Vincent Lévesque


Virtual Display of Tactile Graphics and Braille by Lateral Skin Deformation

Vincent Lévesque

Ph.D. Thesis, McGill University, August 2009.

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Graphical content is increasingly pervasive in digital interfaces and documents yet it remains accessible to visually impaired persons almost exclusively on media with limited flexibility such as embossed paper. Textual content is more accessible but nevertheless limited by the cost and functionality of refreshable Braille displays and voice synthesis. This thesis explores the use of a novel tactile stimulation approach that relies on lateral skin deformation for the computerized display of virtual Braille and tactile graphics.

Tactile synthesis by lateral skin deformation is initially explored in the context of Braille. The feasibility of producing virtual Braille by laterotactile stimulation is first demonstrated by creating the illusion of brushing against a line of Braille dots through the synchronization of a travelling wave of skin deformation with the displacement of a tactile array of eight actuators. This principle is then extended to complete 6-dot Braille cells by distributing lines of virtual dots onto the rows of actuators of a general-purpose STReSS2 tactile array. Reading the resulting virtual Braille is shown to generally be feasible but demanding, suggesting that a specialized laterotactile Braille display should be devised or that dots be rendered for contrast rather than realism.

Tactile rendering by lateral skin deformation is then further explored with the gradual development of a virtual tactile graphics framework that emulates conventional features such as raised lines and areal textures through a coherent set of patterns that includes grating textures, stroked and dotted shapes, bitmap-based masks, and composite patterns. Dynamic rendering is also exploited to produce novel effects such as tactile flow, reactive textures dependent on the exploration behaviour, and interactive content with alternate views. The usability of the framework is informally evaluated with visually impaired volunteers and early tactile patterns studied through formal experiments. The tactile patterns are presented on the Tactograph, a haptic interface redesigned specifically for the display of tactile graphics that combines a STReSS2 display with an instrumented planar carrier.

This thesis demonstrates the potential of lateral skin deformation for the display of Braille and tactile graphics, and explores in the process the ways in which this novel approach to tactile stimulation can be applied to produce meaningful tactile sensations.

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