Variability of the Surface Area of the V1, V2, and V3 Maps in a Large Sample of Human Observers.

How variable is the functionally defined structure of early visual areas in human cortex and how much variability is shared between twins? Here we quantify individual differences in the best understood functionally defined regions of cortex: V1, V2, V3. The Human Connectome Project 7T Retinotopy Dataset includes retinotopic measurements from 181 subjects (109 female, 72 male), including many twins. We trained four "anatomists" to manually define V1-V3 using retinotopic features. These definitions were more accurate than automated anatomical templates and showed that surface areas for these maps varied more than threefold across individuals. This threefold variation was little changed when normalizing visual area size by the surface area of the entire cerebral cortex. In addition to varying in size, we find that visual areas vary in how they sample the visual field. Specifically, the cortical magnification function differed substantially among individuals, with the relative amount of cortex devoted to central vision varying by more than a factor of 2. To complement the variability analysis, we examined the similarity of visual area size and structure across twins. Whereas the twin sample sizes are too small to make precise heritability estimates (50 monozygotic pairs, 34 dizygotic pairs), they nonetheless reveal high correlations, consistent with strong effects of the combination of shared genes and environment on visual area size. Collectively, these results provide the most comprehensive account of individual variability in visual area structure to date, and provide a robust population benchmark against which new individuals and developmental and clinical populations can be compared.SIGNIFICANCE STATEMENT Areas V1, V2, and V3 are among the best studied functionally defined regions in human cortex. Using the largest retinotopy dataset to date, we characterized the variability of these regions across individuals and the similarity between twin pairs. We find that the size of visual areas varies dramatically (up to 3.5×) across healthy young adults, far more than the variability of the cerebral cortex size as a whole. Much of this variability appears to arise from inherited factors, as we find very high correlations in visual area size between monozygotic twin pairs, and lower but still substantial correlations between dizygotic twin pairs. These results provide the most comprehensive assessment of how functionally defined visual cortex varies across the population to date.

Cultural differences in perceptual reorganization in US and Pirahã adults.

Visual illusions and other perceptual phenomena can be used as tools to uncover the otherwise hidden constructive processes that give rise to perception. Although many perceptual processes are assumed to be universal, variable susceptibility to certain illusions and perceptual effects across populations suggests a role for factors that vary culturally. One striking phenomenon is seen with two-tone images-photos reduced to two tones: black and white. Deficient recognition is observed in young children under conditions that trigger automatic recognition in adults. Here we show a similar lack of cue-triggered perceptual reorganization in the Pirahã, a hunter-gatherer tribe with limited exposure to modern visual media, suggesting such recognition is experience- and culture-specific.

When and how does autism begin?

Jones and Klin recently found that the well-known decreased fixations to eyes in children with autism spectrum disorder (ASD) are not present throughout infancy; instead a decline in eye fixations between 2 and 6 months predicts diagnosis. This decline is the earliest behavioral pattern linked to autism to date.

Brief report: broader autism phenotype predicts spontaneous reciprocity of direct gaze.

We report evidence for a relationship in the general population between self-reported autism-associated traits and the spontaneous reciprocation of direct gaze, a behavior that we propose may reflect a tendency to synchronize with social partners. Adults viewed videos of actors whose gaze was either directed towards or averted from them. Individuals with lower scores on four subscales of the Autism-Spectrum Quotient (AQ) scale showed a greater tendency to look at directed relative to averted eyes; individuals with higher scores on the AQ did not. This relationship was specific to autism-associated traits and to gaze towards the eyes; it did not generalize to a social anxiety measure or to gaze towards the mouth. We discuss implications for our understanding of the broader autism phenotype.

Differential development of the ventral visual cortex extends through adolescence.

The ventral temporal cortex (VTC) in humans includes functionally defined regions that preferentially respond to objects, faces, and places. Recent developmental studies suggest that the face selective region in the fusiform gyrus ('fusiform face area', FFA) undergoes a prolonged development involving substantial increases in its volume after 7 years of age. However, the endpoint of this development is not known. Here we used functional magnetic resonance imaging (fMRI) to examine the development of face-, object- and place selective regions in the VTC of adolescents (12-16 year olds) and adults (18-40 year olds). We found that the volume of face selective activations in the right fusiform gyrus was substantially larger in adults than in adolescents, and was positively correlated with age. This development was associated with higher response amplitudes and selectivity for faces in face selective regions of VTC and increased differentiation of the distributed response patterns to faces versus non-face stimuli across the entire VTC. Furthermore, right FFA size was positively correlated with face recognition memory performance, but not with recognition memory of objects or places. In contrast, the volume of object- and place selective cortical regions or their response amplitudes did not change across these age groups. Thus, we found a striking and prolonged development of face selectivity across the VTC during adolescence that was specifically associated with proficiency in face recognition memory. These findings have important implications for theories of development and functional specialization in VTC.

Biological motion displays elicit social behavior in 12-month-olds.

To test the hypothesis that biological motion perception is developmentally integrated with important social cognitive abilities, 12-month-olds (N = 36) were shown a display of a human point-light figure turning to observe a target. Infants spontaneously and reliably followed the figure's "gaze" despite the absence of familiar and socially informative features such as a face or eyes. This suggests that biological motion displays are sufficient to convey rich psychological information such as attentional orientation and is the first evidence to show that biological motion perception and social cognitive abilities are functionally integrated early in the course of typical development. The question of whether common neural substrates for biological motion perception and analysis of gaze direction underlies the functional integration seen behaviorally is discussed.

Communication-induced memory biases in preverbal infants.

Human teaching, a highly specialized form of cooperative information transmission, depends not only on the presence of benevolent communicators in the environment, but also on the preparedness of the students to learn from communication when it is addressed to them. We tested whether 9-month-old human infants can distinguish between communicative and noncommunicative social contexts and whether they retain qualitatively different information about novel objects in these contexts. We found that in a communicative context, infants devoted their limited memory resources to encoding the identity of novel objects at the expense of encoding their location, which is preferentially retained in noncommunicative contexts. We propose that infants' sensitivity to, and interpretation of, the social cues distinguishing infant-directed communication events represent important mechanisms of social learning by which others can help determine what information even preverbal human observers retain in memory.