Effect of citrate on the redox properties of cytochrome C and its kinetic and binding behaviour with cytochrome oxidase /

Increasing citrate concentration, at constant ionic strength (30 mM) decreases the rate of cytochrome ~ reduction by ascorbate. This effect is also seen at both high (600 mM) and low (19 mM) ionic strengths, and the Kapp for citrate increases with increasing ionic strength. Citrate binds d both ferri -and ferrocytochrome ~, but with a lower affinity for the latter form (Kox . .red d = 2 mM, Kd = 8 mM) as shown by an equilibrium assay with N,N,N',N', Tetramethyl E- phenylenediamine. The reaction of ferricytochrome ~with cyanide is also altered in the presence of citrate: citrate increases the K~PP for cyanide. Column chromatography of cytochrome ~-cytochrome oxidase mixtures shows citrate increases the dissociation constant of the complex. These results are confirmed in kinetic assays for the "loose"site (Km = 20 pM) only. The effect of increasing citrate observable at the "tight" site (Km = 0.25 pM) is on the turnover number and not on the K . These results suggest a mechanism m where anion binding to cytochrome £ at the tight site affects the equilibrium between two forms of cytochrome c bound cytochrome oxidase: an active and an inactive one.

Synthesis of fluorescent analogues of a-tocopherol as ligands for the human a-tocopherol transfer protein (a-TTP) /

To further understand in vivo localization and trafficking of a-tocopherol (a-Toe), the most biologically active form of vitamin E, between lipid environments, tocopherols are required that can be followed by teclu1iques such as confocal microscopy and fluorescence resonance energy transfer (FRET) assays. To this end, sixteen fluorescent analogues of a-tocopherol (la-d [(1)anthroy loxy -a-tocopherols, A O-a-Toes], 2a-d [w-nitro benzoxadiazole-a-tocopherols, NBD-aToes], 3a-d [w-dansyl-a-tocopherols, DAN-a-Toes], and 4a-d [w-N-methylanthranilamide-atocopherols, NMA-a-TocsD were prepared by substituting fluorescent labels at the terminus of w-functionalized alkyl chains extending from C-2 of the chroman ring while retaining key binding features of the natural ligand. These compounds were prepared starting from (S)-Trolox® acid VIa esterification, protection, and reduction producing the silyl-protected (S)-Trolox aldehyde that was coupled using Wittig chemistry to different w-hydroxyalkylphosphonium bromides. Reduction of the alkene generated the w-hydroxy functionalized 2-n-alkyl intermediates 9a-d having the necessary 2R stereochemistry. A series of functional group manipulations including mesylation, substitution with azide, and hydride reduction provided w-amino functionalized intermediates 12a-d as well. Coupling intermediates 9a-d and 12a-d with the selected fluorophores (9- anthracene carboxylic acid, 4-chloro-7-nitrobenz-2-oxa-l,3-diazole, 5- dimethylaminonapthalene-l-sulfonyl chloride, and I-methyl-2H-3,1-benzoxazine-2,4(1H)dione), followed by deprotection of the phenolic silyl group, gave the desired fluorescent ligands la-d, 2a-d, 3a-d and 4a-d in good yield. Assessment of their binding affinities with recombinant human a-tocopherol transfer protein (ha-TTP) utilizing fluorescent titration binding assays identified competent ligands for further use in protein studies. Compounds Id (C9-AO-a-Toc) and 2d (C9-NBD-a-Toc) both having nonyl alkyl chain extensions between the chromanol and fluorophore were shown to bind specifically to ha-TTP with dissociation constants (KdS) of approximately 280 nM and 55 nM respectively, as compared to 25 nM for the natural ligand 2R,4'R,^'R-a-tocophQxoL.

