Carryover of scanning behaviour affects upright face recognition differently to inverted face recognition.

Face perception is characterized by a distinct scanpath. While eye movements are considered functional, there has not been direct evidence that disrupting this scanpath affects face recognition performance. The present experiment investigated the influence of an irrelevant letter-search task (with letter strings arranged horizontally, vertically, or randomly) on the subsequent scanning strategies in processing upright and inverted famous faces. Participants’ response time to identify the face and the direction of their eye movements were recorded. The orientation of the letter search influenced saccadic direction when viewing the face images, such that a direct carryover-effect was observed. Following a vertically oriented letter-search task, the recognition of famous faces was slower and less accurate for upright faces, and faster for inverted faces. These results extend the carryover findings of Thompson and Crundall into a novel domain. Crucially they also indicate that upright and inverted faces are better processed by different eye movements, highlighting the importance of scanpaths in face recognition

Detrimental effects of carryover of eye movement behaviour on hazard perception accuracy: Effects of driver experience, difficulty of task, and hazardousness of road.

Novice drivers are more likely to be involved in road accidents than experienced drivers and this relates to their lower performance in hazard perception tasks. Hazard perception performed under dual task conditions is also affected differentially due to driver experience. In this study, we explore the detrimental effect of vertical eye-movement carryover from one task to a second task in drivers of different levels of experience, whilst accounting for road conditions. Participants searched letters presented horizontally, vertically, or in a random array. Following this, they identified a hazard in a driving scene. Carryover of eye movements from the letter search to the driving scene was observed and participants were quicker and more accurate when responding to a hazard following horizontal scanning, compared to following vertical and random scanning. Furthermore, while carryover of eye movements was equivalent for all participants, the negative effect it had on hazard identification accuracy was less prominent in experienced drivers, especially when viewing the most hazardous of images. These results indicate that carryover of eye movements is another potentially distracting effect that can impact on the ability and safety of novice drivers

Evidence for internal field in graphite: A conduction electron spin resonance study

We report conduction electron spin resonance measurements performed on highly oriented pyrolitic graphite samples between 10 K and 300 K using S (f = 4 GHz), X (f = 9.4 GHz), and Q (f = 34.4 GHz) microwave bands for the external dc-magnetic field applied parallel (H || c) and perpendicular (H perp c) to the sample hexagonal c-axis. The results obtained in the H || c geometry are interpreted in terms of the presence of an effective internal ferromagnetic-like field Heff-int(T,H) that increases as the temperature decreases and the applied dc-magnetic field increases. We associate the occurrence of the Heff-int(T,H) with the field-induced metal-insulator transition in graphite and discuss its origin in the light of relevant theoretical models.Comment: 10 pages (tex), 5 figures (ps

Field-induced level crossings in spin clusters: Thermodynamics and magneto-elastic instability

Quantum spin clusters with dominant antiferromagnetic Heisenberg exchange interactions typically exhibit a sequence of field-induced level crossings in the ground state as function of magnetic field. For fields near a level crossing, the cluster can be approximated by a two-level Hamiltonian at low temperatures. Perturbations, such as magnetic anisotropy or spin-phonon coupling, sensitively affect the behavior at the level-crossing points. The general two-level Hamiltonian of the spin system is derived in first-order perturbation theory, and the thermodynamic functions magnetization, magnetic torque, and magnetic specific heat are calculated. Then a magneto-elastic coupling is introduced and the effective two-level Hamilitonian for the spin-lattice system derived in the adiabatic approximation of the phonons. At the level crossings the system becomes unconditionally unstable against lattice distortions due to the effects of magnetic anisotropy. The resultant magneto-elastic instabilities at the level crossings are discussed, as well as the magnetic behavior.Comment: 13 pages, 8 figures, REVTEX

Solving spin quantum-master equations with matrix continued-fraction methods: application to superparamagnets

We implement continued-fraction techniques to solve exactly quantum master equations for a spin with arbitrary S coupled to a (bosonic) thermal bath. The full spin density matrix is obtained, so that along with relaxation and thermoactivation, coherent dynamics is included (precession, tunnel, etc.). The method is applied to study isotropic spins and spins in a bistable anisotropy potential (superparamagnets). We present examples of static response, the dynamical susceptibility including the contribution of the different relaxation modes, and of spin resonance in transverse fields.Comment: Resubmitted to J. Phys. A: Math. Gen. Some rewriting here and there. Discussion on positivity in App.D3 at request of one refere

Soil Moisture and Fungi Affect Seed Survival in California Grassland Annual Plants

Survival of seeds in the seed bank is important for the population dynamics of many plant species, yet the environmental factors that control seed survival at a landscape level remain poorly understood. These factors may include soil moisture, vegetation cover, soil type, and soil pathogens. Because many soil fungi respond to moisture and host species, fungi may mediate environmental drivers of seed survival. Here, I measure patterns of seed survival in California annual grassland plants across 15 species in three experiments. First, I surveyed seed survival for eight species at 18 grasslands and coastal sage scrub sites ranging across coastal and inland Santa Barbara County, California. Species differed in seed survival, and soil moisture and geographic location had the strongest influence on survival. Grasslands had higher survival than coastal sage scrub sites for some species. Second, I used a fungicide addition and exotic grass thatch removal experiment in the field to tease apart the relative impact of fungi, thatch, and their interaction in an invaded grassland. Seed survival was lower in the winter (wet season) than in the summer (dry season), but fungicide improved winter survival. Seed survival varied between species but did not depend on thatch. Third, I manipulated water and fungicide in the laboratory to directly examine the relationship between water, fungi, and survival. Seed survival declined from dry to single watered to continuously watered treatments. Fungicide slightly improved seed survival when seeds were watered once but not continually. Together, these experiments demonstrate an important role of soil moisture, potentially mediated by fungal pathogens, in driving seed survival

Characterizing the conformational dynamics of metal-free PsaA using molecular dynamics simulations and electron paramagnetic resonance spectroscopy

Prokaryotic metal-ion receptor proteins, or solute-binding proteins, facilitate the acquisition of metal ions from the extracellular environment. Pneumococcal surface antigen A (PsaA) is the primary Mn2+-recruiting protein of the human pathogen Streptococcus pneumoniae and is essential for its in vivo colonization and virulence. The recently reported high-resolution structures of metal- free and metal-bound PsaA have provided the first insights into the mechanism of PsaA-facilitated metal binding. However, the conformational dynamics of metal-free PsaA in solution remain unknown. Here, we use continuous wave electron paramagnetic resonance (EPR) spectroscopy and molecular dynamics (MD) simulations to study the relative flexibility of the structural domains in metal-free PsaA and its distribution of conformations in solution. The results show that the crystal structure of the metal-free PsaA is a good representation of the dominant conformation in solution, but the protein also samples structurally distinct conformations that are not captured by the crystal structure. Further, these results suggest that the metal binding site is larger and more solvent exposed than indicated by the metal-free crystal structure. Collectively, this study provides atomic-resolution insight into the conformational dynamics of PsaA prior to metal binding and lays the groundwork for future EPR and MD based studies of PsaA in solution