After-effect Measurements Research Articles

Strain Relaxation and Internal Friction in the Range of the Glass Transition

Abstract For the investigation of structural relaxation near the glass transition quasistatic creep after-effect measurements have been performed on the alloy Zr65Cu17:5Ni10Al7:5 which shows a large stability above the glass temperature T g. By a separation of anelastic local atomic rearrangements and viscous long-range diffusion processes the thermal activation parameters of both processes could be determined from Arrhenius diagrams. Below T g = 606 K an activation enthalpy of 2.1 eV and above T g an activation enthalpy of 5.6 eV has been determined. For a quantitative description of these relaxation phenomena a new dynamic model is developed which takes into account the continuous formation and annihilation of relaxation centers near T g. From measurements of the internal friction after rapid temperature changes it could be shown that extended relaxation centers present above T g become instable below T g and are split up by diffusion processes above 585 K, however, disappear spontaneously below 580 K.

The effect of prism adaptation on state estimates of eye position in the orbit

Prism adaptation (PA) after-effects are assessed using tests that measure changes in sensorimotor systems. After-effects on pointing without feedback to a visual target (open loop pointing – OLP) are traditionally described as being larger than those measured by straight ahead pointing (SAP) with eyes closed, and the difference between them is attributed to a shift in visual localisation. However, neither differences between OLP and SAP, nor shifts in perceptual judgement of visual straight ahead (VSA), are consistently reported. Moreover, since very few studies have directly recorded direction of gaze, an effect of PA on the state estimate of gaze direction has not been reliably documented. The current research aimed to isolate the effects of PA on state estimates of eye position. We measured sensorimotor after-effects through common (OLP, SAP, and VSA) measures, and also recorded eye position and additional after-effect measures to interrogate changes to the oculomotor system and how these might relate to other measures of sensorimotor change. To ascertain if PA's effects on estimates of eye position could be attributed to eye muscle potentiation, we compared the effects of PA to sustained gaze deviation without adaptation. PA induced no effect on visual straight-ahead and no change in direction of gaze, when measured while positioning a target, looking straight ahead in the dark, or looking toward the passively positioned and occluded unexposed hand. We also found that after-effects measured by SAP with the eyes open were larger than SAP with the eyes closed and equal to those observed with OLP. The findings challenge the concept that total adaptation after-effect is a direct sum of arm proprioceptive and visual after-effects as conventionally measured, and suggest that the oculomotor system is altered by prism adaptation only in interaction with an arm motor command when vision is available.

Adaptation to the Direction of Others’ Gaze: A Review

The direction of another person’s gaze provides us with a strong cue to their intentions and future actions, and, correspondingly, the human visual system has evolved to extract information about others’ gaze from the sensory stream. The perception of gaze is a remarkably plastic process: adaptation to a particular direction of gaze over a matter of seconds or minutes can cause marked aftereffects in our sense of where other people are looking. In this review, we first discuss the measurement, specificity, and neural correlates of gaze aftereffects. We then examine how studies that have explored the perceptual and neural determinants of gaze aftereffects have provided key insights into the nature of how other people’s gaze direction is represented within the visual hierarchy. This includes the level of perceptual representation of gaze direction (e.g., relating to integrated vs. local facial features) and the interaction of this system with higher-level social-cognitive functions, such as theory of mind. Moreover, computational modeling of data from behavioral studies of gaze adaptation allows us to make inferences about the functional principles that govern the neural encoding of gaze direction. This in turn provides a foundation for testing computational theories of neuropsychiatric conditions in which gaze processing is compromised, such as autism.

Nonmonotonic aftereffect measurements in perpendicular synthetic ferrimagnets

Aftereffect measurements have been performed on synthetic ferrimagnets showing strong perpendicular magnetic anisotropy, namely (Co/Pt)/Ir/(Co/Pt), by measuring the magnetization of the sample as a function of time for several different applied magnetic fields. Unexpected magnetic relaxation has been observed. Indeed, for some particular applied magnetic fields, the magnetization as a function of time first plummets and then increases. This nonmonotonic aftereffect can be understood by considering the possible magnetic states and the transitions between those states. This understanding has been confirmed and detailed using magneto-optical Kerr effect (MOKE) microscopy. Indeed, the measurements show nucleation and propagation of a transient metastable magnetic configuration. Furthermore, we were able to obtain a good qualitative agreement between a simple one-dimensional model and the experimental observation. We could strongly support the hypothesis that this peculiar nonmonotonic behavior could be a very general feature that should be observed in any antiferromagnetically coupled system (synthetic ferrimagnets, synthetic antiferromagnets) with perpendicular magnetic anisotropy.