A mass spectrometric study of some pesticides /|nK. S. Subramanian. -- 260 St. Catharines, Ont. : [s. n.],

The fragmentation processes in the mass spectra of a series of organophosphorus, organochlorine, thio and dithiocarbamate as well as a number of miscellaneous pesticides have been studied i n detail by using the Bendix timeof- flight, MS-12 single-focussing and MS-30 double-focussing mass spectrometers. Interpretation of all the spectra have been presented; their mode s of dissociation elucidated, aided by metastable transitions wherever possible and the structures of the various f ragmentation species postulated wherever f easible. The fragmentation mechanisms are based on the concepts of inductive, resonance and steric ef~ects. Multiple bond cleavages accompanied by simultaneous bond formation and rearrangement reactions involving cycli c t r ansition states have clarified t he formation of various ions . Due emphasis has been placed on the effect of the functional groups or substituents in altering the mass spectral behaviour of the pesticides as they form the basis for the identifi cation of the otherwise identical pesticides. The organophosphorus pesticides which have been studied include i) the phosphates (eg: DDVP and Phosdrin ); ii) phosphorothionates (eg: Parathion, 0-2, 4 dichloro phenyl 0, O-diethyl thionophosphate); iii) phosphorothioites (eg: Tributyl phosphorotrithioite); i V) phosphorothioates (eg: Ethion) and v) phosphorodithioates (eg: Carbophenolthion). Cleavages and rearrangements of the ester moiety dominate the spectrum of phosdrin while that of DDVP is + dominated by t he fragmentation modes of the (OH30)2P=0 + moiety. Fragmentation §f the (CH30)2P=S characterises the spectrum of (OH30)2"P -Cl while cleavages of the + (C2H50 )2P=S species mark the spectra of parathion and 0-2, 4- di chlorophenyl O, O-diethyl thiophosphate. The 0(, cl eavages of the thioether f unction rather than + cleavages of the (C2H50)2P=S signify the spectrum of carbophenolthion. Tributyl phosphorotrithioite behaves more like an aliphatic hydrocarbon than like the corresponding phosphites. The isopropyl and butyl esters of 2, 4 dichlorophenoxy acetic acid show cleavage and rearrangement ions typical of an ester. In spite of its structural similari ty to pp' - DDT and pp' - DDD, Kalthane has a completely different mass spectral behaviour due to the influence of its hydroxyl function. The thiocarbamate pesticides studied include Eptam and Perbulate. Both are structurally similar but having different alkyl substituents on nitrogen and sulphur. This structurQlsimilarity leads to similar types of (N-C), (O-S) and (S-alkyl cleavages). However, perbulate differs from Eptam in showing a rearrangement ion at mle 161 and in forming an isocyanate ion as the base peak. In Eptam the base peak i s the alkyl ion. The dithiocarbamate, Vegadex, resembles the thiocarbamates in undergoing simple cleavages but it differs from them in having a weak parent ion; in the formation of its base peak and in undergoing a series of rearrangement reactions. The miscellaneous pesticides studied include 1-Naphthalene acetic aCid- methyl ester, Fiperonyl butoxide and Allethrin. The ester i s stable to electron impact and shows only fewer ions. Piper onyl butoxide, a polyether, shows characteristics of an et her, alcohol and aldehyde . Allethrin is regarded as an ester of the type R-C-O-R1 with n R being a substituted cyclopr opane moiety and o Rt, a substituted cyclopentenone mOiety. Accordingly it shows cleavage ions typical of an aliphatic ester and undergoes bond ruptures of the cyclic moieties to give unusual ions. Its base peak is an odd electron ion, quite contrary to expectations.

NMR studies of the exchange reactions of CH3CN.BX3 with excess CH3CN /|nJoseph Fogelman. -- 260 St. Catharines, Ont. : [s. n.],

Exchange reactions between molecular complexes and excess acid or base are well known and have been extensively surveyed in the literature(l). Since the exchange mechanism will, in some way involve the breaking of the labile donor-acceptor bond, it follows that a discussion of the factors relating to bonding in molecular complexes will be relevant. In general, a strong Lewis base and a strong Lewis acid form a stable adduct provided that certain stereochemical requirements are met. A strong Lewis base has the following characteristics (1),(2) (i) high electron density at the donor site. (ii) a non-bonded electron pair which has a low ionization potential (iii) electron donating substituents at the donor atom site. (iv) facile approach of the site of the Lewis base to the acceptor site as dictated by the steric hindrance of the substituents. Examples of typical Lewis bases are ethers, nitriles, ketones, alcohols, amines and phosphines. For a strong Lewis acid, the following properties are important:( i) low electron density at the acceptor site. (ii) electron withdrawing substituents. (iii) substituents which do not interfere with the close approach of the Lewis base. (iv) availability of a vacant orbital capable of accepting the lone electron pair of the donor atom. Examples of Lewis acids are the group III and IV halides such (M=B, AI, Ga, In) and MX4 - (M=Si, Ge, Sn, Pb). The relative bond strengths of molecular complexes have been investigated by:- (i) (ii) (iii) (iv) (v] (vi) dipole moment measurements (3). shifts of the carbonyl peaks in the IIIR. (4) ,(5), (6) .. NMR chemical shift data (4),(7),(8),(9). D.V. and visible spectrophotometric shifts (10),(11). equilibrium constant data (12), (13). heats of dissociation and heats of reactions (l~), (16), (17), (18), (19). Many experiments have bben carried out on boron trihalides in order to determine their relative acid strengths. Using pyridine, nitrobenzene, acetonitrile and trimethylamine as reference Lewis bases, it was found that the acid strength varied in order:RBx3 > BC1 3 >BF 3 • For the acetonitrile-boron trihalide and trimethylamine boron trihalide complexes in nitrobenzene, an-NMR study (7) showed that the shift to lower field was. greatest for the BB~3 adduct ~n~ smallest for the BF 3 which is in agreement with the acid strengths. If electronegativities of the substituents were the only important effect, and since c~ Br ,one would expect the electron density at the boron nucleus to vary as BF3

