Priscilla Heard

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.

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.

Richard Langton Gregory. 24 July 1923—17 May 2010

Richard Gregory was a pioneer of cognitive psychology. Much of his scientific work involved the development and interpretation of visual illusions, which he used as a tool to work out the perceptual mechanisms involved in the way that the visual world is normally perceived. He was also an inventor, developing a technique for viewing microscopic objects in three dimensions, and a method for taking sharp telescope images through an unstable atmosphere. He was a man of great charm, enthusiasm and wit, who listed his hobbies as punning and pondering. He was to become an outstanding public communicator of scientific ideas. He gave the Royal Institution Christmas Lectures (‘The intelligent eye’) in 1967, was a founder member of the Experimental Psychology Society, set up his own journal, Perception, in 1972, and in 1978 founded the Exploratory, a hands-on science centre in Bristol. His work on illusions and his interest in painting led to a collaboration with the art historian Sir Ernst Gombrich, resulting in the book Illusion in nature and art (1973) and an exhibition at the Institute of Contemporary Art. Other books included Mind in science (1981) and The Oxford companion to the mind (1987), for which he was both editor and a major contributor. The book for which he is best known is the wonderfully accessible Eye and brain, whose five editions (1966–1997) and many translations have inspired students of all ages.

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.

Development and Evaluation of a Forensic Exhibit for Science Centres

A new hands-on experiment was devised for science centres to demonstrate EvoFIT, a facial-composite system used by police with witnesses to construct facial likenesses of villains. Visitors watch a video of a man pretending to commit a crime and then construct a composite of his face by repeatedly selecting from an array of faces, with the software breeding together choices to evolve a face. The new hands-on EvoFIT (Version D) takes a few minutes to complete compared with an hour or so for the police version. It has many differences from its first incarnation in 2007 (Version A): some changes incorporated recent improvements in the EvoFIT program, such as adding the hair last, while others improved engagement of the visitors and incorporated an attractive Graphical User Interface (GUI). Two main evaluations of the hands-on EvoFIT were carried out. Firstly, we compared the original exhibit (Version A) with one where external features such as hair were added at the end (Version B). Both were enjoyed by users and given similar likenesses for faces created. Secondly, we evaluated the effect of adding a new GUI and holistic tools (Versions C and D) to allow visitors to adjust features such as age and face weight. Again, use of the exhibit with and without the holistic tools were both enjoyed and gave better likenesses than the previous versions evaluated.

Trumping eyes. Part 2.

Postulates It is suggested that vision works immediately by patterns of cues, and indirectly by inferences from clues. These terms are generally used without distinction; but it is useful to think of cues as giving direct responses by innate neural mechanisms, while clues are cognitive, depending on more-or-less explicit knowledge of the world of objects. This distinction between cues and clues appears in the evolution of vision; from innate responses to stimuli, to inferences of what may be out there, causing stimuli. The notion is that cues trigger innate responses, as inherited in the genetic code, while clues are learned from individual experienceöenhanced by individual interests and understanding, as for Sherlock Holmes momentous inferences from small clues to life ^ death decisions. Again, the notion is that cues trigger innate neural mechanisms, while clues are cognitive, depending on knowledge and understanding of the world of objects. Pictures have their significance from familiar cues and clues, represented by patterns of paint. Although this trick is obvious to the intellect, the visual system responds to patterns of paint much as for genuine objects. This is not too surprising, as both are mediated by pictures in the eyes. Editorial essay Perception, 2009, volume 38, pages 1265 ^ 1266

Do engineers and artists make good love objects ? (panel session)

BACKGROUND In this panel, issues deriving from the experience of collaboration between technical specialists and artists are to be outlined and discussed, with reference to the production of the non-screen based interactive new media installation artwork, “Love Object”. The panel is comprised of both artists: Terry1 Bacon, Martin Rieser and Constance Fleuriot; and people with a science, social science and/or technology background: Priscilla Heard and Glenn Easy. The three artists are members of an artists’ group called “Ship Of Fools” who work with new media and technology. Dr. Heard is a consultant for the Bristol Exploratory Museum and has collaborated with Martin Rieser on previous projects, and Glenn Easy is the leader of the engineering team who produced “Love Object”.