Representational momentum in the motor system?

PURPOSE: If presented with a moving object which suddenly disappears observers usually misjudge the object's last seen position as being further forward along the path of motion. This effect, called representational momentum, can also be seen in objects that change size or shape. It has been argued that the effect is due to perceptual anticipation. We tested whether a similar effect is present in the motor system. METHODS: Using stereo computer graphics we presented cubes of different sizes on a CRT monitor. In each trial three cubes were successively presented for 200 msec with increasing or decreasing size (steps of 1 cm width difference). Ten participants either compared the last cube to a comparison cube (perceptual task) or grasped the cube using a virtual haptic setup (motor task). The setup consisted of two robot arms (Phantom TM) attached to index finger and thumb. The robot arms were controlled to create forces equivalent to the forces created by real objects. The CRT monitor was viewed via a mirror such that the visual position of the cubes matched the position of the virtual haptic objects. RESULTS: In the motor task participants opened their fingers by 1.1+/-0.4 mm wider if they grasped a cube that was preceded by smaller cubes than if they grasped a cube that was preceded by larger cubes. This is the well-known representational momentum effect. In the perceptual task the effect was reversed (-2.2+/-0.4 mm). The effects correlated between observers (r=.71, p=.02). CONCLUSIONS: It seems that a representational momentum occurs also in grasping tasks. The correlation between observers suggests that the motor effect is related to the perceptual effect. However, our perceptual task showed a reversed effect. Reasons for this discrepancy will be discussed

Galactose uncovers face recognition and mental images in congenital prosopagnosia: The first case report

A woman in her early 40s with congenital prosopagnosia and attention deficit hyperactivity disorder observed for the first time sudden and extensive improvement of her face recognition abilities, mental imagery, and sense of navigation after galactose intake. This effect of galactose on prosopagnosia has never been reported before. Even if this effect is restricted to a subform of congenital prosopagnosia, galactose might improve the condition of other prosopagnosics. Congenital prosopagnosia, the inability to recognize other people by their face, has extensive negative impact on everyday life. It has a high prevalence of about 2.5%. Monosaccharides are known to have a positive impact on cognitive performance. Here, we report the case of a prosopagnosic woman for whom the daily intake of 5 g of galactose resulted in a remarkable improvement of her lifelong face blindness, along with improved sense of orientation and more vivid mental imagery. All these improvements vanished after discontinuing galactose intake. The self-reported effects of galactose were wide-ranging and remarkably strong but could not be reproduced for 16 other prosopagnosics tested. Indications about heterogeneity within prosopagnosia have been reported; this could explain the difficulty to find similar effects in other prosopagnosics. Detailed analyses of the effects of galactose in prosopagnosia might give more insight into the effects of galactose on human cognition in general. Galactose is cheap and easy to obtain, therefore, a systematic test of its positive effects on other cases of congenital prosopagnosia may be warranted

Do congenital prosopagnosia and the other-race effect affect the same face recognition mechanisms?

Congenital prosopagnosia (CP), an innate impairment in recognizing faces, as well as the other-race effect (ORE), a disadvantage in recognizing faces of foreign races, both affect face recognition abilities. Are the same face processing mechanisms affected in both situations? To investigate this question, we tested three groups of 21 participants: German congenital prosopagnosics, South Korean participants and German controls on three different tasks involving faces and objects. First we tested all participants on the Cambridge Face Memory Test in which they had to recognize Caucasian target faces in a 3-alternative-forced-choice task. German controls performed better than Koreans who performed better than prosopagnosics. In the second experiment, participants rated the similarity of Caucasian faces that differed parametrically in either features or second-order relations (configuration). Prosopagnosics were less sensitive to configuration changes than both other groups. In addition, while all groups were more sensitive to changes in features than in configuration, this difference was smaller in Koreans. In the third experiment, participants had to learn exemplars of artificial objects, natural objects, and faces and recognize them among distractors of the same category. Here prosopagnosics performed worse than participants in the other two groups only when they were tested on face stimuli. In sum, Koreans and prosopagnosic participants differed from German controls in different ways in all tests. This suggests that German congenital prosopagnosics perceive Caucasian faces differently than do Korean participants. Importantly, our results suggest that different processing impairments underlie the ORE and CP

The role of familiarity in the recognition of static and dynamic objects

Although the perception of our world is experienced as effortless, the processes that underlie object recognition in the brain are often difficult to determine. In this article we review the effects of familiarity on the recognition of moving or static objects. In particular, we concentrate on exemplar-level stimuli such as walking humans, unfamiliar objects and faces. We found that the perception of these objects can be affected by their familiarity; for example the learned view of an object or the learned dynamic pattern can influence object perception. Deviations in the viewpoint from the familiar viewpoint, or changes in the temporal pattern of the objects can result in some reduction of efficiency in the perception of the object. Furthermore, more efficient sex categorization and cross-modal matching was found for familiar than for unfamiliar faces. In sum, we find that our perceptual system is organized around familiar events and that perception is most efficient with these learned events

