abstract: Magnocellular-Dorsal pathway’s function had been related to reading ability, and visual perceptual learning can effectively increase the function of this neural pathway. Previous researches training people with a traditional dot motion paradigm and an integrated visual perceptual training “video game” called Ultimeyes pro, all showed improvement with regard to people’s reading performance. This research used 2 paradigms in 2 groups in order to compare the 2 paradigms’ effect on improving people’s reading ability. We also measured participants’ critical flicker fusion threshold (CFFT), which is related to word decoding ability. The result did not show significant improvement of reading performance in each group, but overall the reading speed improved significantly. The result for CFFT in each group only showed significant improvement among people who trained with Ultimeyes pro. This result supports that the beneficial effect of visual perceptual learning training on people’s reading ability, and it suggests that Ultimeyes pro is more efficient than the traditional dot motion paradigm, and might have more application value. / Dissertation/Thesis / Masters Thesis Psychology 2015

Identifying targets in cluttered scenes is critical for our interactions in complex environments. Our visual system is challenged to both detect elusive targets that we may want to avoid or chase and discriminate between targets that are highly similar. These tasks require our visual system to become an expert at detecting distinctive features that help us differentiate between indistinguishable targets. As the human brain is trained on this type of visual tasks, we observe changes in its function that correspond to improved performance. We use functional brain imaging, to measure learning-dependent modulations of brain activation and investigate the processes that mediate functional brain plasticity. I propose that dissociable brain mechanisms are engaged when detecting targets in clutter vs. discriminating between highly similar targets: for the former, background clutter needs to be suppressed for the target to be recognised, whereas for the latter, neurons are tuned to respond to fine differences. Although GABAergic inhibition is known to suppress redundant neuronal populations and tune neuronal representations, its role in visual learning remains largely unexplored. Here, I propose that GABAergic inhibition plays an important role in visual plasticity through training on these tasks. The purpose of my PhD is to investigate the inhibitory mechanisms that mediate visual perceptual learning; in particular, learning to detect patterns in visual clutter and discriminate between highly similar patterns. I show that BOLD signals as measured by functional Magnetic Resonance Imaging (fMRI) do not differentiate between the two proposed mechanisms. In contrast, Magnetic Resonance Spectroscopy (MRS) provides strong evidence for the distinct involvement of GABAergic inhibition in visual plasticity. Further, my findings show GABA changes during the time-course of learning providing evidence for a distinct role of GABA in learning-dependent plasticity across different brain regions involved in visual learning. Finally, I test the causal link between inhibitory contributions and visual plasticity using a brain stimulation intervention that perturbs the excitation-inhibition balance in the visual cortex and facilitates learning.