CE: Jishana ED: Maitreyee Op: Sampath WNR 55: LWW_WNR_55 Brain imaging; Cognitive neuroscience and neuropsychology 1 Event-related potential P correlates of implicit aesthetic experience Xiaoyi Wang a,b, Yujing Huang a,b, Qingguo Ma a,b and Nan Li c Using event-related potential measures, the present study investigated the affective responses to aesthetic experience. To differentiate the objective aesthetic value from subjective aesthetic evaluation, an amended oddball task was used in which pendant pictures were presented as frequent nontarget stimuli, whereas the landscape pictures were presented as a rare target. The pendant pictures were chosen from the largest online store in China and divided into beautiful and less beautiful conditions by the sales ranking. A positive component, P, was recorded for each condition on the participants frontal, central and parietal scalp areas. Less beautiful pendants elicited greater amplitudes of P than the beautiful ones. This indicates that emotion arousal seems to occur at the early stage of processing of aesthetics and can be detected by the P component, implying that the event-related potential methodology may be a more sensitive measure of the beauty-related attention bias. From the perspective of artwork design and marketing, our finding also shows that P can potentially be used as a reference measure in consumer aesthetic experience. NeuroReport : c 1 Wolters Kluwer Health Lippincott Williams & Wilkins. NeuroReport 1, : Keywords: aesthetic experience, emotion, event-related potentials, neuroaesthetic, neurodesign, neuroindustrial engineering, neuromanagement, P a School of Management b Neuromanagement Laboratory and c College of Public Administration, Zhejiang University, Hangzhou, People s Republic of China Correspondence to Qingguo Ma, MS, Neuromanagement Laboratory, School of Management, Zhejiang University, 3# Zheda Road, Hangzhou 315, People s Republic of China Tel: + 57179579; fax: + 57179579; e-mail: maqingguo39@zju.edu.cn Received 19 June 1 accepted July 1 Introduction Aesthetic experience of a specific object is a part of daily life, such as choosing jewels. In the classical aesthetic theory, the subjectivist suggests that aesthetic value lies in eyes of the beholder; in contrast, the objectivist disputes that it exists in the object. Whether the aesthetic characteristics of objects interact with viewers mental process is still unclear. Neuroaesthetic is defined as the neural mechanism of aesthetic experiences [1]. Aesthetic value is reflected by the brain activity of distinct cerebral areas, including reward-related cognitive processes such as subcortical and limbic areas [] or visualmotor regions [3], and the core emotion centre [], which are presumably associated with aesthetic appraisal and aesthetic pleasure [5], respectively. In actual application, neuroaesthetic is essential to neurodesign/neuroindustrial engineering [] and neuromanagement/neuromarketing [7]. Winkielman and Cacioppo [] assessed participants affective responses to aesthetic stimuli with facial electromyography and found that beautiful objects elicited a stronger positive emotion before participants made overt judgements. Di Dio et al. [9] also found that insula was activated to the original arts compared with proportion-modified ones during a simple observation task, indicating the existence of intuitive emotional process. Furthermore, Jacobsen et al. [1] found that even in the proportion judgement task, aesthetic value modulated activation in some areas such as the left intraparietal sulcus, which also indicated that the brain areas processed aesthetic stimuli intrinsically. However, in these studies, a common problem is the difficulty in differentiating the stimuli s objective aesthetic value from the participant s subjective aesthetic evaluation. Thus, aesthetic value processes should be studied by using a task-irrelevant paradigm [11] to avoid the influence of the intention of participants, which may mask neural processes of aesthetic value [1]. In earlier event-related brain potential (ERP) studies, it was proposed that the visual positive component with a peak latency from 1 to ms (P) was sensitive to the emotionality of stimuli. P, usually referring to the tail end of the N1 P complex or the vertex potential, was associated with the primary evaluation of the affective content of a stimulus [13]. This line of studies found that compared with pictures [1] or words arousing positive feelings [15], increased P amplitude was elicited in response to pictures or words arousing negative feelings. In the study, we proposed that emotional processes were activated spontaneously by objective aesthetic value in the early stage of an aesthetic pleasure experience. A task-irrelevant paradigm, an oddball task [1], wherein rare target events are interspersed with frequent nontarget events, was used; pendants were used as nontarget stimuli and landscape pictures were presented as the target. Our prediction related to the manipulation of degrees of beauty is that compared with less beautiful pendants, beautiful ones would spontaneously arouse 959-95 c 1 Wolters Kluwer Health Lippincott Williams & Wilkins DOI: 1.197/WNR.b13e335711
