My area of specialization is information processing in animals, including learning, memory, timing, and decision making. Recent work has been concerned with the processes underlying extinction (the loss of responding following exposure to a previously conditioned stimulus). This research has focused on identifying the mechanisms responsible for extinction and the renewal effect. These studies have found that extinction is the result of an easily disrupted inhibitory association that is rich in its informational content. Additionally, I have been investigating whether similar mechanisms are responsible for spontaneous recovery of conditioned responding following extinction. These lines of research seek to identify variables that might lead to more effective and enduring forms of behavioral treatment of acquired fears (i.e., phobias).
Other work has been concerned with the role of temporal variables in cue competition, conditioned inhibition, and extinction. Specifically, how do animals represent and use temporal information in determining whether and when to respond? The primary finding from these investigations is that inhibitory stimuli can act as signals for US omission at a specific temporal location. This finding further demonstrates the richness of inhibitory associations (e.g., conditioned inhibitors encode both the identity and the temporal location of omitted events). Additional research has distinguishing between contemporary models of cue competition using both human and non-human participants. This work has led to an extension of the Comparator Hypothesis (Denniston, Savastano, & Miller, 2001). The Comparator Hypothesis is a response rule for the expression of Pavlovian associations, which posits that responding to a CS is not only proportional to the strength of the CS-US association, but is also an inverse function of the associative strength of other stimuli present during training of the target stimulus. That is, as the associative strength of other stimuli trained in the presence of the target stimulus (i.e., comparator stimuli) increase relative to the target CS-US association, excitatory behavioral control by the target stimulus decreases (and inhibitory behavioral control by the target stimulus increases). The elaborated version of the Comparator Hypothesis allows for the effectiveness of comparator stimuli to be modulated in turn by their own comparator stimuli. In other words, the ability of a comparator stimulus to modulate responding to a target stimulus is determined by its own comparator stimuli. This extended version of the Comparator Hypothesis is able to explain many of the frequently reported cue competition effects and has inspired a wealth of research aimed at distinguishing between acquisition- and performance-based models of Pavlovian behavior. Future work will continue to explore the representation of omitted events (i.e., conditioned inhibition) in human and non-human participants in order to gain a better understanding of both the associative structure and response rules underlying inhibitory behavioral control and associative competition between stimuli that occur together.