The influence of water on the glucose affinity of hexokinase

In the present thesis, the role of hydration during the glucose induced conformational change of hexokinase is investigated. This is accomplished by applying the osmotic stress technique. The osmotic stress technique is founded on varying of the activity of water in a system in order to determine ifs effects. This is accomplished by adding inert solute molecules that are excluded from the system under study. The solute molecules used within the present investigation are Polyethylene glycols (PEGs). PEGs aid in the removal of water from hexokinase by exerting osmotic pressure. The osmotic pressures of the PEG solutions are also measured with both vapour pressure osmometry and secondary osmometry with phospholipids. An interesting discovery is made in that the osmotic pressures of PEG and co-solute solutions are non-additive. This indicates that PEG concentrates co-solutes in solution by making a certain proportion of the water inaccessible. Glucose binding was measured fluorometrically and the glucose equilibrium dissociation constant (GEDC) of hexokinase is measured in solutions containing the different MW PEGs. Changes in the sensitivity of the glucose affinity with osmotic pressure allows the calculation of the change in the numbers of polymer-inaccessible water molecules upon the binding of glucose to hexokinase ~Nw. It was determined the ~Nw decreases with increases in osmotic pressure in the presence of all MW PEGs. ~Nw decreases from values between 45-290 water molecules at low pressure to approximately 15 at high pressure. There is also a molecular weight dependence observed. There are large decreases in ~Nw with osmotic pressure in the presence of PEGs above MW 1000. However, below MW 1500 changes in ~Nw with osmotic pressure are relatively small. These findings are interpreted with respect to two possible mechanisms involving changes in the conformation of hexokinase u~der osmotic pressure and the access of the PEG molecules to water surrounding hexokinase.

The role of personality and situational factors in forgiveness /

This study deals with personality and situational variables that influence forgiveness. The relations between empathy and forgiveness were studied, followed by the examination of the relation of these two variables to the Big Five personality traits, as well as honesty, absorption, the propensity to mystical experiences, and dissociation. Empathy was then tested as a mediating variable between the personality variables and forgiveness. Empathy and forgiveness were then studied in relation to childhood maltreatment. Finally, the effects of six different motivations to forgive were examined in relation to the personality variables. Participants were 142 undergraduate students recruited from the ftrst year psychology class at Brock University; 75% were either 18 or 19 years of age, and 84% were female. All of the variables were measured using self-report questionnaires. The relation between empathy and forgiveness was only partially replicated. In terms of personality, forgiveness was found to be related to honesty, emotionality, and agreeableness. Empathy at least partially mediated the relations between forgiveness and agreeableness, honesty and emotionality. Childhood maltreatment was negatively related to forgiveness, and positively related to openness to experience, absorption, and dissociation from reality, but not to the propensity for mystical experiences. Six different motivations for forgiveness emerged from an exploratory factor analysis. Out of these, Forgiveness to Promote Reconciliation was related to emotionality and dispositional empathy. Religious Forgiveness was related to honesty, emotionality, and mystical experiences. Forgiveness to Feel Better was related to honesty, emotionality, agreeableness, conscientiousness, absorption, mystical experiences, and empathy. Forgiveness to Assert Moral Superiority over the Injurer was negatively related to honesty, empathy, and positively related to extraversion. Forgiveness out of Fear was related to agreeableness. Finally, Altruistic Forgiveness was related to honesty, emotionality, and agreeableness, absorption and the propensity to mystical experiences. Altruistic Forgiveness correlated most highly with all the measures of forgiveness, followed by Forgiveness to Feel better. Altruistic forgiveness was also the motivation for forgiveness that correlated the highest with absorption.

