Nonlinear analysis of saccade speed fluctuations during combined action and perception tasks.
BACKGROUND
Saccades are rapid eye movements used to gather information about a scene which requires both action and perception. These are usually studied separately, so that how perception influences action is not well understood. In a dual task, where the subject looks at a target and reports a decision, subtle changes in the saccades might be caused by action-perception interactions. Studying saccades might provide insight into how brain pathways for action and for perception interact.


METHODS
We applied two complementary methods, multifractal detrended fluctuation analysis and Lempel-Ziv complexity index to eye peak speed recorded in two experiments, a pure action task and a combined action-perception task.


RESULTS
Multifractality strength is significantly different in the two experiments, showing smaller values for dual decision task saccades compared to simple-task saccades. The normalized Lempel-Ziv complexity index behaves similarly i.e. is significantly smaller in the decision saccade task than in the simple task.


METHODS
Compared to the usual statistical and linear approaches, these analyses emphasize the character of the dynamics involved in the fluctuations and offer a sensitive tool for quantitative evaluation of the multifractal features and of the complexity measure in the saccades peak speeds when different brain circuits are involved.


CONCLUSIONS
Our results prove that the peak speed fluctuations have multifractal characteristics with lower magnitude for the multifractality strength and for the complexity index when two neural pathways are simultaneously activated, demonstrating the nonlinear interaction in the brain pathways for action and perception.
Department of Physics, Politehnica University of Bucharest, 313 Spl. Independentei, RO 060042, Romania. Electronic address: cstan@physics.pub.ro.
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Stan
Physics Department, University Alexandru Ioan Cuza, 11 Blvd. Carol I., Iasi, Romania. Electronic address: corina_astefanoaei@yahoo.com.
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Astefanoaei
Eye-tracking & Visual Application Lab EVALab, Department of Medicine Surgery and Neuroscience, University of Siena, Siena 53100, Italy. Electronic address: elena.pretegiani@nih.gov.
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Pretegiani
Laboratory of Sensorimotor Research, IRP, National Eye Institute, DHHS, Bethesda, MD 20892, USA. Electronic address: lmo@lsr.nei.nih.gov.
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Optican
Physics Department, University Alexandru Ioan Cuza, 11 Blvd. Carol I., Iasi, Romania. Electronic address: dorina.creanga@gmail.com.
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Creanga
Eye-tracking & Visual Application Lab EVALab, Department of Medicine Surgery and Neuroscience, University of Siena, Siena 53100, Italy. Electronic address: rufa@unisi.it.
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Rufa
Department of Physics, Politehnica University of Bucharest, 313 Spl. Independentei, RO 060042, Romania. Electronic address: cpcris@physics.pub.ro.
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Cristescu
D001288:Attention / Q000502:physiology; D006801:Humans; D016014:Linear Models; D017711:Nonlinear Dynamics; D010775:Photic Stimulation; D011930:Reaction Time / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*
Action–perception task; Lempel–Ziv complexity; Multifractal properties; Saccade speed peak