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  1. Abstract

    Head movement relative to the stationary environment gives rise to congruent vestibular and visual optic-flow signals. The resulting perception of a stationary visual environment, referred to herein as stationarity perception, depends on mechanisms that compare visual and vestibular signals to evaluate their congruence. Here we investigate the functioning of these mechanisms and their dependence on fixation behavior as well as on the activeversuspassive nature of the head movement. Stationarity perception was measured by modifying the gain on visual motion relative to head movement on individual trials and asking subjects to report whether the gain was too low or too high. Fitting a psychometric function to the data yields two key parameters of performance. The mean is a measure of accuracy, and the standard deviation is a measure of precision. Experiments were conducted using a head-mounted display with fixation behavior monitored by an embedded eye tracker. During active conditions, subjects rotated their heads in yaw ∼15 deg/s over ∼1 s. Each subject’s movements were recorded and played backviarotating chair during the passive condition. During head-fixed and scene-fixed fixation the fixation target moved with the head or scene, respectively. Both precision and accuracy were better during active than passive head movement, likely due to increased precision on the head movement estimate arising from motor prediction and neck proprioception. Performance was also better during scene-fixed than head-fixed fixation, perhaps due to decreased velocity of retinal image motion and increased precision on the retinal image motion estimate. These results reveal how the nature of head and eye movements mediate encoding, processing, and comparison of relevant sensory and motor signals.

     
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  2. A bstract In two-derivative theories of gravity coupled to matter, charged black holes are self-attractive at large distances, with the force vanishing at zero temperature. However, in the presence of massless scalar fields and four-derivative corrections, zero-temperature black holes no longer need to obey the no-force condition. In this paper, we show how to calculate the long-range force between such black holes. We develop an efficient method for computing the higher-derivative corrections to the scalar charges when the theory has a shift symmetry, and compute the resulting force in a variety of examples. We find that higher-derivative corrected black holes may be self-attractive or self-repulsive, depending on the value of the Wilson coefficients and the VEVs of scalar moduli. Indeed, we find black hole solutions which are both superextremal and self-attractive. Furthermore, we present examples where no choice of higher-derivative coefficients allows for self-repulsive black hole states in all directions in charge space. This suggests that, unlike the Weak Gravity Conjecture, which may be satisfied by the black hole spectrum alone, the Repulsive Force Conjecture requires additional constraints on the spectrum of charged particles. 
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  3. null (Ed.)
  4. In this design-based research project, researchers and activity developers across four institutions are investigating how narratives can evoke empathy and influence girls’ participation and engagement in museum-based engineering design activities. The project involves the development and testing of six pairs of engineering activities. Through iterative development of these activity pairs, we have refined a conceptual model defining how engineering activities can incorporate a variety of narrative elements to support empathy and engagement. In addition, each pair includes one version of the activity with narrative elements, and one without — for example, children design a vehicle that can move over different textured surfaces (non-narrative) or that can help someone travel around the world across different landscapes (narrative), allowing us to examine how narrative elements influence girls’ ideation and persistence in iterating their designs. We analyzed the number of children who participated in each version of the activities, average hold times, and detailed observations and follow-up interviews with girls between ages 7-14 who tried the activities with their families. Results showed that narrative versions invited greater participation among both girls and boys, and that different narrative elements (such as characters and settings) evoked different aspects of empathy (such as affective responses and cognitive perspective-taking). We discuss the implications of the results for the design and facilitation of inclusive engineering design experiences in informal learning settings. 
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