Correlating the internal length in strain gradient plasticity theory with the microstructure of material

The internal length is the governing parameter in strain gradient theories which among other things have been used successfully to interpret size effects at the microscale. Physically, the internal length is supposed to be related with the microstructure of the material and evolves during the deformation. Based on Taylor hardening law, we propose a power-law relationship to describe the evolution of the variable internal length with strain. Then, the classical Fleck–Hutchinson strain gradient theory is extended with a strain-dependent internal length, and the generalized Fleck–Hutchinson theory is confirmed here, by comparing our model predictions to recent experimental data on tension and torsion of thin wires with varying diameter and grain size. Our work suggests that the internal length is a configuration-dependent parameter, closely related to dislocation characteristics and grain size, as well as sample geometry when this affects either the underlying microstructure or the ductility of the material.     

Yielding and strain hardening in aluminium single-crystal foils subjected to tension and bending

A series of tensile and microbend tests were conducted on aluminium single-crystal foil specimens with different thicknesses ranging from 20 to 90?µm. Two different crystal orientations relative to the tensile direction were considered in the tests: one is an orientation that was excepted to activate at least four slip systems on four different slip planes, and the other is an orientation that was expected to activate only a single-slip system. In the tensile tests, typical size dependence of initial yield strength was observed. The microbend test method was extended to include a reversal of bending direction. Using the curves of bending moment normalized by the square of foil thickness versus surface strain, which were obtained from the reversed bending tests, the total amounts of strain hardening were divided into isotropic and kinematic hardening components. In the microbend tests, a pronounced size-dependent kinematic hardening behaviour was clearly observed; meanwhile, the amounts of isotropic hardening were very small, particularly for the single-slip orientation.     

Wear behaviour of a gradient surface produced by a punching process in a Cu-30 Ni alloy

The grain size variation in a gradient surface produced by a punching and recovery process on a Cu-30Ni alloy has been observed by atomic force microscopy. The friction characteristics of the gradient surface in a 3.5 wt% NaCl solution were investigated using a micro-indenter probe, a pin-on-disc type tribometer, a strain sensor and an optical microscope. The results showed that the hardness and grain size can be well represented by the Hall–Petch relationship when the gain size is more than 30?nm. The wear rate, friction coefficient and adhesive force all increase depth below the surface. These variations are attributed to a gradual increasing grain size with depth. The morphologies of the worn track were also studied to understand further the corrosive wear behaviour of gradient surfaces.     

List context effects on masked phonological priming in the lexical decision task

A lexical decision experiment tested the effects of briefly presented masked primes that were homophones or pseudohomophones of target words. Different types of nonword foil (pseudohomophones, orthographically regular nonwords, orthographically irregular nonwords) were mixed with the word targets. Pseudohomophone priming effects were independent of nonword foil variations, whereas homophone priming effects varied from being facilitatory in the presence of orthographically regular nonwords, inhibitory in the presence of pseudohomophones, and null in the presence of irregular nonwords. This dissociation in the way nonword foil variations influence masked pseudohomophone and homophone priming effects in the lexical decision task is discussed within the framework of a bimodal extension of the multiple readout model of visual word recognition (Grainger & Jacobs, 1996).     

Semantic and phonological influences on the processing of words and pseudohomophones

In two experiments, we investigated the relationship between semantics and phonology in the lexical decision task. In the first experiment, lexical decisions to words with large semantic neighborhoods were faster than those to words with sparse semantic neighborhoods. Conversely, this effect of semantic neighborhood was reversed for pseudohomophones (e.g., nale). That is, pseudohomophones based on words with large semantic neighborhoods took longer to reject than did those based on words with sparse semantic neighborhoods. In the second experiment, we found the magnitude of the semantic neighborhood effect for words to be a function of nonword foil type. Taken together, these results indicate that semantic neighborhood size affects processing of both words and pseudohomophones, and that the effect of semantic neighborhood size for words is more pronounced when pseudohomophone foils are employed. These effects are discussed in terms of a model in which the orthographic, phonological, and semantic systems are fully interactive.     

