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Infants’ recognition of objects using canonical color
Journal of Experimental Child Psychology 105 (2010) 256–263
Contents lists available at ScienceDirect
Journal of Experimental Child Psychology journal homepage: www.elsevier.com/locate/jecp
Brief Report
Infants’ recognition of objects using canonical color Atsushi Kimura a, Yuji Wada a,*, Jiale Yang b, Yumiko Otsuka c,d, Ippeita Dan a, Tomohiro Masuda a, So Kanazawa d, Masami K. Yamaguchi b,e,* a
Sensory and Cognitive Food Science Laboratory, National Food Research Institute, Ibaraki 305-8642, Japan Department of Psychology, Chuo University, Tokyo 192-0393, Japan Japan Society for the Promotion of Science, Tokyo 102-8472, Japan d Department of Psychology, Japan Women’s University, Kanagawa 214-8565, Japan e Precursor Research for Embryonic Science and Technology, Japan Science and Technology Agency (JST–PRESTO), Saitama 351-0198, Japan b c
a r t i c l e
i n f o
Article history: Received 8 May 2009 Revised 9 November 2009 Available online 16 December 2009 Keywords: Typical color Infant cognition Canonically colored object Child development Color vision Color diagnosticity
a b s t r a c t We explored infants’ ability to recognize the canonical colors of daily objects, including two color-specific objects (human face and fruit) and a non-color-specific object (flower), by using a preferential looking technique. A total of 58 infants between 5 and 8 months of age were tested with a stimulus composed of two color pictures of an object placed side by side: a correctly colored picture (e.g., red strawberry) and an inappropriately colored picture (e.g., green–blue strawberry). The results showed that, overall, the 6- to 8-month-olds showed preference for the correctly colored pictures for color-specific objects, whereas they did not show preference for the correctly colored pictures for the non-color-specific object. The 5-month-olds showed no significant preference for the correctly colored pictures for all object conditions. These findings imply that the recognition of canonical color for objects emerges at 6 months of age. Ó 2009 Elsevier Inc. All rights reserved.
Introduction The canonical, or typical, color of daily objects is one of the dominant cues for object recognition. For example, we can immediately detect ripe strawberries among unripe ones; although they are nearly identical in shape and surface texture, they are different in hue.
* Corresponding authors. E-mail addresses: [email protected] (Y. Wada), [email protected] (M.K. Yamaguchi). 0022-0965/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jecp.2009.11.002
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A number of studies have reported strong effects of canonical color recognition on our color perception and cognition. Hering (1878/1964) was the first to claim that all objects known to us through past experience are seen through the filter of the memory of colors, which are recalled in association with familiar objects. Recently, Hansen, Olkkonen, Walter, and Gegenfurtner (2006) clearly demonstrated that the recognition of canonical color strongly influences the visual perception of objects. They asked their participants to adjust the color of natural fruit and vegetable pictures until they appeared to be achromatic on the isoluminant color space. As a result, surprisingly, the subjective gray points of the pictures were shifted away from the physical gray point in a direction opposite to the canonical color of the objects. Hansen and colleagues concluded that perception of an object’s color was not determined by the incoming sensory data alone but rather was modulated by the prior experience of having seen the natural color of the objects. The aim of the current study was to investigate when the ability to recognize canonical color emerges in development. So far, relatively little is known about the emergence of the association of particular colors with specific objects. Previous studies have tested children between 2 and 5 years of age and reported that the ability to retrieve object–color association develops in accordance with the development of color-naming skills (e.g., Davidoff & Mitchell, 1993; Gleason, Fiske, & Chan, 2004; Mitchell, Davidoff, & Brown, 1996). For example, Mitchell and colleagues (1996) showed that children skilled at identifying the canonical colors of objects appear to use the verbal association between the object name and the color name to choose the correct visual choice. In addition, Gleason and colleagues (2004) also demonstrated that the canonical color choice in 2- to 5-year-olds was partly predicted by the children’s color-labeling skills. These previous studies suggest that a child’s ability to identify an object’s canonical colors not only depends on the visual association but also includes the use of verbal mediation. However, no study has investigated the emergence of visual association between an object and its color during the early stage of the development of canonical color recognition. Apart from the recognition of canonical color, there is evidence that even infants can learn an arbitrary relationship between the color and other attributes of an object. Reardon and Bushnell (1988) demonstrated that 7-month-olds were able to learn an arbitrary association between the color of a container and the taste of the food it contained. In their experiment, infants between 6.5 and 7 months of age were familiarized with sweet and tart foods fed from distinctively colored cups (e.g., sweet applesauce in a red cup and tart applesauce in a blue cup). The results of a subsequent choice trial showed that the infants consistently reached for the color that had been paired with sweet applesauce. If infants can learn an experimentally generated arbitrary relationship between a color and an object, they are likely to be able to learn an association between particular colors and specific objects in daily experience. Thus, we sought to investigate the ability of infants to recognize the canonical colors of daily objects. The ability to identify and discriminate colors is considered as essential to the recognition of canonical color. Both behavioral and electrophysiological studies on infant color vision have provided evidence that nearly all of the retinal components necessary for trichromatic vision are functional by at least 4 weeks of age (Knoblauch, Bieber, & Werner, 1998; Volbrecht & Werner, 1987) and that the neural pathways for distinguishing tritan stimuli (L–M cone pathway and S cone pathway) are functional by around 4 months of age (e.g., Hamer, Alexander, & Teller, 1982; Peeples & Teller, 1978; Suttle, Banks, & Graf, 2002). These results suggest that infants have trichromatic color vision by at least 4 months of age. Because of the development of low-level sensitivity to chromatic information as summarized above, most of the studies on infant color perception and cognition have examined infants over 5 months of age (e.g., Okamura, Kanazawa, & Yamaguchi, 2007). Considering this and the learning abilities during infancy as suggested by Reardon and Bushnell (1988), we hypothesized that the association between daily objects and their canonical colors emerges between 5 and 7 months of age. In the current study, we explored infants’ ability to identify the canonical colors of daily objects by testing whether 5- to 8-month-olds discriminate canonically colored objects from inappropriately colored ones. By using a preferential looking technique, we recorded and compared infants’ preference between two pictures of the same object: one colored correctly and the other colored inappropriately.