NeuroReport 1, Vol No more positive emotion, resulting in a lower amplitude of P. Materials and methods Study participants Data were collected from 1 female right-handed participants ranging in age from to 5 years (mean age. years). All the participants reported normal or corrected-to-normal vision and had no history of current or past neurological or psychiatric illness. They provided informed consent and were paid for their participation. Materials We selected 5 types of pendants, whose prices were controlled, from Taobao.com (the largest e-store in China) and then prepared a ranking list in descending order according to the sales in the last month. Forty pendant pictures at the top of the ranking list of sales were classified as beautiful pendants; another pendant ones at the bottom of the ranking list were defined as less beautiful ones. In addition, 1 landscape pictures were chosen from Google. These stimuli were processed digitally using Adobe Photoshop digital image manipulation software (Adobe Co., San Jose, California, USA) so that each one had the same luminance (1 cd/m ) and root mean square (RMS) contrast. The visual stimuli were presented on a 19-inch computer monitor (1 1 pixels, Hz) connected to a GHz Pentium computer. Stimulus presentation and data collection were controlled by Stim software (Neurosoft Labs Inc., Sterling, Virginia, USA). Those stimuli were viewed from a distance of 1 cm at the center and had a visual angle of.7.71. The background of monitor was greyscale (R = 1, G = 1, B = 1). Stimulus presentation and timing An oddball task was used in which participants were asked to respond as quickly and accurately as possible with the thumb on the 1 button on the keyboard only to the randomly occurring target stimuli among a series of nontarget stimuli (Fig.1). The assignments of the responses to the response hands were counterbalanced across individuals. The frequent nontarget stimuli were pendant pictures, which were presented one at a time in a pseudorandom manner. The target, occurring randomly 11% of the time, was landscape pictures. The experiment, lasting for a total of 3.5 min, included two blocks of 5 trials each. During each trial, the stimulus occurred for a 5-ms presentation duration and a blank screen was shown for 1 ms. Before the experimental blocks, participants performed one training block for familiarization with the task. Electroencephalogram recording Electroencephalogram (EEG) was recorded continuously (bandpass.5 1 Hz, sampling rate 5 Hz) using a Fig. 1.. LB B LB B B B LB D LB... LB B D B LB LB LB B B... Blank screen B. 5 ms Blank screen Blank screen LB. 5 ms Time Illustration of the stimulus paradigm applied. D. 5 ms Neuroscan Synamp Amplifier (Neurosoft Labs Inc.) by a set of Ag/AgCl electrodes placed according to the 1/ system and referenced to the left mastoid with a cephalic (forehead) location as the ground. The vertical electrooculogram was recorded from the right eye by supra-orbital and infra-orbital electrodes. The horizontal electrooculogram was recorded from electrodes on the outer canthi of both eyes. All EEG electrode impedances were maintained below 5 ko. Electroencephalogram analysis EEG was epoched off-line into 1 ms periods, starting ms before the onset of the first display. Individual trials containing eye movement artefacts, as well as individual channels with amplitude differences larger than 1 mv, were rejected before averaging. At least 3 epochs per condition were available after the rejection of artefacts for all participants. The averages per channel were low-pass filtered at 3 Hz ( db/octave) and were computed on the basis of the EEG elicited in response to the beautiful pendants as well as the less beautiful pendants using within-participant repeated-measures analysis of variance (ANOVA). Results On the basis of the ERP grand averaged waveforms and topographic map, the following nine electrode points were chosen for statistical analysis: F3, FZ, F, C3, CZ, C, P3, PZ and P. For the N1 components, we adopted the same windows as those in the study by Minati et al. [17], yielding 1 ms. The latency window for P in the present study is similar to that used by Spironelli and Angrilli [1] for the component they labelled P, yielding 19 and ms. Within each time window, the average potential was fed into the within-participant repeatedmeasures ANOVA, with condition (beautiful vs. less beautiful pendant pictures) and site (frontal, central or parietal) as two within-participant factors.
