Introduction
The journey of language acquisition in children is a fascinating field of study, filled with intriguing patterns and questions. One such enduring observation is that nouns are generally acquired more readily than verbs in early vocabulary development. This phenomenon has been consistently noted across various studies and languages. However, the presence of verbs in children’s initial word sets presents a seeming contradiction. Is the noun advantage simply due to grammatical category, or are other factors at play? This article delves into the hypothesis that the ease of learning a word is not solely determined by whether it’s a noun or a verb, but rather by its imageability – the ease with which a word evokes a mental image. We will explore how imageability ratings correlate with the age of acquisition of words, utilizing data from the MacArthur-Bates Communicative Development Inventory (CDI), and investigate whether imageability is a key driver in early word learning, potentially overshadowing the role of grammatical form class.
Nouns tend to precede verbs in a child’s lexicon and often dominate the early vocabulary of children learning English. This trend is not limited to English; it has been observed in languages as diverse as German, Mandarin, Kaluli, Japanese, Turkish, Spanish, Italian, and French. Even in controlled laboratory settings, children demonstrate a greater capacity to learn novel nouns compared to novel verbs. This holds true even in languages like Japanese and Chinese, where verbs might hold syntactical advantages.
Several theories attempt to explain this noun preference in early language. One perspective highlights attentional biases, suggesting that children naturally pay more attention to objects and are inclined to associate new words with objects rather than actions. According to this view, object names must be established before children proceed to learn action words. Another explanation centers on perceptual differences. Objects are often stable and concrete, while actions are dynamic, fleeting, and unfold over time. Abstracting a consistent representation of actions is perceptually more challenging than categorizing objects labeled by nouns. Learning action words requires children to discern the core elements of an action across varied instances. For example, different individuals and even animals can perform the same action, like running, in diverse ways. A third perspective points to parental input patterns. English-speaking parents are more likely to ask children to repeat noun labels but to act out verb meanings. Even in languages where verbs are more prominent, parents tend to discuss objects more frequently with young children than actions.
These explanations move beyond merely documenting vocabulary composition to exploring the underlying mechanisms driving the differences in noun and verb acquisition. However, they all assume that the grammatical distinction between “noun” and “verb” is the primary factor in this disparity. An alternative hypothesis suggests that the noun-verb difference may be less about grammatical form and more about the nature of the concepts these word classes typically represent. Two observations support this idea. First, some nouns, such as “idea” or “passenger,” are acquired later than verbs like “hug” or “kiss.” Second, despite the general noun advantage, verbs are indeed present in children’s earliest vocabularies. These points suggest that a different explanation for early noun dominance might be warranted.
Gentner’s “natural partitions” hypothesis proposes that noun dominance reflects the tendency of nouns to label tangible entities, while verbs label relational concepts. Object nouns often refer to standalone entities, whereas verbs describe actions that require an agent. Furthermore, the referents of verbs may be less perceptually obvious than those of nouns. Early nouns often label whole objects, while verbs can encode a range of concepts, such as the path or manner of an action. Children must learn how their language typically structures verb concepts, a challenge Gentner and Boroditsky termed “relational relativity.”
Gentner and Boroditsky’s work emphasizes a critical distinction between nouns and verbs: noun concepts are generally more imageable and easily perceived as distinct entities compared to verb concepts. It is plausible that the differentiation between nouns and verbs is not primarily a linguistic phenomenon of form class, but a conceptual difference in what these word categories tend to label. Measuring word imageability may be a way to reveal this conceptual distinction.
Imageability: A Key Factor in Word Acquisition
Imageability refers to the ease with which a concept evokes a mental image. It is a well-established concept in psychology, known to influence learning and memory. While related to other concepts, imageability captures unique aspects of word meaning. For instance, although highly correlated with concreteness, imageability is not entirely synonymous with it. A word can be concrete but low in imageability (e.g., “originator”) or highly imageable but less concrete (e.g., “fun”). Words with high imageability and lower concreteness often share characteristics like association with sensory experiences. Thus, imageability and concreteness are related but distinct constructs.
