Thirty-one children with specific language impairment participated in 48 intervention sessions designed to assist them in the use of 3rd-person singular -s or auxiliary is/are/was. Gains in the use of these target forms were significantly greater than gains on developmentally comparable morphemes serving as control forms. Untreated verb forms that mark both tense and agreement showed greater change during the intervention period than did past -ed. The findings suggest that by gaining skill in the use of morphemes that mark both tense and agreement, the children were able to identify and acquire other morphemes in the language that mark both of these features. This increase in sensitivity did not appear to apply to forms in the language that express tense only.
Although the results provide clear evidence for intervention effects, it appeared as if maturational factors also played a role. The findings are discussed in terms of their implications for treatment and for characterizing development in SLI.
New, productive fluvial marshes may develop along regulated canyon rivers through reduction in flood frequency, thereby increasing diversity, production, and wildlife habitat availability. Few fluvial marshes occurred along the eddy‐dominated Colorado River in the Grand Canyon prior to construction of Glen Canyon Dam in 1963. Reduction of flooding after 1963 permitted widespread marsh development. Fluvial marshes exhibited low stability but high resilience, quickly redeveloping after scouring by high flows between 1983 and 1986. In 1991, 253 fluvial wet marshes (cattail/reed and horseweed/Bermudagrass) and 850 dry marshes (horsetail/willow) occupied 25.0 ha (1%) of the 363 km mainstream riparian corridor between Lees Ferry and Diamond Creek, Arizona. Fluvial marsh development and composition varied in relation to local and reach‐based geomorphology, and microsite gradients in inundation frequency and soil texture. Colorado River marsh density (number/km2) increased with distance downstream, and marshes were larger and more abundant in wide reaches. Wet marsh cattail/reed stands developed on silty loam soils in low velocity depositional environments that were inundated 54% of the days from 1986 to 1991, whereas dry horsetail/willow marshes occupied less frequently inundated sites with sandy soils. Mean marsh standing mass (641 g C/m2) was comparable with values from regulated alluvial river marshes, but litter retention appeared limited by flow variability in both regulated and unregulated fluvial marshes. We discuss implications of flow management on the four marsh assemblages, and the need for consensus on priorities for management of regulated fluvial wetlands.
Steroid aromatase activity was measured in homogenates of combined hypothalamic and amygdaloid specimens obtained from 17- to 21-day-old male and female rat fetuses. The fetuses were obtained both from normal mothers and mothers exposed to a regimen of stress that results in a failure of behavioral masculinization and defeminization of male offspring. Tissue samples from stressed mothers and controls were obtained during the dark phase of the day (Villanova group, days 17, 18, 19, 20 and 21 postconception). Additional samples were obtained during the light phase (Hershey group, days 17.5, 18.5, 19.5 and 20.5 postconception). The aromatase assay used, based on the measurement of tritiated water formed during an incubation with [lβ-3H] androstenedione, had a sensitivity of 10–15 fmol per tube. There was no sex difference in aromatase activity in fetuses of either control or stressed mothers. When data from the two sexes were combined, the following sfatistically significant effects were identified: (1) lower aromatase activity in stressed compared with control fetuses on days 18, 19 and 20 postconception, (2) a progressive decline in enzyme activity between days 18.5 and 20.5 postconception in the Hershey group (controls) and between days 19 and 20 in both the control and stressed fetuses in the Villanova group, and (3) an increase in enzyme activity in the stressed fetuses between days 20 and 21. No relationship was evident between steroid aromatase activity in brain and circulating testosterone levels in male fetuses as determined in a previous study. Failure to detect sex differences or an effect of testosterone on aromatase activity could be due to tissue dilution since enzyme activity may be concentrated in a few discrete nuclear regions. Measurement of enzyme activity in these regions is needed before arriving at any definitive conclusions.
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