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In this study, human faces and fruits were chosen as the color-specific objects, and flowers were chosen as the non-color-specific objects. A systematic preference for the color-specific objects could be interpreted as evidence of canonical color recognition. Method Participants The sample consisted of a total of 58 infants: 13 5-month-olds (5 girls and 8 boys, mean age = 151 days, SD = 7.7), 15 6-month-olds (7 girls and 8 boys, mean age = 178 days, SD = 8.3), 15 7month-olds (9 girls and 6 boys, mean age = 209 days, SD = 8.0), and 15 8-month-olds (10 girls and 5 boys, mean age = 239 days, SD = 5.7). All infants were full-term at birth and healthy at the time of testing. An additional 29 infants were tested but excluded from data analysis because of fussiness (15), inattentiveness (11), or equipment failure (3). Participants’ caregivers provided written informed consent according to the guidelines specified by the ethics committee at the National Food Research Institute, and the study was conducted according to the Declaration of Helsinki. Due to privacy constraints, we could not obtain any information about participants’ family history of color deficiency. However, we can assume that protanopes and deuteranopes could distinguish between a correctly colored picture and an inappropriately colored picture in the current study because, theoretically, they have the ability to discriminate yellow and blue. Stimuli Stimuli were created from digitized color images of three Japanese female full frontal faces, three side view fruits (a banana, a strawberry, and a section of watermelon), and three frontal view flowers (see Fig. 1). All faces were unfamiliar to the participants, with models posing with neutral expressions. Using Adobe Photoshop software, face images were cropped in facial contour with hair and ears. The inappropriately colored picture for each stimulus was created with a 180° hue inversion using the color adjustment function of Adobe Photoshop CS2 to change the hues of pictures to their opposite colors
Fig. 1. Stimuli used in this study. Mean CIE 1931 (x, y) chromaticity coordinates and mean luminance of picture are shown under each picture (CIEx, CIEy, and mean luminance [cd/m2], respectively). In the experiment, infants were tested for recognition of correctly colored and inappropriately colored images for each object.
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in the hue luminance and saturation (HLS) color space. By changing a picture’s hues, the mean luminance of the inappropriately colored picture was also shifted away from that of the correctly colored picture (see Fig. 1). All stimuli appeared on a white background whose CIE 1931 (x, y) chromaticity coordinates and mean luminance were 0.31, 0.32, and 91.1 cd/m2, respectively. Stimuli were presented on a CRT monitor in side-by-side pairs of images of the same object, one of which was colored correctly and one of which was colored inappropriately. The size of each stimulus was approximately 9.8 9.8 cm (14.0 14.0 degrees). The distance between stimuli was 15.0 cm (23.2 degrees). We conducted a separate pilot survey with young Japanese adults to test the validity of our assumption that the color diagnosticity was higher in faces and fruit than in flowers. A total of 113 university students (76 women and 37 men) participated in this survey, where two pictures of the same object—one in its original color and the other in its opposite color—were presented side by side on a screen as in the main experiment. Participants were asked to rate which image was more appropriate for the object using a 6-point scale ranging from the left image is extremely appropriate (1) to the right image is extremely appropriate (6), with the scale numbers not being visible to the participants. The position of the correctly colored image was randomized. When analyzing data, if the image with original color was presented on the left side, the scale was reversed. The results of the analysis of variance (ANOVA) with a factor of object (face, fruit, or flower) on the appropriateness of the correctly colored pictures revealed a significant main effect of object, F(2, 224) = 93.59, p < .001, gp2 = .46. The appropriateness of the correctly colored pictures of fruits (M = 5.71, SD = 0.55) was significantly higher than that of faces (M = 5.35, SD = 0.75) and flowers (M = 4.67, SD = 0.72), p < .01, and the appropriateness of the correctly colored pictures of faces was higher than that of flowers, p < .01. These results verify our assumption that fruits and faces have a higher color diagnosticity than flowers. Apparatus All stimuli were presented on a 22-inch CRT monitor (Mitsubishi Diamond Pro 2070SB) calibrated with a Totoku-Pro Calix Calibrator. The resolution of the CRT was set at 1024 768 pixels with an 8bit color mode. The refresh rate of the CRT was 85 Hz. One speaker was located to each side of the CRT. There was a charge-coupled device (CCD) camera just below the monitor screen with which each infant’s behavior was videotaped throughout the experiment. The experimenter observed the infant’s behavior via a television monitor connected to the camera. The presentation of stimulus and sound was controlled by a computer (Dospara Prime Galleria). Procedure In the experimental booth, each infant sat on her or his caretaker’s lap in front of the CRT. The viewing distance was approximately 40 cm. The caregiver was asked not to look at the monitor. Each trial began with the presentation of a colorful fixation figure (approximately 9.0 9.0 degrees of visual angle) at the center of the CRT accompanied by a short beeping sound to attract the participant’s attention. When the infant looked at the center of the screen, the fixation disappeared and a stimulus was presented. Each stimulus remained for 15 s. Each infant was exposed to two trials for each of three conditions (face, fruit, and flower). In each condition, the position of the correctly colored picture was reversed across the trials. The order of the two trials was randomized for each infant. Throughout the experiment, the behavior of the infant and caregiver was videotaped. Data analysis One observer, who was unaware of the stimulus identity, measured the infant’s looking time based on an offline video recorded during the experiments. The observer recorded the infant’s looking time for the right or left presentation field by pressing one of two keys when the infant was looking at the relevant field. When the infant looked away from the presentation field, no recording was made. To compute interobserver agreement, a second observer’s measurement of infant looking time was
