Olivia Carter

Vision Sciences Lab, Harvard University

One pervading mystery in neuroscience is the question of how the brain is able to generate an "internal" perceptual experience from the available "external" sensory information. Ambiguous stimuli, like binocular rivalry and the Necker cube, offer a unique means to investigate this process experimentally because observers generally experience changes between multiple perceptual states without corresponding changes in the stimulus. I will present results obtained using a variety of methods including pharmacology (hallucinogens), pupillometry and basic psychophysics. The data relates primarily to vision, but I will also describe recent studies looking at auditory and tactile rivalry. Together the results suggest that the cycle of perceptual switching characteristic of rivalry may reflect a generalized mechanism that allows the brain to decide between multiple valid alternatives, without becoming stuck on a non-optimal decision. While the exact mechanisms are unknown, my data, and research from other groups, suggest that the process may depend heavily on the coordinated activity of defuse neurotransmitter systems like serotonin and noradrenaline. Because I wish to claim that this mechanism is common to the domains of perception, attention and action, I will conclude by briefly discussing my results in relation to current theories of behavioral decision making.