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BioMed Research International
Volume 2013 (2013), Article ID 420509, 11 pages
http://dx.doi.org/10.1155/2013/420509
Research Article

Investigation of Nonlinear Pupil Dynamics by Recurrence Quantification Analysis

1Mathematical Biology and Physiology Group, Department of Electronics and Telecommunications, Politecnico di Torino, Torino 10129, Italy
2Department of Health Sciences, Università di L’ Aquila, L’ Aquila 67010, Italy

Received 18 April 2013; Revised 13 August 2013; Accepted 27 August 2013

Academic Editor: Liam McGuffin

Copyright © 2013 L. Mesin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Pupil is controlled by the autonomous nervous system (ANS). It shows complex movements and changes of size even in conditions of constant stimulation. The possibility of extracting information on ANS by processing data recorded during a short experiment using a low cost system for pupil investigation is studied. Moreover, the significance of nonlinear information contained in the pupillogram is investigated. We examined 13 healthy subjects in different stationary conditions, considering habitual dental occlusion (HDO) as a weak stimulation of the ANS with respect to the maintenance of the rest position (RP) of the jaw. Images of pupil captured by infrared cameras were processed to estimate position and size on each frame. From such time series, we extracted linear indexes (e.g., average size, average displacement, and spectral parameters) and nonlinear information using recurrence quantification analysis (RQA). Data were classified using multilayer perceptrons and support vector machines trained using different sets of input indexes: the best performance in classification was obtained including nonlinear indexes in the input features. These results indicate that RQA nonlinear indexes provide additional information on pupil dynamics with respect to linear descriptors, allowing the discrimination of even a slight stimulation of the ANS. Their use in the investigation of pathology is suggested.