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A PRELIMINARY STUDY OF APPLYING ERP ON USERS’ REACTIONS TO WEB PAGES

WITH DIFFERENT PRESENTATION FORMATS

Ming-Huang Lin *, Yu-Min Fang **,***, Ching-Yi Wang****

* Institute of Applied Arts, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 300, Taiwan

** Graduate School of Design, National Taiwan University of Science and Technology, 43 Kee-lung Road, Section 4, Taipei 106, Taiwan, *** Department of Industrial Design, First International Computer Corporation, 300 Yang-Guang Street, Nei-Hu, Taipei 114, Taiwan

**** Institute of Applied Arts, National Chiao Tung University, 1001 Ta-Hsueh Road, Hsinchu 300, Taiwan

Abstract: Instead of text, usually web design experts suggest more proper images, especially human faces or figures, will evoke the viewers’ sympathy and increase the attractiveness of the web pages. To investigate this design principle, this research introduced the ERP (Event-related potential) method to analyze viewers’ brainwave component P300, N170, and N400 to compare the different visual stimuli - brief description (text), product photos, human face images, and body images. The result showed that the photos and human figures were confirmed positively for increasing attractiveness, diminishing the time of communication. But experts’ suggestion is not always valid since sometimes the proper word impresses viewers more in the first glance, comparing to visual images. Key words: design cognition; interface design; information design; event-related potential (ERP)

1. Introduction

Globally accessible web site enables corporations to communicate with a wide variety of constituencies. World Wide Web also represents a resource for any organization seeking a broad audience. For successful communication, designing a commercial web page with appropriate responses from viewers is the crucial key [1].

With limited available time, viewers surf a large number of web sites to search for product information. Thus, the commercial sites, especially the homepages, need to catch the attention and let them be satisfied of what they are staring. Otherwise, viewers can tend to leave the sites in a matter of seconds. But what kind of web pages will satisfy this communication? What kind of design guidelines will help to evoke viewers' appropriate responses?

One of the critical attributes of the web page is the diversity of the presentation formats. For designing a web, designers need to select the formats: textual contents or different visual images. From the viewpoint of information processing theory, usually texts and images can be considered as two of the different types of information input. Imagery theorists emphasized the distinction between the codes used for images versus textual information. The dual-code model stated that the two types of information are encoded in working memory by separate subsystems, one specialized for sensory images and the other specialized for verbal language [2-4]. It is thought that the images contain information that is encoded from a sensory event after perceptual analysis and pattern recognition, and are organized into subunits at the time of perception [5-8].

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Peracchio and Meyers-Levy indicated that researchers have long posited that visual images can communicate ideas beyond those that are depicted literally [9]. Scott and Batra also indicated that images can convey semantically meaningful, descriptive concepts via their stylistic properties [10]. These claims correspond to the phrase “A picture is worth a thousand words”, and web design experts adopt the same principles. Instead of textual contents, usually experts suggest that more proper images, especially human faces or figures, will evoke viewers’ sympathy and increase the attractiveness of the web pages [11-12]. Although these guidelines are widely acknowledged, few scientific analyses and confirmations have been carried out to verify these common rules. Accordingly this research tries to explore the following questions: 1) Do viewers respond to images more positively than to the commercial texts as the specialists’ claim? 2) Do human figures or face images attract more attention? 3) If the improper or unrelated images will obstruct communication and invoke confusion? 4) Can we apply scientific instrument to examine these design guidelines?

2. Research Method 2.1 The Measurement Methods

In the design studies, the popular method of measuring subjects’ reactions to the objects or images is applying adjective descriptions of the semantic differences (SD) and further to the multidimensional scale (MDS), for example, the numerous researches into Kansei Engineering in Japan [13], and multidimensional space [14-15]. They use questionnaires with Liker Scale, mostly based on the Semantics Analysis developed by Osgood in 1957, to acquire the subject’s subjective responses to the stimuli. Though fruitful results have been achieved, skeptical criticism to this measurement arises since that: 1) the subjects’ respond might be misguided by questionnaire design, 2) the insufficient reliability and accuracy, and 3) the distrust about subjects’ patience with answering all questions [16]. As the process of acquiring the raw data is not well-controlled, therefore the further analysis might be invalid.

