engleski

Deviant and target face processing in an oddball paradigm

Spatio-temporal source localization methods were used to investigate cortical neuromagnetic activity evoked by deviant and target faces presented in an oddball paradigm. Eight male subjects with available MRI scans participated in the study. Gray-scale face stimuli were presented in the centre of the visual field in an oddball paradigm. A non-target deviant neutral face was presented among standard happy faces in condition 1. In condition 2, the same deviant neutral face was presented with a standard neutral face of another person. The task was silent counting of a target face with glasses. Conditions 3 and 4 consisted of inverted faces from conditions 1 and 2, respectively. Neurodynamic measurements were conducted at the BioMag Laboratory with a 306-channel Vectorview system (Elekta Neuromag Ltd., Helsinki). MRIVIEW and Neuromag software were used in data analysis. Spatio-temporal localization assumed multiple current dipoles in a spherical volume conductor. Visual inspection of the field maps at early latencies around 100 ms revealed slight differences between responses to standards and deviants and more prominent differences between standards and targets. Later, the differences between standards and deviants became more evident, while targets had completely different field pattern. Spatio-temporal analysis of neuromagnetic data demonstrated that locations and dynamics of the identified sources were comparable for standards and deviants till the time window 200-300 ms when a difference in the activity of the occipital-temporal sources was evident. However, target faces elicited different cortical sources, i.e., left temporal or left or right frontal sources, depending on the subject. Intersubject differences increased around 170 ms when locations and dynamics of the active sources started to diverge. Rather similar results were obtained for all four conditions. Spatio-temporal analysis of neuromagnetic responses to deviants and targets indicated an early detection of the target and modulated activity in response to the deviant. Later activity in occipital-temporal region was shown to be deviance-sensitive. Activity in the left temporal and frontal regions might be connected to the task of counting target faces.

MEG; face processing; oddball paradigm

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