Mirror Invariance Research Articles

Breaking the symmetry: Mirror discrimination for single letters but not for pictures in the Visual Word Form Area

Humans and primates can quickly recognize mirror images of previously exposed pictures. This spontaneous mirror invariance, though advantageous for visual recognition, makes it difficult to distinguish the orientation of letters (e.g. to differentiate a “b” from a “d”), and may result in classical mirror reading and writing errors in preschoolers. Mirror invariance must therefore be overcome during reading acquisition. The Visual Word Form Area (VWFA), a region in the ventral stream that develops with reading expertise, was previously shown to discriminate words from their mirror images in literate adults. Here we investigate whether this region underlies mirror-image discrimination at the most elementary level of the orthographic code, the single-letter level. Using an fMRI priming paradigm, we demonstrate that the VWFA distinguishes the left–right orientation of single letters in skilled readers, and yet exhibits mirror invariance for simple pictures of matched complexity. These results clarify how letter shapes, after reading acquisition, escape the process of mirror invariance which is a basic property of the ventral visual shape recognition pathway.

Why do children make mirror errors in reading? Neural correlates of mirror invariance in the visual word form area

Young children often make mirror errors when learning to read and write, for instance writing their first name from right to left in English. This competence vanishes in most adult readers, who typically cannot read mirror words but retain a strong competence for mirror recognition of images. We used fast behavioral and fMRI repetition priming to probe the brain mechanisms underlying mirror generalization and its absence for words in adult readers. In two groups of French and Japanese readers, we show that the left fusiform visual word form area, a major site of learning during reading acquisition, simultaneously shows a maximal effect of mirror priming for pictures and an absence of mirror priming for words. Thus, learning to read recruits an area which possesses a property of mirror invariance, seemingly present in all primates, which is deleterious for letter recognition and may explain children's transient mirror errors.

Approximate Nature of Physical Symmetries

Since Leibniz it has become clearer and clearer that a priori judgment is inadequate to establish the presence of exact symmetries in the physical laws, and the exact conservation laws which flow from them. The latest example has been the Yang-Lee demonstration of the failure of mirror invariance in the weak interactions. It is possible to conjecture that even the kinematical symmetries under continuous transformations which give energy-momentum conservation may be inexact; their failure may be expressed, for example, in the spontaneous creation of nucleons postulated by Bondi and Gold. Still further, one may at least raise the question of the exactness of general relativity, or rather of the principle of equivalence between acceleration and a uniform gravitational field. If this equivalence is regarded as an approximate consequence of the predominance of matter over antimatter in our environment, it is possible to frame a consistent scheme which predicts large-scale symmetry between matter and antimatter, but at the expense of introducing gravitational repulsion. Conceptual experiments are constructed to show the consistency of this picture at least in the Newtonian limit; certain specified conditions on the gravitational behavior of various types of inertial mass must be satisfied.