To supplement the insufficiency of the current measurement method, objective scientific instrument might

be useful for examining the subjects’ responses. Through the development in science and technology in recent years, the objective psychological responses can be measured by the ERP (Event-related potential) signal, utilizing the scientific instrument without causing any negative influence on the mankind. The ERP method can be borrowed as a new tool for design assessment. Different from the questionnaires, ERP can detect subjects’ initial and earliest responses. By asking subjects to watch the different presentation formats of web pages, brainwave variations can be recorded. The data of inattentive subjects or false response can be excluded via examining the waveform. The subjects’ behavioral response data can be designed to collect precise information, accumulated by the subjects’ repeatedly and continuous reactions by clicking the mouse (right/left button). 2.2 The ERP Research on the Mental Processing of Visual Stimuli

ERPs are associated in time with some physical or mental occurrence, and can provide important information about how the human brain normally processes information [17]. These potentials can be recorded from the human scalp and extracted from the ongoing electroencephalogram (EEG) by means of filtering and signal averaging. As the EEG reflects thousands of simultaneously ongoing brain processes, the brain response to a single stimulus or event of interest is not usually visible in the EEG recording of a single trial. To see the brain response to the stimulus, the experimenter must conduct many trials and average the results together, causing random brain activity to be averaged out and the relevant

ERP to remain [8]. Generally ERP recording instrument includes an elastic

fabric head cap with sintered electrodes, a monopolar digital amplifier, and an acquisition and analysis software for processing and analyzing ERP data. The stimuli are put in the visual image display software, and the display time, interval, and sequence are determined.

In this study, the different visual stimuli of web page were manipulated, therefore analysis was carried out to the specific ERP components, related to image processing (P300), facial recognition (N170), and confusion (N400). The first study utilizing the ERP on the mental processing of visual stimuli was by Johnston and co-workers. They

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established that some late components of ERP could reflect the emotional processing of different visual stimuli [18-19]. Several research groups have also reported that the positive ERP component P300 is evoked specifically by emotional pictures [20-22]. The P300 is the classic index of attention, recognition, and stimulus probability [23]. And the emotionally positive and negative stimuli evoked greater P300 amplitudes than neutral ones [24]. The N170 is the index of facial recognition, and the visual encoding of this cognition processing has been reported at around 170 ms [25-26]. In this case, texts, product images, faces, and nude bodies on web pages were compared, to examine weather there is any specific activity associated with N170 and P300.

The N400 is associated with the emotion of confusion. ERP studies have elicited a large negative component peaking around 400 ms (N400 effect) by presenting incongruent (relative to congruent) word pairs, or unrelated pictures [27-28]. In this research, incongruent visual stimuli (e.g., presenting male’s face with female’s shaver, or presenting female’s nude body with male’s shaver) were manipulated to evoke N400. 3. Experiment Procedure 3.1 Subject

Twelve of the graduate and undergraduate students of National Taiwan University of Science and Technology were selected for the experiment. Among them, we rejected two subjects who contributed insufficient trials in any group (were smaller than 16 trials). And the remaining ten subjects (six males and four females, Mean = 23 years old) were used as subjects for further analysis. None of the subjects has neural disease of visual illness or brain injury. 3.2. Stimuli

The stimuli of this experiment included 7 groups of web pages (Table 1), illustrating seven formats of presenting products, and each group presented four different electrical home appliances products, including men’s face shaver, women’s shaver, toasters, and irons (Table 2). The seven formats of presenting products were the combination results of the different visual stimuli - brief descriptions (texts), product photos, human faces, and bodies. The seven groups of web pages were: Group 1 (brief description of the

