Date of Award


Degree Type


Degree Name

Master of Science


Psychological Science


Psychological Science (MS)

First Advisor/Chairperson

Joshua Carlson


The P300 subcomponent, P3b, is an event related potential detected at the scalp surface when a working memory comparison results in differences between the contents of working memory and incoming stimulus information. Previous research has indicated that as infrequent targets become more difficult to detect (morphologically similar to a frequent non-target stimulus) the P300 becomes attenuated. fMRI research has also indicated increased prefrontal cortex (PFC) activity during P300 generation. To examine the relationship between P3b amplitude and PFC activity participants performed an easy and difficult target detection task in both EEG and NIRS called the oddball. The EEG and behavioral results confirmed prior reports that difficult to detect targets result in attenuated P3b amplitude, as well as increased misses and reaction time, in comparison to easy to detect targets. NIRS results indicated that detection of targets generally lead to greater increases in oxygenated hemoglobin and decreases in deoxygenated hemoglobin in lateral compared to medial optodes. Additionally, oxygenated hemoglobin increased in the right medial PFC in easy compared to difficult conditions. Taken together, the results of this study and theories behind P3b attenuation suggest that the right medial PFC is involved in attention to salient stimulus features (bottom-up attention) and the lateral PFC is involved in sustained attention to the task (top-down attention). Thus, P3b attenuation is reflective of delimiting attention to salient features and allowing task driven attention to initiate the working memory comparison.

Access Type

Open Access