Partial correlation analysis reveals abnormal retinotopically organized functional connectivity of visual areas in amblyopia.

Amblyopia is a prevalent developmental visual disorder of childhood that typically persists in adults. Due to altered visual experience during critical periods of youth, the structure and function of adult visual cortex is abnormal. In addition to substantial deficits shown with task-based fMRI, previous studies have used resting state measures to demonstrate altered long-range connectivity in amblyopia. This is the first study in amblyopia to analyze connectivity between regions of interest that are smaller than a single cortical area and to apply partial correlation analysis to reduce network effects. We specifically assess short-range connectivity between retinotopically defined regions of interest within the occipital lobe of 8 subjects with amblyopia and 7 subjects with normal vision (aged 19-45). The representations of visual areas V1, V2, and V3 within each of the four quadrants of visual space were further subdivided into three regions based on maps of visual field eccentricity. Connectivity between pairs of all nine regions of interest in each quadrant was tested via correlation and partial correlation for both groups. Only the tests of partial correlation, i.e., correlation between time courses of two regions following the regression of time courses from all other regions, yielded significant differences between resting state functional connectivity in amblyopic and normal subjects. Subjects with amblyopia showed significantly higher partial correlation between para-foveal and more eccentric representations within V1, and this effect associated with poor acuity of the worse eye. In addition, we observed reduced correlation in amblyopic subjects between isoeccentricity regions in V1 and V2, and separately, between such regions in V2 and V3. We conclude that partial correlation-based connectivity is altered in an eccentricity-dependent pattern in visual field maps of amblyopic patients. Moreover, results are consistent with known clinical and psychophysical vision loss. More broadly, this provides evidence that abnormal cortical adaptations to disease may be better isolated with tests of partial correlation connectivity than with the regular correlation techniques that are currently widely used.

Effects of prosodic stress and serial position on syllable omission in first words.

The authors documented syllable omission in one child's multisyllabic vocabulary from 10 to 20 months of age to evaluate L. Gerken's (1991, 1994a, 1994b) proposal that children organize their productions according to a trochaic metrical (strong-weak) template and omit syllables from target utterances that do not conform to this pattern. The trochaic template hypothesis was not supported by these early productions. Results indicated that the likelihood of producing a target syllable was influenced primarily by the strength of the prosodic stress placed on it and secondarily by its serial order within a word. Over time, the child demonstrated an increasing ability to include syllables with weaker prosodic stress in multisyllabic productions. Omissions became much less common with the onset of 2-word speech.

Young children's overgeneralizations with fixed transitivity verbs.

The present study examined English-speaking children's tendency to make argument structure overgeneralization errors (e.g., I disappeared it). Children were exposed to several English verbs of fixed transitivity (exclusively intransitive or exclusively transitive) and then asked questions that encouraged them to overgeneralize usage of the verbs. Seventy-two children (24 in each of three age groups: 3, 4/5, and 8 years of age) experienced four actions performed by puppets. Each action had two verbs of similar meaning associated with it in the context of the experimental action: one more familiar to young children and one less familiar. Children at all ages were more likely to overgeneralize usage of verbs that were less familiar to them, supporting the hypothesis that children's usage of verbs in particular construction types becomes entrenched over time. As children solidly learn the transitivity status of particular verbs, they become more reluctant to use those verbs in other argument structure constructions.

A production limitation in syllable number: a longitudinal study of one child's early vocabulary.

The present paper reports on the phonological form of one child's productive vocabulary from age 0;10 to 1;8 with primary focus on his production of multisyllabic targets. A large percentage of his multisyllabic vocabulary was produced as one syllable until the age of 1;6. This limitation was not due to a tendency to extract only single syllables from the speech stream, but rather due primarily to a limitation on production. While some portion of his one-syllable productions could be interpreted as the result of single syllable extraction, a sizeable portion affirmed that he extracted the target size correctly by his inclusion of first and final target phonemes in his productions (e.g. [po] for piano and [kiz] for candies). The resolution of this limitation coincides with his move toward two-word speech. We conclude that there is a developmental and perhaps maturational limitation in the capacity to carry out the processes underlying word and sentence production.