Relaxation dynamics of magnetization transitions in synthetic antiferromagnet with perpendicular anisotropy

Two synthetic antiferromagnet bilayer systems with strong perpendicular anisotropy CoFeB/Ta/CoFeB and Pt/Co/Ir/Co/Pt have been grown using sputtering techniques. For both systems two types of magnetization transitions have been studied. The first one concerns transitions from a state where magnetizations of the two magnetic layers are parallel (P state) to a state where magnetizations of the two layers are aligned antiparallel (AP state). The second one concerns transitions between the two possible antiparallel alignments (AP+ to AP−). For both systems and both transitions after-effect measurements can be understood in the frame of nucleation—propagation model. Time derivative analysis of magnetic relaxation curves and mapping of the first order reversal curves at different temperature allowed us to demonstrate the presence of different pinning centers, which number can be controlled by magnetic field and temperature.

Magnetic aftereffects in CoFeB/Ta/CoFeB spin valves of large area

Magnetic aftereffect measurements on a synthetic antiferromagnet with strong perpendicular anisotropy are presented. Two types of magnetic transitions are observed in the CoFeB/Ta/CoFeB bilayer where the two ferromagnetic CoFeB layers are antiferromagnetically coupled: the transition from a parallel to an antiparallel CoFeB layers magnetization alignment and the transition between two possible antiparallel magnetization states. Magnetic relaxation measurements show a complete reversal in the case of the transition between the two antiferromagnetic configurations. The experimental data can be well fitted in the frame of extended exponential relaxation using the Fatuzzo-Labrune model. Consequently, the domain nucleation and domain-wall propagation can be studied as a function of temperature and applied field.

The difficulty of letting go: moderators of the deactivation of completed intentions

Recent studies showed that prospective memory (PM) intentions might not be deactivated directly after completion. The residual activation leads to aftereffects which are reflected as interference in performance when former PM cues of old intentions are interspersed in the new task (i.e., intention deactivation failure, Walser et al., J Exp Psychol Learn Mem Cogn 38(4):1030-1044, 2012). In the present study, we investigated potential mechanisms that might support the deactivation process of completed intentions by manipulating the task demands (e.g., working memory load) between intention completion and measurement of aftereffects. Aftereffects on repeated PM-cue trials were found when working memory load was low (control condition), but were reduced when available resources were sparse (working memory load condition). When participants were asked to reflect upon the to-be-deactivated PM cue, subsequent aftereffects were increased. Further, overall aftereffects were larger for participants low in self-reported action control. Results show that the nature of the filler-task activity determines whether the representation of the completed intention is destabilized (working memory load) or strengthened (intention reflection). The (at least partial) overwriting of completed intention representations by new working memory task representations seems therefore to reflect a supporting factor for the deactivation of completed intentions.

Spontaneous recovery of motion and face aftereffects

The ability of the visual system to rapidly adjust to changing environmental conditions is one of its key characteristics. Environmental changes can occur over a variety of timescales, however, and it remains unknown how the visual system adapts to these. Does a single mechanism control adaptation across all timescales, or is adaptation subserved by multiple mechanisms, each of which is tuned to its preferred duration? To address this question, we conducted three experiments in which subjects viewed motion (Exp. 1 and 2) or faces (Exp. 3) in a sequence designed to produce opposing aftereffects. A first adapter was presented for a relatively long duration, while a second one was presented only long enough to extinguish the effects of the initial adapter. Continued measurement of aftereffects revealed a spontaneous recovery of adaptation caused by the initial, longer-lasting adapter in all three experiments. This pattern of results suggests that adaptation in the visual system generally reflects a combination of multiple temporally-tuned mechanisms.

Magnetic After-Effect Analysis of Dislocation Relaxations in Thermally Aged and Neutron Irradiated Fe-Cu Alloys

Magnetic after-effect measurements of thermally aged and neutron irradiated, cold-worked Fe-Cu model alloys are performed in the temperature range between 100 K and 500 K in order to study the effects of copper precipitates and the irradiation induced defects on dislocation relaxation processes. For these two conditions, by increasing the level of plastic deformation, we show the clear difference in the behavior of dislocation related peaks. The effect of irradiation induced defects on dislocations is clearly pronounced by the increased number of relaxed dislocations compared to the number in the thermally aged samples. Furthermore, we observe a non-monotonic change in the behavior of the intensities of dislocation-related peaks in neutron irradiated samples, which occurs due to dislocation annihilation of the irradiation induced defects.

Internal Friction and Magnetic After-Effect Study of Dislocation Dynamics in Thermally Aged Fe-1%Cu-C Alloys

The effect of Cu-precipitation on the dislocation dynamics is studied by internal friction and magnetic after-effect measurements of thermally aged Fe1%CuC. We found that the copper precipitation in these alloys is accompanied by carbon redistribution. The results of both experiments showed that the hardening regime is governed by an increase of the dislocation density due to the growth of copper precipitates, while in the softening regime carbon redistribution plays a major role.

