John F Ryan | PubMed Health

PubMed2006

Directional motion contrast sensitivity in developmental dyslexia.

The present study compared the perception of visual motion in two dyslexia classification schemes; the [Boder, E. (1973). Developmental dyslexia: a diagnostic approach based on three atypical reading-spelling patterns. Developmental Medicine and Child Neurology, 15, 663-687.] dyseidetic, dysphonetic and mixed subgroups and [Williams, M. J., Stuart, G. W., Castles, A., & McAnally, K. I. (2003). Contrast sensitivity in subgroups of developmental dyslexia. Vision Research, 43, 467-477.] surface, phonological and mixed subgroups by measuring the contrast sensitivity for drifting gratings at three spatial frequencies (1.0, 4.0, and 8.0 c/deg) and five drift velocities (0.75, 3.0, 6.0, 12.0, and 18.0 cyc/s) in a sample of 32 children with dyslexia and 32 matched normal readers. The findings show that there were no differences in motion direction perception between normal readers and the group with dyslexia when dyslexia was taken as a homogeneous group. Motion direction perception was found to be intact in the dyseidetic and surface dyslexia subgroups and significantly lowered in both mixed dyslexia subgroups. The one inconsistency in the findings was that motion direction perception was significantly lowered in the [Boder, E. (1973). Developmental dyslexia: a diagnostic approach based on three atypical reading-spelling patterns. Developmental Medicine and Child Neurology, 15, 663-687.] dysphonetic subgroup and intact in the [Williams, M. J., Stuart, G. W., Castles, A., & McAnally, K. I. (2003). Contrast sensitivity in subgroups of developmental dyslexia. Vision Research, 43, 467-477.] phonological subgroup. The findings also provide evidence for the presence of a disorder in sequential and temporal order processing that appears to reflect a difficulty in retaining sequences of non-meaningful auditory and visual stimuli in short-term working memory in children with dyslexia.

Adolescent↗

PubMed2005

Unfolding and extraction of a transmembrane alpha-helical peptide: dynamic force spectroscopy and molecular dynamics simulations.

An atomic force microscope (AFM) was used to visualize CWALP(19)23 peptides ((+)H(3)N-ACAGAWWLALALALALALALWWA-COO(-)) inserted in gel-phase DPPC and DSPC bilayers. The peptides assemble in stable linear structures and domains. A model for the organization of the peptides is given from AFM images and a 20 ns molecular dynamics (MD) simulation. Gold-coated AFM cantilevers were used to extract single peptides from the bilayer through covalent bonding to the cystein residue. Experimental and simulated force curves show two distinct force maxima. In the simulations these two maxima correspond to the extraction of the two pairs of tryptophan residues from the membrane. Unfolding of the peptide precedes extraction of the second distal set of tryptophans. To probe the energies involved, AFM force curves were obtained from 10 to 10(4) nm/s and MD force curves were simulated with 10(8)-10(11) nm/s pulling velocities (V). The velocity relationship with the force, F, was fitted to two fluctuation adhesive potential models. The first assumes the pulling produces a constant bias in the potential and predicts an F approximately ln (V) relationship. The second takes into account the ramped bias that the linker feels as it is being driven out of the adhesion complex and scales as F approximately (ln V)2/3.

1,2-Dipalmitoylphosphatidylcholine↗