Behavior Of Spandrel Beams Strengthened With Steel Fibers Under Combined Loading

Anggota konkrit mengalami kilasan diiringi juga dengan lenturan dan ricihan. Sehingga kini, kod amalan reka bentuk anggota-anggota konkrit bertetulang menganggap bahawa kesan kilasan dapat dielakkan dengan selamat disebabkan faktor keselamatan yang tinggi digunakan dalam lenturan dan ricihan. Justeru itu, gabungan beban terhadap anggota-anggota tidak diberi perhatian yang serius. Namun demikian, andaian ini sudah tidak boleh diaplikasi lagi kerana isu kilasan kini merupakan perkara biasa dan memainkan peranan yang signifikan dalam struktur, contohnya rasuk spandrel. Rasuk spandrel atau dikenali juga sebagai rasuk-L, amat bergantung pada perimeter bangunan. Sebarang kegagalan pada rasuk spandrel boleh menjadi serius sehingga mencacatkan papak, sumbungan tiang-rasuk dan tebukan plat rata konkrit. Dengan mencampurkan gentian keluli sebagai bahan tambahan, ia boleh meningkatkan kekuatan kilasan rasuk spandrel di bawah beban gabungan dan prestasi struktur konkrit seperti beban maksimum, kemuluran dan rintangan retak. Gentian keluli boleh merintangi gabungan beban seperti rakap dan tetulang membujur, namun penyelidikan di dalam bidang ini masih samar dan terhad. Lebih-lebih lagi kepentingan menggunakan bertetulang gentian dalam struktur konkrit untuk diaplikasi dalam infrastruktur awam telah meningkat. Oleh yang demikian, pengetahuan sedia ada tentang konkrit gentian keluli sepaiknya digabungjalinkan dalam kod amalan reka bentuk. Eksperimen dijalankan untuk menilai perlakuan rasuk spandrel gentian yang diperkukuh dengan gentian keluli tertakluk pada gabungan kilasan, lenturan dan ricihan. Sejumlah 18 rasuk spandrel disediakan dan diuji dengan dua gabungan beban biasa i.e. kilasan tinggi terhadap nisbah lenturan dan kilasan rendah terhadap nisbah lenturan. Sampel rasuk dibahagikan kepada tiga kumpulan, iaitu rasuk konkrit biasa, spesimen dengan tetulang pengukuh memanjang, dan spesimen dengan tertulang dan rakap. Semua kes dikaji dengan pecahan isipadu gentian keluli 0%, 1%, dan 1.5%. Rasuk konkrit bertetulang gentian mempamerkan prestasi keseluruhan yang baik berbanding dengan rasuk kawalan tanpa gentian. Diperhatikan sumbangan utama daripada gentian keluli ke atas tingkah laku kilasan adalah terhadap keretakan konkrit. Penambahan gentian keluli adalah penting untuk rasuk tanpa tetulang keluli konvensional, penambahan ini terbukti mampu meningkatkan kapasiti semasa kilasan. Di samping itu, analisis berangka melalui kaedah elemen terhingga dilakukan terhadap data eksperimen untuk meramalkan tingkah laku struktur rasuk spandrel. Satu teknik baru diutara untuk mengambilkira kesan gentian keluli dalam elemen konkrit dan kesan titik lembut konkrit dalam mampatan dan tegangan. Kelakuan umum model unsur terhingga yang diwakili plot kilas-piuh dan plot bebanlenturan menunjukkan hubungan yang baik dengan data ujian daripada rasuk kawalan dan rasuk spandrel. Walau bagaimanapun, model unsur terhingga menunjukkan kekukuhan yang tinggi berbanding dengan data ujian dalam julat tidak linear untuk rasuk tanpa tetulang keluli. ________________________________________________________________________________________________________________________ Important concrete members are subjected to significant torsion accompanied by bending and shear. Until recent years, the design codes of reinforced concrete members assumed that the effects of torsion could be safely neglected due to high safety factors for shear and bending moment. Thus, members under combined loading were not treated with serious attention. However, this assumption cannot be applied anymore as torsion issues become common and play a significant role in structural members, such as spandrel beams. The spandrel beam, or the L-beam, lies on the perimeter of buildings. Any failure in spandrel beams can seriously damage slabs, beam-column connections, and punch concrete flat-plates. By incorporating steel fibers, it can enhance torsional behavior of spandrel beam under combined load in addition to the structural performance such as maximum load, ductility and cracking resistance. Steel fibers may provide resistance to combined loading as stirrups and longitudinal bars, this investigation is still scare and limited. Moreover, a worldwide interest in utilizing fiber reinforced concrete structures for civil infrastructure applications has increased. This study presents the advantage of using steel fiber concrete in strengthening spandrel beams under different reinforcement and loading cases. An experimental investigation was conducted to assess the behavior of steel fiber reinforced concrete spandrel beams subjected to combined torsion, bending, and shear. A total of 18 spandrel beams were prepared and tested with two common loading combinations i.e. high torque to bending ratio and low torque to bending ratio. All beams were divided into three groups, namely, plain concrete beams, specimens with longitudinal reinforcing bars and specimens with bars and stirrups. All cases were examined with 0%, 1%, and 1.5% steel fiber volume fractions. Fibrous concrete beams exhibited improved overall torsional performance with respect to the corresponding non-fibrous control beams. The main contribution of steel fibers on the torsional behavior is mainly observed after concrete cracking. The addition of steel fibers was essential to the beams without conventional steel reinforcement since fibers were the only reinforcement and proved capable to provide enhanced torsional moment capacities. Besides, a numerical analysis by finite element method was suggested against the experimental data to predict the structural behavior of spandrel beams. A new technique was presented to incorporate the effects of steel fibers within concrete element and the softening effect of concrete in compression and tension. The general behavior of the finite element model represented by the torque-twist plot and load-deflection plots show good agreement with the test data from the plain and fiber reinforced spandrel beam. However, the finite element models show higher stiffness than the test data in the nonlinear ranges for beams without steel reinforcement

