Abstract
Stereosensitivity changes as a function of both task-demands and stimulus-context. In two experiments, we ask here how this in turn affects object categorization both behaviourally and in the brain (EEG). We presented stereoscopic objects that belonged to 4 categories which were organized by two independent dimensions: natural/man-made × manipulability (manipulable vs non-manipulable). Observers (N = 37) were asked to perform a speeded discrimination task in which they judged whether each stereoscopically presented object was natural or man-made. Results showed that response times for manmade non-manipulable objects were longer than for manmade manipulable objects. By contrast, there was no significant difference between response times for natural manipulable and natural non-manipulable objects. To further investigate the temporal dynamics of the observed effects, a new group of observers (N = 27) completed the same task while electroencephalogram (EEG) signals were concurrently measured. Support Vector Machines (SVM) were trained to compare response patterns of different object categories using EEG data of all electrodes except M1, M2 and EOG. We found that response patterns for manipulable vs non manipulable man-made objects, and between man-made vs. natural non-manipulable objects could be well-predicted by the SVM, especially between 500-600 ms post-stimulus onset. Our data suggest that abstract attribute recognition of stereoscopic objects is modulated by object nature. The relatively late emergence of the relevant neural responses suggest that these modulations could arrive downstream to well-reported modulations of stereosensitivity (in turn) by object context.