Table 1. Seven groups of web pages. Group Group 1 Group 2 Descrip- tion

brief description of the product

brief description of the product plus the product photo

Web Pages Example

Group Group 3 Group 4 Descrip- tion

the product photo along the photo of product and human face with strong relation

Web Pages Example

Group Group 5 Group 6 Descrip- tion

the photo of product and human body with strong relation

the photo of product and human face with less relation

Web Pages Example

Group Group 7 Descrip- tion

the photo of product and human body with less relation

Web Pages Example

Table 2. Four different types of electrical appliances products as stimuli. Product Men’s Face Shaver Women’s Shaver

Web Pages Example

Product Toaster Iron Web Pages Example

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product), Group 2 (brief description of the product plus the product photo), Group 3 (the product photo along), Group 4 (the photo of product and human face with strong relation), Group 5 (the photo of product and human body with strong relation), Group 6 (the photo of product and human face with less relation), and Group 7 (the photo of product and human body with less relation). In this experiment design, the following groups were compared: 1) Group 3, 4, and 5, controlling the proportion of appearing human face (none, large, and small) with the same product image, were manipulated to examine if human figures or face images were more attractive than product images; 2) Groups 1, 2, and 3, the combinations of text and product image, were manipulated to test if viewers respond to images more positively than to the commercial texts; 3) Groups 4, 5, 6, and 7, the combinations of two images with strong/weak relation, were manipulated to simulate the incongruent situation to see if the improper or unrelated images will obstruct communication and invoke confusion.

In order to exclude the extraneous interference, a typical background of the commercial web page was chosen. All stimuli shared the same background. 3.3 Procedure

After short briefing, the subject sat and wore the

electrode cap. Then the subject was instructed to watch the

web page images and answer question (“Is this web page

attractive?”) by clicking the mouse. If the subject agreed

with this question, they clicked left-button, if not, the

right-button. These mouse-clicking actions also help

subjects to concentrate their attention. The stimuli were

presented one by one for 1.5 seconds, and inter-trial interval

was 0.5 seconds. To avoid Oddball Effect, which is usually

evoked by the infrequent presentation of incongruent

stimuli versus frequently displayed congruent stimuli, we

need to make sure the equal probability of presenting for the

different formats. Usually infrequent presentation of

specific stimuli group will evoke greater P300 amplitude,

simply due to the imbalanced presentation of stimuli in the

improper experiment design.

We assumed that the photos of products with male or

female human faces can be regarded as the same group

(Group 4 & 6), and the photos of products with male or

female human bodies (Group 5 & 7) as well. Accordingly

each stimulus in Group 1, 2, 3 randomly presented 20 times,

and web pages in Group 4, 5, 6, 7 presented 10 times. There

were totally 400 trials each person. An experiment lasted

about 13 minutes.

3.4 Recording

EEG was recorded by 32 electrodes Ag/AgCl sintered electrode cap (Quick cap, Compumedics Neuroscan, USA,). Electrode positions included the standard 10-20 system locations and additional intermediate positions. Horizontal and vertical EOG were monitored using four facial electrodes laces on the outer canthi of the eyes and in the inferior and superior areas of the orbit. To construct this experiment, the Quick-Cap should be connected to the amplifier (NuAmps, Compumedics Neuroscan, USA), and to the computer with installed acquisition and analysis software SCAN 4.3 for processing and analyzing ERP data.

Visual Image Display System (STIM2), displayed by a laptop computer monitor, is a browser interface which presents digital images for custom stimulus and task design. Through STIM2, the stimuli were put in, and the display time, interval, and sequence were determined. The researcher can observe the ongoing experiment through another monitor (see figure 1). The STIM2 controlled time setting and provided the time signal to the SCAN 4.3 while recording the data. The mixed data can be analyzed later by the analysis software.

