A large body of research has shown spatial distortions in the perception of tactile distances on the skin. For example, perceived tactile distance is increased on sensitive compared to less sensitive skin regions, and larger for stimuli oriented along the medio-lateral axis than the proximo-distal axis of the limbs. In this study we aimed to investigate the spatial coherence of these distortions by reconstructing the internal geometry of tactile space using multidimensional scaling (MDS). Participants made verbal estimates of the perceived distance between 2 touches applied sequentially to locations on their left hand. In Experiment 1 we constructed perceptual maps of the dorsum of the left hand, which showed a good fit to the actual configuration of stimulus locations. Critically, these maps also showed clear evidence of spatial distortion, being stretched along the medio-lateral hand axis. Experiment 2 replicated this result and showed that no such distortion is apparent on the palmar surface of the hand. These results show that distortions in perceived tactile distance can be characterized by geometrically simple and coherent deformations of tactile space. We suggest that the internal geometry of tactile space is shaped by the geometry of receptive fields in somatosensory cortex.
In recent years, the data traffic has grown exponentially and the forecasts indicate a huge market that could be addressed by communication infrastructure and service providers. However, the processing capacity, space, and energy consumption of the available technology is a serious bottleneck for the exploitation of these markets. Chip-integrated optical communication systems hold the promise of significantly improving these issues related to the current technology. At the moment, the answer to the question which material is best suited for ultrafast chip integrated communication systems is still open. In this manuscript we report on ultrafast graphene photodetectors with a bandwidth of more than 76 GHz well suitable for communication links faster than 100 GBit/s per channel. We extract an upper value of 7.2 ps for the timescale in which the bolometric photoresponse in graphene is generated. The photodetectors were fabricated on 6" silicon-on-insulator wafers in a semiconductor pilot line, demonstrating the scalable fabrication of high-performance graphene based devices. Optical communication in general and especially chip integration of optic and electronic components has been considered as a promising way to significantly increase the performance of datalinks in terms of capacity, energy consumption, and costs [1-3]. The current bottleneck that hinders the mass production of chip integrated electro-optic components like modulators and photodetectors is the lack of a material that is compatible to established processing technology of chips while giving high performance devices. The electronic and optic properties of graphene [4], the two dimensional allotrope of carbon, were studied extensively in the last years [5-9]. Moreover, competitive chip-integrated electro-optical devices like electro-optical modulators [10,11], efficient waveguide heaters [12] and ultrafast photodetectors [13-16] were fabricated using graphene as active material. The performance of graphene photodetectors on integrated silicon waveguides in terms of speed and sensitivity has improved significantly in the last years and the gap between the performance of graphene and competing technologies is vanishing [17-21]. The possible monolithic integration on various substrates that are not necessarily crystalline is a key merit that distinguishes graphene from Ge or III/V materials. The bandwidth reported for graphene photodetectors of up to 65 GHz [16] and sensitivity around 0.4 A/W without bias and 1 A/W with bias [22] underline the potential of graphene for chip integrated photodetectors. Besides an excellent device performance the integration in a large scale production environment is essential. However, the introduction of new materials into an existing fabrication process flow and the required adoption as well as development of entirely new process steps are among the most challenging tasks in the fabrication of integrated circuits. So far, graphene photodetectors on silicon waveguides were fabricated on small chips and the transition to w...
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