Modulation of Saccadic Curvature by Spatial Memory and Associative Learning

The way the eye travels during a saccade typically does not follow a straight line but rather shows some curvature instead. Converging empirical evidence has demonstrated that curvature results from conflicting saccade goals when multiple stimuli in the visual periphery compete for selection as the saccade target (Van der Stigchel, Meeter, & Theeuwes, 2006). Curvature away from a competing stimulus has been proposed to result from the inhibitory deselection of the motor program representing the saccade towards that stimulus (Sheliga, Riggio, & Rizzolatti, 1994; Tipper, Howard, & Houghton, 2000). For example, if participants are instructed to perform a saccade towards a defined target stimulus and to ignore a simultaneously presented nearby distractor stimulus, a saccade landing on the target typically exhibits curvature away from the distractor (e. g. Doyle & Walker, 2001). The present thesis reports how trajectories of saccadic eye movements are affected by spatial memory and associative learning. The final objective was to explore if the curvature effect can be used to investigate associative learning in an experimental paradigm where competing saccade targets are retrieved from associative memory rather than being sensory events. The thesis incorporates manuscripts on the following working steps to accomplish this objective: The first manuscript presents the computer software that was written in order to derive measure of saccadic curvature from the recorded eye movement traces. The second manuscript replicates and extends prior reports on the effect of (non-associative) spatial working memory on saccade deviations (Theeuwes, Olivers, & Chizk, 2005). The third manuscript uses a novel associative learning task to demonstrate that changes in saccadic curvature during associative learning comply with the acquisition and extinction of competing associations as predicted by the Rescorla-Wagner model (Rescorla & Wagner, 1972), originally put forward to explain classical conditioning in animals

Mechanisms of contextual control: The role of cue-outcome associations in renewal

The renewal effect is the recovery of an extinguished response that occurs when the target stimulus is presented outside of the extinction context. Renewal is relevant because it offers an explanation for relapse, which is frequent after exposure-based treatments. The renewal effect thus shows that the original problematic behavior will recover when the patient leaves the treatment context. Due to this problem some manipulations have been experimentally examined, that could potentially prevent relapse. Bouton (1991) suggested that conducting extinction in multiple contexts, and the use of retrieval cues for extinction, could be useful in preventing relapse. The present work examined the associative mechanisms of both manipulations. Contemporary learning theories can be divided in two classes of mechanisms. The Rescorla-Wagner model, for instance, sees the context as another CS that can enter into a direct association with the US. Bouton’s retrieval model assumes on the other hand that contextual cues modulate the retrieval of the complete CS-US association. To differentiate between both accounts this work was based on previous studies that manipulated the associative history of contextual cues to examine their associative mechanisms. The first part of the thesis examined the effect of extinction in multiple contexts on renewal when additional excitatory trials are presented in the extinction context. The second part examined the effect of retrieval cues on renewal when the associative history of each retrieval cue is manipulated. The results showed that a direct association with the US is not necessary for both manipulations to attenuate renewal. Thus, the results of the present studies are consistent with the idea that both contexts and retrieval cues help recall the memory of the CS-US association

Emergence of complex dynamics of choice due to repeated exposures to extinction learning

Extinction learning, the process of ceasing an acquired behavior in response to altered reinforcement contingencies, is not only essential for survival in a changing environment, but also plays a fundamental role in the treatment of pathological behaviors. During therapy and other forms of training involving extinction, subjects are typically exposed to several sessions with a similar structure. The effects of this repeated exposure are not well understood. Here, we studied the behavior of pigeons across several sessions of a discrimination-learning task in context A, extinction in context B, and a return to context A to test the context-dependent return of the learned responses (ABA renewal). By focusing on individual learning curves across animals, we uncovered a session-dependent variability of behavior: (1) during extinction, pigeons preferred the unrewarded alternative choice in one-third of the sessions, predominantly during the first one. (2) In later sessions, abrupt transitions of behavior at the onset of context B emerged, and (3) the renewal effect decayed as sessions progressed. We show that the observed results can be parsimoniously accounted for by a computational model based only on associative learning between stimuli and actions. Our work thus demonstrates the critical importance of studying the trial-by-trial dynamics of learning in individual sessions, and the power of "simple" associative learning processes