Figure 1. The ongoing experiment

Epoch continuous EEG data were segmented from 200

ms prior to stimulus to 1000 ms. And a band pass digital filter was between 0.1-40 Hz and later applied to remove

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unwanted frequency components. The average re-reference were transformed into the M1 and M2 sites and baseline-corrected relative to the interval -100 to 0 ms. After VEOG channel was subjected to an artifact rejection of ± 75 μV to reject trial with excessive EMG or other noise transients and linear trends were rectified. The ERP data at least 16 trials free were further average proceeded directly for the identified conditions separately whether didn’t achieve the value were rejected. 3.5 Data reduction and analysis

The subjects’ data, recorded by ERP record system, was then processed by statistic operation and examined by the analysis software (SCAN 4.3). According to the above-mentioned ERP studies[20-28], three possible earlier components were investigated as following: 1) N170, identified with the interval between 130-180 ms at T5 and T6 electrodes, generally found to be largest over temporal scalp sites ; 2) P300, identified with the interval between 270-450 ms at Cz and Pz electrodes, relative to reference electrodes placed on the parietal and positive scalp; and 3) N400, identified with the interval between 380-500 ms at Fz and Cz electrodes, the largest over anterior and parietal scalp sites (see figure 2). Many researchers [29-32] mentioned that though there is a typical range for the components, specific interval need to be adjusted and determined according to the variety of different ERP waveform for each different case. In this study, the interval for each component was adjusted and determined in accordance with the suggestion and observation that if the peak of amplitude shown in the appropriate range.

Figure 2. The selected 6 electrodes for ERP included medial

part scalp sites (Fz, Cz, Pz and Cpz) and temporal scalp sites (T5 and T6).

In order to correctly obtain the ERP data for peak of amplitude and latency in each component, we defined the rules as following: First, set the parameter of the investigated interval in the analysis software (e.g., set the interval range for P300 around the 270-450 ms time window). Secondly, make sure the peak of amplitude was located on the setting range. If not, the range of time window should be adjusted to get the modified interval with effective peak of amplitude. Thirdly, after adjusting and identifying that each component exhibited peak of amplitude in defined interval, the value of peak of amplitude and the related latency can be obtained and further calculated.

ANOVA were used to calculate the behavioral and ERP data in these three components. The ANOVA was performed on two with-subject factors for each time window: Group 1-7 and Electrode (Fz, Cz, Pz, Cpz, T5 and T6, see figure 2). Post-hoc comparison was conducted when there were significant effects involving group of interest. The Turkey’s two-factor HSD (p<0.05) was applied when necessary. 4. Result

The subjects’ ERP waveform and data were analyzed and summarized as following: 4.1. Behavioral Result

The subjects were instructed to watch the stimuli and answer the question about the attractiveness of the web pages by clicking the mouse. On the users’ click, the subjects’ response data were recorded by ERP record system, and were integrated and summarized. The result showed that the attractiveness of the web pages was significantly different (p<0.05) between all groups of presentation style (see table 3). The subjects’ preference of the web pages was that: 1) Group 1 (text along) was less attractive; 2) The web pages presenting the photos of products were more attractive. The first two results confirmed the experts’ claim; 3) However, these behavioral data showed no significant difference in the attractiveness between the product images, human faces, and figures.

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Table 3 Behavioral result in all groups for the attractiveness of

web pages (standard deviation of means in parentheses). Value of attractive=1 and unattractive=2.

Group Mean

1 1.81 (0.39)

2 1.27 (0.44)

3 1.24 (0.43)

4 1.29 (0.45)

5 1.26 (0.44)

6 1.31 (0.45)

7 1.32 (0.46)

4.2. ERP Result 4.2.1. N170 epoch (130–180 ms)

The negative ERP component N170 is usually associated with the face recognition processes [18-19]. This study was attended to evoke N170 by presenting human faces on the controlled web pages. In the experiment design, three groups of stimuli related to the presentation of human faces were manipulated: 1) Group 3, the controlled group, with product photo but without any human face; 2) Group 4, the product photo with largest proportion of human face; 3) Group 5, product photo with human body (with smaller proportion of face).

The table 4 and figure 3 illustrates the average of N170 for Group 3, 4 and 5 under the T5 electrode (the largest amplitudes for N170 in this case, corresponding to the left temporal lobe). After the onset of a stimulus beginning around 130-180 ms, we noted that the negative waveforms reached peaks at the 150.8 ms, 147.3 ms and 153.0 ms for Group 3, 4 and 5 separately (see figure 3 A, the marked peaks in these groups). Table 4. The mean of peak amplitude and latency of Group 3, 4, and 5 for N170 at T5 site (standard deviation of means in parentheses).

