Walking on Visual Illusions.

In nature, sensory and physical characteristics of the environment tend to match; for example, a surface that looks bumpy is bumpy. In human-built environments, they often don't. Here, we report observations from people exploring if mismatch between visual and physical characteristics affected their perceived walking experience. Participants walked across four flat floors, each comprising of a visual illusion: two patterns perceived as alternating 3D "furrows and ridges," the Primrose Field illusion, and a variant of the Cafe Wall illusion as a control pattern without perceived 3D effects. Participants found all patterns intriguing to look at; some describing them as "playful" or "gentle." More than half found some of the patterns uncomfortable to walk on, aversive, affecting walking stability, and occasionally even evoking fear of falling. These experiences raise crucial research questions for the vision sciences into the impact of architectural design on well-being and walkability.

Expanding Universe Illusion.

We present a new induced movement illusion from global expansion or contraction in a triangular region filled with rising or falling textures. Objective global expansion or contraction induces lateral movement in the oblique edges of the triangle. The effects may be due to common and relative movements operating within a single texture.

Dissociation of perception and action unmasked by the hollow-face illusion.

It has been suggested that there are two separate visual streams in the human cerebral cortex: a ventral pathway that provides perceptual representations of the world and serves as a platform for cognitive operations, and a dorsal pathway that transforms visual information for the control of motor acts. Evidence for this distinction comes from neuropsychology, neuroimaging, and neurophysiology. There is also evidence from experimental psychology, with normal observers experiencing an illusion-where perception and action can be dissociated, although much of this evidence is controversial. Here, we report an experiment aimed at demonstrating a large dissociation between perception and fast action using the hollow-face illusion, in which a hollow mask looks like a normal convex face. Participants estimated the positions of small targets placed on the actually hollow but apparently normal face and used their fingers to 'flick' the targets off. Despite the presence of a compelling illusion of a normal face, the flicking movements were directed at the real, not the illusory locations of the targets. These results show that the same visual stimulus can have completely opposite effects on conscious perception and visual control of fast action.

What's up with witch rings?

'Witch rings' are well-known novelty rings that show a size-change illusion when rotated. We have replicated the illusion of expansion of the reflections in the rings in a variety of contexts with animations, though not as yet so successfully imitated the sense that the whole ring expands and contracts.

The triangle-bisection illusion.

In the triangle-bisection illusion, a dot is inscribed exactly halfway up the height of an equilateral triangle, but it looks apparently far more than halfway up. The illusion is found for second-order triangles defined by stereo depth and by equiluminous texture. It is strongest for equilateral triangles, and even stronger for concave triangles with curved sides. We propose that the observers are probably responding to the centre of area or centre of gravity of the triangle rather than to its half-height.