The role of water in determining structure and function of macromolecules and macromolecular assemblies /

The interaction of biological molecules with water is an important determinant of structural properties both in molecular assemblies, and in conformation of individual macromolecules. By observing the effects of manipulating the activity of water (which can be accomplished by limiting its concentration or by adding additional solutes, "osmotic stress"), one can learn something about intrinsic physical properties of biological molecules as well as measure an energetic contribution of closely associated water molecules to overall equilibria in biological reactions. Here two such studies are reported. The first of these examines several species of lysolipid which, while present in relatively low concentrations in biomembranes, have been shown to affect many cellular processes involving membrane-protein or membrane-membrane interactions. Monolayer elastic constants were determined by combining X-ray diffraction and the osmotic stress technique. Spontaneous radii of curvature of lysophosphatidylcholines were determined to be positive and in the range +30A to +70A, while lysophosphatidylethanolamines proved to be essentially flat. Neither lysolipid significantly affected the bending modulus of the monolayer in which it was incorporated. The second study examines the role of water in theprocess of polymerization of actin into filaments. Water activity was manipulated by adding osmolytes and the effect on the equilibrium dissociation constant (measured as the criticalmonomer concentration) was determined. As water activity was decreased, the critical concentration was reduced for Ca-actin but not for Mg-actin, suggesting that 10-12 fewer water molecules are associated with Ca-actin in the polymerized state. Thisunexpectedly small amount of water is discussed in the context of the common structural motif of a nucleotide binding cleft.

Hydrogen sulphide as inhibitor and substrates for the cytochrome c-cytochrome c oxidase system /

It has previously been recognized that the major biochemical toxicity induced by sulphide is due to an inhibition of cytochrome ~ oxidase. Inhibition of this enzyme occurs at 30°C and pH 7.4 with a Ki of approximately 0.2 ~M, and a kon of 104 M-1 s-l, under catalytic conditions. However, the equimo1ar mixture of sulphide and the enzyme shows identical catalytic behaviour to that of the native enzyme. This cannot readily be attributed to rapid dissociation of sulphide, as both spectroscopic and plot analysis indicate the koff value is low. The addition of stoichiometric sulphide to the resting oxidized enzyme gives rise to the appearance of a low-spin ferric-type spectrum not identical with that seen on the addition of excess sulphide to the enzyme aerobically. Sulphide added to the enzyme anaerobically gives rise to another low-spin, probably largely ferric, form which upon admission of oxygen is then converted into a 607 nm species closely resembling Compound C. The 607 nm form is probably the precursor of oxyferricytochrome aa3. The addition of successive a1iquots of Na2S solution to the enzyme induces initial uptake of approximately 3 moles of oxygen per mole of the enzyme. Thus, it is concluded that: 1. the initial product of sulphide-cytochrome c oxidase interaction is not an inhibited form of the enzyme, but the low-spin (oxyferri) ~3+~+ species; 2. a subsequent step in which sulphide reduces cytochrome ~ occurs; 3. the final inhibitory step, in which a further molecule of sulphide binds to the cytochrome ~ iron centre in the cytochrome ~2+~+ species, gives the cytochrome a2+~+-H2S form which is a half-reduced fully inhibited species;4. a 607 run form of the enzyme is produced which may be converted into a catalytically active low-spin (oxyferri) state; and therefore 5. liganded sulphide may be able to reduce the cytochrome 33 -Cu centre without securing the prior reduction of the cytochrome a_ haem group or the Cud centre associated with it.