Recognition vs. classification of ill-defined category exemplars

In Experiment 1, subjects were trained on three ill-defined categories represented by 4, 8, and 12 exemplars. Learning was followed by either a classification test on old, new, and random exemplars or a recognition test in which each learning exemplar was presented with two foils, both equidistant to the learning exemplar, but one more similar to the category prototype than the other. In Experiment 2, category size was manipulated between subjects, followed by the recognition test. Recognition data indicated that increasing the number of learning exemplars did not increase the total amount of exemplar information retained for each category. In addition, the more prototypical foil was incorrectly recognized more often than the less prototypical foil. Classification data replicated previous findings that increasing category size in learning enhances classification of new exemplars. The results were interpreted in terms of the relative amounts of categorical and idiosyncratic information that were retained from the original learning stimuli. It was proposed that categorical information can become a more dominant determinant of performance as category size increases.     

The whole is indeed more than the sum of its parts: perceptual averaging in the absence of individual item representation

We tested Ariely's (2001) proposal that the visual system represents the overall statistical properties of sets of objects against alternative accounts of rapid averaging involving sub-sampling strategies. In four experiments, observers could rapidly extract the mean size of a set of circles presented in an RSVP sequence, but could not reliably identify individual members. Experiment 1 contrasted performance on a member identification task with performance on a mean judgment task, and showed that the tasks could be dissociated based on whether the test probe was presented before or after the sequence, suggesting that member identification and mean judgment are subserved by different mechanisms. In Experiment 2, we confirmed that when given a choice between a probe corresponding to the mean size of the set and a foil corresponding to the mean of the smallest and largest items only, the former is preferred to the latter, even when observers are explicitly instructed to average only the smallest and largest items. Experiment 3 showed that a test item corresponding to the mean size of the set could be reliably discriminated from a foil but the largest item in the set, differing by an equivalent amount, could not. In Experiment 4, observers rejected test items dissimilar to the mean size of the set in a member identification task, favoring test items that corresponded to the mean of the set over items that were actually shown. These findings suggest that mean representation is accomplished without explicitly encoding individual items.     

Creating proactive interference in immediate recall: Building a DOG from a DART, a mop, and a FIG

Phonemic codes are accorded a privileged role in most current models of immediate serial recall, although their effects are apparent in short-term proactive interference (PI) effects as well. The present research looks at how assumptions concerning distributed representation and distributed storage involving both semantic and phonemic codes might be operationalized to produce PI in a short-term cued recall task. The four experiments reported here attempted to generate the phonemic characteristics of a nonrhyming, interfering foil from unrelated filler items in the same list. PI was observed when a rhyme of the foil was studied or when the three phonemes of the foil were distributed across three studied filler items. The results suggest that items in short-term memory are stored in terms of feature bundles and that all items are simultaneously available at retrieval.     

Eyewitness recognition errors: the effects of mugshot viewing and choosing in young and old adults

Eyewitness memory is vulnerable to information encountered prior to a lineup. Young (18-30 years) and older (60-80 years) witnesses viewed a crime video. Some witnesses were then exposed to mugshots of innocent suspects that included a critical foil. After a 48-h delay, all the witnesses took part in a target-absent lineup that included the critical foil and five new foils. Witnesses who picked one of the mugshots as the likely perpetrator showed inflated rates of choosing the critical foil from the lineup. Context reinstatement instructions did not reduce choices of innocent foils following mugshot exposure. Despite age-related increases in false choosing, age did not qualify other effects. The results are discussed in terms of commitment, source memory, and gist-based processing.     

Space, object, and task selection

Within the field of selective attention, two separate literatures have developed, one examining the effect of selection of objects and another examining the effect of selection of features. The present study bridged these two traditions by examining the compatibility effects generated by two features of attended and unattended nontarget (foil) stimuli. On each trial, participants determined either the identity or the orientation of a visual stimulus. Spatial attention was controlled using cues (presented prior to the target frame) designed to involuntarily capture attention. We independently manipulated the stimulus dimension the participants prepared for and the stimulus dimension on which they actually executed the task. Preparation had little influence on the magnitude of compatibility effects from foil stimuli. For attended stimuli, the stimulus dimension used in executing the task produced large compatibility effects, regardless of whether that dimension was prepared. These and other compatibility effects (e.g., Stroop effects) are discussed in relation to an integrative model of attentional selection. The key assumptions are that (1) selection occurs at three distinct levels (space, object, and task), (2) spatial attention leads to semantic processing of all dimensions, and (3) features do not automatically activate responses unless that object is selected for action.     

