AIM AND PURPOSE: The aim of this research project is to investigate within-language and cross-language semantic facilitation and interference effects in English-Spanish bilingual persons with aphasia and neurotypical adults. The purpose of the project described in this protocol is to gain insight into how languages are initiated in bilingual speakers who present with aphasia, specifically when presented with semantically related stimuli. METHODS: To achieve this aim, participants wore an eye-tracking device and were presented with an image and four word choices. They were asked to match the picture to the most correct word. The word choices included the correct target word, semantically related words in English or Spanish, and at least two semantically unrelated words. The exact distribution of word type was dependent on the experimental condition. Their trial duration, dwell time per area of interest, and total fixation count per area of interest was collected for each trial and analyzed using mixed linear effects models. RESULTS: The results of this study showed that bilinguals with aphasia (BWA) spent significantly more time on trials that included a semantically related word in Spanish, compared to semantically unrelated words in either language or semantically related words in English. This pattern was not seen in neurologically healthy control participants. We also showed that across group all participants spent more time on the target word compared to semantically related words, however, BWA demonstrated increased fixation measures in trials that included a Spanish semantically related word. This pattern was not seen in neurologically healthy control participants. These results demonstrate increased semantic interference in BWA when compared to neurologically healthy control participants. CONCLUSION: Spanish-English BWA may be more susceptible to cross-language semantic interference compared to neurologically healthy bilingual individuals. However, both BWA and neurologically healthy individuals may experience within language semantic interference.

Our lives are dominated by a complex visual world, and spatially selective attention allows us to process only the most relevant information. Previous evidence suggests that if possible locations of stimulus presentation are delineated, attention affects processing in a spatially graded manner. This gradient is seen in both behavioral measures and in visual evoked potentials (VEPs). Stimuli presented close to cued regions elicit faster responses and larger VEPs than those presented farther away. However, both position in the visual field and allocation of attention may contribute to the observed gradients. These relative contributions can be distinguished by comparing responses on physically identical trials when attention is directed to locations at various distances from the stimuli. In the current study, participants attended to one of 12 squares arranged in a circle around fixation. Letters appeared individually, each in one of the squares; 80% were O’s (standards) and 20% were X’s (deviants). Participants were instructed to press a button when an X appeared at the attended location. The largest amplitude N1s (150-200 ms) were observed when participants attended to the location where a standard was presented. VEPs elicited by standards showed evidence of asymmetric attentional gradients. Specifically, the gradient of facilitation spread down more than up. Results also showed that attention had differential effects on the stages of processing indexed at specific time windows. These results confirm that attention can be applied to visual processing in a spatial gradient, reveal its asymmetric distribution, and elaborate on the timing of its selectivity.

Short-term facilitation, a form of synaptic plasticity, takes place at GABAergic synapses between cerebellar Purkinje cells (PCs). We studied the mechanism of this short-term facilitation by directly patch-clamp recording from a PC axon terminal in cerebellar cultures. We show that the Ca2+ currents elicited by high-frequency action potentials were augmented depending on intracellular [Ca2+] on the terminal. The facilitation of synaptic transmission showed 4-5th power dependence on the Ca2+ current facilitation, and was abolished when the Ca2+ current facilitation was supressed. We conclude that short-term facilitation of Ca2+ currents predominantly mediates short-term facilitation at synapses between PCs. / 博士(理学) / Doctor of Philosophy in Science / 同志社大学 / Doshisha University

Coastal wetland plants serve as ecological engineers in a physiologically stressful environment and the loss of coastal wetlands can cause negative effects throughout the estuarine system. Due to increased degradation of coastal habitats worldwide, interest in restoration has increased around the world. An understanding of the biotic processes affecting species distribution and diversity is critical for future conservation, management, and restoration of coastal wetlands. The purpose of my study was to test the effects of biotic interactions on native coastal wetland plants and determine how these interactions may be incorporated into current and future restoration projects. I had three primary goals for my dissertation. First, I evaluated the effectiveness of natural regeneration of coastal wetland communities following hydrological restoration. Second, I examined effects of biotic interactions between mangroves and other wetland species by experimentally testing: 1) trapping capabilities of early successional plant species on Rhizophora mangle propagules, 2) effects of pre-dispersal propagule damage on native mangrove species, 3) facilitative and competitive interactions between the plants Rhizophora mangle, Batis maritima, Sarcocornia perennis, and the fiddler crab, Uca pugilator using mesocosms. Third, I evaluated the combined effects of biotic and abiotic interactions on survival and growth of R. mangle propagules during their first year of establishment using a manipulative field experiment. Results from my study increase our knowledge of the importance of biotic interactions in coastal wetland communities, their role in early successional stages, and have direct applications to coastal wetland restoration and management.

Pollinator-mediated competition and facilitation are two important mechanisms mediating co-flowering community assembly. Experimental studies, however, have mostly focused on evaluating outcomes for a single interacting partner at a single location. Studies that evaluate spatial variation in the bidirectional effects between co-flowering species are necessary if we aim to advance our understanding of the processes that mediate species coexistence in diverse co-flowering communities. Here, we examine geographic variation (i.e. at landscape level) in bidirectional pollinator-mediated effects between co-flowering and We evaluated effects on pollen transfer dynamics (conspecific and heterospecific pollen deposition) and plant reproductive success. We found evidence of asymmetrical effects (one species is disrupted and the other one is facilitated) but the effects were highly dependent on geographical location. Furthermore, effects on pollen transfer dynamics did not always translate to effects on overall plant reproductive success (i.e. pollen tube growth) highlighting the importance of evaluating effects at multiple stages of the pollination process. Overall, our results provide evidence of a spatial mosaic of pollinator-mediated interactions between co-flowering species and suggest that community assembly processes could result from competition and facilitation acting simultaneously. Our study highlights the importance of experimental studies that evaluate the prevalence of competitive and facilitative interactions in the field, and that expand across a wide geographical context, in order to more fully understand the mechanisms that shape plant communities in nature.

Community composition results from an integrated combination of random processes, regional habitat spatial structure, local environmental conditions, and species interactions. For example, the outcome of plant interactions can change depending on local environmental conditions such as nutrient availability, land management, or herbivory intensity. In particular, plant interactions may vary between facilitation and competition depending on ecological context, with facilitation expected to be prevalent under stressful conditions. I present the results of four studies that address different aspects of the community assemblage and dynamics emphasizing the synergistic effect of different processes. In the first, I investigated the importance of habitat isolation in determining species richness of wetlands with contrasting land use. The second describes an experiment to test the hypothesis that plant interactions with an unpalatable plant (Juncus effusus) would range from competition in ungrazed areas to facilitation in grazed areas and predicted that facilitative effects of Juncus would differ among functional groups of beneficiary species and be strongest when grazing was intense. In the third, I examine the community composition impacts of Juncus and predicted that Juncus would preserve functional diversity in grazed wetlands but that the effects of Juncus would vary along a grazing gradient. The fourth study investigated the relative importance of competition and nutrients in determining wetland invasion in two different land use types. Broadly, I demonstrate that the importance of different processes (habitat isolation, nutrient availability, competition/facilitation) to community composition is dependent on ecological conditions. This integrated view of community dynamics is interesting from a purely ecological perspective but also can be applied to understanding ecological problems such as exotic invasions and restoration of disturbed habitats.

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