This study examines two current ideas regarding the control of eye-head gaze shifts. The first idea stems from recent studies involving electrical stimulation in the primate superior colliculus that suggest that a residual feedback of gaze displacement persists for approximately 100 ms after completion of a gaze shift. In light of this hypothesis, we examined the accuracy of gaze shifts generated very soon after the end of a preceding gaze shift. Human subjects were presented with a visual or auditory target along with an accompanying stimulus of the other modality. The accompanying stimulus appeared either at the same place as the target or at the diametrically opposite position, in which case it was termed a distractor. Subjects often made an incorrect gaze shift (IGS) in the direction of the distractor, followed by a recorrect gaze shift (RGS) in the direction of the target. We found that RGSs were accurately driven to the target, even when they followed IGSs by <5 ms, regardless of the size of the IGS. The second idea is that a gaze shift cannot be cancelled in midflight. The end point of IGSs frequently fell short of the distractor. The dynamics of these movements, and of the head movement components during the IGSs in particular, suggests that these hypometric IGSs were planned for a much larger excursion but were truncated and superceded by the reversing RGSs. These results emphasize that the gaze shifting system can change the desired goal of a gaze shift in midflight and that the superceding movement is accurate regardless of the metrics or timing of the preceding movement.

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. Can. J. Chem. 60,2583Chem. 60, (1982. Mononuclear, binuclear, and trinuclear copper(I1) complexes of the tetradentate ligands 1,4-di(2'-pyridyl) aminophthalazine (PAP) and 1,4-di(4'-methyl-2'-pyridyl) aminophthalazine (PAP4Me) and binuclear complexes of the tetradentate ligand 1,4-di(6'-methyl-2'-pyridyl) aminophthalazine (PAP6Me) are reported. In a series of binuclear carboxylate derivatives carboxylate bridges exist between copper centres in all cases and in some cases oxygen bridges (hydroxide or methoxide) are indicated. In all other polynuclearderivatives hydroxide bridges are anticipated on the basis of analytical, spectral, and magnetic data. The ligandsexist as anionic groups in some binuclear carboxylate derivatives while in the other polynuclear systems neutral ligands are found. In reactions in aqueous solution protonated mononuclear derivatives are obtained for both PAP and PAP4Me in cases where solutions of the metal salts are inherently acidic, followed by polynuclear, neutral ligand complexes which form when the pH increases. On a prepare les complexes mono-, bi-et trinuclkaires du cuivre(I1) des ligands tetradentates di(pyridy1 2')-1,4 aminophtalazine (PAP) et di-(methyl-4' pyridyl-2')-1,4 aminophtalazine (PAP4Me) et les complexes binuclkaires du ligand tetradentate di(methy1-6' pyridyl-2')-1,4 aminophtalazine (PAP6Me). Dans une sCrie de derives carboxylates binucltaires, il existe dans tous les cas des ponts carboxylates entre les centres cuivre et, dans certains cas, on trouve des ponts oxygknes (hydroxyde ou methylate). En se basant sur des donnees analytiques, spectrales et magnetiques, on prkvoit qu'il existera des ponts hydroxydes dans tous les autres derivks polynucleaires. Les ligands existent sous forme de groupes anioniques dans certains carboxylates binucleaires tandis que, dans d'autres systkmes polynuclkaires, on trouve des ligands neutres. Lorsque les solutions de sels mCtalliques sont intrinsequement acides, on obtient des derives mononuclCaires protones avec le PAP et le PAP4Me en solution aqueuses e t des complexes polynucleaires de ligands neutres lorsque le pH augmente. On n'obtient pas de complexes mononucleaires protones avec le PAP6Me alors que des facteurs stCriques empechent la formation de tels derives. On a observe de faibles moments magnetiques ( 1.1-1.5 BM) pour la plupart des complexes ayant un pont hydroxyde tandis qu'on observe des valeurs plus faibles (< 0.70 BM) pour deux complexes binucleaires du PAP6Me; ceci indique qu'il existe une possibilitk d'un fort echange antiferromagnetique entre les centres mCtalliques. Une etude preliminaire du complexe [CU,(PAP~M~)(OH)(NO,)~(H~O)~]NO, par cristallographie de rayons X indique une structure binuclkaire triplement pontCe incluant un pont nitrate bidentate et un pont hydroxyde avec un angle du pont oxygkne de 115,2".[Traduit par le journal]

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