Synesthesia is an unusual blending of the senses that occurs in about four percent or more of the human population. Much effort has been devoted to establishing criteria to define what synesthesia is ever since the phenomenon reemerged as a fascination within the scientific community in the late 1970s. To date, the most common criteria for synesthesia are that synesthetic experiences be automatic, consistent, rely on an external stimulus that triggers the phenomenological experience, and that this experience is fully conscious to the mind. This framework allows for some differentiation of synesthetes compared to non-synesthetes within the human population, and yet it also creates a self-selecting bias in the synesthetic population; if the scientific community defines criteria for synesthesia, and then only studies people whom fit those criteria, the resulting data will likely validate the definitions if only because they have been defined that way. What is left unknown are ways that synesthetes, as a community of otherwise normal human beings, vary in subtle ways, both in their psychophysical behavior and in their neurobiological form and function in relation to other human beings who do not experience any form of conscious, unusual sensory blendings yet defined as synesthesia.
The studies described in this thesis explore whether perception in the population of individuals currently defined as synesthetes is in fact uniquely different from perception in the rest of the human population. These unique differences in perception are also used here to better inform our understanding of the functions of the human brain. Chapter 2 introduces the concept of perceptual binding and its relation to synesthesia. Some synesthetes experience colors that are associated with letters and numbers, and these so-called grapheme-color synesthetes may rely on similar brain mechanisms to bind their synesthetic colors to space as the ones they (and most humans) use to bind color to space normally. Chapter 3 addresses the question of binding with regard to an unusual phenomenon specific to grapheme-color synesthetes: that it is possible for some of these synesthetes to experience two colors that are spatially co-localized without blending. The results of this behavioral study will be shown to correlate with the vividness of visual imagery, a measure that extends beyond synesthetic phenomenology. Finally, Chapter 4 demonstrates how synesthetes differ from well-matched non-synesthetes in relation to behavior and the anatomy of the brain. Specifically, synesthetes have more vivid visual imagery as a population, more arborized white matter, and show a positive correlation between vivid imagery and increased axonal branching that is absent in non-synesthete controls. Together, these studies suggest that the brains of synesthetes rely on attention-specific mechanisms used by most humans to bind color to space. However, synesthesia as a whole may not simply be one end of a continuum of brain differences. Rather, synesthetes may be unique both in their phenomenological experiences of the world, and in some ways, the organization of the brain that creates them.
|Advisor:||Robertson, Lynn C.|
|Commitee:||Bunge, Silvia, Prinzmetal, William, Silver, Michael|
|School:||University of California, Berkeley|
|School Location:||United States -- California|
|Source:||DAI-B 75/08(E), Dissertation Abstracts International|
|Subjects:||Neurosciences, Behavioral psychology, Cognitive psychology|
|Keywords:||Color priming, Diffusion tensor imaging, Perceptual binding, Synesthesia|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be