Prior experience affects amodal completion in pigeons

In a three-alternative forced-choice task, 4 pigeons were trained to discriminate a target stimulus consisting of two colored shapes, one of which partially occluded the other, from two foil stimuli that portrayed either a complete or an incomplete version of the occluded shape. The dependent measure was the percentage of total errors that the birds committed to the complete foil. At the outset of training, the pigeons committed approximately 50% of total errors to the complete foil, but as training progressed, the percentage of errors to the complete foil rose. When the pigeons were given a second exposure to the initial set of stimuli, they committed 70% of total errors to the complete foil, suggesting that they now saw the complete foil as more similar to the occluded target than the incomplete foil. These results suggest that experience with 2-D images may facilitate amodal completion in pigeons, perhaps via perceptual learning.     

Proactive interference and cuing effects in short-term cued recall: Does foil context matter?

Tehan and Humphreys's (1995, 1996) short-term cued recall paradigm showed that recall in short-term memory is cue driven. In critical trials, the participants studied two blocks of four words each and were required to forget the first block while remembering the second block. A foil in the first block (e.g., orange) was related to a target (e.g., carrot) in the second block. Proactive interference (PI) was evident when a retrieval cue was used that subsumed the foil and the target (e.g., type of juice), but not when a cue was used that subsumed only the target (e.g., type of vegetable). Four experiments were performed to examine the extent to which contextual organization in the foil block would enhance or diminish the foil's efficacy in creating PI. A novel condition was included in which the words in the foil block were studied in a phonologically related context but the target was cued semantically, and vice versa with a semantic context and phonological cue. There were no differences in recall accuracy between conditions with and without contextual organization, but reliable increases in foil intrusions were observed when contextual organization was present. Contextual organization enhanced the foil, rather than diminished it, but the strengthened foil generated PI only when the cue subsumed the foil and the target and had no effect when the cue subsumed only the target. The results are consistent with a cue-driven retrieval interpretation of short-term recall.     

Simultaneous manipulation of propositional and analog codes in picture memory

Revealing a picture as a whole or as momentarily displayed strips presumably manipulated the propositional coding of the picture. Analog manipulation employed superimposition of a grid pattern. Effectiveness of simultaneous manipulations was tested via recognition with three foil categories, each of which presumably tapped the analog or propositional codes mainly, or both of them in detection. While figural units' perspective reversals should presumably be detected via the analog code, their locational displacements should be detected via the propositional code. Foils with novel item substitution should be detected by both codes. On the basis of such presumptions about encoding and recognition manipulations, certain predictions were made for scan and grid effects in "reversal," "displacement," and "novelty" foil categories. Full confirmation of these predictions was then taken as evidence that both analog and propositional codes do exist. Once such evidence was established, other issues were tackled, showing that target detection involves the propositional code only, while foil detection involves both codes. Further, recognition hypermnesia, where performance improves with repeated testing, was obtained only when both codes were attenuated. Data suggested that subjects might be switching from analog to propositional codes when both codes were strong, thereby preventing hypermnesia.     

早期ERP效应与视觉注意空间等级的脑调节机制

通过事件相关电位(ERP)记录研究注意的空间等级的脑内时程动态变化。视觉搜索任务的目标受不同大小提示范围的启动。提示范围增大时,识别目标的反应时延长,P1波幅增大而N1波幅减小,该效应在短间隔条件下尤为明显。P1增大反映了促进目标识别时,适当注意范围的空间等级变化需要额外的运算资源。而N1波幅减小则可能扩散了空间注意倾斜。研究结果提供了以下电生理学证据：注意空间等级的改变调节了早期视皮层的神经活动,并激活了视觉搜索中至少2个时间重叠的ERP成分。     

Effects of pre-experimental knowledge on recognition memory

The influence of pre-experimental autobiographical knowledge on recognition memory was investigated using as memoranda faces that were either personally known or unknown to the participant. Under a dual process theory, such knowledge boosted both recollection- and familiarity-based recognition judgements. Under an unequal variance signal detection model, pre-experimental knowledge increased both the variance and the separation of the target and foil memory strength distributions, boosting hits and correct rejections. Thus, pre-experimental knowledge has profound effects on the multiple, interacting processes that subserve recognition memory, and likely in the neural systems that underpin them.     

