The human visual system is tasked with transforming variations in light within our environment into a coherent percept, typically described using properties such as luminance and contrast. The experiments described in this dissertation examine how the human visual cortex responds to each of these stimulus properties at the population-level, and explores the degree to which contrast adaptation can alter these response properties. The first set of experiments (Chapter 2) demonstrate how saturating sigmoidal contrast response functions can be captured using human fMRI by leveraging sustained contrast adaptation to reduce the heterogeneity of response profiles across neural populations. The results obtained using this methodology have the potential to rectify the qualitatively different findings reported across visual neuroscience, when comparing electrophysiological and population-based neuroimaging measures. The second set of experiments (Chapter 3) demonstrate how under certain conditions a well-established visuocortical response property, contrast response, can also reflect luminance encoding, challenging the idea that luminance information plays no significant role in supporting visual perception. Specifically, these results show that the mean luminance information of a visual signal persists within visuocortical representations, even after controlling for pupillary dynamics, and potentially reflects an inherent imbalance of excitatory and inhibitory components. The final set of experiments (Chapter 4) examine how the time course of population activity during initial periods of adaptation differs across seemingly slightly different adapter conditions. The degree to which stimulus adapter orientation bias (radial vs. concentric orientation) or stimulus adapter luminance (2409 cd/m2 vs. 757.3 cd/m2) can alter adaptation time course dynamics is examined in detail, as well as investigating the prevalence of any retinotopic bias. In an effort to coalesce the findings across all three chapters, the shape and efficacy of the initial adaptation time course is ultimately compared against the contrast and luminance response function parameters reported in previous chapters. As a whole, the findings reported in this dissertation challenge some common assumptions about how the early human visual cortex adjusts and responds to the environment, provide methodological tools and stimulus design caveats vision neuroscientists will need to consider, and play a significant role in cortical models of vision.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/42329 |
| Date | 28 March 2021 |
| Creators | Vinke, Louis Nicholas |
| Contributors | Ling, Samuel |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
| Rights | Attribution-NonCommercial-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nc-nd/4.0/ |
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