The Effect of Task on Object Processing revealed by EEG decoding

At which phase(s) does task demand affect object processing? Previous studies showed that task demand affects object representations in higher-level visual areas but not so much in earlier areas. There are, however, limitations in those studies concerning the relatively weak manipulation of task due to the use of familiar real-life objects, and/or the low temporal resolution in brain activation measures such as fMRI. In the current study, observers categorized images of artificial objects in one of two orthogonal dimensions, shape and texture. Electroencephalogram (EEG), a technique with higher temporal resolution, and multivariate pattern analysis (MVPA) were employed to reveal object processing across time under different task demands. Results showed that object processing along the task-relevant dimension was enhanced starting from a relatively late time (~230ms after image onset), within the time range of the event-related potential (ERP) components N170 and N250. The findings are consistent with the view that task exerts an effect on object processing at the later phases of processing in the ventral visual pathway.