视觉工作记忆回溯线索效应的产生机制：认知阶段分离

以往研究关于视觉工作记忆回溯线索效应的产生机制主要存在5种假设,目前依然存在争议。本研究通过改进前人研究实验范式,采用包含内源性回溯线索的颜色回忆报告范式,进一步对这5种假设进行检验。在实验1中,我们调控了线索与探测阵列之间的时间间隔,发现不同时间间隔不影响无线索条件的行为表现,而在正常线索条件中被试的记忆精度以及能记住的项目数量均优于无线索条件;在实验2中,我们对回溯线索伴随的干扰刺激类型进行控制,结果显示,在不同条件下记忆精度不存在差别,但当回溯线索伴随干扰刺激呈现时,被试能记住的项目数量会被降低,降低程度受干扰刺激的类型调制;在实验3中,我们对伴随回溯线索的干扰刺激的呈现时间进行控制,发现虽然回溯线索效应仍然存在,但干扰刺激的呈现时间不会影响效应程度。研究结果表明,回溯线索的出现使得被试能够在决策加工前完成内部注意资源的再分配,从而避免了同时进行这两种认知加工与记忆表征维持本身竞争认知资源。本研究为认知阶段分离假设提供了支持证据,对解决回溯线索效应产生机制的争议以及理解内部注意与视觉工作记忆的关系有重要意义。     

Deformed substructures in fine-grained tetragonal zirconia

Transmission electron microscopy (TEM) has been employed to examine the deformed microstructures of a high-purity tetragonal zirconia polycrystal containing 3mol% yttria. The TEM observations reveal that piled-up and tangled dislocations are developed within grains at a high stress, but such substructures do not appear at a lower stress, except for a small number of isolated dislocations. The stress-dependent deformed microstructures suggest that the dislocation substructures observed at a high stress are not due to any experimental artefacts. Applying a model proposed by Eshelby et al. to the observed pile-up dislocations, it can be estimated that a stress concentration of the order of 14-25 is generated around multiple-grain junctions during deformation.     

Linear instability signals the initiation of motion of a twin plane under load

This letter presents a study of the atomic mechanism of the initiation of motion of a static twin plane under applied mechanical load in a model shape-memory material. By tracking the deformation under load and using linear stability analysis, we find that the eigenvalues of the Hessian matrix provide an indicator of the initiation of motion of the twin plane. The initiation of motion is signaled by a linear instability and a drop in the lowest eigenvalue to zero as well as a sharp drop in higher eigenvalues. Additionally, by comparing with direct molecular dynamics, we see that the eigenmode associated with the zero eigenvalue is found to accurately predict the initial mode of motion. We also find that the initial motion occurs through the formation of a stacking fault just ahead of the existing twin plane and the broadening of the stacking fault drives further transformation.     

Application of the stagnant stage concept for monitoring Mn partitioning at the austenite-ferrite interface in the intercritical region for Fe–Mn–C alloys

The length of the stagnant stage during the new ferrite growth starting from a mixture of austenite and ferrite has been investigated for a Fe-0.17Mn-0.023C (wt%) alloy. It was found that the stagnant stage depends on the thermal path followed to create the mixture, and deduce that the tie-lines for austenite to ferrite transformation are quite different from those for ferrite to austenite transformation. The length of the stagnant stage is determined by the very local partitioning effect at the interface, and it can be used as a tool to monitor the Mn partitioning.     

Precipitation in a Cu–4Ti–2Be alloy

It is known that the binary Cu–2?wt.% Be alloy can be strengthened by ageing its supersaturated solution at 523?K. The increase in the strength arising from ageing is because of the formation of GP zones. The same level of strength is achieved by ageing the supersaturated solid solution of a dilute binary Cu–4?wt.% Ti alloy at 723?K. In contrast to Cu–2?wt.% Be alloy, the increase in strength in this alloy occurs on account of spinodal decomposition of the as-quenched microstructure through the mechanism of clustering and ordering. In the present study, decomposition of a supersaturated solid solution of the ternary Cu–4?wt.% Ti–2?wt.% Be alloy was studied. Whereas ageing of this alloy at 523?K resulted in the formation of GP zones like in a Cu–2?wt.% Be alloy, ageing at 723?K resulted in a spinodally decomposed microstructure as in a Cu–4?wt.% Ti alloy. The decomposition of the ternary alloy at the two temperatures by two different mechanisms indicates that Be and Ti in solution in Cu act, more or less, independently of each other during ageing.     

