Browsing by Subject "Visual perceptual learning"
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Item Open Access Functional changes in the human cortex over the course of visual perceptual learning(Bilkent University, 2020-03) Akkoyunlu, BeyzaIn this study we assessed functional changes through visual perceptual learning with bisection discrimination task. Before learning, after third session of learning and after learning ended, behavioral threshold and fMRI data has been collected. Our results showed that while participants showed threshold decrease in the midlearning session, the post-learning thresholds are turned to pre-learning levels. These results might be due to fatigue which caused by our experiment. Besides to training condition, we also tested location and task specificity. The results showed that only 150◦polar angle location showed significant change between sessions. Along with the behavioral data, we collected task-based fMRI data while participants performing training and control conditions in the scanner. The analysis showed task-based BOLD response changed with session. However, post-hoc tests did not reveal significant results. The resting-state functional connectivity analysis showed that the functional connectivity between V1 and V2 regions is significantly increased. The Post Hoc analysis showed significant change in the 210◦and 150◦polar angle conditions. The changes in the behavioral and functional connectivity measurements at 150◦polar angle conditions, these results might indicate the effect of the inter-hemispheric connections. Moreover, our analysis on resting state data also revealed that, while there is no change between pre-learning and mid-learning sessions, connectivity changes significantly in the post-learning session compared to other sessions. This finding supports the idea that functional connectivity changes related to perceptual learning might be occurring at the late phases of the learning. Overall, to rule out the confounds in the behavioral measurements and to link the behavioral data with the neural data, additional measurements should be taken in the future.Item Open Access Investigating motion detection of aging zebrafish with optomotor response(Bilkent University, 2021-07) Karaduman, AyşenurVarious aspects of visual functioning including motion perception have been shown to be significantly altered throughout aging. Contrary to the traditional view focusing on structural changes in the eye and retina, accumulating evidence suggests that subtle alterations in neural circuitry and functioning are respon-sible for the age-related changes in visual sensitivity and perception. However, the mechanisms underlying age-related changes in motion perception are still poorly understood. This thesis was aimed to investigate the detection of first-and second-order motion direction during aging by using zebrafish optomotor re-sponses (OMR). Furthermore, exposure-based visual learning was investigated by repeated presentation of first-order motion. The studies included both wild-type and achesb55/+ zebrafish with decreased levels of acetylcholinesterase which has been previously shown to delay age-related cognitive decline. In this way, it was also aimed to explore the possible functional links between cholinergic functioning and age-related changes in visual motion processing. The results indicated that adult zebrafish mainly exhibit negative OMR (i.e., position shift in the opposite direction of visual motion) to drifting first-order gratings which is significantly dependent on spatial frequency and contrast level of the motion. Rather than an overall effect of aging, the results revealed a three-way interaction between the contrast level of first-order motion, genotype, and age. Therefore, the findings pointed out a complex relationship between the physical characteristics of first-order motion stimulation and the cholinergic system during neural aging. Contrary to the first-order motion, the second-order motion did not induce strong optomotor responses in adult zebrafish. Although young and old zebrafish exhibited OMR with different polarities (negative and positive OMR, respectively), future work revealing robust responses will be informative to better understand and characterize age-related changes. Lastly, passive exposure of repeated first-order motion induced significant improvements in negative OMR of young and old zebrafish, suggesting that adult zebrafish can be used as a model organism to study passive forms of visual perceptual learning. Overall, these behavioral results pave the way for a detailed investigation of the functional links between the physical motion characteristics and the cholinergic system in the zebrafish aging model which will ultimately have important implications for developing interventions to improve human visual performance during aging.Item Open Access Investigating the effects of perceptual learning on the function and microstructure of the visual cortex(Bilkent University, 2020-12) Erişen, DilaraPerceptual learning is the long-term improvement of the ability to process sensory stimuli through experience. Although an extensively studied field, the mechanism and locus of plasticity underlying visual perceptual learning is subject of debate. Here, we investigated the experience-dependent plasticity in the visual cortex across the time course of perceptual learning of bisection discrimination task. Population receptive field (pRF) analysis was used to examine functional architecture of the visual cortex. Microstructural properties of the visual cortex were characterized with neurite orientation dispersion and density imaging (NODDI). We compared pre-, mid-, and post-training values of pRF size, neurite density, and orientation dispersion in the trained location as well as in two control locations where no training has been received. The values in the trained location did not change with time and did not differ from control locations. In addition, we assessed the microstructural properties in the white matter tract between the training location and the mirror-symmetric control location and did not observe any change with training. In conclusion, we found no training-related changes in the early visual cortex (V1-V3). Our results are limited by the lack of performance improvement with training and the small sample size. Moreover, we were not able to identify visual areas beyond V1-V3 leaving high-level visual areas unexplored. Suggestions for further research include redesigning the behavioral training paradigm, optimization of pRF protocol to identify high-level visual areas, and repeating the study with a larger sample size.