Synthesis and characterization of BODIPY-α-tocopherol : a new ligand to explore the intracellular transfer of Vitamin E

Since its discovery nearly a century ago, a-tocopherol (vitamin E) research has been mainly focused on its ability to terminate the cycle of lipid peroxidation in membranes. Nitrobenzoxadiazole fluorescent analogues were made previously to study the intracellular transfer of vitamin E in cells. However, these molecules were reportedly susceptible to photobleaching while under illumination for transfer assays and microscopy. Here is reported the synthesis of a series of fluorescent analogues of vitamin E incorporating the more robust dipyrrometheneboron difluoride fluorophore (BDP-a-Tocs; Aex = 507 nm, Aem = 511 nm). C8-BDP-a-Toc 42c, having an eight-carbon chain between the chromanol and fluorophore, wa<; shown to bind specifically to a-tocopherol transfer protein with a dissociation constant of approximately 100 nM. Another fluorescent analogue of vitamin E with a thienyl derivative of BODIPY that is excited and fluoresces at longer wavelengths (Aex = 561 nm, Aem = 570 nm) is in development.

Sleep and information processing in individuals who have sustained a traumatic brain injury

Individuals who have sustained a traumatic brain injury (TBI) often complain of t roubl e sleeping and daytime fatigue but little is known about the neurophysiological underpinnings of the s e sleep difficulties. The fragile sleep of thos e with a TBI was predicted to be characterized by impairments in gating, hyperarousal and a breakdown in sleep homeostatic mechanisms. To test these hypotheses, 20 individuals with a TBI (18- 64 years old, 10 men) and 20 age-matched controls (18-61 years old, 9 men) took part in a comprehensive investigation of their sleep. While TBI participants were not recruited based on sleep complaint, the fmal sample was comprised of individuals with a variety of sleep complaints, across a range of injury severities. Rigorous screening procedures were used to reduce potential confounds (e.g., medication). Sleep and waking data were recorded with a 20-channel montage on three consecutive nights. Results showed dysregulation in sleep/wake mechanisms. The sleep of individuals with a TBI was less efficient than that of controls, as measured by sleep architecture variables. There was a clear breakdown in both spontaneous and evoked K-complexes in those with a TBI. Greater injury severities were associated with reductions in spindle density, though sleep spindles in slow wave sleep were longer for individuals with TBI than controls. Quantitative EEG revealed an impairment in sleep homeostatic mechanisms during sleep in the TBI group. As well, results showed the presence of hyper arousal based on quantitative EEG during sleep. In wakefulness, quantitative EEG showed a clear dissociation in arousal level between TBls with complaints of insomnia and TBls with daytime fatigue. In addition, ERPs indicated that the experience of hyper arousal in persons with a TBI was supported by neural evidence, particularly in wakefulness and Stage 2 sleep, and especially for those with insomnia symptoms. ERPs during sleep suggested that individuals with a TBI experienced impairments in information processing and sensory gating. Whereas neuropsychological testing and subjective data confirmed predicted deficits in the waking function of those with a TBI, particularly for those with more severe injuries, there were few group differences on laboratory computer-based tasks. Finally, the use of correlation analyses confirmed distinct sleep-wake relationships for each group. In sum, the mechanisms contributing to sleep disruption in TBI are particular to this condition, and unique neurobiological mechanisms predict the experience of insomnia versus daytime fatigue following a TBI. An understanding of how sleep becomes disrupted after a TBI is important to directing future research and neurorehabilitation.

The Molecular Consequences of CK2-mediated Phosphorylation of the TGA2 Transcription Factor within Systemic Acquired Resistance of Arabidopsis thaliana

During infection, the model plant Arabidopsis thaliana is capable of activating long lasting defence responses both in tissue directly affected by the pathogen and in more distal tissue. Systemic acquired resistance (SAR) is a type of systemic defence response deployed against biotrophic pathogens resulting in altered plant gene expression and production of antimicrobial compounds. One such gene involved in plant defence is called pathogenesis-related 1 (PR1) and is under the control of several protein regulators. TGA II-clade transcription factors (namely TGA2) repress PR1 activity prior to infection by forming large oligomeric complexes effectively blocking gene transcription. After pathogen detection, these complexes are dispersed by a mechanism unknown until now and free TGA molecules interact with the non-expressor of pathogenesis-related gene 1 (NPR1) protein forming an activating complex enabling PR1 transcription. This study elucidates the TGA2 dissociation mechanism by introducing protein kinase CK2 into this process. This enzyme efficiently phosphorylates TGA2 resulting in two crucial events. Firstly, the DNA-binding ability of this transcription factor is completely abolished explaining how the large TGA2 complexes are quickly evicted from the PR1 promoter. Secondly, a portion of TGA2 molecules dissociate from the complexes after phosphorylation which likely makes them available for the formation of the TGA2-NPR1 activating complex. We also show that phosphorylation of a multiserine motif found within TGA2’s N terminus is responsible for the change of affinity to DNA, while modification of a single threonine in the leucine zipper domain seems to be responsible for deoligomerization. Despite the substantial changes caused by phosphorylation, TGA2 is still capable of interacting with NPR1 and these proteins together form a complex on DNA promoting PR1 transcription. Therefore, we propose a change in the current model of how PR1 is regulated by adding CK2 which targets TGA2 displacing it’s complexes from the promoter and providing solitary TGA2 molecules for assembly of the activating complex. Amino acid sequences of regions targeted by CK2 in Arabidopsis TGA2 are similar to those found in TGA2 homologs in rice and tobacco. Therefore, the molecular mechanism that we have identified may be conserved among various plants, including important crop species, adding to the significance of our findings.

