Cortical response to categorical color perception in infants--论文代写范文精选

这些差异在基于分类关系，观察血流动力学。我们确认分类颜色差异产生婴儿行为的差异，同时也观察到类似的血流动力学反应。目前的研究提供了第一个证据,不同类别的颜色代表不同的视觉皮层。下面的paper代写范文进行叙述。

Abstract
Perceptual color space is continuous; however, we tend to divide it into only a small number of categories. It is unclear whether categorical color perception is obtained solely through the development of the visual system or whether it is affected by language acquisition. To address this issue, we recruited prelinguistic infants (5- to 7-mo-olds) to measure changes in brain activity in relation to categorical color differences by using near-infrared spectroscopy (NIRS). We presented two sets of geometric figures to infants: One set altered in color between green and blue, and the other set altered between two different shades of green. We found a significant increase in hemodynamic responses during the between-category alternations, but not during the within-category alternations. 

These differences in hemodynamic response based on categorical relationship were observed only in the bilateral occipitotemporal regions, and not in the occipital region. We confirmed that categorical color differences yield behavioral differences in infants. We also observed comparable hemodynamic responses to categorical color differences in adults. The present study provided the first evidence, to our knowledge, that colors of different categories are represented differently in the visual cortex of prelinguistic infants, which implies that color categories may develop independently before language acquisition.

Humans can discriminate thousands of colors among continuous color space. However, we use only a handful of color terms to describe colors in our daily communication. From the analyses of data for the World Color Survey , a corpus of color-naming data from 110 universal languages, many studies have revealed that particular structures of color terms used by speakers exist, and that these structures possess some common features (1, 2). Furthermore, these common features had been found even in the color perception of infants before the acquisition of the color terms (3–5). 

These results imply that categorical color perception may have some biological basis across cultures and languages. On the other hand, one argument for categorical color perception is that the color lexicon changes perceptual differences among colors so that colors from the same linguistic category appear much closer than colors of different categories (6, 7). A possible hypothesis is that categorical color perception has an innate perceptual foundation, and then could be modified along with the acquisition of language (8). A recent set of studies focusing on hemispheric asymmetries in categorical color perception has added another perspective to this hypothesis. Gilbert et al. (9) found that the reaction time for detecting a colored target among differently colored distractors was faster when the target and distractors belonged to different categories than when they belonged to the same category. 

They named this phenomenon the color-category effect, and reported that this category effect is evident only when the target was in the right visual field (RVF) [i.e., when the information was processed through visual cortex in the left hemisphere, where language-related areas reside in adults (e.g., 10)]. Further evidence for the RVF category effect was provided in a series of behavioral, event-relatedpotential (ERP) (11), and functional MRI (fMRI) (12) studies. One such recent study has reported that the category effect in prelinguistic infants was, unlike in adults, lateralized to the left visual field (13), but switches to the right (RVF) when the color words for the relevant categories are learned (14). However, the neurophysiological basis for this lateralization of the category effect in infants was not reported in an ERP study (15). Furthermore, recent psychophysical studies have raised questions about visual-field asymmetry and the repeatability of the category effects (16, 17). 

Although evidence has suggested that prelinguistic infants hold categorical color perception, no prior study has identified how the categorical relationship of color is encoded in infants, and whether it is lateralized to a hemisphere. In the present study, we address this question by using a functional brain activity imaging technique, near-infrared spectroscopy (NIRS), to investigate the neural activity related to categorical color perception, along with behavioral experiments. A hierarchy of color-information processing has been demonstrated by several physiological studies in monkeys (18, 19) and humans (20), starting from the occipital to the temporal cortex through the ventral visual areas. Thus, we recorded responses of bilateral occipitotemporal (OT) regions in an attempt to obtain responses to categorical color differences; responses in occipital regions were also recorded to compare responses to a lower level visual feature. The results of the present study suggest the presence of some categorical color representation in the OT regions in infants, which appears to be achieved independent of or before the acquisition of language, and which is probably not driven by mere perceptual color differences.

NIRS Measurement We conducted measurements of infant brain activity using a NIRS system (ETG-4000; Hitachi Medical), and then tested adults for comparison, because it is easier to measure the brain activity of infant participants using NIRS than fMRI. Additionally, previous studies by our group have revealed the interhemispheric differences in face information processing in infants by using NIRS (e.g., 21). One benefit of this method is that identical procedures and measures can be used for both infants and adults, and can be used to verify whether a similar hemodynamic response exists in both groups. In our NIRS experiment, we presented infants and adults with two sets of geometric figures (Fig. 1A). 

The color of the figures in one set alternated between green and blue at 1 Hz (Green 1 and Blue 1 in Table 1: between-category condition), whereas the color of the other set of figures alternated between two different shades of green at 1 Hz (Green 1 and Green 2 in Table 1: within-category condition). (Blue 1, Green 1, and Green 2 are referred to as B1, G1, and G2, hereafter.) For easier comparisons with a previous study, the chromaticity coordinates of G1, G2, and B1 were chosen from the chromaticity coordinates specified in an article on infant color categorization (5), but were slightly modified to minimize luminance artifacts. Because our experiment alternated the color of the stimuli in a time sequence with a squared waveform, residual luminance contrast at the instance of color alternation could lead to an artifact in the infants’ cortical response. Although a previous study reported the similarity of luminous efficiency function between infants and adults except in the short wavelength range (22), it is better to minimize any cause of artifactual stimulation for recording cortical responses to color changes (23). 

To attempt to minimize the stimulation of luminance-sensitive mechanisms, we selected colors among those colors that selectively differ in terms of short-wavelength–sensitive cone excitations (24), while retaining an equal color difference between G1/G2 and G1/B1 in a uniform color space defined by Commission internationale de l’éclairage (International Commision on Illumination), so called CIE LAB (1976), (Table 1; details about the luminance control are provided in Supporting Information). The cone fundamentals of Smith and Pokorny (25) were used to calculate the cone responses. The NIRS responses to the categorical perception of color under the between- and within-category conditions were contrasted against the response during the baseline period in which gray geometric patterns changed their shape at the same frequency as the color alternations. We measured the NIRS responses in the bilateral OT regions (Fig. 1B) to test lateralization in the categorical processing of color. Data were obtained from 12 infants between 5 and 7 mo of age, each of whom had more than three valid trials in both the within-category and between-category conditions (average of 3.7 trials in within-category conditions and average of 3.8 trials in the between-category conditions).

To elucidate NIRS channels that exhibited significant signal changes from the baseline during the measurement, regardless of stimulus conditions, we conducted a repeated-measure ANOVA on the time-series data for each channel, in each participant (26, 27). Channels with consistent activations would display repeatable time-series patterns between trials under the same condition. We took NIRS recording time as a main factor in ANOVA analysis by assuming no significant difference at any time point as a null hypothesis. Fig. 2A illustrates the localization of the activated channels in oxy-Hb (P < 0.01, Bonferroni-corrected) with the statistically significant main effect of time. A wide area of channels was activated under the between- and within-category conditions. However, when this ANOVA on the time-series data was carried out across all participants, we could not find a significant channel that was common among all participants (i.e., no channel exhibited n = 12 in Fig. 2A). This low signal-to-noise ratio is possibly because the absolute amplitude of NIRS signals contained nonnegligible differences among individuals. Therefore, we normalized the signal amplitude (Z-scores) using the mean and the SD of the prestimulus period (details are provided in Supporting Information) for each channel and each participant before applying further statistical analyses(paper代写)

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