Grasping at laws:Speed-accuracy trade-offs in manual prehension

Most of human performance is subject to speed-accuracy trade-offs. For spatially constrained aiming, the trade-off is often said to take the specific form of Fitts' law, in which movement duration is predicted from a single factor combining target distance and target size. However, efforts to extend this law to the three-dimensional context of reaching to grasp (prehension) have had limited success. We suggest that there are potentially confounding influences in standard grasping, and we introduce a novel task to regularize the direction of approach and to eliminate the influences of nearby surfaces. In six participants, we examined speed-accuracy trade-offs for prehension, manipulating the depth (in the plane of the reach), height (orthogonal to the reach), and width (the grasped dimension) of the target object independently. We obtained lawful relationships that were consistent at the group and individual levels. It took longer to reach for more distant objects, and more time was allowed when placing the fingers on a contact surface smaller in either depth or height. More time was taken to grasp wider objects, but only beyond a critical width that varied between individuals. These speed-accuracy trade-offs showed substantial departures from Fitts' law, and were well described by a two-factor model in which reach distance and object size have separate influences on movement duration. We discuss empirical and theoretical reasons for preferring a two-factor model, and we propose that this may represent the most general form of speed-accuracy trade-off, not only for grasping but also for other spatially constrained aiming tasks. (PsycINFO Database Record [Abstract copyright: (c) 2018 APA, all rights reserved).

Quantifying the RR of harm to self and others from substance misuse:results from a survey of clinical experts across Scotland

OBJECTIVE: To produce an expert consensus hierarchy of harm to self and others from legal and illegal substance use. DESIGN: Structured questionnaire with nine scored categories of harm for 19 different commonly used substances. SETTING/PARTICIPANTS: 292 clinical experts from across Scotland. RESULTS: There was no stepped categorical distinction in harm between the different legal and illegal substances. Heroin was viewed as the most harmful, and cannabis the least harmful of the substances studied. Alcohol was ranked as the fourth most harmful substance, with alcohol, nicotine and volatile solvents being viewed as more harmful than some class A drugs. CONCLUSIONS: The harm rankings of 19 commonly used substances did not match the A, B, C classification under the Misuse of Drugs Act. The legality of a substance of misuse is not correlated with its perceived harm. These results could inform any legal review of drug misuse and help shape public health policy and practice

Structure of the Golgi and Distribution of Reporter Molecules at 20°C Reveals the Complexity of the Exit Compartments

Incubating cells at 20°C blocks transport out of the Golgi complex and amplifies the exit compartments. We have used the 20°C block, followed by EM tomography and serial section reconstruction, to study the structure of Golgi exit sites in NRK cells. The dominant feature of Golgi structure in temperature-blocked cells is the presence of large bulging domains on the three trans-most cisternae. These domains extend laterally from the stack and are continuous with “cisternal” domains that maintain normal thickness and alignment with the other stacked Golgi cisternae. The bulging domains do not resemble the perpendicularly extending tubules associated with the trans-cisternae of control cells. Such tubules are completely absent in temperature-blocked cells. The three cisternae with bulging domains can be identified as trans by their association with specialized ER and the presence of clathrin-coated buds on the trans-most cisterna only. Immunogold labeling and immunoblots show a significant degradation of a medial- and a trans-Golgi marker with no evidence for their redistribution within the Golgi or to other organelles. These data suggest that exit from the Golgi occurs directly from three trans-cisternae and that specialized ER plays a significant role in trans-Golgi function

Muscle Nicotinic Acetylcholine Receptors May Mediate Trans-Synaptic Signaling at the Mouse Neuromuscular Junction

Block of neurotransmitter receptors at the neuromuscular junction (NMJ) has been shown to trigger upregulation of the number of synaptic vesicles released (quantal content, QC), a response termed homeostatic synaptic plasticity. The mechanism underlying this plasticity is not known. Here, we used selective toxins to demonstrate that block of α1-containing nicotinic acetylcholine receptors (nAChRs) at the NMJ of male and female mice triggers the upregulation of QC. Reduction of current flow through nAChRs, induced by drugs with antagonist activity, demonstrated that reduction in synaptic current per se does not trigger upregulation of QC. These data led to the remarkable conclusion that disruption of synaptic transmission is not sensed to trigger upregulation of QC. During studies of the effect of partial block of nAChRs on QC, we observed a small but reproducible increase in the decay kinetics of miniature synaptic currents. The change in kinetics was correlated with the increase in QC and raises the possibility that a change in postsynaptic nAChR conformation may be associated with the presynaptic increase in QC. We propose that, in addition to functioning in synaptic transmission, ionotropic muscle nicotonic nAChRs may serve as signaling molecules that participate in synaptic plasticity. Because nAChRs have been implicated in a number of disease states, the finding that nAChRs may be involved in triggering synaptic plasticity could have wide-reaching implications. SIGNIFICANCE STATEMENT The signals that initiate synaptic plasticity of the nervous system are still incompletely understood. Using the mouse neuromuscular junction as a model synapse, we studied how block of neurotransmitter receptors is sensed to trigger synaptic plasticity. Our studies led to the surprising conclusion that neither changes in synaptic current nor spiking of the presynaptic or postsynaptic cell are sensed to initiate synaptic plasticity. Instead, postsynaptic nicotinic acetylcholine receptors (nAChRs), in addition to functioning in synaptic transmission, may serve as signaling molecules that trigger synaptic plasticity. Because nAChRs have been implicated in a number of disease states, the finding that they may mediate synaptic plasticity has broad implications

