Interaction effects in simultaneous motor control and movement perception tasks

Recent findings in neuroscience suggest an overlap between those brain regions involved in the control and execution of movement and those activated during the perception of another’s movement. This so called ‘mirror neuron’ system is thought to underlie our ability to automatically infer the goals and intentions of others by observing their actions. Kilner et al. (Curr Biol 13(6):522–525, 2003) provide evidence for a human ‘mirror neuron’ system by showing that the execution of simple arm movements is affected by the simultaneous perception of another’s movement. Specifically, observation of ‘incongruent’ movements made by another human, but not by a robotic arm, leads to greater variability in the movement trajectory than observation of movements in the same direction. In this study we ask which aspects of the observed motion are crucial to this interference effect by comparing the efficacy of real human movement to that of sparse ‘point-light displays’. Eight participants performed whole arm movements in both horizontal and vertical directions while observing either the experimenter or a virtual ‘point-light’ figure making arm movements in the same or in a different direction. Our results, however, failed to show an effect of ‘congruency’ of the observed movement on movement variability, regardless of whether a human actor or point-light figure was observed. The findings are discussed, and future directions for studies of perception-action coupling are considered.     

The computational exploration of visual word recognition in a split model

We argue that the projection of the visual field to the cortex constrains and informs the modeling of visual word recognition. On the basis of anatomical and psychological evidence, we claim that the higher-level cognition involved in word recognition does not completely transcend initial foveal splitting. We present a schematic connectionist model of word recognition that instantiates the precise splitting of the visual field and the contralateral projection of the two hemifields. We explore the special nature of the exterior (i.e., first and last) letters of words in reading. The model produces the correct behavior spontaneously and robustly. We analyze this behavior of the model with respect to words and random patterns and conclude that the systematic division of the visual input has predictable, general informational consequences and is chiefly responsible for the exterior letters effect.     

Key-space analysis of double random phase encryption technique

We perform a numerical analysis on the double random phase encryption/decryption technique. The key-space of an encryption technique is the set of possible keys that can be used to encode data using that technique. In the case of a strong encryption scheme, many keys must be tried in any brute-force attack on that technique. Traditionally, designers of optical image encryption systems demonstrate only how a small number of arbitrary keys cannot decrypt a chosen encrypted image in their system. However, this type of demonstration does not discuss the properties of the key-space nor refute the feasibility of an efficient brute-force attack. To clarify these issues we present a key-space analysis of the technique. For a range of problem instances we plot the distribution of decryption errors in the key-space indicating the lack of feasibility of a simple brute-force attack.     

Biodilution of heavy metals in a stream macroinvertebrate food web: evidence from stable isotope analysis

Analysis of carbon (delta13C) and nitrogen (delta15N) stable isotopes provides an increasingly important means of understanding the complex trophic structure of macroinvertebrate communities in streams. We coupled a stable isotope approach with a contaminant analysis of six metals (Pb, Ag, Zn, Hg, Cu, As) to trace the accumulation and dilution of metals from an abandoned mine across trophic levels of the benthic community in Ginzan Creek, Japan. The delta15N signature increased with trophic level, with mean increases of 4.70 per thousand from producers to primary consumers and 3.06 per thousand from primary to secondary consumers. Tissue Pb and Ag concentrations were negatively correlated with delta15N, indicating biodilution of both metals through the food web. Although macroinvertebrate taxon body mass was negatively correlated with tissue metal concentration at several sites, it did not increase with trophic level (as delta15N) in any of the sites, suggesting that changes in body mass were not the cause of biodilution. Our findings suggest invertebrates at higher trophic levels may exhibit increasingly efficient excretion of metals. Autotrophic epilithon (mean delta13C= -21.3 per thousand) had a much higher concentration of mined metals than did riparian vegetation (mean delta13C= -29.3 per thousand); nonetheless, a carbon-mixing model indicated that taxa feeding on autochthonous carbon sources did not accumulate more metal than allochthonous feeders. It is likely that the notably high metal concentration of allochthonous FPOM plays an important role in the trophic transfer of metals. Our data suggest the strong potential for stable isotope analysis to enhance our understanding of metal transfer through stream macroinvertebrate food webs.