Dancing shapes: a comparison of luminance-induced distortions

We present an illusory display in which a grid of outlined squares is positioned in front of a moving luminance gradient. Observers perceive a strong, illusory, 'wavelike' motion of the superimposed squares. We compared luminance effects on dynamic and static aspects of this illusion. The dynamic aspect was investigated by means of a temporal gradient, which induced an illusory pulsing of the outlined squares. The static aspect was investigated in two different ways. In one experiment, the outlined squares were positioned on a spatial gradient, which caused the squares to look like trapezoid shapes. In another experiment, the squares were positioned on different luminance fields, which affected their apparent size. In all experiments, luminance settings were the same, and observers were asked to indicate the direction and strength of the induced distortions. The overall results show large agreements between the dynamic distortion and the first-mentioned static distortion, whereas different tendencies emerged for the second static distortion. In a second series of experiments, we examined these distortions for various ranges of the luminance gradient and for border gradients as well. On the basis of these data, we explored how the directions of the perceived distortions of the single-gradient displays examined in this paper could be related to each other.     

The impact of emotion on perception: bias or enhanced processing?

Recent studies have shown that emotionally significant stimuli are often better identified than neutral stimuli. It is not clear, however, whether these results are due to enhanced perceptual processing or to a bias favoring the identification of emotionally significant stimuli over neutral stimuli. The present study used a two-alternative forced-choice perceptual identification task to disentangle the effects of bias and enhanced processing. We found that emotionally significant targets were better identified than neutral targets. In contrast, the emotional significance of the foil alternative had no effect on performance. The present results support the hypothesis that perceptual encoding of emotionally significant stimuli is enhanced.     

Anisotropic grain growth kinetics in nanocrystalline nickel

ABSTRACT

Intriguing properties exhibited by nanocrystalline metals, including a high level of mechanical strength, arise from their nanometer-scale grain sizes. It is critical to determine the evolution of grain size of nanocrystalline materials at elevated temperature, as this process can drastically change the mechanical properties. In this work, a nanocrystalline Ni foil with grain size ～ 25?nm was annealed in situ in an X-ray diffractometer. X-ray diffraction peaks were analysed to determine the grain growth kinetics. The grain growth exponents obtained were ～ 2–4 depending upon the crystallographic direction, indicating the anisotropic nature of the grain growth kinetics.     

The influence of spatial context and the role of intentionality in the interpretation of animacy from motion

We present three experiments investigating how spatial context influences the attribution of animacy to a moving target. Each of our displays contained a moving object (the target) that might, depending on the way it moved, convey the impression that it was alive (animate). We investigated the mechanisms underlying this attribution by manipulating the nature of the spatial context surrounding the target. In Experiment 1, the context consisted of a simple static dot (the foil), whose position relative to the target's trajectory was manipulated. With some foil positions--for example, when the foil was lying along the path traveled by the target--animacy judgments were elevated relative to control foil locations, apparently because this context supported the impression that the target was "reacting to" or was in some other way mentally influenced by the foil. In Experiment 2, contexts consisted of a static oriented rectangle (the "paddle"). On some trials, the target collided with the paddle in a way that seemed to physically account for the target's motion pattern (in the sense of having imparted momentum to it); this condition reduced animacy ratings. Experiment 3 was similar, except that the paddles themselves were in motion; again, animacy attribution was suppressed when the target's motion seemed to have been caused by a collision with the paddle. Hence, animacy attributions can be either elevated or suppressed by the nature of the environment and the target's interaction with it. Animacy attribution tracks intentionality attribution; contrary to some earlier proposals, we conclude that attributing animacy involves, and may even require, attributing to the target some minimal mental capacity sufficient to endow the target with intentionality.     

The size-constancy of underwater swimmers

The size-constancy of divers was measured by requiring them to adjust the distance between two disks of unequal size so that they appeared phenomenally equal. In clear water divers showed greater constancy-ratios than on land. In murky water, where visibility was reduced by suspended particles, constancy-ratios were the same as, or less than, on land. It is suggested that these effects may be due to changes in apparent distance: in clear water objects appear nearer through refraction, but in murky water they appear further away because of the distance cues provided by the visibility gradient.

The orientation of the display, or of the diver's body, did not affect constancy under water, though it does on land. It is argued that the effect on land is due to visual and proprioceptive cues which are absent in the water.