P correlates of aesthetic experience Wang et al. 3 Figure shows the time windows for the ERP components of interest at the frontal, central and parietal electrodes. The results of ANOVA show that for the N1 time window (1± ms), there was no main effect of condition [F(1,17) =.5, P =.7], without interactions between condition and side [F(,3) = 1.31, P =.5], or site [F(,3) =.97, P =.75]. Yet, for the P time window (19 ms), the condition main effect was significant [F(1,17) =.3, P =.], without interactions between condition and side [F(,3) =.75, P =.79], or site [F(,3) = 1.19, P =.33]. The potentials for each condition and time window are presented in Table 1. Consistent with the outcomes from the ANOVA analysis, the peak potential of P was distributed on the frontal, central and parietal scalp areas. It was stronger in the leftparietal and central-parietal areas (Fig. 3). Discussion From the ERP data in our study, significant differences were found in processing distinct degrees of beauty in an implicit oddball task. Specifically, less beautiful pendants automatically elicited higher amplitudes of the P component than beautiful ones. For N1, no significant effect was found between beautiful and less beautiful pendants at all electrodes. Fig. Beautiful Less beautiful F3 FZ F 1 1 1 C3 CZ C 1 1 1 1 1 1 P3 Grand averaged ERP elicited by beautiful pendants vs. less beautiful pendants at nine electrodes in the frontal, central and parietal areas. ERP, event-related potential. PZ P
NeuroReport 1, Vol No Table 1 Potentials (expressed in lv, as mean±sd) recorded at the frontal, central and parietal electrodes for beautiful pendants (B) and less beautiful pendants (LB) in the time window of 19 ms and the results of a two-sample paired t-test in two conditions at different sites Sites B LB t value P value F3.1±1.7 1.±1. 1.3.11 FZ.7±1.1.77±1.5 1.. F 3.1±.7.13±1.7 1..17 C3 1.9±1.9.±1.7 1.11. CZ.±.1 3.±.9 3.335. C 3.77±.7.7±3.51.99.3 P3.1±3..9±3.7.1. PZ.93±.1 5.7±3.7..3 P.±.7.73±3.19 1.17.7 Fig. 3 Beautiful pendants Less beautiful pendants Topographic maps of the maximal amplitudes of P from beautiful pendants and less beautiful pendants. The P in less beautiful pendants was more remarkable than the beautiful ones in the left frontal, central and parietal scalp areas. +1. +5. 5. N1 appeared to be insensitive to the emotionality of stimuli. As the N1 component responds to the perceptual characteristics of visual stimuli, this confirms the absence of a perceptual mismatch between two conditions [19]. Previous evidences have shown that although P, the tail end of the N1 P complex, covaries with N1 in many studies, P could be dissociated experimentally [] and topographically [1]. Although the functional correlates of the visual P remain controversial, three interpretations can be considered. One possibility is that P over central-parietal or occipital sites was a reflection of greater automatic mobilization of attention resources to negative stimuli [1,], that is negative pictures elicited a higher amplitude and a faster latency than positive ones. According to this interpretation, participants would pay more attention to the less beautiful pendants more intensely, resulting in a higher P amplitude than preferable ones. Another interpretation, according to the literature, is that P prominent at frontal or parietal sites is possibly viewed as indexing some aspect of a stimulus classification process as these brain areas are involved in protecting against interference from irrelevant 1. stimuli [3]. Third, according to Zajonc [], the early evaluation of affective connotation is processed automatically and independent of conscious inferences. This suggests that the underlying processes can be considered as a global affective evaluation depending on whether a stimulus is attractive for an individual. In our study, the P amplitude modulation observed may be interpreted cautiously as differences in the early stage of emotion evaluation. Traditionally, in the objectivist hypothesis, many features have been discussed such as symmetry [1], contrast and clarity [5]. More recently, an interaction perspective suggests [] that aesthetic experience emerges from the dynamic interaction of stimulus properties and observers cognitive and affective processes. In this study, we observed that beauty is based on the spontaneous processing experiences of the beholders, particularly the emotional processes. Our experimental conditions differed from traditional ones in several major aspects. First, the fact that emotion arousal seemed to occur at the early stage of beauty processing in the P component indicates that the ERP methodology may be a more sensitive measure of the beauty-related attention bias. According to ERP measures, the amplitudes of ERP components generally indicate the degree or the intensity of the engagement of cognitive processes, whereas latencies are assumed to indicate the time course of stages of processing [13]. Second, unlike traditional explicit judgements of preference, we used an implicit method to examine aesthetic processing. To investigate subtle human abilities, the implicit task is a useful way to avoid the influence of participants intention [1]. Third, our study selected pendants as stimuli and classified them into beautiful and less beautiful according to the sales in the real market (the circumstances of sales and the prices of pendants were controlled), which is different from previous studies on aesthetic experience that failed to distinguish degrees of beauty objectively. Conclusion The ERP data support the idea that less beautiful objects elicit a higher amplitude of P than beautiful ones and indicate that at the early stage of an aesthetic experience, negative emotional experience is automatically aroused for less beautiful objects. As such, the present study underscores the usefulness of the ERP methodology as a sensitive measure for the study of aesthetic processing. Acknowledgements The research was supported by grants (No. 791 and 993) from the National Natural Science Foundation and a grant (No. 9JZD) from the State Education Ministry of China, and was supported by the 11 project,
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