Stereo disparity facilitates view generalization during shape recognition for solid multipart objects

Current theories of object recognition in human vision make different predictions about whether the recognition of complex, multipart objects should be influenced by shape information about surface depth orientation and curvature derived from stereo disparity. We examined this issue in five experiments using a recognition memory paradigm in which observers (N = 134) memorized and then discriminated sets of 3D novel objects at trained and untrained viewpoints under either mono or stereo viewing conditions. In order to explore the conditions under which stereo-defined shape information contributes to object recognition we systematically varied the difficulty of view generalization by increasing the angular disparity between trained and untrained views. In one series of experiments, objects were presented from either previously trained views or untrained views rotated (15°, 30°, or 60°) along the same plane. In separate experiments we examined whether view generalization effects interacted with the vertical or horizontal plane of object rotation across 40° viewpoint changes. The results showed robust viewpoint-dependent performance costs: Observers were more efficient in recognizing learned objects from trained than from untrained views, and recognition was worse for extrapolated than for interpolated untrained views. We also found that performance was enhanced by stereo viewing but only at larger angular disparities between trained and untrained views. These findings show that object recognition is not based solely on 2D image information but that it can be facilitated by shape information derived from stereo disparity

Priming of plane-rotated objects depends on attention and view familiarity

Three experiments investigated the role of attention in visual priming across rotations in the picture plane. Experiment 1 showed that naming latencies increased with the degree of misorientation for objects commonly seen in an upright view (base objects) but not for objects seen familiarly from many views (no-base objects). In Experiment 2, no-base objects revealed a priming pattern identical to that observed previously for left-right reflections (Stankiewicz, Hummel, & Cooper, 1998): Attended objects primed themselves in the same and rotated views, whereas ignored images primed themselves only in the same view, with additive effects of attention and orientation. In Experiment 3 ignored base objects only primed themselves in a familiar (upright) view, indicating that priming only obtains when that image makes contact with object memory. These data challenge theories of object recognition that rely on any single representation of shape and contribute to evidence suggesting holistic (view-like) representations for ignored and analytic (view-insensitive) representations for attended objects

Perceived Object Stability Depends on Multisensory Estimates of Gravity

BACKGROUND: How does the brain estimate object stability? Objects fall over when the gravity-projected centre-of-mass lies outside the point or area of support. To estimate an object's stability visually, the brain must integrate information across the shape and compare its orientation to gravity. When observers lie on their sides, gravity is perceived as tilted toward body orientation, consistent with a representation of gravity derived from multisensory information. We exploited this to test whether vestibular and kinesthetic information affect this visual task or whether the brain estimates object stability solely from visual information. METHODOLOGY/PRINCIPAL FINDINGS: In three body orientations, participants viewed images of objects close to a table edge. We measured the critical angle at which each object appeared equally likely to fall over or right itself. Perceived gravity was measured using the subjective visual vertical. The results show that the perceived critical angle was significantly biased in the same direction as the subjective visual vertical (i.e., towards the multisensory estimate of gravity). CONCLUSIONS/SIGNIFICANCE: Our results rule out a general explanation that the brain depends solely on visual heuristics and assumptions about object stability. Instead, they suggest that multisensory estimates of gravity govern the perceived stability of objects, resulting in objects appearing more stable than they are when the head is tilted in the same direction in which they fall

The effect of social context on the use of visual information

Social context modulates action kinematics. Less is known about whether social context also affects the use of task relevant visual information. We tested this hypothesis by examining whether the instruction to play table tennis competitively or cooperatively affected the kind of visual cues necessary for successful table tennis performance. In two experiments, participants played table tennis in a dark room with only the ball, net, and table visible. Visual information about both players’ actions was manipulated by means of self-glowing markers. We recorded the number of successful passes for each player individually. The results showed that participants’ performance increased when their own body was rendered visible in both the cooperative and the competitive condition. However, social context modulated the importance of different sources of visual information about the other player. In the cooperative condition, seeing the other player’s racket had the largest effects on performance increase, whereas in the competitive condition, seeing the other player’s body resulted in the largest performance increase. These results suggest that social context selectively modulates the use of visual information about others’ actions in social interactions