Imageability is also related to, but not the same as, word frequency. Studies have shown that imageability ratings of early words are not always correlated with input frequency. Furthermore, imageability and input frequency can independently predict the age of acquisition of words. Common words like “the,” while highly frequent, are not particularly imageable.
Recent studies with adults provide evidence that imageability plays a role in word acquisition. For example, in studies where adults were asked to guess words from silent videos of mother-child interactions, they were more successful at guessing nouns than verbs. Nouns were also rated as more imageable than verbs by another group of adults. Imageability significantly predicted word identifiability, while grammatical form class did not. This aligns with findings from studies with both neurologically typical and aphasic adults, where controlling for imageability eliminates form class effects in lexical recognition tasks.
Imageability is also a strong predictor of naming performance in both adults and children. Research with young children naming pictures of objects and actions revealed that imageability was a significant predictor of naming accuracy. Word frequency, in contrast, was less consistent as a predictor. Studies examining the relationship between imageability and age of acquisition have found a significant negative correlation: more imageable words are reported to be acquired earlier. These collective findings suggest that highly imageable words, regardless of their grammatical class, are not only easier to identify but also potentially easier to learn.
However, previous research linking imageability and word acquisition has limitations. First, age of acquisition data often relies on adults’ retrospective recall, which can be unreliable due to memory limitations. Parental reports of children’s vocabulary offer a potentially more reliable measure. Second, age of acquisition scales used in studies often cover broad time spans, making it difficult to pinpoint the acquisition age of early words. Third, much of the imageability research has focused primarily on nouns, with fewer studies examining verb imageability or comparing imageability across nouns and verbs, which is crucial for understanding the noun-verb gap in early language learning.
This study addresses these limitations by investigating two key questions: Is there a relationship between imageability and children’s age of word acquisition as reported by parents? And does imageability predict word acquisition age independently of grammatical form class? Exploring these questions using existing data can provide valuable insights into the role of imageability in early word learning.
Methodological Approach
Measuring Imageability
This study utilized published imageability ratings from Masterson and Druks (1998), based on Paivio et al.’s (1968) scale. This scale ranges from 1 to 7, where 1 indicates words that are very difficult to visualize and 7 represents words that readily evoke mental images. This particular measure was chosen for its rigorous methodology and careful word selection. Masterson and Druks ensured clear instructions for participants rating nouns and verbs, especially for homonyms, and controlled for factors like word frequency and familiarity. Their word sample included 164 nouns and 102 verbs.
Assessing Age of Acquisition
Determining when children acquire words can be approached through various methods, including speech corpora, standardized tests, and parental reports. Parental reports are often considered a valid, reliable, and comprehensive source of information, especially for early vocabulary. For this study, age of acquisition data was derived from the MacArthur-Bates Communicative Development Inventory: Words and Sentences (CDI). The CDI is a widely used tool where parents report when their child produces a word from a provided list. Age of acquisition in this study was defined as the age (between 14 and 30 months) at which at least 50% of children productively use a given noun or verb, based on norms from a large sample of 1130 children. The CDI’s age of acquisition measure correlates well with children’s vocabulary performance in laboratory settings, demonstrating its validity.
From the CDI database, 76 nouns and 44 verbs also had corresponding imageability ratings from Masterson and Druks (1998) and were included in this study. While a more balanced sample of nouns and verbs might be statistically ideal, the existing ratio was deemed acceptable and representative of the natural noun-verb distribution in early vocabulary. Trimming the sample would risk reducing statistical power.
Data Analysis Strategy
The CDI age of acquisition was the dependent variable in this study. The predictors were grammatical form class (noun or verb) and imageability ratings. Initial analyses involved simple correlations between age of acquisition and imageability, both across all words and within noun and verb categories separately. Subsequently, hierarchical multiple regression was employed to examine the independent contributions of form class and imageability to predicting age of acquisition. This approach allowed for assessing whether imageability explains variance in acquisition age beyond what is accounted for by grammatical class alone.
