Influence of Sparkle and Saccades on Tongue Electro-Stimulation-Based Vision Substitution of 2D Vectors
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Influence of Sparkle and Saccades on Tongue Electro-Stimulation-Based Vision Substitution of 2D Vectors Abdessalem Chekhchoukh • Nicolas Glade
Received: 11 January 2012 / Accepted: 17 January 2012 / Published online: 3 February 2012 Springer Science+Business Media B.V. 2012
Abstract Vision substitution by electro-stimulation has been studied since the 60s beginning with P. Bach-y-Rita. Camera pictures or movies encoded in gray levels are displayed using an electro-stimulation display device on the surface of a body part, such as the skin or the tongue. Medical-technical devices have been developed on this principle to compensate for sensory-motor disabilities such as blindness or loss of balance, or to guide specific actions, such as surgery. However, the electrical signals of stationary or moving slowly moving objects, displayed on a Tongue display unit (TDU), are quickly lost due to saturation of receptors undergoing electrostimulation. We propose to add random saccades or sparkle to the displayed visual scene to increase the quality of pattern recognition by the subjects. In the present experimental trimodal study (normal vision, TDU vision substitution, or both), we show that the presence of a moderate sparkle level enhances the perception of the direction of lines drawn on a TDU and reduces the response time. Keywords Sensory substitution Tongue display unit Vision Eye micro-saccades Sparkle
1 Introduction The eyes are not limited to an arrangement of photoreceptors like electronic sensors of digital cameras. These biologicals sensor also come with a neuromuscular motion control. In addition to playing a stabilizing role of the eye and gaze control, this also allows a feature of modern eyes to function: a reflex called micro-saccades. A. Chekhchoukh N. Glade (&) AGIM Laboratory (Laboratory of AGeing Imaging and Modeling), University of Grenoble, CNRS FRE 3405, Domaine de la Merci, 38700 La Tronche, France e-mail: [email protected]
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The ocular micro-saccades were introduced after millions of years by evolution certainly at the onset of evolved predators (Rodieck 2003). Indeed, they allow the predator to detect and hunt immobile preys while former predators (like reptiles) can not. When an eye is maintained stationary and forced to fix a visual scene, as it is the case in the Troxler’s fading effect (Troxler 1804), the scene perceived by the peripheral vision rapidly shades away and disappears. Eyes’ photoreceptors are saturated when subjects to an unvarying stimulation. In these conditions, the signal blends with the surrounding perceived scene. This constitutes a problem in the development of vision substitution systems based on electrostimulation on the skin or the tongue. Eyes’ moves, and in particular micro-saccades, avoid photoreceptors to be always stimulated by the same signal, so the scene is always refreshed and continues to be perceived. What is true for the eyes is certainly also true for other kinds of biological sensors. Sensory and in pa
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