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of accurate visual-motor pointing. (Bedford)

The growth transformation characterizing plasticity required to maintain accurate pointing despite physical growth was derived and shown to depend on a changing ratio of shoulder width to arm length. Analysis of growth studies surprisingly found the ratio for adults and children to be comparable, implying that even without plasticity, pointing would remain accurate with growth. The finding suggests that the British Associationists may have been correct: touch can be used to educate vision. Comparison of growth to prism adaptation suggested that adaptation is more like felt rotation of the shoulder than like growth but at a deeper level, both development and adaptation reflect linear changes - displacements, rotations, and magnifications - to body segments. Finally, cross-modal comparison suggested that growth has complimentary effects on audition and the motor system. Other conditions modeled include different pointing instructions and target distance as well as azimuth angle.

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It has been assumed that the distal evolutionary function of perceptual plasticity in adults, especially prism adaptation, is to accommodate transformations caused by physical growth in childhood. Naturally occurring transformations of translation, rotation and magnification of two body segments (shoulder axis, pointing arm) were analyzed to determine 1) shoulder angles required for accurate pointing and 2) pointing errors caused by the transformations. The plasticity required by shoulder magnification in growth was found not to closely match the displacement component of prism adaptation, but the latter was a perfect match to shoulder rotation that occurs in ordinary movement. However, transformations from growth and natural movement overlapped considerably, with all accommodated by combinations of 3 simple changes to the "shoulder-angle difference" function. Overall, the findings suggest that the general adaptive function of the plasticity is to keep track of a continuously changing body envelope without distinguishing whether the cause is growth or "drift" from natural movement, consistent with Perceptual Learning Theory.

 For further information contact bedford@u.arizona.edu

It has become increasingly common for theories to rely on a constraint that one object cannot be in more than one place at the same time. Analysis suggests that the constraint as literally stated is false, that a modified constraint is biased towards the visual modality, that the constraint may not be a correct description of the physical world, is not true of how objects must appear on sensory surfaces, and does not mean that two simultaneous spatially separated samples must be interpreted as two different objects. However, once object numerosity or identity is determined in some other way, the modified constraint can be used to trigger learning. A far-removed implication is that the What-Where distinction is misleading.

For further information see the full article in JEP:HPP on the website or contact bedford@u.arizona.edu

A general solution is offered for how two non-identical samples are judged to refer to one object . Observers exploit an entire family of geometries, despite the difficulty in reasoning about just one (Euclidean) geometry consciously. The geometries are applied to apparent motion, where it is shown that a figure will preferentially map onto the "same form" (Exp. 1), despite controversy in the literature. When the same form is not available, next preferred is a similarity transformation ("different size"; Exps. 2 and 3), but a figure will even match to an extreme topological transformation ("plastic deformation"; Exp. 4) if that is the lowest-level geometric transformation available. The hierarchy satisfyingly captures intuitions about what is "similar", while at the same time pointing to dangers of relying exclusively on such intuition. The experiments demonstrate for the first time a hierarchical structure of preferences for object identity which explains how the exact same pair of stimuli can sometimes refer to the same object, but sometimes not. The work points to a general law that runs counter to the explosion of research on independent modules of mind.

For further information contact bedford@u.arizona.edu

A cross-modal conflict over location was resolved in an unexpected way. When vision and proprioception provide conflicting information, which modality should dominate is ambiguous. A visual-propioceptive conflict was created with a prism and to logically disambiguate the problem, auditory information was added that either agreed with vision (Group 1), agreed with proprioception (Group 2), or was absent (Group 3). While a scarcity of research addresses the interaction of three modalities, we predicted error should be attributed to the modality in the minority. Instead, the opposite was found: Adaptation consisted of a large change in arm proprioception and a small change affecting vision in Group 2, and the reverse in Group 1. Group 1 was not different than Group 3. Findings suggested adaptation to separate two-way conflicts, possibly influenced by direction of attention, rather than a direct solution to a three-way modality problem..

 For further information see the full article in Perception on the website or contact bedford@u.arizona.edu

Quantitative assessments of plasticity required by growth to maintain accurate perception and behavior are infrequent. Published measurements of shoulder width and arm length for 2 to 17 year-old children were entered into our manual growth transformation model. Unexpectedly, only a small amount of plasticity was found required to maintain accurate pointing because the shoulder width to arm length ratio is the same in 8 and 17 year olds. Before age 8, 2° plasticity is required or pointing would be too far left for a straight-ahead target, with smaller errors for non-central targets. In Exp. 2, 98 local infants were measured (3.5 to 17 months); as much plasticity was found required than in 15 years, although other factors limit the systematic directional plasticity needed in infancy. Finally, an auditory growth transformation was derived; audition and pointing were found to have complementary plasticity needs for different azimuth angles of space. Conclusions: relative invariance of pointing may support British Associationist views, the mathematical function in growth is unlike adult prism adaptation, and auditory-pointing trade-offs may be useful.

For further information contact bedford@u.arizona.edu

We report a striking illusory misidentification of faces that further calls into question the accuracy of eyewitnesses even within race. The illusion was created by swapping facial essences on pairs of photos. Following study of a single individual, 60 to 81% of subjects misidentified an individual with the same hair, facial outline, and clothing, but the wrong core face, compared to 0 to 1% when untransformed faces or facial features alone were viewed. Misidentification occurred after delays of 2 and 32 minutes and unlimited study time. The results extend findings that external features are used for novel faces to testing with whole faces and mesh well with claims that expertise in face recognition is not privileged and requires domain-general perceptual discrimination learning. It is suggested that an analogous phenomenon in word recognition points to the inspection of external properties as a general bias that underlies how we individuate objects.

For further information contact bedford@u.arizona.edu

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