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obtained for approximately 30% of the data set. Interobserver agreement was r = .84 throughout the experiments. The looking times were summed across the two trials for each condition. A 3 4 (object infants’ age) ANOVA was performed on the total looking time. When significant effects were detected, post hoc multiple comparisons of means were performed using Tukey’s honestly significant difference (HSD) test. Because our main interest was to see whether infants of each age looked longer at one of the test stimuli over the other, we calculated the infants’ preference for the correctly colored picture using the following equation: preference for target = looking time for correctly colored picture/(looking time for ‘‘right” + looking time for ‘‘left”). To examine the significance of the mean preference for a target, a two-tailed t test versus chance (.5) was performed. The r was calculated as the effect size. Results Total looking time To determine whether the kind of object and the infants’ age differentially affected the looking time, we conducted a two-way ANOVA for the total looking time with object and infants’ age as within- and between-participant factors, respectively. We found a significant main effect of object, F(2, 108) = 18.04, p < .001, gp2 = .25. Post hoc analysis revealed that the total looking times for faces were longer than those for fruits and flowers, both ps < .01. Also, the total looking times for flowers were longer than those for fruits, p < .05. We did not find any significant difference in the total looking times among the four age groups, nor did we find any interaction among factors. Preferential looking behavior Fig. 2 shows the mean preference for the correctly colored target in each experimental condition. Two-tailed t tests on the preference for the correctly colored target versus the chance level (.5) showed that the 6-month-olds significantly preferred the correctly colored pictures under the face condition, t(14) = 3.79, p < .01, r = .71, and under the fruit condition, t(14) = 4.13, p < .01, r = .74, whereas there was no significant preference under the flower condition, t(14) = 0.64. The 7-month-olds significantly preferred the correctly colored pictures under the face condition, t(14) = 2.88, p < .05, r = .61, whereas
Preference for correctly colored object
0.7
5 months
6 months
7 months
8 months
** 0.6
* **
*
n.s.
* n.s. n.s.
0.5 n.s.
n.s.
n.s.
Face
n.s.
Fruit
Flower
0.4 Fig. 2. Preference (mean rates of duration of looking time) for correctly colored images in each condition. Two-tailed t test versus chance: *p < .05; **p < .01; n.s., not significant. Error bars indicate the standard errors (5 months: n = 13; 6 months: n = 15; 7 months: n = 15; 8 months: n = 15).
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there were no significant preferences under the flower condition, t(14) = 0.60, or under the fruit condition, t(14) = 0.40. As with the 6-month-olds, the 8-month-olds significantly preferred the correctly colored pictures under the face condition, t(14) = 2.59, p < .05, r = .57, and under the fruit condition, t(14) = 2.83, p < .05, r = .60, whereas there was no significant preference under the flower condition, t(14) = 1.94, p = .07. The youngest age group showed no significant preference for the correctly colored pictures under any object condition.
Discussion Using the preferential looking technique, we explored infants’ recognition of the canonical color of daily objects. In this study, the 6-, 7-, and 8-month-olds showed preference for the correctly colored pictures of faces, and the 6- and 8-month-olds also showed preference for the correctly colored pictures of fruit. However, infants in all age groups did not show preference for the correctly colored images of flowers, whose color diagnosticities were lower than those of faces and fruit. These results suggest that the recognition of the canonical color of objects emerges at 6 months of age. One may argue that there is a possibility that color-related biases were responsible for the infants’ preferences for the correctly colored pictures because the correct colors of stimuli in all conditions were biased toward warm hues, especially yellows and reds. Previous studies have revealed that 3to 6-month-olds show visual preferences among chromatic stimuli. Adams (1987) found that 3month-olds prefer yellow and red to blue and green. On the other hand, it has been reported that 4- to 6-month-olds prefer blue to yellow (Bornstein, 1975; Zemach, Chang, & Teller, 2007). These reports seem to imply that color preference changes with age. If this is the case, it can be assumed that our participants of 5 and 6 months of age would prefer blue, which was a dominant hue of the inappropriately colored pictures in the current study, rather than yellow. However, our participants actually showed a preference for the correctly colored pictures of faces and fruits whose original colors were yellow and red. Furthermore, in the flower condition, no age group examined in the current study showed preferences for any specific hues despite the fact that the canonical colors of the pictures of flowers were equivalent to those of fruits (Fig. 1). For the same reason, our results cannot be explained according to luminance-related preferences in infants: The procedure used to invert hues for the inappropriately colored pictures also led to luminance differences between the correctly and inappropriately colored pictures. Our participants, however, showed different patterns of preference for the fruit and flower conditions, whereas these two conditions had similar variation of luminance relationship between the correctly and inappropriately colored pictures (see Fig. 1). Thus, the preference for the correctly colored picture in color-specific objects in the current study cannot be explained by general preferences for specific hues or the luminance relationship of images. Rather, our results suggest that infants develop a visual association between object and color for faces and fruits and that they prefer the objects in their canonical colors. To elucidate the relationship between the ability to recognize