Seeing Your Error Alters My Pointing: Observing Systematic Pointing Errors Induces Sensori-Motor After-Effects

During the procedure of prism adaptation, subjects execute pointing movements to visual targets under a lateral optical displacement: As consequence of the discrepancy between visual and proprioceptive inputs, their visuo-motor activity is characterized by pointing errors. The perception of such final errors triggers error-correction processes that eventually result into sensori-motor compensation, opposite to the prismatic displacement (i.e., after-effects). Here we tested whether the mere observation of erroneous pointing movements, similar to those executed during prism adaptation, is sufficient to produce adaptation-like after-effects. Neurotypical participants observed, from a first-person perspective, the examiner's arm making incorrect pointing movements that systematically overshot visual targets location to the right, thus simulating a rightward optical deviation. Three classical after-effect measures (proprioceptive, visual and visual-proprioceptive shift) were recorded before and after first-person's perspective observation of pointing errors. Results showed that mere visual exposure to an arm that systematically points on the right-side of a target (i.e., without error correction) produces a leftward after-effect, which mostly affects the observer's proprioceptive estimation of her body midline. In addition, being exposed to such a constant visual error induced in the observer the illusion “to feel” the seen movement. These findings indicate that it is possible to elicit sensori-motor after-effects by mere observation of movement errors.

Independent measures of adaptation and aftereffect

Independent measures of adaptation and aftereffect

The correlation between motion aftereffect and fMRI measures of visual and auditory attention

The correlation between motion aftereffect and fMRI measures of visual and auditory attention

Visuomotor adaptive improvement and aftereffects are impaired differentially following cerebellar lesions in SCA and PICA territory

The aim of the present study was to elucidate the contribution of the superior and posterior inferior cerebellum to adaptive improvement and aftereffects in a visuomotor adaptation task. Nine patients with ischemic lesions within the territory of the posterior inferior cerebellar artery (PICA), six patients with ischemic lesions within the territory of the superior cerebellar artery (SCA) and 17 age-matched controls participated. All subjects performed center-out reaching movements under 60° rotation of visual feedback. For the assessment of aftereffects, we tested retention of adaptation and de-adaptation under 0° visual rotation. From this data we also quantified five measures of motor performance. Cerebellar lesion-symptom mapping was performed using magnetic resonance imaging subtraction analysis. Adaptive improvement during 60° rotation was significantly degraded in PICA patients and even more in SCA patients. Subtraction analysis revealed that posterior (Crus I) as well as anterior cerebellar regions (lobule V) showed a common overlap related to deficits in adaptive improvement. However, for aftereffect measures as well as for motor performance variables only SCA patients, but not PICA patients showed significant differences to control subjects. Subtraction analysis showed that affection of lobules V and VI were more common in patients with impaired retention and de-adaptation, respectively. Data shows that areas both within the superior and posterior inferior cerebellum are involved in adaptive improvement. However, only the superior cerebellum including lobules V and VI appears to be important for aftereffects and therefore true adaptive ability.

Orientation-sensitivity of face identity aftereffects

Our ability to recognize faces despite their similarity as visual patterns depends on high-level face-coding mechanisms that are strongly tuned to upright faces. If face aftereffects reflect adaptation of these mechanisms, as widely assumed, then they should be sensitive to face orientation. Previous studies have not supported this hypothesis, but have generally used a figural aftereffect paradigm, which may not optimally engage expert face-coding mechanisms. Here, we used an identity aftereffect paradigm, which requires identification of target faces, to provide a stronger test of the hypothesis. We measured identity aftereffects for upright and inverted faces, with and without eliminating low-level retinotopic adaptation. Baseline identification performance was substantially better for upright than inverted faces, confirming that our task tapped orientation-selective face expertise. With orientation varied between participants, aftereffects were almost twice as large for upright as inverted faces, on three different aftereffect measures (change in threshold, change in overall proportion correct, change in perceived identity of the average face). With orientation varied within participants, the results were less clear. We suggest that adaptation of expert face-coding mechanisms can contribute to face identity aftereffects, although the effect may not be very robust.