Role of Phosphorylation of the Oxysterol Binding Protein (OSBP) in (PI(4)P) and Sterol-Containing Membrane Recognition and Binding

Studies have demonstrated that the oxysterol binding protein (OSBP) acts as a phosphatidylinositol phosphate (PIP)-sterol exchanger at membrane contact sites (MCS) of the endoplasmic reticulum (ER) and Golgi. OSBP is known to pick up phosphatidylinositol-4-phosphate (PI(4)P) from the ER, transfer it to the trans-Golgi in exchange for a cholesterol molecule that is then transferred from the trans-Golgi to the ER. Upon further examination of this pathway by Ridgway et al. (1), it appeared that phosphorylation of OSBP played a role in the localization of OSBP. The dephosphorylation state of OSBP was linked to Golgi localization and the depletion of cholesterol at the ER. To mimic the phosphorylated state of OSBP, the mutant OSBP-S5E was designed by Ridgway et al. (1). The lipid and sterol recognition by wt-OSBP and its phosphomimic mutant OSBP-S5E were investigated using immobilized lipid bilayers and dual polarization interferometry (DPI). DPI is a technique in which the protein binding affinity to immobilized lipid bilayers is measured and the binding behavior is examined through real time. Lipid bilayers containing 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and varying concentrations of PI(4)Ps or sterols (cholesterol or 25-hydroxycholesterol) were immobilized on a silicon nitride chip. It was determined that wt-OSBP binds differently to PI(4)P-containing bilayers compared to OSBP-S5E. The binding behavior suggested that wt-OSBP extracts PI(4)P and the change in the binding behavior, in the case of OSBP-S5E, suggested that the phosphorylation of OSBP may prevent the recognition and/or extraction of PI(4)P. In the presence of sterols, the overall binding behavior of OSBP, regardless of phosphorylation state, was fairly similar. The maximum specific bound mass of OSBP to sterols did not differ as the concentration of sterols increased. However, comparing the maximum specific bound mass of OSBP to cholesterol with oxysterol (25-hydroxycholesterol), OSBP displayed nearly a 2-fold increase in bound mass. With the absence of the wt-OSBP-PI(4)P binding behavior, it can be speculated that the sterols were not extracted. In addition, the binding behavior of OSBP was further tested using a fluorescence based binding assay. Using 22-(N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino)-23,24-bisnor-5-cholen-3β-ol (22-NBD cholesterol), wt-OSBP a one site binding dissociation constant Kd, of 15 ± 1.4 nM was determined. OSBP-S5E did not bind to 22-NBD cholesterol and Kd value was not obtained.

