An ERP study on self-relevant object recognition
Introduction
Our own property is unmistakably distinguishable from that of others, just as our own names and faces are. This salience indicates the existence of a top-down bias of processing self-relevant information. This self-relevance effect has been investigated by researchers. Previous event-related potential (ERP) studies have reported that the self-relevance effect is reflected in P300. P300 is known to reflect the engagement of higher-order cognitive functions (Farwell and Donchin, 1991, Johnston et al., 1986, Johnston and Wang, 1991, Nasman and Rosenfeld, 1990). These higher-order cognitive functions are considered to be involved in self-relevance processing, therefore, self-relevance has been investigated with P300 (Berlad and Pratt, 1995, Fischler et al., 1987, Folmer and Yingling, 1997, Gray et al., 2004, Muller and Kutas, 1996, Ninomiya et al., 1998, Perrin et al., 1999, Perrin et al., 2005). Despite previous efforts, however, the role of self-relevance in object recognition remains unclear. As far as we know, the only psychophysiological research on self-relevant object recognition was Sugiura, Shah, Zilles, and Fink (2005b). However, because they did not dissociate self-relevance from familiarity, their interpretation inevitably remains ambiguous.
In order to measure the self-relevance effect in object recognition, we performed an ERP experiment. In the present study, we attempted to distinguish self-relevance from less-self-relevant familiarity. This approach is in line with recent face recognition studies, in which self-relevance is compared to less-self-relevant familiarity (for familiarity defined as familiar–famous, Caharel et al., 2002, Platek et al., 2004 for familiarity defined as familiar–intimate, Herzmann et al., 2004, Kircher et al., 2000, Kircher et al., 2001, Platek et al., 2006, Sugiura et al., 2005a, Uddin et al., 2005). In our experiment, self-relevant objects were compared to less-self-relevant familiar objects, which were defined as pre-experimentally known but not belonging to the participants, to dissociate self-relevance from familiarity.
In terms of the methodology, we adopted the visual recognition processing model proposed by Bruce and Young (1986). In their model, several visual processing stages are assumed, and these stages were later studied by ERP researchers to identify corresponding ERP components. Although the model originally concerns face recognition, we believe it also provides a model of visual information processing and an established methodology to measure the activity of each processing stage with ERP components. The first component is P100, which is sensitive to the perceptual aspects of stimuli such as brightness, contrast, size, and visual acuity (Allison et al., 1999, Pfütze and Sommer, 2002). The second component is N170, which reflects the structural encoding process (Eimer, 1998, Eimer, 2000, Pfütze and Sommer, 2002). N170 shows larger amplitude for faces compared to other objects (Bentin et al., 1996, Eimer, 1998, Itier and Taylor, 2004, Rossion et al., 2002, Schweinberger et al., 2004). Some researchers reported that N170 did not reflect familiarity (Pfütze and Sommer, 2002, Schweinberger et al., 2002; see also Rossion et al., 1999), while other researchers reported it did (Caharel et al., 2002, Caharel et al., 2005, Campanella et al., 2000). Therefore, N170’s sensitivity to familiarity remains ambiguous. The third component is N250, which reflects the process of matching input information to stored representations (Pfütze and Sommer, 2002, Schweinberger et al., 2002, Schweinberger et al., 2004). Importantly, N250 is reported to be sensitive to familiarity in repetitive (up to 100 times) stimulus presentation paradigms (Caharel et al., 2002) as well as in immediate priming paradigms (familiarity as familiar–famous, Begleiter et al., 1995, Pfütze and Sommer, 2002, Pickering and Schweinberger, 2003, Schweinberger et al., 1995, Schweinberger et al., 2002 the dissociation of familiar–famous from familiar–intimate in N250 was reported Herzmann et al., 2004). Therefore, N250 was expected to serve as the index of familiarity. In the last stage, N400 reflects access to the person identity node and semantic processing. N400 is not only sensitive to perceptive priming but also to semantic priming (Pfütze and Sommer, 2002, Pickering and Schweinberger, 2003, Schweinberger et al., 2002), reflecting wide range of cognitive activities. Both N400 and P300 are commonly characterized as slow (i.e. low-frequency) waveforms, they show modulation in late time-course (typically after 300 ms poststimulus), and reflect higher-order cognitive processes including self-relevance. We defined these types of ERP components as the late slow wave (LSW).
According to the above mentioned studies, we adopted four ERP components as indices: P100 as the index of perceptual features; N170 as the index of the structural encoding process; N250 as the index of familiarity, reflecting the process of matching input information to stored representations; the late slow wave (LSW) which captures ERP activities after 300 ms poststimulus as the index of higher-order cognitive functions. Our interest was to identify and examine a self-relevance effect that is dissociated from less-self-relevant familiarity in object recognition. We adopted a passive viewing task to exclude task-relevant effects. For the same purpose, stimulus categories were separated by blocks and all stimuli were presented with equal probability.
Section snippets
Participants
Eighteen right-handed healthy undergraduate students of Nagoya University participated in the experiment (mean age of 20.0 and aged between 19 and 24 years, 13 women). Informed consent was obtained from all the participants. All participants reported normal or corrected-to-normal vision.
Stimuli
Four kinds of objects served as stimuli: an umbrella, shoes, a cup, and a bag. Three versions of each object kind were presented, corresponding to three levels of FAMILIARITY: personally familiar objects
Results
Fig. 3 shows the grand mean ERP for all the scalp electrodes in all the conditions. Fig. 4 shows the results of multiple comparisons with scalp electrode locations.
Discussion
The purpose of this study was to examine the self-relevance effect dissociated from non-self-relevant familiarity in object recognition with ERP. Results are discussed below.
In P100, the interaction FAMILIARITY × ELECTRODE was significant. The result indicates different visual features across stimuli (Allison et al., 1999, Pfütze and Sommer, 2002), which was interpreted to be due to variation in the shape and appearance of the objects.
N170 did not reveal any significant main effect or
Acknowledgments
This study was supported by Japan Society for the Promotion of Science (JSPS). We thank Akitaka Ariga for hardware support, and Alex Lamey for editing English.
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