Item peak amplitude (µV) latency (ms)

T5 Group 3 0.97 (1.34) 150.80 (9.99)

Group 4 -2.30 (1.29) 147.30 (9.50)

Group 5 -0.08 (1.92) 153.00 (8.08)

Figure 3. (A) The top figure displays the waveform of Group 3, 4, and 5 for N170 at the T5 electrode, and (B) the scalp topography of bottom figure clearly shows the scalp distributions of the N170 differences in these groups between 4 and -3.5 amplitudes.

ANOVA restricted to Group 3, 4 and 5 revealed that

the peak amplitude of N170 was significantly different

(F(2, 27)＝11.72, p＝0.000) at the T5 electrode. In this case,

the post hoc tests indicated that the ERPs effect of Group 4 was more negative-going than Group 3 and 5. The results suggested that the appearance of human faces (Group 4) on web pages did evoke N170 at the T5 electrode, and confirmed the activation of face recognition mechanism for inducing the view’s attention.

4.2.2 P300 epoch (270–450 ms) The main purpose of this study was to investigate

whether the subjects respond to the product photos more positively than to commercial texts. P300 was confirmed to be associated with the attention and emotional stimulus [20-24]. If a picture is worth a thousand words, that is, design experts’ preference for the images rather than the texts on web page is valid, larger amplitude and less latency of P300 by images should be evoked. In order to test this assumption, we examined three groups of stimuli related to the presentation of product photos and texts in this experimental design: 1) Group 1, text only, 2) Group 2, the combination of product photo and text, 3) Group3, the product photo.

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The table 5 and figure 4 illustrates the average of P300 at the Cz and Pz electrodes. In figure 4 (A), the clear waveforms of LPC (Late Positive Component), usually elicited largest amplitudes around 400-500 ms at central-parietal scalps in response to affective or incongruent pictures [33-35], was observed at the Pz site about 480 ms in Group 1-3 groups. This finding helped us to identify the time windows of P300. After that, we set the time windows of P300 between 270 ms and 450ms just before the onset of the LPC. According to the results of peak amplitudes for P300 (see table 5), in this time window, Table 5. The mean of peak amplitude and latency for P300 in Group 1, 2, and 3 at Cz and Pz sites (standard deviation of means in parentheses).

Item peak amplitude (µV) latency (ms)

Cz Group 1 3.45 (6.24) 405.10 (42.72)

Group 2 -0.04 (5.49) 375.10 (59.02)

Group 3 0.11 (6.18) 336.10 (44.60)

Pz Group 1 7.76 (5.99) 409.60 (40.49)

Group 2 5.13 (5.18) 361.30 (52.64)

Group 3 5.90 (6.26) 327.90 (38.79)

Figure 4. (A) The top figure showed the waveform of Group

1, 2, and 3 for P300 at the representative Pz site, and (B) the bottom figure was illustrated the scalp topography for P300 between 4 and -6 amplitudes.

we detected that the Group 3 was appeared obviously positive-going around 327.90 ms (see figure 4 A) and then begun negative-going, whereas the P300 effects of Group 1 and 2 were less obvious around 409.60 ms and 361.30 ms.

ANOVA restricted to Group 1, 2 and 3 revealed that the latency at the Cz and Pz sites was significantly different

(CZ: F(2, 27)＝4.92, p＝0.015; PZ: F(2, 27)＝8.56,

p＝0.001). The post hoc tests showed that despite the fact

that the latency of Group 2 was not different from Group 1 and 3, Group 1 was significantly longer than Group 3 at Cz and Pz electrodes. It indicated that that the brief description (text along) on the web page consumed more time period for the subjects to react to the messages. Since the viewers browse the large number of web sites with limited time and tend to leave the site in a matter of seconds, the time-consuming communication will exceed viewers’ patience and can be regarded as the negative design. This result matched the experts’ claim.