canonical color and preferential looking behavior in infants, further experiments tightly controlling stimuli in hue and luminance are required. A promising strategy would be the use of artificial objects (e.g., crayons, vehicles) as non-color-specific objects because artificial objects may be less color specific than natural ones. This would enable stricter control of color between color-specific and non-color-specific objects. Our findings suggest that the recognition of canonical color in natural objects becomes apparent at 6 months of age. This phenomenon is in accordance not only with the emergence of trichromatic color vision (Hamer et al., 1982; Peeples & Teller, 1978; Suttle et al., 2002) but also with the emergence of color constancy during infancy. Several studies have shown that color constancy emerges around 5 months of age (Dannemiller, 1989; Dannemiller & Hanko, 1987). The perceived colors of objects remain approximately the same despite frequent changes in the illuminant. A lack of color constancy would mean that the perceived color of an object would depend on the source of illumination and could complicate the process of object identification. Thus, color constancy might be related to development of the object–color association. Another candidate that might relate to canonical color recognition is the categorical perception of hue, which enables the identification of the object category among objects with slightly different properties of color. Several studies have shown that the categor-
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ical perception of hue emerges at around 4 months of age (e.g., Bornstein, Kessen, & Weiskopf, 1976; Franklin, Pilling, & Davies, 2005). Our results imply that at around 6 months of age, infants begin to associate particular colors with specific objects, with the development of functions being related to the basis of color perception such as categorical perception of hue and color constancy. In the current study, however, infants displayed an incoherent pattern of performance between the two color-specific objects adopted. The 6- to 8-month-olds showed consistent preferences for the canonically colored pictures of the face target. On the other hand, the 7-month-olds did not show preference for the canonically colored pictures of the fruit target, whereas the 6- and 8-month-olds did. It remains unclear why infants in this study showed such a different pattern of preference between faces and fruit. One possible reason is differences in infants’ preferences regarding these objects. As a number of works have reported, infants have strong preferences for face images, whereas they might not have had enough opportunities to develop special interest in fruits given that they likely have little autonomous experience with fruits. In fact, the total looking times were shorter for the fruit and flower conditions than those for the face condition in the current experiment. However, we obtained no measure of infants’ experience with fruits (including toys, pictures, and illustrations of fruits), so we cannot be certain whether fruits were as familiar as human faces among the participants. This prevented us from determining which factors in our experimental settings led to the current results. To make clear the developmental process of the canonical color recognition in nonface objects, a further study, using targets that are equally familiar to infants participating in the study, is necessary. The current results provide the first behavioral evidence of the functional association between objects and colors in visual processing during early infancy. The ability to identify canonical colors of objects is not solely a function of learned association in visual experience but rather is mediated by verbal codes during the later stages of development (Beauvois, 1982; Davidoff & Mitchell, 1993; Mitchell et al., 1996). Further research is necessary to make clear when and how infants integrate their visual experience and verbal nature to represent the canonical color of objects. Acknowledgments We are grateful to the participants and their parents. We thank Yuko Hibi, Megumi Kobayashi, Emi Nakato, Midori Takashima, Aki Tsuruhara, Yuka Yamazaki, Sho-ichi Goto, and Kentaro Takahashi for their assistance. This work was supported in part by a Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (18300090 awarded to M.K.Y.), Grants-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (20730489 awarded to Y.W. and 20700588 awarded to A.K.), and the Program for Promotion of Basic Research Activities for Innovative Bioscience (PROBRAIN). References Adams, R. J. (1987). An evaluation of color preference in early infancy. Infant Behavior and Development, 10, 143–150. Beauvois, M.-F. (1982). Optic aphasia: A process of interaction between vision and language. Philosophical Transactions of the Royal Society pf London B, 298, 35–47. Bornstein, M. H. (1975). Qualities of color vision in infancy. Journal of Experimental Social Psychology, 19, 401–419. Bornstein, M. H., Kessen, W., & Weiskopf, S. (1976). Color vision and hue categorization in young human infants. Journal of Experimental Psychology: Human Perception and Performance, 2, 115–129. Dannemiller, J. L. (1989). A test of color constancy in 9- and 20-week-old human infants following simulated illuminant changes. Developmental Psychology, 25, 171–184. Dannemiller, J. L., & Hanko, S. A. (1987). A test of color constancy in 4-month-old human infants. Journal of Experimental Child Psychology, 44, 255–267. Davidoff, J., & Mitchell, P. (1993). The colour cognition of children. Cognition, 48, 121–137. Franklin, A., Pilling, M., & Davies, I. (2005). The nature of infant color categorization: Evidence from eye movements on a target detection task. Journal of Experimental Child Psychology, 91, 227–248. Gleason, T. R., Fiske, K. E., & Chan, R. K. (2004). The verbal nature of representations of the canonical colors of objects. Cognitive Development, 19, 1–14. Hamer, R. D., Alexander, K. R., & Teller, D. Y. (1982). Rayleigh discriminations in young human infants. Vision Research, 22, 575–587. Hansen, T., Olkkonen, M., Walter, S., & Gegenfurtner, K. R. (2006). Memory modulates color appearance. Nature Neuroscience, 9, 1367–1368. Hering, E. (1964). Outlines of a theory of the light sense. In L. M. Hurvich & D. Jameson (Eds.), Trans. Cambridge, MA: Harvard University Press [Original work published 1878].
