Spatial patterns presented on the tongue using electro-tactile sensory substitution devices (SSDs) have been suggested to be recognized better by tracing the pattern with the tip of the tongue. We examined if the functional benefit of tracing is overcoming the poor sensitivity or low spatial resolution at the back of the tongue or alternatively compensating for limited information processing capacity by fixating on a segment of the spatial pattern at a time. Using a commercially available SSD, the Brainport, we compared letter recognition performance in three presentation modes; tracing, static, and drawing. Stimulation intensity was either constant or increased from the tip to the back of the tongue to partially compensate for the decreasing sensitivity. Recognition was significantly better for tracing, compared to static and drawing conditions. confusion analyses showed that letters were confused based on their characteristics presented near the tip in static and drawing conditions. the results suggest that recognition performance is limited by the poor spatial resolution at the back of the tongue, and tracing seems to be an effective strategy to overcome this. Compensating for limited information processing capacity or poor sensitivity by drawing or increasing intensity at the back, respectively, does not improve the performance. Visual-to-tactile sensory substitution devices (SSDs) convey visual information to a blind person through touch. Since the seminal work of Bach-y-Rita in the 1960s 1 , tactile representation of visual information has been studied on various body parts including the back 1,2 , abdomen 3-5 , fingers 6-8 , and tongue 9-11. The tongue has been suggested to be a good platform for SSDs because it has higher sensitivity and spatial resolution compared to other body parts 9,12. Users can recognize simple shapes, differentiate a small set of objects, detect motion, point to and avoid high-contrast-staged obstacles when the stimulus is presented sufficiently on the tongue (roughly 30 seconds) 9,13-17. However, navigation and object recognition tasks in real-life situations, where the scene is usually dynamic, may require these tasks to be achieved at shorter times. Vincent, et al. 18 showed that when a stimulus is presented for a short time (0.5 seconds), performance in discriminating basic shapes was not significantly above chance and performance in discriminating different line orientations deteriorated substantially compared to those reported by previous studies. They attributed the better performance in the earlier studies to the longer stimulation durations. This allowed participants to explore the stimulus actively and serially using the tip of the tongue ("tip" from here on), which may be required for spatial recognition through tactile input 19. Our experience with the BrainPort, an FDA-cleared electro-tactile tongue SSD (Wicab Inc., Madison, WI), is consistent with Vincent, et al. 18. The BrainPort delivers the visual information acquired through a head-mounted camera to a 20 × 20 grid...

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What we perceive is modulated by the context in which it appears. Contextual modulations are especially robust when processing upright face stimuli but are found throughout the human visual system. Face contextual modulations have been attributed to specialized (holistic) mechanisms implemented in high-level regions of the processing hierarchy. Here we examine their potential functional link to low-level contextual mechanisms, i.e. the relationship of contextual modulations between basic (contrast detection task) and complex (face) stimuli (eye matching task). Face stimuli were shown in upright and inverted orientations, to investigate the extent to which the neural specialization for upright faces influences the potential functional link between low- and high-level contextual mechanisms. Both the profile and magnitude of the contextual modulations correlated between inverted eye matching and contrast detection tasks. Neural specialization modulated this functional relationship as contextual modulation in upright eye matching and contrast detection tasks only correlated at the level of their profile suggesting the functional independence but the similar working principles of the mechanisms involved. The combined study of low- and high-level contextual modulations sheds new light on the functional relationship between the different levels of the visual processing hierarchy, and thus on its functional organization.

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