AIC – M ID TERM M EET ING 201 1 , ZU R ICH – IN TER ACT IO N OF CO LOU R & LIGHT IN THE AR T S AN D SC IE NCE S 1
The Effect of Color Contrast between Text and Background on Human Comfort – Psychological and Physiological
Investigations
Eunsol LEE and Hyeon-Jeong SUK
Department of Industrial Design, Korea Advanced Institute of Science and Technology
Abstract
In this study, we focused on the affective effect of color contrast between text and the background when humans read the text on a LED display. We recorded subjects' brainwaves while they were reading a given text for one minute and asked them about the cognitive as well as emotional quality of the text stimuli. The results showed that the subject felt most comfortable when they were reading the text in dark gray (60%
grayscale) against a white background. The subjects later read the text in chromatic colors and gave poor ratings to the text-background combinations of complementary colors. However, the subjects' physiological reaction, as measured by their brainwaves, did not vary across the chromatic text stimuli (p>0.05).
1. Background and goal of research
People nowadays receive text information more through screen-based displays rather than via paper. As setting various text and background color combinations is easy on a screen-based display, the choice of a more suitable color combination psychologically and physiologically is necessary. Song (2009) and other researchers typically focused on comparisons with traditional media such as paper. Moreover, Jung (2006) and others have used subjective surveys to measure human emotional responses. In this study, we focused on the affective effect including both psychological and physiological response of color contrast between text and the background when humans read the text on a LED-based display.
2. Plan for the experiment
2.1 Environment settings
The text and background color contrast was presented on an all-in-one LED display computer, a Samsung DM-U200, to the subjects.
The distance between the screen and the subject was maintained uniformly for all subjects.
2.2 Measuring the emotional response
In order to measure the comfortable state of the subjects, their brainwaves were recorded using a 14-channel EEG headset (Emotiv EPOC,
Figure 1. Experiment environment and subject wearing the EEG head set
AICMIDTERM MEETING 2011,ZURICH –INTER ACTION O F CO LOU R &LIG HT IN THE ARTS AND SCIEN CES – PROCEEDINGS
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research edition). The fourteen receptors were placed based on international 10-20 location system. From the collected EEG data, the ratio of the alpha frequency (7.5~13Hz) to entire range (0.5~50Hz) was calculated as the alpha ratio was used as the comfort level. The Telescan program (Laxha Co.) was used to extract these ratio values.
The psychological emotional response was measured by questionnaires on a five-point scale (-2~2) regarding the readability (good to read) and preference for each stimulus.
3. Experiment 1
The purpose of experiment 1 was to investigate the emotional response, especially the level of comfort, by collecting and analyzing EEG information and subjective survey data pertaining to various brightness differences between the text and the background.
After an orientation session regarding the experiment, the subjects read presented text for one minute and then completed two questionnaires about the stimuli for 15 seconds.
These two steps were repeated 20 times. There were twelve subjects, consisted of seven male students and five female students. They were not color-blind and their eyesight level exceeded 0.7. Their native language was Korean. Their average age was 26.08 (SD=3.45).
3.1 Stimuli
There were 10 levels of stimuli with positive polarity and other 10 levels of stimuli with negative polarity. The brightness difference of one level was 10% grayscale. As the positive polarity stimuli, the background color was fixed as white (0% grayscale), and ten different text colors, from 10% to 100%
grayscale, were provided. As the negative polarity stimuli, the background color was black (100% grayscale) and grayscale text from 0% to 90% was provided. The text material was easy to read and easily understandable content.
3.2 Result and analysis
Figure 3 displays the ratio of alphawaves for the ten positive polarity stimuli. Stimulus’
label pN indicates positive stimulus that combined with white background and N%
grayscale text. Among the positive polarity stimuli, there is the tendency that from p10 to p60 the ratio of alphawaves is increasing except p30. Self-reporting result also shows that p60 get the highest score about readability (1.29) and preference (1.21) from participants.(Figure 4) There seems to be positive correlation between physiological response indicating comfortness and psychological response indicating readability [r=.58, p=.08] and preference level [r=.53, p=.12]. The lack of statistical significant result is perhaps caused by the limited number of compared items, as the mean values were taken for the analysis. Both physiological response and psychological response indicates that p100 is better for reading a context than p90. It does not match the general pattern that proves it to be getting worse above p70.