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Knoblauch, K., Bieber, M. L., & Werner, J. S. (1998). M- and L-cones in early infancy: I. VEP responses to receptor-isolating stimuli at 4- and 8-weeks of age. Vision Research, 38, 1753–1764. Mitchell, P., Davidoff, J., & Brown, C. (1996). Young children’s ability to process object colour: Coloured pictogens and verbal mediation. British Journal of Developmental Psychology, 14, 339–354. Okamura, H., Kanazawa, S., & Yamaguchi, K. M. (2007). Development of chromatic induction in infancy. Infant and Child Development, 16, 629–648. Peeples, D. R., & Teller, D. Y. (1978). White-adapted photopic spectral sensitivity in human infants. Vision Research, 18, 49–53. Reardon, P., & Bushnell, E. W. (1988). Infants’ sensitivity to arbitrary pairings of color and taste. Infant Behavior and Development, 11, 245–250. Suttle, C. M., Banks, M. S., & Graf, E. W. (2002). FPL and sweep VEP to tritan stimuli in young human infants. Vision Research, 42, 2879–2891. Volbrecht, V. J., & Werner, J. S. (1987). Isolation of short-wavelength-sensitive cone photoreceptors in 4- to 6-week-old human infants. Vision Research, 25, 821–831. Zemach, I., Chang, S., & Teller, D. Y. (2007). Infant color vision: Prediction of infants’ spontaneous color preferences. Vision Research, 47, 1368–1381.
Contents lists available at ScienceDirect
Journal of Experimental Child Psychology journal homepage: www.elsevier.com/locate/jecp
Brief Report
Infants’ recognition of objects using canonical color Atsushi Kimura a, Yuji Wada a,*, Jiale Yang b, Yumiko Otsuka c,d, Ippeita Dan a, Tomohiro Masuda a, So Kanazawa d, Masami K. Yamaguchi b,e,* a
Sensory and Cognitive Food Science Laboratory, National Food Research Institute, Ibaraki 305-8642, Japan Department of Psychology, Chuo University, Tokyo 192-0393, Japan Japan Society for the Promotion of Science, Tokyo 102-8472, Japan d Department of Psychology, Japan Women’s University, Kanagawa 214-8565, Japan e Precursor Research for Embryonic Science and Technology, Japan Science and Technology Agency (JST–PRESTO), Saitama 351-0198, Japan b c
a r t i c l e
i n f o
Article history: Received 8 May 2009 Revised 9 November 2009 Available online 16 December 2009 Keywords: Typical color Infant cognition Canonically colored object Child development Color vision Color diagnosticity
a b s t r a c t We explored infants’ ability to recognize the canonical colors of daily objects, including two color-specific objects (human face and fruit) and a non-color-specific object (flower), by using a preferential looking technique. A total of 58 infants between 5 and 8 months of age were tested with a stimulus composed of two color pictures of an object placed side by side: a correctly colored picture (e.g., red strawberry) and an inappropriately colored picture (e.g., green–blue strawberry). The results showed that, overall, the 6- to 8-month-olds showed preference for the correctly colored pictures for color-specific objects, whereas they did not show preference for the correctly colored pictures for the non-color-specific object. The 5-month-olds showed no significant preference for the correctly colored pictures for all object conditions. These findings imply that the recognition of canonical color for objects emerges at 6 months of age. Ó 2009 Elsevier Inc. All rights reserved.
Introduction The canonical, or typical, color of daily objects is one of the dominant cues for object recognition. For example, we can immediately detect ripe strawberries among unripe ones; although they are nearly identical in shape and surface texture, they are different in hue.
* Corresponding authors. E-mail addresses: [email protected] (Y. Wada), [email protected] (M.K. Yamaguchi). 0022-0965/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jecp.2009.11.002
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A number of studies have reported strong effects of canonical color recognition on our color perception and cognition. Hering (1878/1964) was the first to claim that all objects known to us through past experience are seen through the filter of the memory of colors, which are recalled in association with familiar objects. Recently, Hansen, Olkkonen, Walter, and Gegenfurtner (2006) clearly demonstrated that the recognition of canonical color strongly influences the visual perception of objects. They asked their participants to adjust the color of natural fruit and vegetable pictures until they appeared to be achromatic on the isoluminant color space. As a result, surprisingly, the subjective gray points of the pictures were shifted away from the physical gray point in a direction opposite to the canonical color of the objects. Hansen and colleagues concluded that perception of an object’s color was not determined by the incoming sensory data alone but rather was modulated by the prior experience of having seen the natural color of the objects. The aim of the current study was to investigate when the ability to recognize canonical color emerges in development. So far, relatively little is known about the emergence of the association of particular colors with specific objects. Previous studies have tested children between 2 and 5 years of age and reported that the ability to retrieve object–color association develops in accordance with the development of color-naming skills (e.g., Davidoff & Mitchell, 1993; Gleason, Fiske, & Chan, 2004; Mitchell, Davidoff, & Brown, 1996). For example, Mitchell and colleagues (1996) showed that children skilled at identifying the canonical colors of objects appear to use the verbal association between the object name and the color name to choose the correct visual choice. In addition, Gleason and colleagues (2004) also demonstrated that the canonical color choice in 2- to 5-year-olds was partly predicted by the children’s color-labeling skills. These previous studies suggest that a child’s ability to identify an object’s canonical colors not only depends on the visual association but also includes the use of verbal mediation. However, no study has investigated the emergence of visual association between an object and its color during the early stage of the development of canonical color recognition. Apart from the recognition of canonical color, there is evidence that even infants can learn an arbitrary relationship between the color and other attributes of an object. Reardon and Bushnell (1988) demonstrated that 7-month-olds were able to learn an arbitrary association between the color of a container and the taste of the food it contained. In their experiment, infants between 6.5 and 7 months of age were familiarized with sweet and tart foods fed from distinctively colored cups (e.g., sweet applesauce in a red cup and tart applesauce in a blue cup). The results of a subsequent choice trial showed that the infants consistently reached for the color that had been paired with sweet applesauce. If infants can learn an experimentally generated arbitrary relationship between a color and an object, they are likely to be able to learn an association between particular colors and specific objects in daily experience. Thus, we sought to investigate the ability of infants to recognize the canonical colors of daily objects. The ability to identify and discriminate colors is considered as essential to the recognition of canonical color. Both behavioral and electrophysiological studies on infant color vision have provided evidence that nearly all of the retinal components necessary for trichromatic vision are functional by at least 4 weeks of age (Knoblauch, Bieber, & Werner, 1998; Volbrecht & Werner, 1987) and that the neural pathways for distinguishing tritan stimuli (L–M cone pathway and S cone pathway) are functional by around 4 months of age (e.g., Hamer, Alexander, & Teller, 1982; Peeples & Teller, 1978; Suttle, Banks, & Graf, 2002). These results suggest that infants have trichromatic color vision by at least 4 months of age. Because of the development of low-level sensitivity to chromatic information as summarized above, most of the studies on infant color perception and cognition have examined infants over 5 months of age (e.g., Okamura, Kanazawa, & Yamaguchi, 2007). Considering this and the learning abilities during infancy as suggested by Reardon and Bushnell (1988), we hypothesized that the association between daily objects and their canonical colors emerges between 5 and 7 months of age. In the current study, we explored infants’ ability to identify the canonical colors of daily objects by testing whether 5- to 8-month-olds discriminate canonically colored objects from inappropriately colored ones. By using a preferential looking technique, we recorded and compared infants’ preference between two pictures of the same object: one colored correctly and the other colored inappropriately.
