assume that the expressions of the sympathetic system would follow.  In the following article I believe one may assume that decisions based solely on emotions would lead to a naive and loosely dedicated commitment to matters of interest.  What one would expect to see in a “naive audience” would be a highly reactive attention with a significant variability in the course of a discussion of a valued topic.

Read the following article and see if you would agree.

Pupil size shows reliability of decisions

Press release from PLOS Computational Biology

The precision with which people make decisions can be predicted by measuring pupil size before they are presented with any information about the decision, according to a new study published in PLOS Computational Biology this week.

The study, conducted by Peter Murphy and colleagues at Leiden University, showed that spontaneous, moment-to-moment fluctuations in pupil size predicted how a selection of participants varied in their successful decision making. A larger pupil size indicated poorer upcoming task performance, due to more variability in the decisions made once the relevant information was presented. The authors also found that certain individuals who had the largest pupils overall also tended to be the least consistent in their decisions.

The results were obtained by measuring pupil size before each segment of the task began and monitoring each participant’s subsequent performance in deciding which direction a cloud of dots was moving in. These results were then combined with a simple mathematical model that described how people make decisions.

These findings reveal that a person’s state of responsiveness, as measured by pupil size, is a key determinant of the variability of the decisions they make about the world around them.When hyper-responsive, our decision making appears to be less reliable and will more likely lead to undesirable outcomes. Critically, the findings also open up areas for future research aimed at improving the precision with which we make decisions, to help us achieve better outcomes from the choices that we make.

The results were obtained by measuring the pupil size of 26 volunteers as they performed a visual choice-based task designed to mimic the kinds of challenging perceptual decisions that are frequently encountered in everyday life. Pupil size gives a good indication of how responsive a person is at any given moment, with larger pupils correlating with increased responsiveness, though little was previously understood about how pupil size might relate to our ability to make reliable perceptual judgements.

Dr Murphy comments, “we are constantly required to make decisions about the world we live in. Researchers have long known that the accuracy and reliability of such everyday decision making can be tremendously variable for different people at different times, but we understand quite little about where this variability comes from. In this study, we show that how precise and reliable a person is in making a straightforward decision about motion can be predicted by simply measuring their pupil size. This finding suggests that the reliability with which an individual will make an upcoming decision is at least partly determined by pupil-linked ‘arousal’ or alertness, and furthermore, can potentially be deciphered on the fly. This new information could prove valuable for future research aimed at enhancing the precision of decision making in real time.”

All works published in PLOS Computational Biology are open access, which means that everything is immediately and freely available. Use this URL in your coverage to provide readers access to the paper upon publication:

Press-only preview: 

Contact Details:

Dr Peter Murphy


Phone: (071) – 527 3874

Citation: Murphy PR, Vandekerckhove J, Nieuwenhuis S (2014) Pupil-Linked Arousal Determines Variability in Perceptual Decision Making. PLoS Comput Biol 10(9): e1003854. doi:10.1371/journal.pcbi.1003854

Funding: This research was supported by a Starting Independent Researcher Grant of the European Research Council awarded to SN. JV was supported by NSF grant #1230118 from the Methods, Measurements, and Statistics panel. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.


About PLOS Computational Biology

PLOS Computational Biology features works of exceptional significance that further our understanding of living systems at all scales through the application of computational methods. All works published in PLOS Computational Biology are open access. Everything is immediately available subject only to the condition that the original authorship and source are properly attributed. Copyright is retained. For more information, visit, and follow @PLOSCompBiol on Twitter. 

About the Public Library of Science

PLOS is a nonprofit organization that accelerates progress in science and medicine by leading a transformation in research communication. For more information, visit


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