Figure 2.The 20 stimuli for experiment 1
AIC – M ID TERM M EET ING 201 1 , ZU R ICH – IN TER ACT IO N OF CO LOU R & LIGHT IN THE AR T S AN D SC IE NCE S 3 Figure 3,4. The ratio of alphawaves (left) and the score of legibility and preference (right) for positive polarity stimuli. Ratio of alphawaves = (7.5~13Hz)/(0.5~50Hz. p10 indicates positive polarity stimulus that combined with white background and 10% grayscale text.
Regarding the negative polarity stimuli, there is no significant finding or tendency from the brainwaves response (Figure 5). However, in the self-assessment result, n60 receives the highest readability (0.88/2.00)and preference score. (0.71/2.00) (Figure 6) Moreover, there is no significant relationship between response of brainwaves and self- reporting result.
Figure 5,6.The ratio of alphawaves (left) and the score of readability and preference (right) for negative polarity stimuli. Ratio of alphawaves = (7.5~13Hz)/(0.5~50Hz. n10 indicates negative polarity stimulus that combined with black background and 10% grayscale text.
4. Experiment 2
The purpose of experiment 2 was to investigate the emotional response about various hue differences between the text and the background with the same brightness difference (60%). The experiment procedure was identical to the experiment 1. There were thirteen subjects for experiment 2, comprised of seven male students and six female students. Their characteristics are identical to those in experiment 1. Their average age was 25.15 (SD=3.95).
4.1 Stimuli
There were 5 different hues (red, yellow, green, blue and black) that consisted of the positive polarity stimuli with a 80% brightness contrast, 5 negative polarity stimuli, and
Figure 7. 14 Stimuli for experiment 2
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4 complementary color contrast stimuli. The complementary colors were defined based on the HSB color system (Red / Cyan, Green/Purple).
4.2 Result and analysis
According to the EEG data, there were no significant differences between the stimuli.
As proven in the self-assessment result, there were significant difference among three contrast types for readability level (repeated measures one-way ANOVA, F(2,13) = 12.98, p<.01, eta-squared = .52) and preference level (repeated measures one-way ANOVA, F(2,13) = 50.73, p<.01, eta-squared = .81). Post-hoc test indicated that the mean score of readability and preference level for complementary color contrast was significantly different from both positive polarity and negative polarity.
Conclusion
Among positive polarity stimuli, white background and 60% grayscale text combination is the best for reading context like Lee et al. (2007). Otherwise, the black background and 60% grayscale text combination is the best. Moreover, complementary color contrast should be avoided for the reading task. It can be also concluded that brightness difference between text and background is more influential to people than hue difference. However, hue contrast affected physiological context intensely, so that designer should concern difference in hue as well as difference in brightness. This study can be applied to practical design work with objective and convincing data.
Acknowledgements
This research was supported by following programs: 1) BK21 Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (MEST), 2) Woman Scientist Program through the NRF funded by MEST (NRF 2010-0006319).
References
Jung, H. 2006. The impact of brightness, polarity and hue difference on legibility and emotional effect of word in visual display. Journal of the Korean Society for Cognitive Science 17(5) : 337-356.
Lee, S.J. and J.W. Kim. 2007. An experimental study on the impacts of luminance contrast upon readability in VDT environments. Journal of the Ergonomics Society of Korea 26(2) : 21-33.
Song, Y.W. 2009. Effects of the syllable number, font type, color contrast, display type, letter size and age group on the legibility of the Korean Characters. Journal of the Korean Society of Safety 24(5) : 92-100
Address: Eunsol Lee, Dept. of Industrial Design, KAIST
#373-1 Guseong-dong, Yuseong-gu, Daejeon, Republic of Korea E-mails: [email protected], [email protected]
Figure 8.Self-reporting result of experiment 2