Treacherous pavements:Paving slab patterns modify intended walking directions

Current understanding in locomotion research is that, for humans, navigating natural environments relies heavily on visual input; in contrast, walking on even ground in man-made obstacle and hazard-free environments is so highly automated that visual information derived from floor patterns should not affect locomotion and in particular have no impact on the direction of travel. The vision literature on motion perception would suggest otherwise; specifically that oblique floor patterns may induce substantial veering away from the intended direction of travel due to the so-called aperture problem. Here, we tested these contrasting predictions by letting participants walk over commonly encountered floor patterns (paving slabs) and investigating participants' ability to walk "straight ahead" for different pattern orientations. We show that, depending on pattern orientation, participants veered considerably over the measured travel distance (up to 8% across trials), in line with predictions derived from the literature on motion perception. We argue that these findings are important to the study of locomotion, and, if also observed in real world environments, might have implications for architectural design

Non-linear perfect reconstruction filter banks for image coding

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A novel secure H.264 transcoder using selective encryption

In digital broadcast TV systems, video data is normally encrypted before transmission. For in-home redistribution, it is often necessary to transcode the bitstream to achieve optimum utilization of available bandwidth. If a signal is decrypted before transcoding and re-encrypted, this may lead to a security loophole. This paper presents a solution in the form of a novel H.264 selective encryption algorithm that encrypts sign bits of transform coefficients and motion vectors to allow secure transcoding without decryption. The performance of this system is compared with I-frame encryption. The results show that sign encryption is more secure than I-frame encryption and has a lower complexity. A hybrid system using a modified transcoder and sign encryption is found to give an optimal compromise between security and transcoding performance

The influence of visual flow and perceptual load on locomotion speed

Visual flow is used to perceive and regulate movement speed during locomotion. We assessed the extent to which variation in flow from the ground plane, arising from static visual textures, influences locomotion speed under conditions of concurrent perceptual load. In two experiments, participants walked over a 12-m projected walkway that consisted of stripes that were oriented orthogonal to the walking direction. In the critical conditions, the frequency of the stripes increased or decreased. We observed small, but consistent effects on walking speed, so that participants were walking slower when the frequency increased compared to when the frequency decreased. This basic effect suggests that participants interpreted the change in visual flow in these conditions as at least partly due to a change in their own movement speed, and counteracted such a change by speeding up or slowing down. Critically, these effects were magnified under conditions of low perceptual load and a locus of attention near the ground plane. Our findings suggest that the contribution of vision in the control of ongoing locomotion is relatively fluid and dependent on ongoing perceptual (and perhaps more generally cognitive) task demands