Key Findings
Imageability and Age of Acquisition: A Significant Link
Descriptive statistics revealed that nouns in the sample, on average, were acquired at a significantly younger age and had significantly higher imageability ratings compared to verbs. Examining the relationship between age of acquisition and imageability rating across all words showed a significant negative correlation. This indicates that higher imageability is associated with earlier acquisition. This significant negative correlation was also observed when analyzing nouns and verbs separately.
Table 1. Distributional Statistics for CDI Words’ (N = 120) Age of Acquisition, Form Class and Imageability Rating
| Overall | Nouns(N = 76) | Verbs(N = 44) |
|---|---|---|
| CDI Age of Acquisition(in months) | 22.18 (3.32) | 21.33 (3.54) |
| range | 14 – 30 | 19 – 29 |
| Form Class | 0.37 (0.48) | 0 |
| Imageability Rating | 5.46 (0.95) | 6.08 (0.38) |
| range | 4.78 – 6.64 | 3.00 – 5.47 |
Notes:
Standard deviations are presented in parentheses.
Form class was coded with nouns being 0 and verbs being 1.
Imageability’s Predictive Power Beyond Form Class
Hierarchical multiple regression analysis confirmed that both grammatical form class and imageability rating significantly correlated with CDI age of acquisition. Form class alone accounted for 11% of the variance in age of acquisition. Importantly, after controlling for form class, imageability rating explained an additional significant 11% of the variance. Together, form class and imageability accounted for 22% of the variance in CDI word acquisition age. The analysis also indicated that imageability rating had a stronger predictive power for age of acquisition than grammatical form class in this model.
Table 2. Hierarchical Multiple Regression of CDI Words’ Form Class and Imageability Rating on Age of Acquisition
| Variable | CDI AgeofAcquisition(DV) | FormClass(nounvs. verb) | B | SE B | β | sr2(ΔR2) |
|---|---|---|---|---|---|---|
| Form Class(noun vs. verb) | .34*** | −1.63 | 1.14 | −.24 | .11*** | |
| Imageability Rating | −.45*** | −.87*** | −2.31 | .58 | −.66 | .11*** |
| Constant | 35.36 | 3.56 |
R2 = .22; Adjusted R2 = .20
***p < .001
Considering Word Frequency
To further explore factors influencing word acquisition, word frequency was included in an expanded regression analysis. Frequency data was obtained from the CHILDES database, reflecting language input to children. In this analysis, form class was entered first, followed by frequency, and then imageability. Frequency was found to account for an additional 9% of the variance in age of acquisition, beyond form class. Crucially, imageability still contributed a significant and unique 10% of variance, even after accounting for both form class and frequency. Imageability remained a stronger predictor of age of acquisition than both form class and frequency in this more comprehensive model. Together, form class, frequency, and imageability explained 30% of the variance in CDI age of acquisition.
Table 3. Hierarchical Multiple Regression of CDI Words’ Form Class, Frequency, and Imageability Rating on Age of Acquisition
| Variable | CDI AgeofAcquisition(DV) | FormClass(nounvs.verb) | CHILDESFrequency | B | SE B | b | sr2(ΔR2) |
|---|---|---|---|---|---|---|---|
| Form Class(noun vs.verb) | .34*** | −1.21 | 1.09 | −.18 | .11*** | ||
| CHILDESFrequency | −.25** | .14 | −.001 | .00 | −.30 | .09*** | |
| Imageability Rating | −.45*** | −.87*** | −.11 | −2.23 | .55 | −.64 | .10*** |
| Constant | 35.70 | 3.37 |
R2 = .30; Adjusted R2 = .29
**p <.01
***p < .001
Discussion: Imageability as a Conceptual Key to Early Word Learning
The observation that nouns are more prevalent than verbs in early vocabularies does not fully explain the reasons behind this difference. This study shifted focus from grammatical class distinctions to a conceptual factor, imageability, which is independent of form class. The findings indicate a significant relationship between word imageability and parent-reported age of acquisition. Words rated as more imageable tend to be acquired earlier, a pattern observed across nouns, verbs, and the combined word set. This is particularly notable given the narrow age range (14-30 months) captured by the CDI.