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In this study, human faces and fruits were chosen as the color-specific objects, and flowers were chosen as the non-color-specific objects. A systematic preference for the color-specific objects could be interpreted as evidence of canonical color recognition. Method Participants The sample consisted of a total of 58 infants: 13 5-month-olds (5 girls and 8 boys, mean age = 151 days, SD = 7.7), 15 6-month-olds (7 girls and 8 boys, mean age = 178 days, SD = 8.3), 15 7month-olds (9 girls and 6 boys, mean age = 209 days, SD = 8.0), and 15 8-month-olds (10 girls and 5 boys, mean age = 239 days, SD = 5.7). All infants were full-term at birth and healthy at the time of testing. An additional 29 infants were tested but excluded from data analysis because of fussiness (15), inattentiveness (11), or equipment failure (3). Participants’ caregivers provided written informed consent according to the guidelines specified by the ethics committee at the National Food Research Institute, and the study was conducted according to the Declaration of Helsinki. Due to privacy constraints, we could not obtain any information about participants’ family history of color deficiency. However, we can assume that protanopes and deuteranopes could distinguish between a correctly colored picture and an inappropriately colored picture in the current study because, theoretically, they have the ability to discriminate yellow and blue. Stimuli Stimuli were created from digitized color images of three Japanese female full frontal faces, three side view fruits (a banana, a strawberry, and a section of watermelon), and three frontal view flowers (see Fig. 1). All faces were unfamiliar to the participants, with models posing with neutral expressions. Using Adobe Photoshop software, face images were cropped in facial contour with hair and ears. The inappropriately colored picture for each stimulus was created with a 180° hue inversion using the color adjustment function of Adobe Photoshop CS2 to change the hues of pictures to their opposite colors
Fig. 1. Stimuli used in this study. Mean CIE 1931 (x, y) chromaticity coordinates and mean luminance of picture are shown under each picture (CIEx, CIEy, and mean luminance [cd/m2], respectively). In the experiment, infants were tested for recognition of correctly colored and inappropriately colored images for each object.
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in the hue luminance and saturation (HLS) color space. By changing a picture’s hues, the mean luminance of the inappropriately colored picture was also shifted away from that of the correctly colored picture (see Fig. 1). All stimuli appeared on a white background whose CIE 1931 (x, y) chromaticity coordinates and mean luminance were 0.31, 0.32, and 91.1 cd/m2, respectively. Stimuli were presented on a CRT monitor in side-by-side pairs of images of the same object, one of which was colored correctly and one of which was colored inappropriately. The size of each stimulus was approximately 9.8 9.8 cm (14.0 14.0 degrees). The distance between stimuli was 15.0 cm (23.2 degrees). We conducted a separate pilot survey with young Japanese adults to test the validity of our assumption that the color diagnosticity was higher in faces and fruit than in flowers. A total of 113 university students (76 women and 37 men) participated in this survey, where two pictures of the same object—one in its original color and the other in its opposite color—were presented side by side on a screen as in the main experiment. Participants were asked to rate which image was more appropriate for the object using a 6-point scale ranging from the left image is extremely appropriate (1) to the right image is extremely appropriate (6), with the scale numbers not being visible to the participants. The position of the correctly colored image was randomized. When analyzing data, if the image with original color was presented on the left side, the scale was reversed. The results of the analysis of variance (ANOVA) with a factor of object (face, fruit, or flower) on the appropriateness of the correctly colored pictures revealed a significant main effect of object, F(2, 224) = 93.59, p < .001, gp2 = .46. The appropriateness of the correctly colored pictures of fruits (M = 5.71, SD = 0.55) was significantly higher than that of faces (M = 5.35, SD = 0.75) and flowers (M = 4.67, SD = 0.72), p < .01, and the appropriateness of the correctly colored pictures of faces was higher than that of flowers, p < .01. These results verify our assumption that fruits and faces have a higher color diagnosticity than flowers. Apparatus All stimuli were presented on a 22-inch CRT monitor (Mitsubishi Diamond Pro 2070SB) calibrated with a Totoku-Pro Calix Calibrator. The resolution of the CRT was set at 1024 768 pixels with an 8bit color mode. The refresh rate of the CRT was 85 Hz. One speaker was located to each side of the CRT. There was a charge-coupled device (CCD) camera just below the monitor screen with which each infant’s behavior was videotaped throughout the experiment. The experimenter observed the infant’s behavior via a television monitor connected to the camera. The presentation of stimulus and sound was controlled by a computer (Dospara Prime Galleria). Procedure In the experimental booth, each infant sat on her or his caretaker’s lap in front of the CRT. The viewing distance was approximately 40 cm. The caregiver was asked not to look at the monitor. Each trial began with the presentation of a colorful fixation figure (approximately 9.0 9.0 degrees of visual angle) at the center of the CRT accompanied by a short beeping sound to attract the participant’s attention. When the infant looked at the center of the screen, the fixation disappeared and a stimulus was presented. Each stimulus remained for 15 s. Each infant was exposed to two trials for each of three conditions (face, fruit, and flower). In each condition, the position of the correctly colored picture was reversed across the trials. The order of the two trials was randomized for each infant. Throughout the experiment, the behavior of the infant and caregiver was videotaped. Data analysis One observer, who was unaware of the stimulus identity, measured the infant’s looking time based on an offline video recorded during the experiments. The observer recorded the infant’s looking time for the right or left presentation field by pressing one of two keys when the infant was looking at the relevant field. When the infant looked away from the presentation field, no recording was made. To compute interobserver agreement, a second observer’s measurement of infant looking time was