Effect of Water Removal On Introduced Caddisflies from a Tropical Mountain Stream

Tropical island streams worldwide are being threatened by existing or proposed dams and diversions. Numerous streams of the Hawaiian Islands have diversions that remove freshwater for human use; however, little research has addressed diversion effects on aquatic insect communities in tropical streams. We studied the effect of water removal by a stream diversion on density and biomass of two introduced Trichoptera, Cheumatopsyche analis (Banks) (Hydropsychidae) and Hydroptila potosina (Buenoa- Soria) (Hydroptilidae), in Iao Stream, Maui, Hawaii, from April-August 2000. Both species seem to have multivoltine life cycles. Pooled Trichoptera (both species) biomass was significantly greater above the diversion (178.3 mg.m-2 and 112.9 mg.m-2 for upstream and downstream, respectively). For each individual species the mean total instar biomass was significantly reduced below the diversion (38 % and 54 % reduction for C. analis and H. potosina, respectively). Both species had greater densities above the diversion; however, individual larval mass of H. potosina instars, but not C. analis instars, was significantly lower below the diversion. Our results suggest that reduced habitat quality, due to lowered stream flow, limits density of both species below the diversion, whereas lowered food quantity and quality may differentially affect H. potosina biomass through reduced body sizes. These data suggest that water removal not only reduces habitat quality, but significantly lowers the community biomass of these introduced Trichoptera species, affecting the trophic energetics of stream reaches downstream of a diversion in Hawaii. Similar changes to macroinvertebrate communities would be expected below dams and diversions of streams in other tropical regions

Involvement of TolC protein in the export of siderophore enterobactin in Escherichia coli

Abstract only availableTo acquire the necessary iron against harsh competition in the environment, iron starved bacteria synthesize, excrete and retrieve iron scavenging molecules termed siderophores, one of which is enterobactin. TolC protein may play a vital role in the secretion of enterobactin. Enterobactin molecules destined for secretion must cross both the inner (cytoplasmic) and outer membranes and the intervening periplasmic space, believed to be a distance of at least 130Å across. TolC resembles a trans-periplasmic tunnel embedded in the outer membrane of the cell. It is open to the external environment but is closed at its periplasmic entrance. In order for the cell to export enterobactin, TolC is recruited by substrate specific membrane complexes (translocases) in the periplasmic space and inner membrane. When TolC is recruited, the entrance is opened to allow substrate passage through a continuous machinery spanning the entire cell envelope, from the cytosol to the external environment. PCR primers specific for TolC were designed to amplify the TolC gene. The quality of the PCR product was confirmed using agarose gel electrophoresis. The TolC gene was cloned into a pBAD directional TOPO vector containing an N-terminal His-tag and a gene for kanamycin resistance. The recombinant vector was then transformed into One Shot TOP10 competent Escherichia coli cells. Transformants were selected for by plating on LB medium supplemented with kanamycin. Transformed colonies were analyzed using PCR and restriction digestion. Positive transformants were selected and expression was induced with arabinose. SDS-PAGE assay with His-tag In-gel stain revealed TolC expression. Furthermore, analysis of TolC-null mutations using high performance liquid chromatography (HPLC) reveals that the TolC mutant secretes little, if any, enterobactin. However, some levels of breakdown products 2,3-dihydroxybenzoylserine (DHBS) monomer, dimer, and trimer are observed. These data establish that TolC may be a critical component of the E. coli enterobactin secretion machinery and may represent a type of siderophore export mechanism previously undescribed. TolC family proteins are ubiquitous among gram-negative bacteria, and the conserved apertures present a possible chemotherapeutic target in multidrug-resistant pathogens.Molecular Biology Progra

Exploring the potential of the internet of things at a heritage site through co-design practice

Our multidisciplinary team faced the challenge of creating an engaging visiting experience for Chesters museum that hosts John Clayton’s collection of Roman antiquities found along Hadrian’s Wall. The museum, created in 1896, is still in its original form and has a large collection of altars and religious sculptures displayed in a continuous sequence on several rows, as was the fashion in Victorian and Edwardian times. This layout was overwhelming for most visitors who only spent very little time in the museum. In an iterative co-design process we generated multiple concepts and prototyped the most promising: the aim was to make the visitors slow down and look around in a meaningful way. We assessed three prototypes in place finding physical impediments and management issues for two. The design and implementation then focused on a single concept that explores the relationship between the Romans and their gods. The final interactive installation uses the Internet of Things technology to offer a personalised experience that engages visitors at a physical level while simultaneously provoking them to explore and take action. This paper contributes to a better understanding of how design practice can create a novel interactive visiting experience centered on meaning-making rather than on the latest technology