The silhouette illusion published online a number of years ago by the Japanese Flash designer Nobuyuki Kayahara has received substantial attention from the online community. One feature that seems to make it interesting is an apparent rotational bias: Observers see it spinning more often clockwise than counter-clockwise. Here, we show that this rotational bias is in fact due to the visual system's preference for viewpoints from above rather than from below.

Orthographically projected biological motion point-light displays are generally ambiguous with respect to their orientation in depth, yet observers consistently prefer the facing-the-viewer interpretation. There has been discussion as to whether this bias can be attributed to the social relevance of biological motion stimuli or relates to local, low-level stimulus properties. In the present study we address this question. In Experiment 1, we compared the facing-the-viewer bias produced by a series of four stick figures and three human silhouettes that differed in posture, gender, and the presence versus absence of walking motion. Using a paradigm in which we asked observers to indicate the spinning direction of these figures, we found no bias when participants observed silhouettes, whereas a pronounced degree of bias was elicited by most stick figures. We hypothesized that the ambiguous surface normals on the lines and dots that comprise stick figures are prone to a visual bias that assumes surfaces to be convex. The local surface orientations of the occluding contours of silhouettes are unambiguous, and as such the convexity bias does not apply. In Experiment 2, we tested the role of local features in ambiguous surface perception by adding dots to the elbows and knees of silhouettes. We found biases consistent with the facing directions implied by a convex body surface. The results unify a number of findings regarding the facing-the-viewer bias. We conclude that the facing-the-viewer bias is established at the level of surface reconstruction from local image features rather than on a semantic level.

Uncontrolled opioid withdrawal and pain often drive inpatients with opioid use disorder to leave hospital against medical advice, resulting in suboptimal medical and addiction treatment. When oral opioid agonist treatments such as methadone and buprenorphine/naloxone fail for management of craving and withdrawal, injectable opioid agonist treatment may serve to retain patients in care and link them to addiction services. We describe the case of a 47-year-old man with a severe, active opioid use disorder and daily use of illicitly manufactured fentanyl, who was re-admitted to hospital for post-operative management after leaving against medical advice due to uncontrolled opioid withdrawal. Intravenous hydromorphone was used to retain him in care, allowing for completion of his antibiotics and enrolment in ongoing community injectable opioid agonist treatment. [McAdam M, Brar R, Young S. Initiation of injectable opioid agonist treatment in hospital: A case report. Drug Alcohol Rev 2020;39:138-141]

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