Origin of the anomalous contributions to the ac magnetic susceptibility of rare-earth–iron intermetallic compounds

A systematic ac magnetic susceptibility, ${\ensuremath{\chi}}_{\text{ac}}(T)$, study has been performed on several ${R}_{2}{\text{Fe}}_{14}{\text{BH}}_{x}$ ($R=\text{rare}$ earth) compounds in order to determine the origin of the anomalous behavior of ${\ensuremath{\chi}}_{\text{ac}}(T)$ not related to spin reorientation transitions---the so-called non-SRT anomalies. All the measurements have been performed on magnetically oriented samples to identify the anomalies due to domain-wall displacements. Different types of non-SRT anomalies have been found. It has been found that the anomalous behavior is mainly due to the existence of mobile defects coupled to the domain walls, which existence has been confirmed by performing magnetic aftereffect measurements. However, this mechanism alone cannot explain the whole phenomenology and other influences on ${\ensuremath{\chi}}_{\text{ac}}(T)$ have to be taken into account to correctly describe the non-SRT anomalies. Specifically, three situations are possible when analyzing the anomalous behavior of ${\ensuremath{\chi}}_{\text{ac}}(T)$: (1) compounds with no magnetic $R$ anisotropy, in which the non-SRT anomalies are due to the existence of one or more mobile defects coupled to the domain walls, (2) compounds in which a large magnetic $R$ anisotropy can influence the domain-wall mobility at very low temperatures, and (3) compounds in which a large magnetic $R$ anisotropy and the existence of SRTs can influence the response of the domain walls coupled to mobile defects. Different fitting models have been proposed for each case.

The direction of measured face aftereffects

Prolonged viewing of a face can result in a change of our perception of subsequent faces. This process of adaptation is believed to be functional and to reflect optimization-driven changes in the neural encoding. Because it is believed to target the neural systems underlying face processing, the measurement of face aftereffects is seen as a powerful behavioral technique that can provide deep insights into our facial encoding. Face identity aftereffects have typically been measured by assessing the way in which adaptation changes the perception of images from a test sequence, the latter commonly derived from morphing between two base images. The current study asks to what extent such face aftereffects are driven by the test sequence used to measure them. Using subjects trained to respond either to identity of expression, we examined the effects of identity and expression adaptation on test stimuli that varied in both identity and expression. We found that face adaptation produced measured aftereffects that were congruent with the adaptation stimulus; the composition of the test sequences did not affect the measured direction of the face aftereffects. Our results support the view that face adaptation studies can meaningfully tap into the intrinsically multidimensional nature of our representation of facial identity.

Dynamic magnetization reversal inCoPt3dots: Magnetic force microscopy measurements at remanence

We have studied the magnetization reversal of ${\mathrm{Co}}_{28}{\mathrm{Pt}}_{72}$ single crystal dots down to $0.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ diameter with perpendicular anisotropy under slow magnetic field sweep rates $({10}^{4}\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}∕\mathrm{s})$ as well as with field pulses $(6.7\ifmmode\times\else\texttimes\fi{}{10}^{11}\phantom{\rule{0.3em}{0ex}}\mathrm{Oe}∕\mathrm{s})$. The magnetic state of the dots in the remanent state is observed by magnetic force microscopy. After application of short field pulses, $1\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ dots are frequently multidomain, whereas $0.2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ dots are always single domain. The nucleation volume is estimated either from aftereffect measurements or by fitting the increase of the dynamic coercive field versus field sweep rate. Its value amounts to a few ${10}^{\ensuremath{-}19}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{3}$. We show that the wall velocity around nucleation centers is larger than in the rest of the sample.

Enhanced magnetic viscosity at low temperatures in [Fe/Cr(0 0 1)] 10 multilayers

We report on magnetic aftereffect measurements in strongly and weakly antiferromagnetically (AFM)-coupled epitaxial [Fe/Cr(1 0 0)] 10 and in epitaxial Fe(1 0 0), near the orientation transition (OT) between the easy and hard axes, studied at time scales up to 10 3 s and between 300 and 1.8 K. In strongly coupled multilayers, the relaxation is nearly logarithmic in time, has an intrinsic character, and the maximum relaxation rate is almost temperature independent down to 10 K and strongly increases below 10 K. The magnetic relaxation in Fe(0 0 1) films was, however, much faster at T > 10 K, but at lower temperatures it is nearly blocked making possible the observation of magnetization jumps of Barkhausen type. The unusual magnetic aftereffect in the Fe/Cr multilayers could be due to opening of relaxation channels through the Cr that separates the Fe layers.

Magnetic properties of amorphous and nanocrystalline alloys based on iron

In the present paper, two amorphous alloys: Fe 74Cu 1Cr 3Si 13B 9 and Fe 74Cu 1Zr 3Si 13B 9 were studied by applying the following experimental techniques: magnetic permeability, coercive force, magnetic after-effect, Hall constant and electrical resistivity measurements. Structural changes in annealed samples have been examined by X-ray diffraction analysis and high-resolution electron microscopy technique. It has been shown that magnetic properties of the examined alloys can be significantly improved by applying a suitable thermal annealing causing formation of α-Fe(Si) nanocrystalline phase with grain size from the range 2–6 nm and/or annealing out of microvoids. It has been found that the temperature of 1-h optimisation annealing as well as the temperature of first stage of crystallisation process in the first approximation is proportional to the atomic radius of the alloying addition (Cr, Mo, Zr).