Reduced perceptual narrowing in synesthesia.

Synesthesia is a neurologic trait in which specific inducers, such as sounds, automatically elicit additional idiosyncratic percepts, such as color (thus "colored hearing"). One explanation for this trait-and the one tested here-is that synesthesia results from unusually weak pruning of cortical synaptic hyperconnectivity during early perceptual development. We tested the prediction from this hypothesis that synesthetes would be superior at making discriminations from nonnative categories that are normally weakened by experience-dependent pruning during a critical period early in development-namely, discrimination among nonnative phonemes (Hindi retroflex /d̪a/ and dental /ɖa/), among chimpanzee faces, and among inverted human faces. Like the superiority of 6-mo-old infants over older infants, the synesthetic groups were significantly better than control groups at making all the nonnative discriminations across five samples and three testing sites. The consistent superiority of the synesthetic groups in making discriminations that are normally eliminated during infancy suggests that residual cortical connectivity in synesthesia supports changes in perception that extend beyond the specific synesthetic percepts, consistent with the incomplete pruning hypothesis.

Development of SNARC and distance effects and their relation to mathematical and visuospatial abilities.

The current experiment measured symbolic SNARC (Spatial-Numeric Association of Response Codes) and distance effects in school-aged children and investigated the relation between these measures and visuospatial skills and mathematics ability. In the experiment, 6-, 7-, and 8-year-olds performed a magnitude-relevant SNARC task, in which they indicated whether a target number was less or greater than 5, as well as standardized tests of visuospatial skills (Developmental Test of Visual Perception-Second Edition, DTVP-2) and mathematics ability (Test of Early Mathematics Ability-Third Edition, TEMA-3). Consistent with previous research using numerical SNARC tasks with Western children, all age groups exhibited robust distance effects, and SNARC effects were observed only in 7- and 8-year-olds. Distance effects, but not SNARC effects, were moderately but significantly correlated with a subtest of the DTVP-2 measuring the ability to mentally manipulate objects in space but no other subtest. These data suggest that mental orientation abilities, but perhaps not visuospatial skills involved in visual perception and visuomotor coordination, are related to some aspects of mental number line development. Nevertheless, no relation was observed between SNARC or distance effects and mathematics ability. This result is consistent with previous developmental studies investigating the association between SNARC and math skill. However, these data are inconsistent with most experiments assessing the relationship between distance effect strength and math-a difference that can likely be attributed to the fact that a magnitude-relevant SNARC task was employed as opposed to a traditional SNARC parity task.

A computational vector-map model of neonate saccades: modulating the externality effect through refraction periods.

The present study develops an explicit and predictive computational model of neonate saccades based on the interaction of several simple mechanisms, including the tendency to fixate towards areas of high contrast, and the decay and recovery of a world-centered contrast representation simulating a low-level inhibition of return mechanism. Emergent properties similar to early visual behaviors develop, including the externality effect (or tendency to focus on external then internal features). The age-associated progression of this effect is modulated by the decay period of the model's contrast representation, where the high-level behavior of either scanning broadly or locally is modulated by a single decay parameter.