Comparison of early visual ERP components in different object categories with low inter stimulus perceptual variance

Abstract

Event Abstract Back to Event Comparison of early visual ERP components in different object categories with low inter stimulus perceptual variance Sinem Kara1*, M. Cursi1, N. Amato1, A. Inuggi1, S. Velikova1, G. Comi1 and L. Leocani1 1 University Hospital San Raffaele, Department of Neurology and Clinical Neurophysiology, INSPE, Italy Background: In a recent study of Thierry et al. (2007) it was claimed that category effects previously reported in the N170 range may be due in part to uncontrolled inter stimulus perceptual variance (ISPV) differences between experimental conditions. Since neuroimaging studies of visual face and object recognition generally use full front views of faces contrasted with pictures of other objects presented in a variety of sizes and spatial layouts, category contrasts typically involve implicit comparisons of low and high ISPV conditions. They hypothesized that the face selectivity of the N170 might be an artifact driven by ISPV differences which are basically eccentricity, orientation and size. Aim: We examined the P100 and N170 waves with respect to low ISPV condition in different object categories considering that if N170 is sensitive to ISPV but not to the object categories then its amplitude should be relatively insensitive to different object categories with low ISPV. In addition, we also examined the progressive averaging of pictures of our object categories with the aim of evaluating template effect on P100 and N170 waves. Our full front face pictures’ average was still recognizable as a face which might have created a stronger template effect on the working memory even if the faces were presented in a pseudo-random order. Therefore for comparison we preferred cars and fruits so that the average of cars was still recognizable as a car like it was in faces, while the average of fruits wasn’t recognizable as a category but formed a big round border (because all the fruits were chosen from big round fruits like melon and apple). Methods: 15 healthy subjects (8 females, mean age: 27+/-3) were confronted with a visual oddball design, in which they had to detect, as quickly as possible, deviants, a pineapple, amongst a train of standard stimuli with low ISPV (faces, cars and fruits). Recordings were done with 30 channel EEG BrainVision recorder. Results: No significant difference was found amongst the object categories for the P100 latencies and amplitudes and the N170 amplitudes. The only significant difference was seen for the N170 latencies in which the N170 latency of faces was significantly shorter than that of cars and fruits. Conclusion: We saw no difference among the groups for P100 and N170 amplitudes in terms of template effect on working memory. Also we found no measurable effect of object category (face, car and fruits) on both P100 and N170 peak amplitudes. Although our findings for N170 amplitude confirmed the study of Thierry et al about the insensitivity of N170 amplitudes for faces, our data for P100 wave were in conflict with their results about the P100 amplitude being sensitive for object categorization.