Browsing by Subject "N170"

Objectives. This study aimed to clarify the brain-level processing of face stimuli by examining event related potentials. The purpose was to examine whether it is appropriate to make conclusions about the localization of brain-level processing of face expression and identity. Additionally, the study wanted to clarify whether there are observable differences between expression processing and does the intensity of the expression affect on the brain-level differentiation of expressions. Prior studies about the perception of face stimuli have been heavily focused on the modular view of the information processing system, in which every cognitive function has its own anatomical correlates and where the modules are clearly distinguishable from each other. The opposing view to this is the network-assumption in which the confines between modules are vague. Knowledge about these cognitive processes is crucial when new rehabilitation forms are being developed for people, from whom face perception is abnormal. Methods. 17 healthy test subjects took part in the study. In total, subjects were presented with 112 face stimuli, in which face expression and identity varied systematically. Based on prior studies, the event related potentials, which are known to be present in the perception of face stimuli were especially studied: the positive or negative fluctuations that occur 100, 170 and 250 milliseconds after the presentation of face stimulus (so called P1, N170 and N250 components). The effects of expressions and identities on the event related potentials were examined with traditional one-variable analysis (comparison of averages) as well as with multiple variable methods (comparison of correlations of distributions), which better expose the changes caused by face stimuli manipulations. Results and conclusions. The average amplitude and latency of event related potentials did not differe across conditions. The complex interactions between test conditions were exposed by forming 112 x 112 dissimilarity matrices of event related potentials. General linear model, which included eight regressors, was fitted into dissimilarity matrices. Fitted models were also compiled. In those, every every regressor was weighted with beta-coefficients at the time points of P1, N170 and N250 components. Based on the results, it is possible to assume that expression processing happens in an earlier phase than identity processing. Additionally, there was a robust interaction between expression and identity, which clarified the variation in the data. These results give support to the network-assumption in the perception of faces. However, the network-assumption does not deny modularity completely.