L’intégration de la perception visuelle du mouvement

La perception visuelle du mouvement est essentielle à l’exécution de déplacements sécuritaires ainsi qu’à l’interaction efficace avec notre environnement. C’est pourquoi il est nécessaire de comprendre la nature des mécanismes responsables de l’analyse de l’information sur le mouvement, ainsi que l’effet du vieillissement sur la réponse de ces mécanismes. Deux études seront présentées. La première avait pour but l’analyse des mécanismes responsables de la perception du mouvement de rotation fractale, nouveau stimulus introduit par Benton, O’Brien & Curran (2007). Ce type de stimulus a été créé afin d’isoler les mécanismes sensibles à la forme. Plusieurs auteurs ont suggéré que les mécanismes sensibles au mouvement de deuxième ordre utiliseraient les indices de position afin d’extraire l’information sur le mouvement (Seiffert & Cavanagh, 1998). Ainsi, la présente étude visait à déterminer si la rotation fractale est analysée par de tels mécanismes. Les résultats obtenus suggèrent que les mécanismes sensibles à la rotation fractale seraient basés sur l’orientation; tandis que ceux sensibles à la rotation de premier ordre, basés sur l’énergie. De plus, une certaine dissociation des mécanismes responsables du traitement de la rotation fractale et de premier ordre serait présente. La deuxième étude avait pour but, quant à elle, d’établir l’effet du vieillissement sur l’intégration du mouvement de premier et deuxième ordre. Les résultats indiquent que les mécanismes sensibles au mouvement de deuxième ordre seraient davantage affectés, comparativement à ceux de premier ordre. Ainsi, les fonctions visuelles requérant une intégration corticale de plus haut niveau seraient davantage affectées par l’effet du vieillissement.

« Accommodements raisonnables » pour motif religieux : étude d’un débat public

Ce mémoire porte sur la polémique qui a eu lieu au Québec entre mars 2006 et décembre 2007 autour des pratiques d’« accommodements raisonnables » pour motif religieux. À partir d’une approche compréhensive et d’un cadre théorique propre à la sociologie des relations ethniques, il propose une analyse qualitative de lettres d’opinion publiées dans des quotidiens québécois. Une première analyse, thématique, a permis de constituer des registres argumentaires dans lesquels ont puisé les participants au débat public sur les « accommodements raisonnables » par le biais de lettres d’opinion. Une seconde analyse, comparative, a permis de construire des figures d’intervenants du débat public qui témoignent non seulement des forces idéologiques qui se sont affrontées dans le débat public, mais également de leur positionnement au croisement des axes saillants de la différenciation sociale dans cette polémique Les résultats de ces analyses suggèrent d’abord que la polémique résulte d’un conflit entre marqueurs identitaires devant servir au positionnement des frontières ethniques, et ensuite que la polémique des « accommodements raisonnables » a donné lieu à une reconfiguration des rapports ethniques au Québec, attribuable à la dissociation entre le conflit entre deux nations et celui sur les critères d’inclusion à la nation.

Suivez le guide : études comportementales et électrophysiologiques du rôle des contrôles attentionnels descendants dans le déploiement de l’attention visuospatiale

La capture contingente de l’attention est un phénomène dans lequel les mécanismes d’orientation endogène et exogène de l’attention interagissent, de sorte qu’une propriété qui est pertinente à la tâche en cours, et donc qui fait l’objet de contrôles attentionnels descendants, endogènes, capture l’attention de façon involontaire, exogène, vers sa position spatiale. Dans cette thèse, trois aspects de ce phénomène ont été étudiés. Premièrement, en explorant le décours temporel de la capture contingente de l’attention et la réponse électrophysiologique à des distracteurs capturant ainsi l’attention, il a été établi que le déficit comportemental symptomatique de cette forme de capture était lié à un déploiement de l’attention visuospatiale vers la position du distracteur, et que ce traitement spatialement sélectif pouvait être modulé par le partage d’autres propriétés entre le distracteur et la cible. Deuxièmement, l’utilisation des potentiels liés aux événements a permis de dissocier l’hypothèse de capture contingente de l’attention et l’hypothèse de capture pure de l’attention. Selon cette interprétation, un stimulus ne peut capturer l’attention aux stades préattentifs de traitement que s’il présente le plus fort signal ascendant parmi tous les stimuli présents. Les contrôles attentionnels descendants ne serviraient donc qu’à désengager l’attention d’un tel stimulus. Les résultats présentés ici vont à l’encontre d’une telle interprétation, puisqu’un déploiement de l’attention visuospatiale, indexé par la présence d’une N2pc, n’a été observé que lorsqu’un distracteur périphérique possédait une caractéristique pertinente à la tâche en cours, même lorsque ses propriétés de bas niveau n’étaient pas plus saillantes que celles des autres items présents. Finalement, en utilisant un paradigme où la cible était définie en fonction de son appartenance à une catégorie alphanumérique, il a été démontré que des contrôles attentionnels en faveur d’un attribut conceptuel pouvaient guider l’attention visuospatiale de façon involontaire, rejetant une nouvelle fois l’hypothèse de la capture pure de l’attention.