A connectionist approach to making the predictability of English orthography explicit to at-risk beginning readers: evidence for alternative, effective strategies.

A case is made (and illustrated with empirical data with children) for connectionist models that are not only computationally explicit but also instructionally explicit. First-graders (N = 128) at the bottom of their classes in reading (average 11.5 percentile on nationally normed tests) participated in a 3-layer intervention. In the first layer, kept constant for all treatment groups, the alphabet principle was taught, making functional spelling units and alternations explicit. In the second layer, which varied systematically across treatment groups, children received different kinds of tutor modeling in learning a set of words of varying spelling-sound predictability, using different connections between printed and spoken words, singly or in combination. In the third layer, also kept constant, children read and discussed illustrated books. Over the 4-month, 24-lesson intervention, all 7 treatment groups in the second layer improved more in word-specific learning than a contact control group that received phonological and orthographic awareness training without explicit instruction on orthographic-phonological connections. Of these 7, only 3 kinds of explicit modeling (whole word, letter-phoneme, and combined whole word and letter-phoneme) resulted in greater transfer to untrained words than the contact control or the other 4 kinds of explicit modeling. Results are discussed in reference to the controversy over whether dual route or connectionist models best account for the acquisition of reading.

Early intervention for reading disabilities: teaching the alphabet principle in a connectionist framework.

Forty-eight children referred by teachers at the end of first grade for difficulty in reading were randomly assigned to three treatments, all of which modeled connections between written and spoken words but did not teach phonics rules, for eight half-hour individual tutoring sessions. The children were taught 48 words of varying orders of spelling-sound predictability (Venezky, 1995) using a whole-word method, for making connections between a word's name and its constituent letters; a subword method, for making connections between each color-coded spelling unit and its corresponding phonemes; or a combined whole-word and subword method. Regardless of the method used, children improved reliably on standardized reading measures and the taught words, showing that they could make connections between written and spoken words at the whole word and subword levels, even when rules were not taught. By posttest, the subword method showed a reliable advantage on a standardized test of real word reading. Knowledge of sounds associated with both multiletter and single-letter spelling units predicted reading achievement. Order of spelling-sound predictability (easy, moderate, difficult) was correlated with standardized measures of reading at pretest and posttest, and the magnitude of the relationship increased as a result of the intervention. Individual differences in verbal intelligence, rapid automatized naming, and phonological and orthographic skills predicted response to the intervention. Instructional implications of the results are discussed.

Detection mass bias in atmospheric pressure ionization mass spectrometry.

A previously uncharacterized source of detection mass bias is shown to be associated with atmospheric pressure ionization mass spectrometry (APIMS), and is attributed to a mass dependence in the sampling of ions from the supersonic free jet expansion of gas emerging from the ion source. The halide ions Cl (-), Br(-), and I(-) are shown to be transported from the ion source aperture to a quadrupole mass filter with efficiencies that increase linearly with increasing mass of the ion. While the polyatomic anions SF 6 (-) and C7F 14 (-) are detected with even greater efficiencies than would be expected for monatomic anions of the same mass, this additional sensitivity to the polyatomic anions is thought to be related to ion loss processes occurring within the ion source. The experimental conditions under which these mass bias effects can be minimized or enhanced in APIMS are described.

Cluster-assisted decomposition reactions of the molecular anions of SF6 and C 7F 14.

The cluster ions formed by the attachment of dimethylsulfoxide (DMSO) and methanol to the molecular negative ions of C7F14 and SF6 have been studied by a pulsed e-beam high pressure mass spectrometer (PHPMS) and by an atmospheric pressure ionization mass spectrometer (APIMS). The free energy change (ΔG°) for the clustering equilibria reaction, M(-)+S⇌M(-)S, at 35°C are found to be -7.7 and -7.2 kcal/mol for S = DMSO and M(-)=C7F 14 (-) and SF 6 (-) respectively, and -6.4 and -4.5 kcal/mol for S = methanol and M(-)=C7F 14 (-) and SF 6 (-) respectively. While the cluster ions formed by DMSO are found to be stable against side reactions, those formed by methanol undergo decomposition processes in which the central core ion is fragmented. At 35 °C, the rate law for the decomposition of the SF 6 (-) (CH30H)1 ion is second-order, involving the M(-)(CH30H)1 cluster ion and another methanol molecule. While the C7F 14 (-) (CH30H)1 ion also decomposes through this second-order process, a competing unimolecular mechanism is also operative at 35°C. With increases in the PHPMS ion source temperature to 150°C, the unimolecular decomposition process becomes progressively dominant for both of the M(-)(CH30H)1 cluster ions of C7F14 and SF6. Methanol cluster ions of the type M(-)S2 are not observed under any of the conditions examined here. When methanol or water partial pressures of a few torr or higher are present in the buffer gas of the APIMS ion source, the decomposition reactions are very fast and only the fragment ions produced by these reactions are observed in the electron-capture (EC)-APIMS spectra of C7F14 and SF6 . Also, in the methanol-containing APIMS ion source, the course of the SF 6 (-) decomposition reaction is altered so that fragment ions of the type F(-)(S)n dominate the EC-APIMS spectrum of SF6 at all ion source temperatures. For C7F14, fragment ions of the type F-(S)n become dominant at lower ion source temperatures. These previously unknown reactions are expected to be important in the analysis of perfluorinated compounds by mass spectrometric methods that utilize ionization by electron capture or negative chemical ionization. The nature of the fragment ions produced in these cluster-assisted reactions may also provide a new source of information concerning the structures of the molecular negative ions of SF6 and C7F14.

Covalent cross-linking of ribosomal RNA and proteins by methylene blue-sensitized photooxidation.

Ribosomal proteins are covalently cross-linked to ribosomal RNA by irradiation with visible light in the presence of methylene blue and O2. Proteins S3, S4, S5 and S7 from the 30 S subunit of Escherichia coli ribosomes and L2 and L3 from the 50 S subunit are among the cross-linked proteins. S3 and S5 had not previously been identified as RNA-binding proteins.