caratterizzazione della risposta pupillare a diverse profondità di fuoco per applicazioni BCI

The pupil accommodative response (PAR) has been recently studied as a possible binary communication mean for patients affected by neurodegenerative disorders such as Amyotrophic Lateral Sclerosis (ALS), with successful results. These patients may enter, in later stages, the so called complete locked-in state, which implies the impossibility of any communication with the external world. However, smooth muscles such as those controlling the pupils appear to be preserved in this condition. Furthermore, simple binary communication (i.e., constriction vs. no constriction) is slow and the possibility to exploit multiple level of constriction to increase the communication possibilities and the information transfer rate has not been previously explored. The purpose of this thesis is to characterize the dependence of pupil constriction on focal distance and to explore potential Brain-Computer Interface (BCI) applications. We studied the pupil response in 16 healthy subjects through a pair of pupil tracker glasses (pupil-labs). Subjects were asked to shift their focus between several printed textual targets located at different distance from the eye, upon auditory cues and according to seven different protocols, that differed for the number of visual targets, their distance from the eye, the order of presentation and the time duration each target had to be attended. Results consolidate previous findings about the decrease of pupil size changes with depth of focus, highlighting a strong non-linear relation, whereby larger size changes occur at short distance from the eye. Moreover, pupil size attained at different depth levels exhibits poor repeatability. These preliminary indications suggest a limit for BCI applications of no more than 3-4 different constriction levels. Still, these results encourage further investigations of this topic since even an increase from 2 to 4 levels would result in a 4-fold increase in information transfer rate.