The hierarchical regression analysis demonstrated that imageability contributes to predicting age of acquisition beyond grammatical form class. Imageability accounted for a unique and significant portion of the variance, and its predictive power was greater than that of form class and frequency. This suggests that imageability is a crucial factor in early word learning.
Parental reports were used to estimate age of acquisition. While parental recall might be influenced by word imageability, parental reports on the CDI have been shown to have good validity. Furthermore, research across languages like Italian, Portuguese, and Chinese also points to a link between imageability and early word acquisition, reinforcing the robustness of this finding. Cross-linguistic studies suggest that differences in imageability ratings for early words may even explain variations in early vocabulary composition across languages.
These findings suggest that the early noun advantage is not simply a matter of grammatical class but may have a conceptual basis. Highly imageable words might be inherently easier to learn. This raises fundamental questions about the nature of imageability and its influence on acquisition.
Paivio et al. (1968) defined mental images broadly, encompassing visual, auditory, and other sensory experiences. Interestingly, studies with blind individuals have shown similar imagery effects on memory, suggesting imageability is not solely visual. However, whether imageability ratings from sighted adults predict word acquisition in blind children remains an open question.
Why might high-imageability words be learned earlier? It is proposed that highly imageable words label concepts (objects or actions) that are perceptually distinct and easily individuated. Imageability might also relate to the consistency and salience of contexts in which word-referent pairings occur. The Emergentist Coalition Model posits that early words label perceptually salient and accessible concepts encountered in limited contexts. The accessibility and perceptual salience of a word’s referent may contribute to its high imageability, aligning with the principle of “encoding specificity.” Words for salient concepts, frequently heard in consistent contexts, may be easier to represent mentally and thus acquired earlier. While nouns often fit this description, some verbs, like “eat,” also occur in consistent contexts and are highly imageable.
The early acquisition of some broad-meaning verbs in English might seem to contradict the imageability hypothesis. However, research indicates that children initially use these verbs with restricted, specific meanings, not reflecting the full range of adult usage. This suggests that early verb learning may also be grounded in specific, imageable contexts.
While form class and imageability together explain a significant portion of the variance in age of acquisition, other factors also contribute. Word frequency, as shown in the expanded analysis, accounts for additional variance. However, imageability’s unique contribution and stronger predictive power highlight its importance in early word learning.
This research provides a deeper understanding of word learning mechanisms by demonstrating the role of imageability, a meaning-related factor, in children’s real-time word acquisition. It offers a new perspective on the noun-verb differences in early vocabulary. Imageability may serve as a measure of a concept’s concreteness, perceptibility, and individuability. Nouns, being generally more concrete and easier to perceive and individuate, may be learned earlier. Early verbs, like “kiss” and “hug,” are also more imageable and potentially used in more consistent contexts than later-acquired verbs. Across and within word classes, imageability emerges as a significant predictor of early word learning.
Conclusions
This study’s findings emphasize that factors beyond grammatical form class and word frequency are crucial in early word acquisition. Specifically, meaning-related factors like imageability are significant predictors of when words are learned. Highly imageable words are acquired earlier, regardless of whether they are nouns or verbs. The higher imageability of early nouns compared to early verbs in English suggests that early acquisition is influenced by children’s ability to extract the core meaning of a concept, as reflected in its imageability.
Acknowledgements
We extend our gratitude to our former laboratory coordinators Meredith Jones and Rebecca Seston, and to the dedicated students in our laboratories at Temple University and the University of Delaware for their invaluable assistance. This research was supported by joint grants to the third and fourth authors from NSF (Grants SBR9601306 and SBR9615391) and NIH (RO1HD050199).
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