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Analysis of Neural Data

PhD Theses

Processing of expected values in human visual cortex
Citation key Kallerhoff2009
Author Philipp Kallerhoff
Year 2009
School Technische Universität Berlin
Abstract Experience might effectively modulate our choice if prior stimulation reveals some information about future reward. For example, experience might accumulate to an expected reward at different target locations. Following Pascal (1670) the expected reward is given as the predictability of the reward and the amount of reward associated with each location. In the first study, we modulated the expected reward in a simple binary choice task in order to test rational decision making in the context of complex expected value functions. We found that the subjects likely match, but do not maximize the expected reward and likely implement a short‐term average over stimulus appearances, but not the true generative model. In the second study, our aim was to gradually modulate the endogenous orientation of attention with the expected value of distributed reward in the environment. Shifts in attentional focus were induced by linking one location with a higher expected reward than other locations. Larger expected values should then increase the likelihood that subjects would focus their attention on one location rather than distribute it across the entire display. The discrimination performance at a target location is a close indicator of attention. Therefore we setup a discrimination task and measured the behavioral discrimination performance. In fact, we found that subjects increasingly discriminate the target status with a larger expected value. The models proposed in the first study account quite closely for basic properties of the behavioral results. However, a close analysis on a trial‐by‐trial basis showed that the true generative model cannot account for subjects’ behavior, which is however well explained by short‐term average over stimulus appearances. In the third study, we measured the event‐related potential (ERP) during the discrimination task introduced in the second study and compared the ERP modulations to the decision making models proposed in the first study. Grand average ERP waveforms showed an increase in components as early as the N1 component with increasing expected reward of the stimulus location. In fact, the performance in the discrimination task and the rewardmodulation are closely reflected in the amplitude of these early‐visual, attention‐related EEG‐responses. We therefore conclude the processing of expected rewards in early‐visual components of EEG.
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