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obtained for approximately 30% of the data set. Interobserver agreement was r = .84 throughout the experiments. The looking times were summed across the two trials for each condition. A 3 4 (object infants’ age) ANOVA was performed on the total looking time. When significant effects were detected, post hoc multiple comparisons of means were performed using Tukey’s honestly significant difference (HSD) test. Because our main interest was to see whether infants of each age looked longer at one of the test stimuli over the other, we calculated the infants’ preference for the correctly colored picture using the following equation: preference for target = looking time for correctly colored picture/(looking time for ‘‘right” + looking time for ‘‘left”). To examine the significance of the mean preference for a target, a two-tailed t test versus chance (.5) was performed. The r was calculated as the effect size. Results Total looking time To determine whether the kind of object and the infants’ age differentially affected the looking time, we conducted a two-way ANOVA for the total looking time with object and infants’ age as within- and between-participant factors, respectively. We found a significant main effect of object, F(2, 108) = 18.04, p < .001, gp2 = .25. Post hoc analysis revealed that the total looking times for faces were longer than those for fruits and flowers, both ps < .01. Also, the total looking times for flowers were longer than those for fruits, p < .05. We did not find any significant difference in the total looking times among the four age groups, nor did we find any interaction among factors. Preferential looking behavior Fig. 2 shows the mean preference for the correctly colored target in each experimental condition. Two-tailed t tests on the preference for the correctly colored target versus the chance level (.5) showed that the 6-month-olds significantly preferred the correctly colored pictures under the face condition, t(14) = 3.79, p < .01, r = .71, and under the fruit condition, t(14) = 4.13, p < .01, r = .74, whereas there was no significant preference under the flower condition, t(14) = 0.64. The 7-month-olds significantly preferred the correctly colored pictures under the face condition, t(14) = 2.88, p < .05, r = .61, whereas
Preference for correctly colored object
0.7
5 months
6 months
7 months
8 months
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n.s.
* n.s. n.s.
0.5 n.s.
n.s.
n.s.
Face
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Flower
0.4 Fig. 2. Preference (mean rates of duration of looking time) for correctly colored images in each condition. Two-tailed t test versus chance: *p < .05; **p < .01; n.s., not significant. Error bars indicate the standard errors (5 months: n = 13; 6 months: n = 15; 7 months: n = 15; 8 months: n = 15).
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there were no significant preferences under the flower condition, t(14) = 0.60, or under the fruit condition, t(14) = 0.40. As with the 6-month-olds, the 8-month-olds significantly preferred the correctly colored pictures under the face condition, t(14) = 2.59, p < .05, r = .57, and under the fruit condition, t(14) = 2.83, p < .05, r = .60, whereas there was no significant preference under the flower condition, t(14) = 1.94, p = .07. The youngest age group showed no significant preference for the correctly colored pictures under any object condition.
Discussion Using the preferential looking technique, we explored infants’ recognition of the canonical color of daily objects. In this study, the 6-, 7-, and 8-month-olds showed preference for the correctly colored pictures of faces, and the 6- and 8-month-olds also showed preference for the correctly colored pictures of fruit. However, infants in all age groups did not show preference for the correctly colored images of flowers, whose color diagnosticities were lower than those of faces and fruit. These results suggest that the recognition of the canonical color of objects emerges at 6 months of age. One may argue that there is a possibility that color-related biases were responsible for the infants’ preferences for the correctly colored pictures because the correct colors of stimuli in all conditions were biased toward warm hues, especially yellows and reds. Previous studies have revealed that 3to 6-month-olds show visual preferences among chromatic stimuli. Adams (1987) found that 3month-olds prefer yellow and red to blue and green. On the other hand, it has been reported that 4- to 6-month-olds prefer blue to yellow (Bornstein, 1975; Zemach, Chang, & Teller, 2007). These reports seem to imply that color preference changes with age. If this is the case, it can be assumed that our participants of 5 and 6 months of age would prefer blue, which was a dominant hue of the inappropriately colored pictures in the current study, rather than yellow. However, our participants actually showed a preference for the correctly colored pictures of faces and fruits whose original colors were yellow and red. Furthermore, in the flower condition, no age group examined in the current study showed preferences for any specific hues despite the fact that the canonical colors of the pictures of flowers were equivalent to those of fruits (Fig. 1). For the same reason, our results cannot be explained according to luminance-related preferences in infants: The procedure used to invert hues for the inappropriately colored pictures also led to luminance differences between the correctly and inappropriately colored pictures. Our participants, however, showed different patterns of preference for the fruit and flower conditions, whereas these two conditions had similar variation of luminance relationship between the correctly and inappropriately colored pictures (see Fig. 1). Thus, the preference for the correctly colored picture in color-specific objects in the current study cannot be explained by general preferences for specific hues or the luminance relationship of images. Rather, our results suggest that infants develop a visual association between object and color for faces and fruits and that they prefer the objects in their canonical colors. To elucidate the relationship between the ability to recognize canonical color and