M.Sc Thesis

M.Sc StudentDemchenko Igor
SubjectElectroencephalographic responses to disturbances and
distractors during continuous reaching movements
DepartmentDepartment of Mechanical Engineering
Supervisor PROF. Miriam Zacksenhouse
Full Thesis textFull thesis text - English Version


Electroencephalography (EEG) is a noninvasive method to record electrical activity of the brain. Event related potentials (ERP) are EEG signals evoked in response to specific sensory, cognitive or motor events. If the event is an error, then the ERP is referred to as Error-related potential (ErrP). Error processing has been investigated extensively in the context of cognitive tasks, and was shown to evoke an error-related negativity (ERN), which is hypothesized to reflect task monitoring and to originate from the Anterior Cingulate Cortex (ACC). However, in the context of reaching movements, it has been demonstrated that target jumps evoke ERN only if they are uncorrectable, i.e. the movement of the cursor cannot be corrected to reach the new target, and hence result in high level error. In contrast, the low-level error associated with the target jump itself - whether correctable or not, elicited a P300 like component.

P300 has been studied extensively in cognitive tasks and in particular the three-stimulus oddball paradigm. This paradigm revealed two sub-components, known as P3a and P3b, whose relative contributions depend on saliency and task-relevance, respectively. However, the existence and roles of these sub-components in response to low-level errors are poorly understood. Here we investigated responses to low level errors generated by disturbances - including target and cursor jumps, versus responses to distractors, i.e., environmental changes that are irrelevant to the reaching task. Additionally, we examined the response to matching cursor and target jumps (dual jumps), which generate estimation errors (and are thus considered task relevant disturbances) but not low level errors.

These issues were investigated in this Thesis in a series of experiments with healthy subjects using 3-Dimensional mouse to manipulate a cursor on a computer screen. Predefined disturbances and distractors were introduced during the movement. EEG was measured using the Brain-Products system (64 electrodes) and used for extracting ERP synchronized to the time of the error.

A significant P3a-like component appeared in the response to both disturbances and distractors, whereas the P3b-like component was significantly stronger in response to disturbances than distractors. The P3b-like component appeared also in response to dual jumps, even though they do not evoke low level errors. The results indicate that disturbances and distractors elicit distinct responses, and that the P3b-like component, reflect estimation rather than low level errors.