Our preliminary assumption was that the viewer might

get more impression on the image than the text as the

experts’ claim. Therefore, more amplitude of P300

stimulated by images should be evoked. But comparing the

peak amplitude of P300, there was no significant difference

(p>0.05) between Group 1, 2, and 3. Examining the figure 4,

the amplitudes of Group 1 (text only) showed even greater

than others. Therefore we should modify our assumption

and conclude that in our study, contrary to the web design

principle, product photos did not evoke greater cognition

processing than text.

In addition, there were no significant difference (p>0.05) between Group 3, 4, 5, 6, and 7. It meant that presenting varied photos (products, human faces, or human body images) on web page might be not differential enough to evoke significant different waveform of the P300. This result corresponded with the previous behavioral result for P300, showing no significant difference among Group 3~7.

4.2.3. N400 epoch (380–500 ms)

The negative ERP component N400 is usually associated with the subjects’ emotional confusion in incongruent situation [27-28]. Comparing Group 4 and 5 (reasonable combinations of product photos and human faces or bodies) with group 6 and 7 (unreasonable situation),

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the result showed that there was no specific N400 induced by group 6 and 7, and no evidence of viewers’ confusing response to unreasonable situation in this experiment.

In the previous reports with successful inducing for N400, the chosen stimuli were purposefully contrasted to each other. But regarding our stimuli selection, the assumption that subjects will consider the selected images to be the incongruent condition might be not convincing.

Furthermore in our stimuli arrangement, presenting two pictures simultaneous might cause the subject’s back-and-forth cognitive process for perceptual analysis and pattern recognition [5-6] and decrease the incongruent effect. Since ERP tracks the time course of processing activity in milliseconds, the subjects’ complicated information processing might exceed the ERP recording range, and cannot be controlled in our experiment design. Therefore we suggested that, referred to previous study, these stimuli should be presented sequentially to evoke N400 (e.g., present the first picture, then show the second incongruent picture and start the ERP recording). Through this failure of evoking N400, we experienced the limitation of ERP method. Some design issues could be not suitable for ERP method, and the experiment design need to be carefully manipulated to induce the interpretable component.

5. Conclusions

In design practice, experts try to generalize the simplified principle from sophisticated experience. Therefore, investigation into this well-accepted principle can reveal more profound insight. In addition to its superficial meanings, the simplified principle “more images will help” has been revealed further useful conclusions by this study.

The behavioral results showed that photos of products were more attractive than texts. By analyzing N170, it showed that the appearance of human faces or figures on web page did evoke N170 effect, activate the face recognition processing, and arouse the viewers’ attention. The analysis of ERP component P300 showed that providing the textual description of products consumes subjects more time to react to the messages. These results evidenced that experts’ suggestion to add photos and human figures could be effective to increase attractiveness, and diminish the time of communication. Therefore we can

confirm the following expected conclusions: 1) adding human faces on the web pages will attract viewers for further reading; 2) avoiding large amount of texts on the web page will help to communicate the target audiences before they lose their patience.

But a picture is not always worth a thousand words.

Contrary to the web design principle, the result of this

experiment showed that images did not generate greater

amounts of P300 amplitude. It meant that, in some case,

product photos did not evoke greater cognition processing

than texts do. Therefore, we can concluded that the

presentation formats and images for web page should be

carefully well-planned and selected, since that the

meaningful words can possibly impress viewers more in the

first glance in comparison with uninteresting images. Though the knowledge of Neuroscience and the

application of ERP are rather new in design field, this experiment has successfully evoked viewers’ varied ERP latency and amplitude by presenting the web pages with different presentation formats. This study has justified experts’ suggestion, and demonstrated that utilizing the ERP method can explore the fact beyond the reach of traditional methods. We acquired the precious experience in this new tool, acknowledged the limitation of ERP, and recognized that there is still more knowledge to learn. We hope that the results of this study can inspire other researchers to develop the examinations for their own design topics applying this new tool in the future.

Acknowledgements The authors would like to thank Robert Liao from

NeuroScan for the technical support, the National Science Council for the financial support (under grant number NSC 94-2411-H-011-011), and the First International Computer, Inc..

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