Masking Level Difference (MLD) tests are an established component of auditory processing test batteries; however, normative data for these tests vary according to procedure. In this study, forty normal, native-English speaking adults between the ages of 18 and 26 were tested for MLD via a newly developed computer software program using both an adaptive procedure (MLDA) and a Bekesy procedure (MLDB). The results from the two procedures were analyzed for sex differences and compared with each other. For both the MLDA and MLDB, the results showed statistically significant sex differences in the masked thresholds used to obtain the MLD (NoSo and NoSπ), but no significant difference in the calculated MLD value (NoSo - NoSπ). These results suggest that since the MLD was similar for both sexes, the normative data need not be reported separately by sex. The results also showed statistically significant differences between procedures, with the MLDA procedure producing higher MLDs than the MLDB procedure. The MLDA procedure lent itself to a d´ analysis, which could not be determined using MLDB due to the nature of a Bekesy assessment. For MLDA, d´ = 1.4, test sensitivity = 96.4%, and test specificity = 60.3%. The results of this study indicate that MLDA is a better testing procedure due to MLDA’s higher MLD average and the statistical data available (d´, and measures of sensitivity and specificity) when using the MLDA procedure.

The research discussed here examines how normal healthy aging affects spatial suppressive mechanisms in a variety of visual tasks using both static and dynamic stimuli. Prior research has suggested that younger adults demonstrate a center-surround antagonistic pattern in which they show spatial summation at low contrast and spatial suppression at high contrast in brief motion direction discrimination tasks. Older adults have been shown to have reduced spatial suppression at high contrast and this is thought to be related to reduced GABAergic inhibition in the visual cortex. The results obtained from this program of research suggest that age-related changes in optical and neural visual mechanisms do not affect spatiotemporal mechanisms for static stimuli when the target is presented with the mask (embedded masking). However, when the mask appears immediately before (forward masking) or after (backward masking) the target, older adults require more contrast to detect the target (Chapter 2). In addition, spatial suppression is not reduced for older adults in a task with moving stimuli presented at long durations, even with increasing speed (Chapter 3). In Chapter 4, we used static stimuli presented at brief durations to induce a sudden motion onset and found that although there was no significant age difference in spatial suppression, there was a trend showing reduced levels of spatial suppression in older adults. These results taken together suggest that inhibitory neural mechanisms in the visual cortex may mediate spatial suppression for briefly presented stimuli only. / Thesis / Doctor of Philosophy (PhD)

The effects of taste masking are determined by interactions between drug and excipients as well as the microstructures of the particulate drug delivery systems (DDS). Cyclodextrin (CD) is a widely used taste masking agent, to which the relationship between kinetic parameters (Ka and Kd) of a drug and taste masking remains unexplored, which is investigated for the first time in this study. A data base of the kinetic parameters for drug-CD was established by Surface Plasmon Resonance Imaging (SPRi) and High Performance Affinity Chromatography (HPAC). Combined with the electronic tongue, Ka and Kd based models for the taste masking effect of HP-β-CD were successfully established and applied to the prediction of taste masking effects. Paracetamol was used as a model drug for taste masking formulation optimization. As well as drug release the microstructure of solid DDS has considerable influence on drug taste. The microstructure of lipid microspheres and the molecular distribution of drug and excipients in lipid microspheres were investigated by Synchrotron radiation-based micro-computed tomography (SR-μCT) and Synchrotron radiation-based Fourier-transform infrared spectromicroscopy (SR-FTIR), respectively. The results demonstrated that the polymeric formulation components as well as shape and particle size of the drug were the key factors to taste masking of paracetamol by inhibiting bust release thereby reducing the interaction intensity of the bitterness. The FTIR absorption spectra confirmed the deposition and formation of chitosan and gelatin films on the drug microsphere surface by layer-by-layer coating. In conclusion, this research demonstrates the molecular kinetic basis of CD taste-masking as well as microstructural basis of particle systems for bitter taste masking.

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<p>This dissertation examined perturbation effects during complex tactile information transmission. The four experiments provide evidence regarding sensory and information processing demands in early stages of complex tactile learning.</p> <p>Experiment 1 established complex tactile learning behavioural performance. Vibrotactile stimuli representing Morse code letters were communicated to participants with or without induced perturbation to the finger of letter reception. Response performance was measured and augmented feedback was provided retroactively. Perturbation conditions lead to poor performance during tactile acquisition, but improved performance during application of knowledge.</p> <p>Experiment 2 determined if the experiment 1 results demonstrated masking or response competition paradigms. Target “masking” is the reduced ability to detect or interpret a stimuli pattern by presentation of other information (Craig, 1985; Verrillo, 1985). Response competition is the competition or distraction from target response generation by secondary stimuli (Craig, 2000; Bolanowski et al., 2000). Experiment 2 tested response competition by spatially separating the perturbation and tactile information delivery sites.</p> <p>Experiments 3 and 4 served to replicate behavioural acquisition data from experiments 1 and 2. They also extended the findings of the first two experiments by introducing neurophysiological measurement to reflect the changes associated with the two perturbation conditions. The study discerned whether the masking and response competition paradigms from experiments 1 and 2 were predominantly impacting the peripheral or central information processing.</p> <p>Results from the four studies collectively demonstrate that increased demands are placed on the sensory system during early stages of complex tactile learning when perturbation is spatially congruent with tactile information delivery. Experiments 1 and 2 revealed that attention does not supersede spatial location of perturbation, and perturbation location is paramount to yield sufficient interference to impede acquisition yet lead to enhanced knowledge retention and transfer. Experiments 3 and 4 determined that cortical information processing associated with complex tactile information acquisition are neurophysiologically differentiated when relative locations of meaningful and perturbation stimuli are congruent or spatially separated. The findings from this dissertation serve as an advancement of our understanding of masking and response competition phenomenon as they pertain to complex tactile learning.</p> / Doctor of Philosophy (PhD)

The significance of the removal of the “White Mask” in Ayitian Vodou is to provide an Afrocentric analysis regarding the detriment of Catholicism/Protestantism has inflicted on African agency in Ayiti. The Practice of Ayitian Vodou derives from a variety of West African Spiritual Belief Systems like the Yoruba, Kongo, and Dahomean. During the imperialist era in Ayiti, Ayitians utilized biblical figures to hide their African gods in order to partake in Ayitian Vodou overtly. Due to classism, colorism, racism, and white domination, the camouflage aspect of Ayitian Vodou became a permanent component within Ayitian Vodou. This study proposes that scholars should rely on the method of Masking rather than the popular notion of Double Consciousness in examining African phenomena. W.E.B. Dubois coined Double Consciousness, which does not accurately explain or articulate how African people endured the institution of mental and physical enslavement. Double Consciousness derives from a Eurocentric ideology that operates from depriving African people of their history, culture, perspective, and personal development. / African American Studies