preferential looking behavior in infants, further experiments tightly controlling stimuli in hue and luminance are required. A promising strategy would be the use of artificial objects (e.g., crayons, vehicles) as non-color-specific objects because artificial objects may be less color specific than natural ones. This would enable stricter control of color between color-specific and non-color-specific objects. Our findings suggest that the recognition of canonical color in natural objects becomes apparent at 6 months of age. This phenomenon is in accordance not only with the emergence of trichromatic color vision (Hamer et al., 1982; Peeples & Teller, 1978; Suttle et al., 2002) but also with the emergence of color constancy during infancy. Several studies have shown that color constancy emerges around 5 months of age (Dannemiller, 1989; Dannemiller & Hanko, 1987). The perceived colors of objects remain approximately the same despite frequent changes in the illuminant. A lack of color constancy would mean that the perceived color of an object would depend on the source of illumination and could complicate the process of object identification. Thus, color constancy might be related to development of the object–color association. Another candidate that might relate to canonical color recognition is the categorical perception of hue, which enables the identification of the object category among objects with slightly different properties of color. Several studies have shown that the categor-
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ical perception of hue emerges at around 4 months of age (e.g., Bornstein, Kessen, & Weiskopf, 1976; Franklin, Pilling, & Davies, 2005). Our results imply that at around 6 months of age, infants begin to associate particular colors with specific objects, with the development of functions being related to the basis of color perception such as categorical perception of hue and color constancy. In the current study, however, infants displayed an incoherent pattern of performance between the two color-specific objects adopted. The 6- to 8-month-olds showed consistent preferences for the canonically colored pictures of the face target. On the other hand, the 7-month-olds did not show preference for the canonically colored pictures of the fruit target, whereas the 6- and 8-month-olds did. It remains unclear why infants in this study showed such a different pattern of preference between faces and fruit. One possible reason is differences in infants’ preferences regarding these objects. As a number of works have reported, infants have strong preferences for face images, whereas they might not have had enough opportunities to develop special interest in fruits given that they likely have little autonomous experience with fruits. In fact, the total looking times were shorter for the fruit and flower conditions than those for the face condition in the current experiment. However, we obtained no measure of infants’ experience with fruits (including toys, pictures, and illustrations of fruits), so we cannot be certain whether fruits were as familiar as human faces among the participants. This prevented us from determining which factors in our experimental settings led to the current results. To make clear the developmental process of the canonical color recognition in nonface objects, a further study, using targets that are equally familiar to infants participating in the study, is necessary. The current results provide the first behavioral evidence of the functional association between objects and colors in visual processing during early infancy. The ability to identify canonical colors of objects is not solely a function of learned association in visual experience but rather is mediated by verbal codes during the later stages of development (Beauvois, 1982; Davidoff & Mitchell, 1993; Mitchell et al., 1996). Further research is necessary to make clear when and how infants integrate their visual experience and verbal nature to represent the canonical color of objects. Acknowledgments We are grateful to the participants and their parents. We thank Yuko Hibi, Megumi Kobayashi, Emi Nakato, Midori Takashima, Aki Tsuruhara, Yuka Yamazaki, Sho-ichi Goto, and Kentaro Takahashi for their assistance. This work was supported in part by a Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (18300090 awarded to M.K.Y.), Grants-in-Aid for Young Scientists (B) from the Japan Society for the Promotion of Science (20730489 awarded to Y.W. and 20700588 awarded to A.K.), and the Program for Promotion of Basic Research Activities for Innovative Bioscience (PROBRAIN). References Adams, R. J. (1987). An evaluation of color preference in early infancy. Infant Behavior and Development, 10, 143–150. Beauvois, M.-F. (1982). Optic aphasia: A process of interaction between vision and language. Philosophical Transactions of the Royal Society pf London B, 298, 35–47. Bornstein, M. H. (1975). Qualities of color vision in infancy. Journal of Experimental Social Psychology, 19, 401–419. Bornstein, M. H., Kessen, W., & Weiskopf, S. (1976). Color vision and hue categorization in young human infants. Journal of Experimental Psychology: Human Perception and Performance, 2, 115–129. Dannemiller, J. L. (1989). A test of color constancy in 9- and 20-week-old human infants following simulated illuminant changes. Developmental Psychology, 25, 171–184. Dannemiller, J. L., & Hanko, S. A. (1987). A test of color constancy in 4-month-old human infants. Journal of Experimental Child Psychology, 44, 255–267. Davidoff, J., & Mitchell, P. (1993). The colour cognition of children. Cognition, 48, 121–137. Franklin, A., Pilling, M., & Davies, I. (2005). The nature of infant color categorization: Evidence from eye movements on a target detection task. Journal of Experimental Child Psychology, 91, 227–248. Gleason, T. R., Fiske, K. E., & Chan, R. K. (2004). The verbal nature of representations of the canonical colors of objects. Cognitive Development, 19, 1–14. Hamer, R. D., Alexander, K. R., & Teller, D. Y. (1982). Rayleigh discriminations in young human infants. Vision Research, 22, 575–587. Hansen, T., Olkkonen, M., Walter, S., & Gegenfurtner, K. R. (2006). Memory modulates color appearance. Nature Neuroscience, 9, 1367–1368. Hering, E. (1964). Outlines of a theory of the light sense. In L. M. Hurvich & D. Jameson (Eds.), Trans. Cambridge, MA: Harvard University Press [Original work published 1878].
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