Tracing the Formation of Perceptual Decisions in the Human Brain

Redmond O'Connell
Trinity College Dublin

For decades, theoretical and psychophysics work have implicated a central mediating 
process or Òdecision variableÓ (DV) as the key component of decision formation. The 
defining properties of a DV are that it integrates sensory information in favor of a 
decision alternative and triggers the appropriate course of action once a reliable 
quantity has been gathered.  Single-cell recording studies in monkeys have provided 
extensive validation of this framework by identifying signals in higher-order brain areas 
that explicitly encode these ingredients. However, the technical limitations of non-
invasive electrophysiological and functional imaging methods have hampered efforts to 
make equivalent observations in the human brain. In this talk I will present data from a 
series of experiments in which we identify a novel signal in the human 
electroencephalogram (EEG) that exhibits all of the predicted dynamical properties of a 
DV. Unlike any previous observations, we found that this signal maintained a close 
deterministic relationship to decision making regardless of the specific sensory or motor 
requirements of the task.  Finally, I will outline recent experiments in which we utilize 
this signal to provide new insights into the role of factors such as attention, prior 
information and consciousness during human decision making.