Psychology ETDs


Brian Coffman

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This investigation studied the effects of transcranial direct current stimulation (tDCS) on learning of a difficult visual search task. We also examined the effects of several variables relating to context in which the task was performed, and the relationship of these variables to the effects of tDCS. For this discovery-learning task, participants were trained for one hour to detect objects hidden in a virtual environment. Anodal tDCS was applied over the right inferior frontal cortex at 0.1 mA or 2.0 mA for 30 minutes during training. Participants were tested immediately before and after training and again one hour later. Some test stimuli were repeated during training and testing, while others were novel but contained hidden objects similar to those presented during training. In Experiment 1 we present a reanalysis of our previously published data (Clark et al., 2010) and replication data from an additional group of subjects using an optimized task design. Higher tDCS current was associated with increased test performance for both novel and repeated test stimuli. In addition, participants responses were more accurate for repeated than novel test stimuli. An interaction was found between tDCS current and image type, indicating that tDCS performance enhancement was greater for repeated than novel stimuli. These effects were replicated in our second experiment using balanced numbers of novel and repeated test stimuli and a double-blind rather than single-blind design. These results indicate that anodal tDCS over right inferior frontal cortex during training most strongly enhances performance for recognition of objects hidden in images repeated between training and testing, and also enhances the generalization of learned object detection to novel images. In Experiment 2, we examine the effect of high magnetic field on tDCS enhancement of learning by comparing participants tested in active fMRI, at a magnetic field of 3 Tesla, to those tested in a mock MRI scanner, with no active magnetic field. In Experiment 3, we examined the effects of the MRI environment on learning and performance both when participants were trained and received tDCS at a workstation PC and when they were trained and received tDCS in the mock MRI scanner. Results from Experiments 2 and 3 indicate that participants may have been unable or unwilling to perform the task in an MRI environment, and that it is unlikely that either the magnetic field or changed environments from training to test, per se, led to differences in the effects of tDCS present between participants tested inside the MRI scanner environment and those tested at an office workstation PC. The effects of tDCS in these experiments indicate that learning can be enhanced in participants learning a difficult object detection task when participants are willing and able to perform the task. Enhanced learning in the general population could aid millions of people suffering from disability and could even lead to accelerated advancement of society in general.

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First Committee Member (Chair)

Yeo, Ron

Second Committee Member

Clark, Vincent

Third Committee Member

Goldsmith, Tim


Some of this work was supported by The Defense Advanced Research Projects Agency (Government contract NBCHC070103) and the Department of Energy (Government contract DEFG02- 99ER62764)




Pattern perception, Brain stimulation, Magnetic resonance imaging, Frontal cortex.

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