Faces behind bars: illusory eye movements induced by gratings

I describe a novel illusion in which perceived eye movements are induced by moving a vertical grating across a single image of a forward-looking face. By varying properties of the grating, a wide range of illusory eye movements can be generated including nystagmus, a ‘swirling’ motion of the eyes, and vertical scanning/blinking. I suggest that the phenomenon is closely related to the footsteps illusion, but reveals the role that object shape and grating spatial frequency together play in determining the direction of illusory motion that observers perceive. I also discuss the relationship between the current illusion, the footsteps illusion, and Moire pattern animations.

The Bouba-Kiki effect reflects generic shape-sound associations

Humans robustly associate spiky shapes to words like “Kiki” and round shapes to words like “Bouba”. A popular explanation is that the mouth forms an angular shape while saying “Kiki” and a rounded shape while saying “Bouba”, leading to this association. Alternatively, there could be generic associations between the shapes of objects and the sounds they produce. These possibilities can be distinguished using unpronounceable sounds: the mouth-shape hypothesis predicts no effect, whereas the generic shape hypothesis predicts a systematic effect. Here, we show that the Bouba-Kiki effect is present for a variety of unpronounceable sounds ranging from reversed versions of Bouba-like and Kiki-like words and natural real object sounds to even pure tones. The effect was strongly correlated with the mean frequency of a sound independent of its pronounceability. Thus, the Bouba-Kiki effect reflects generic associations between sounds and object shape rather than mouth shape.

Tracer-based 3D surface reconstruction

The continuous advancements of particle imaging techniques for flow field measurements have led to imaging systems and processing approaches matching the demands for 3D velocimetry at large scale (Schanz et al., 2016; Discetti and Coletti, 2018). Often, the flow past an object immersed in the fluid is of key interest, and in some cases the experimentalist exploits the velocimetry data for analysis of the near-surface flow properties such as pressure. It follows that knowledge of the object shape and position is essential. For 2D studies, the issue of identifying the fluid-solid interface often reduces to detection of the intensity gradient resulting from the light sheet striking the object. The latter task is well explored, with a variety of methods providing the object interface in the measurement plane (Canny, 1986; Malik et al., 2001; Gui et al., 2003, among others). These approaches, however, are not applicable in volumetric studies where the illumination is diffuse. A frequently applied alternative in fluid-structure-interaction studies is a dual-measurement approach, where a second measurement system tracks the object shape (e.g., Acher et al., 2019; Zhang et al., 2019) The complexity of operating two measurement systems may not be affordable however, motivating the development of 3D interface detection methods that rely solely on the flow imaging system. Particle imaging based interface detection approaches in 3D have been addressed from various perspectives, containing the detection of fluid-fluid interfaces. Examples utilizing tomographic PIV measurements include the studies of Adhikari and Longmire (2012), Im et al. (2014), and Ebi and Clemens (2016). The two latter examples identify the fluid-solid interface by discriminating a seeded phase (the fluid) from a void phase (the solid). The present work is inspired by this principle, but it assumes a discrete 3D particle distribution as obtained from a generic particle tracking algorithm such as IPR by Wieneke (2012), or “Shake-The-Box” by Schanz et al. (2016), as a foundation. Summarizing, this work aims to detect the surface of a solid object immersed in a seeded flow, solely based on the spatial distribution of flow tracers as recorded by a generic 3D PTV measurement.

A Systematic Analysis of Hand Movement Functionality: Qualitative Classification and Quantitative Investigation of Hand Grasp Behavior

Understanding human hand movement functionality is fundamental in neuroscience, robotics, prosthetics, and rehabilitation. People are used to investigate movement functionality separately from qualitative or quantitative perspectives. However, it is still limited to providing an integral framework from both perspectives in a logical manner. In this paper, we provide a systematic framework to qualitatively classify hand movement functionality, build prehensile taxonomy to explore the general influence factors of human prehension, and accordingly design a behavioral experiment to quantitatively understand the hand grasp. In qualitative analysis, two facts are explicitly proposed: (1) the arm and wrist make a vital contribution to hand movement functionality; (2) the relative position (relative position in this paper is defined as the distance between the center of the human wrist and the object center of gravity) is a general influence factor significantly impacting human prehension. In quantitative analysis, the significant influence of three factors, object shape, size, and relative position, is quantitatively demonstrated. Simultaneously considering the impact of relative position, object shape, and size, the prehensile taxonomy and behavioral experiment results presented here should be more representative and complete to understand human grasp functionality. The systematic framework presented here is general and applicable to other body parts, such as wrist, arm, etc. Finally, many potential applications and the limitations are clarified.

A Perfect Plastic Material for Studies on Self-Propelled Motion on the Water Surface

We describe a novel plastic material composed of camphene, camphor, and polypropylene that seems perfectly suited for studies on self-propelled objects on the water surface. Self-motion is one of the attributes of life, and chemically propelled objects show numerous similarities with animated motion. One of important questions is the relationship between the object shape and its motility. In our previous paper, {R. Löffler et al. PCCP, 2019, 21, 24852–24856}, we presented a novel hybrid material, obtained from the solution of camphor in camphene, that allowed making objects of various shapes. This hybrid material has wax-like mechanical properties, but it has a very high tackiness. Here, we report that a small amount of polypropylene removed this undesirable feature. We investigated the properties of camphor–camphene–polypropylene plastic by performing the statistical analysis of a pill trajectory inside a Petri dish and compared them with those of camphor-camphene wax. The plastic showed the stable character of motion for over an hour-long experiment. The surface activity of objects made of plastic did not significantly depend on the weight ratios of the compounds. Such a significant increase in usefulness came from the polypropylene, which controlled the dissipation of camphor and camphene molecules.