Low level visual features support robust material perception in the judgement of metallicity.

The human visual system is able to rapidly and accurately infer the material properties of objects and surfaces in the world. Yet an inverse optics approach-estimating the bi-directional reflectance distribution function of a surface, given its geometry and environment, and relating this to the optical properties of materials-is both intractable and computationally unaffordable. Rather, previous studies have found that the visual system may exploit low-level spatio-chromatic statistics as heuristics for material judgment. Here, we present results from psychophysics and modeling that supports the use of image statistics heuristics in the judgement of metallicity-the quality of appearance that suggests an object is made from metal. Using computer graphics, we generated stimuli that varied along two physical dimensions: the smoothness of a metal object, and the evenness of its transparent coating. This allowed for the exploration of low-level image statistics, whilst ensuring that each stimulus was a naturalistic, physically plausible image. A conjoint-measurement task decoupled the contributions of these dimensions to the perception of metallicity. Low-level image features, as represented in the activations of oriented linear filters at different spatial scales, were found to correlate with the dimensions of the stimulus space, and decision-making models using these activations replicated observer performance in perceiving differences in metal smoothness and coating bumpiness, and judging metallicity. Importantly, the performance of these models did not deteriorate when objects were rotated within their simulated scene, with corresponding changes in image properties. We therefore conclude that low-level image features may provide reliable cues for the robust perception of metallicity.

Hand-Foot Coupling: An Advantage for Crossed Legs.

It is difficult to perform distinct, simultaneous motor actions with the ipsilateral hand and foot; for example, clockwise circles with the right hand and counter-clockwise circles with the right foot. By chance, we discovered that this hand-foot coupling task is easier when seated with legs crossed. We consider various explanations. First, that there are reduced demands on the contralateral hemisphere when the motor programme of the right foot is executed on the left side of the body. Second, that the legs-crossed scenario is easier because movements are symmetrical with respect to body midline. By considering related motor actions, we conclude that neither of these explanations provides a full account. Thus, we suggest a third explanation, which is that coupling effects are reduced by virtue of increased postural stability and reduced anticipatory postural adjustments.

Raw high-speed schlieren footage of acoustic waves in air for subsequent computational analysis and audio recovery.

The dataset presented here comprises 79 raw, unprocessed video files obtained from the high-speed schlieren imaging of acoustic waves in air, each with a corresponding metadata file. The majority of the footage was recorded at 50,000 frames per second, with each condition filmed for a duration of 20 ms. The dataset includes footage corresponding to a wide range of signals, in terms of waveform, frequency, and amplitude, as well as varied imaging parameters (exposure, frame rate, spatial resolution). This Data in Brief article is to accompany the research article "Visualization of acoustic waves in air and subsequent audio recovery with a high-speed schlieren imaging system: Experimental and computational development of a schlieren microphone" [1].

Bow-shaped caustics from conical prisms: a 13th-century account of rainbow formation from Robert Grosseteste's De iride.

The rainbow has been the subject of discussion across a variety of historical periods and cultures, and numerous optical explanations have been suggested. Here, we further explore the scientific treatise De iride [On the Rainbow] written by Robert Grosseteste in the 13th century. Attempting to account for the shape of the rainbow, Grosseteste bases his explanation on the optical properties of transparent cones, which he claims can give rise to arc-shaped projections through refraction. By stating that atmospheric phenomena are reducible to the geometric optics of a conical prism, the De iride lays out a coherent and testable hypothesis. Through both physical experiment and physics-based simulation, we present a novel characterization of cone-light interactions, demonstrating that transparent cones do indeed give rise to bow-shaped caustics-a nonintuitive phenomenon that suggests Grosseteste's theory of the rainbow is likely to have been grounded in observation.