Self-assembly-assisted growth of two-dimensional Penrose tiling

An algorithm for the growth of two-dimensional Penrose tiling, based on symmetry operations on a seed rhombus, is discussed and demonstrated. Independent of empirical matching rules, as suggested by Penrose [Bull. Inst. Math. Appl. 10 266 (1974)], and also overcoming the scaling-down operation, as proposed by Ramachandrarao et al. (Acta Crystallogr. A 47 210 (1991)], the present algorithm follows a mechanism akin to self-assembly and can be continued ad infinitum.     

Examining the long-term stability of overgeneral autobiographical memory

Overgeneral autobiographical memory (OGM) is a proposed trait-marker for vulnerability to depression, but relatively little work has examined its long-term stability. This study investigated the stability of OGM over several years in 271 late adolescents and young adults participating in a larger longitudinal study of risk for emotional disorders. The Autobiographical Memory Test (AMT) was administered twice, with test–retest intervals ranging from approximately 3 to 6 years. There was evidence of significant but modest stability in OGM over several years. Specifically, Spearman rank correlations (ρs) between the proportions of specific and categoric memories generated on the two AMTs were .31 and .32, respectively. We did not find evidence that the stability of OGM was moderated by the length of the test–retest interval. Furthermore, the stability coefficients for OGM for individuals with and without a lifetime history of major depressive disorder (MDD) were relatively similar in magnitude and not significantly different from one another (ρs=.34 and .42 for the proportions of specific and categoric memories for those with a history of MDD; ρs=.31 for both the proportions of specific and categoric memories for those without a history of MDD). Implications for the conceptualisation of OGM are discussed.     

Variations in Linear and Nonlinear Postural Measurements under Achilles Tendon Vibration and Unstable Support-Surface Conditions

Reduced support-surface stability has been shown to attenuate the effect of Achilles tendon vibration on backward body displacement. In the present study, 20 participants performed a quiet, upright standing task on a stable and sway-referenced support, with and without vibration. The authors calculated equilibrium scores (ES), approximate entropy (ApEn), and mean and peak power spectral density frequencies of center-of-pressure variations. It was found that ES values decreased with the addition of vibration and in the sway-referenced support condition. ApEn values decreased with the addition of vibration but only with a stable support. Conversely, mean and peak frequencies increased with the addition of vibration, independent of support stability. These results suggest that the role of ankle proprioceptive input changes depending on support-surface characteristics and demonstrate the value of using both linear and nonlinear measures of postural sway.     

Eye-Hand Coordination in Rhythmical Pointing

The authors investigated the relation between hand kinematics and eye movements in 2 variants of a rhythmical Fitts's task in which eye movements were necessary or not necessary. P. M. Fitts's (1954) law held in both conditions with similar slope and marginal differences in hand-kinematic patterns and movement continuity. Movement continuity and eye—hand synchronization were more directly related to movement time than to task index of difficulty. When movement time was decreased to fewer than 350 ms, eye—hand synchronization switched from continuous monitoring to intermittent control. The 1:1 frequency ratio with stable π/6 relative phase changed for 1:3 and 1:5 frequency ratios with less stable phase relations. The authors conclude that eye and hand movements in a rhythmical Fitts's task are dynamically synchronized to produce the best behavioral performance.     

Oscillations in Motor Priming: Positive Rebound Follows the Inhibitory Phase in the Masked Prime Paradigm

From among the diverse meanings of stability, the one the author adopts here is that the effects of a perturbation are opposed, and therefore small effects remain small. Except in linear systems, however, instability need not lead to unbounded motion and may actually be desirable when maneuverability is important. Moreover, properties of nerves, muscles, and tendons present serious challenges to stabilization. A review of observations from the motor control literature reveals that responses to perturbations in many common situations assist rather than resist the perturbation and are therefore presumably destabilizing. The observations encompass situations of position maintenance as well as impending or ongoing movement. The author proposes that the motor control system responds to a sudden perturbation by a pattern of muscle activity that mimics an accustomed voluntary movement, oblivious of stability considerations. What prevents runaway motion in the face of short-term instability appears to be voluntary intervention.