Overlapping numerical cognition impairments in children with chromosome 22q11.2 deletion or Turner syndromes.

Children with one of two genetic disorders (chromosome 22q11.2 deletion syndrome and Turner syndrome) as well typically developing controls, participated in three cognitive processing experiments. Two experiments were designed to test cognitive processes involved in basic aspects numerical cognition. The third was a test of simple manual motor reaction time. Despite significant differences in global intellectual abilities, as measured by IQ tests, performance on the two numerical cognition tasks differed little between the two groups of children with genetic disorders. However, both performed significantly more poorly than did controls. The pattern of results are consistent with the hypothesis that impairments were not due to global intellectual ability but arose in specific cognitive functions required by different conditions within the tasks. The fact that no group differences were found in the reaction time task, despite significant differences in the standardized processing speed measure, further supports the interpretation that specific cognitive processing impairments and not global intellectual or processing speed impairments explain the pattern of results. The similarity in performance on these tasks of children with unrelated genetic disorders counters the view that numerical cognition is under any direct genetic control. Instead, our findings are consistent with the view that disturbances in foundational spatiotemporal cognitive functions contribute to the development of atypical representations and processes in the domains of basic magnitude comparison and simple numerical enumeration.

Oculomotor abnormalities parallel cerebellar histopathology in autism.

OBJECTIVE: To investigate cerebellar function in autism by measuring visually guided saccades. METHODS: A visually guided saccade task was performed by 46 high-functioning individuals with autism with and without delayed language acquisition, and 104 age and IQ matched healthy individuals. RESULTS: Individuals with autism had increased variability in saccade accuracy, and only those without delayed language development showed a mild saccadic hypometria. Neither autistic group showed a disturbance in peak saccade velocity or latency. CONCLUSIONS: The observed saccadic abnormalities suggest a functional disturbance in the cerebellar vermis or its output through the fastigial nuclei, consistent with reported cerebellar histopathology in autism. The pattern of mild hypometria and variable saccade accuracy is consistent with chronic rather than acute effects of cerebellar vermis lesions reported in clinical and non-human primate studies, as might be expected in a neurodevelopmental disorder. The different patterns of oculomotor deficits in individuals with autism with and without delayed language development suggest that pathophysiology at the level of the cerebellum may differ depending on an individual's history of language development.

Efficient visual search by category: specifying the features that mark the difference between artifacts and animals in preattentive vision.

In this report, we explored the features that support visual search for broadly inclusive natural categories. We used a paradigm in which subjects searched for a randomly selected target from one category (e.g., one of 32 line drawings of artifacts or animals in displays ranging from three to nine items) among a mixed set of distractors from the other. We found that search was surprisingly fast. Target-present slopes for animal targets among artifacts ranged from 10.8 to 16.0 msec/item, and slopes for artifact targets ranged from 5.5 to 6.2 msec/item. Experiments 2-5 tested factors that affect both the speed of the search and the search asymmetry favoring detection of artifacts among animals. They converge on the conclusion that target-distractor differences in global contour shape (e.g., rectilinearity/curvilinearity) and visual typicality of parts and form facilitate search by category. We argue that existing theories are helpful in understanding these findings but that they need to be supplemented to account for the specific features that specify categories and to account for subjects' ability to quickly locate targets representing heterogeneous and formally complex categories.

Animals and artifacts may not be treated equally: differentiating strong and weak forms of category-specific visual agnosia.

We examined a categorical dissociation hypothesis of category-specific agnosia using hierarchical regression to predict the naming responses of three agnosia patients while controlling a wide variety of perceptual and conceptual between-category differences. The living-nonliving distinction remained a significant predictor for two of the patients after controlling for all the other factors. For one remaining patient, the categorical variable was not significant once the form-function correlation of different objects was controlled. We argue that the visual system may use various subprocesses at different stages, some of which reflect true categorical organization and some of which reflect a unitary feature-based system that distinguishes kinds.