A human-computer interface based on the “voluntary” pupil accommodative response

Objectives: Changes in pupil size are governed by the autonomic nervous system but may be systematically driven by voluntary shifting the gaze in depth. Thus, the pupil accommodative response (PAR) that accompanies voluntary gaze shifts from a far to a near target might be exploited as a simple human-computer interface (HCI), bypassing the somato-motor system. Here we aim to characterize PAR in quasi-natural conditions with low-cost equipment and test the possibility to use PAR as a binary communication tool. Methods: Nineteen healthy subjects were instructed to voluntary switch the focus from a far to a near target upon presentation of an auditory cue. Three protocols addressed the effects of monocular/binocular vision, eye illuminance, duration of near vision, target texture and target brightness on PAR features. In a fourth protocol PAR was used to establish binary communication at different bit rates. Results: PAR amplitude decreased with increasing eye illuminance and was modulated by monocular/binocular vision, duration of near vision or target texture. PAR amplitude was larger with a bright near target and a dark far target than vice-versa. However, PAR was always clearly present, regardless of the experimental manipulations. PAR-based communication performance achieved an accuracy of 100% at 10 bits/min and 96% at 15 bits/min. Significance: Voluntary PAR is a robust signal, and can achieve a high communication speed when used as an HCI. This study provides a proof of concept for a PAR-based HCI, potentially useful to communicate with locked-in patients with preserved visual and autonomic functions.