Prior experiments have demonstrated that infants are able to segment words from fluent speech via transitional probabilities (e.g., Saffran et al., 1996) and to identify relations between words and shapes (e.g., Stager & Werker, 1997; Thiessen, 2007), but no experiments have assessed both simultaneously. Because infants are the primary learners of language, their performance is both theoretically and pragmatically important and can clarify issues related to continuity of learning across the lifespan and the characteristics of the input that facilitate language acquisition. If infants, like adults, learn best when there are multiple relations available to be learned in the input, they should distinguish between words and part-words most successfully in the regular-video condition. In contrast, if infants learn most easily when presented with simplified stimuli, they should be most successful after exposure to the no-video stimuli.
3.2. Results and discussion
As illustrated in Fig. 3, infants in all three conditions looked longer at part-word trials than word trials, replicating the results of Saffran et al. (1996). In the no-video condition, infants looked at word trials for 8.9 s (SD = 3.5) and at part-word trials for 9.9 s (SD = 3.7). In the regular-video condition, infants looked at word trials for 7.7 s (SD = 3.5), and at part-word trials for 9.1 s (SD = 3.7). In the irregular-video condition, infants looked at word trials for 7.8 s (SD = 3.0), and at part-word trials for 9.1 s (SD = 2.8). Paired t tests indicate that the difference between word and part-word looking trials was significant in all three conditions—no-video: t(14) = 2.5, p < .05; irregular-video: t(14) = 2.4, p < .05; regular-video: t(14) = 2.5, p < .05. These results indicate that infants in all three conditions learned enough about words to distinguish them from part-words.
Figure 3. Eight-month-old infants’ looking times to word and part-word test-trials in the No-Video, Irregular-Video, and Regular-Video conditions.
Download figure to PowerPoint
A 2 (test item) × 3 (condition) anova was used to compare the performance across three conditions. There was a main effect of test item, F(1, 42) = 17.9, p < .01, due to the fact that infants in all three conditions preferred the part-word test trials to the word test trials. However, there was neither a main effect of condition, F(2, 42) < 1, ns, nor any interaction between condition and test item, F(2, 42) < 1, ns. This analysis indicates that infants performed equivalently in all three conditions. In contrast, adults were much more successful segmenting words from fluent speech in the regular-video condition than in either the irregular-video or no-video condition. These results raise a question: why do adults benefit from regular relations between words and objects, while infants fail to benefit?
One explanation for infants’ inability to benefit from the regular-video condition is that infants failed to detect the relations between words and shapes present in the regular-video condition. This suggestion is consistent with a variety of converging evidence indicating that 8-month-old infants are relatively insensitive to relations between words and objects in the visual world. Infants at this age have a small vocabulary (e.g., Fenson et al., 2002), and they have difficulty in acquiring names for novel objects in controlled laboratory experiments (e.g., Werker, Cohen, Lloyd, Casasola, & Stager, 1998). If infants do not detect the relation between words and objects in the regular-video condition, they cannot benefit from any facilitation that identifying the relation provides to adult learners.
Indeed, additional testing is consistent with this hypothesis. Although infants in this experiment were not tested on their knowledge of word–object relations, an additional sample of sixteen 8-month-olds was presented with test trials assessing knowledge of word–object pairings. These infants were familiarized with the segmentation stimuli from the regular-video condition, for an equivalent length of time. But rather than being tested on words and part-words, all infants were presented with a word (each infant was tested with only a single word, although all four words were used as test items across the group) paired either with the correct object or with an object that had previously been paired with a different word. These infants showed no difference in their looking time to correct pairings (M = 8.2, SD = 2.9) vs. incorrect pairings (M = 8.4, SD = 3.1), t(15) < 1, ns. This finding replicates prior results indicating that, for infants of this age, identifying word–object relations from a brief laboratory exposure is a difficult task (e.g., Stager & Werker, 1997; Werker et al., 1998).
Infants’ apparent failure to discover word–object relations should not be taken as evidence that infants are insensitive to the presence of the looming objects, or that they are unable to detect audio–visual relations at this age. A wide variety of research indicates that infants are able to make associations between audio and visual stimuli, from studies of early word comprehension (e.g., Tincoff & Jusczyk, 1999) to experiments identifying factors that facilitate infants’ discovery of audio–visual associations (e.g., Bahrick, Flom, & Lickliter, 2002; Gogate & Bahrick, 1998; Lewkowicz, 1986, 2003). But although the ability to learn audio–visual associations has been suggested to be a necessary foundation for later word learning (e.g., Gogate, Walker-Andrews, & Bahrick, 2001), it is not sufficient for adult-like word-learning competence. Young children may be able to discover word–object relations in tasks like the ones used in these experiments (e.g., Smith & Yu, 2008). However, Experiments 1 and 2 converge with a variety of other results (e.g., Stager & Werker, 1997; Werker et al., 1998) to suggest that infants are less adept at discovering such relations than adults. In turn, this makes it less likely that the presence of word–object relations can influence other aspects of learning.