Investigating unconscious visual episodic memory and its underlying neural substrate using fMRI and eye tracking

Classically, episodic memory is considered a subcategory of declarative memory and is accessible to conscious report. But recent clinical and brain imaging findings have led to a new processing-based-memory model. According to this model episodic memory is defined as a rapidly formed memory of novel associations that can be retrieved in a flexible manner. Hypothetically, a memory with these characteristics can exist at both conscious and unconscious levels. The main aim of this thesis is to test the possibility of unconscious encoding and subsequent unconscious retrieval of complex visual associations and investigating their underlying neural correlates using fMRI. In chapter 1, I review the literature about unconscious visual episodic memory and behavioural measures and neural mechanisms related to it. In chapter 2, using eye tracking, I test the possibility of unconscious encoding and unconscious retrieval of complex visual association according to the processing-based-memory model. This makes a foundation for chapter 3, in which I use functional magnetic resonance imaging (fMRI) to test whether the main brain areas known to be involved in conscious episodic memory are also involved in unconscious visual episodic memory. In this chapter I also used eye tracking simultaneously with fMRI to investigate the possibility of a correlation between viewing behaviour and brain activation related to unconscious episodic memory. Chapter 4, presents a functional connectivity analysis on these fMRI data to find the underlying neural mechanism for modulation of viewing behaviour by unconscious episodic memory. Overall, the findings in this thesis provide support for the existence of a memory with the characteristics of episodic memory without conscious awareness. This memory recruits the main brain areas that are involved in conscious episodic memory and modulates viewing behaviour through interaction with bottom-up attention network. Chapter 5, presents a general discussion about the implications of these findings, limitations and questions for future research -- abstract.