Infants' and toddlers' language development during the pandemic: Socioeconomic status mattered.

The disruption caused by the COVID-19 pandemic has raised concerns about children's development. Here, we examined the impact of the pandemic on Canadian infants' and toddlers' (N = 539) language development. Specifically, we assessed changes in 11- to 34-month-olds' activities that are known to affect vocabulary development (i.e., screen and reading times). We also compared these children's vocabulary sizes with those of 1365 children collected before the pandemic using standardized vocabulary assessments. Our results show that screen and reading times were most negatively affected in lower-income children. For vocabulary growth, no measurable change was detected in middle- and high-income children, but lower-income 19- to 29-month-olds fared worse during the pandemic than during pre-pandemic times. Moving forward, these data indicate that educators and policymakers should pay particular attention to children from families with lower socioeconomic status during times of crisis and stress.

The song, not the singer: Infants prefer to listen to familiar songs, regardless of singer identity.

Parent's infant-directed vocalizations are highly dynamic and emotive compared to their adult-directed counterparts, and correspondingly, more effectively capture infants' attention. Infant-directed singing is a specific type of vocalization that is common throughout the world. Parents tend to sing a small handful of songs in a stereotyped way, and a number of recent studies have highlighted the significance of familiar songs in young children's social behaviors and evaluations. To date, no studies have examined whether infants' responses to familiar versus unfamiliar songs are modulated by singer identity (i.e., whether the singer is their own parent). In the present study, we investigated 9- to 12-month-old infants' (N = 29) behavioral and electrodermal responses to relatively familiar and unfamiliar songs sung by either their own mother or another infant's mother. Familiar songs recruited more attention and rhythmic movement, and lower electrodermal levels relative to unfamiliar songs. Moreover, these responses were robust regardless of whether the singer was their mother or a stranger, even when the stranger's rendition differed greatly from their mothers' in mean fundamental frequency and tempo. Results indicate that infants' interest in familiar songs is not limited to idiosyncratic characteristics of their parents' song renditions, and points to the potential for song as an effective early signifier of group membership.

Revisiting the talker recognition advantage in bilingual infants.

Recent work has shown that exposure to multiple languages affects nonlinguistic processing of speech during infancy. Specifically, Fecher and Johnson found that bilingual 9-month-olds outperformed their monolingual peers in a face-voice matching task in an unfamiliar language [Developmental Science (2019a), 22(4), e12778]. What factors were driving this effect? That is, was this finding truly reflective of a bilingual advantage specific to talker processing, or did the study demonstrate a general cognitive advantage in bilingual infants? Here, we revisited this question by testing bilingual and monolingual 9-month-olds (N = 48) on their ability to associate previously unknown voices with animated cartoon characters. In comparison with earlier work, where infants were presented with characters speaking an unfamiliar language (Spanish), the characters in this study spoke a language familiar to both groups of infants (English). Critically, we found that the monolingual and bilingual infants learned the face-voice pairings equally well when they were tested on the familiar language. We conclude that whereas bilingual infants are skilled at recognizing talkers regardless of the language spoken by the talkers, monolingual infants succeed at talker recognition in a familiar language only. These results begin to clarify the underlying nature of the talker recognition benefit previously reported for bilingual infants.

Developmental improvements in talker recognition are specific to the native language.

Previous studies have shown that talker recognition by young children continues to improve into late childhood. But why might this be the case? Are children's gradually improving talker recognition abilities driven primarily by general maturational factors in the cognitive or perceptual domain (general maturation hypothesis), or are these improvements primarily linked to children's increasingly sophisticated linguistic knowledge (language attunement hypothesis)? In the current study, we addressed this question by testing monolingual English-speaking 5- and 6-year-olds (N = 80) on their ability to recognize talkers in a familiar language (i.e., English) and in an unfamiliar language (i.e., Spanish) using a "voice lineup" talker recognition task. We predicted two alternative outcomes. According to the general maturation hypothesis, we should see improvements in talker recognition for both the familiar and unfamiliar languages as children grow older. According to the language attunement hypothesis, however, we should see developmental improvements in talker recognition for the familiar language only. Our findings suggest that early developmental improvements in talker recognition are limited to familiar languages, highlighting the potential central role of language-specific knowledge in talker recognition.

Targeted adaptation in infants following live exposure to an accented talker.

Infants struggle to understand familiar words spoken in unfamiliar accents. Here, we examine whether accent exposure facilitates accent-specific adaptation. Two types of pre-exposure were examined: video-based (i.e., listening to pre-recorded stories; Experiment 1) and live interaction (reading books with an experimenter; Experiments 2 and 3). After video-based exposure, Canadian English-learning 15- to 18-month-olds failed to recognize familiar words spoken in an unfamiliar accent. However, after face-to-face interaction with a Mandarin-accented talker, infants showed enhanced recognition for words produced in Mandarin English compared to Australian English. Infants with live exposure to an Australian talker were not similarly facilitated, perhaps due to the lower vocabulary scores of the infants assigned to the Australian exposure condition. Thus, live exposure can facilitate accent adaptation, but this ability is fragile in young infants and is likely influenced by vocabulary size and the specific mapping between the speaker and the listener's phonological system.

Identifying children's voices.

Human adults rely on both acoustic and linguistic information to identify adult talkers. Assuming favorable conditions, adult listeners recognize other adults fairly accurately and quickly. But how well can adult listeners recognize child talkers, whose speech productions often differ dramatically from adult speech productions? Although adult talker recognition has been heavily studied, only one study to date has directly compared the recognition of unfamiliar adult and child talkers [Creel and Jimenez (2012). J. Exp. Child Psychol. 113(4), 487-509]. Therefore, the current study revisits this question with a much larger and younger sample of child talkers (N = 20); performance with adult talkers (N = 20) was also tested to provide a baseline. In Experiment 1, adults successfully distinguished between adult talkers in an AX discrimination task but performed much worse with child talkers. In Experiment 2, adults were slower and less accurate at learning to identify child talkers than adult talkers in a training-identification task. Finally, in Experiment 3, adults failed to improve at identifying child talkers after three days of training with numerous child voices. Taken together, these findings reveal a sizable difference in adults' ability to recognize child versus adult talkers. Possible explanations and implications for understanding human talker recognition are discussed.

Bilingual infants excel at foreign-language talker recognition.

Bilingual and monolingual infants differ in how they process linguistic aspects of the speech signal. But do they also differ in how they process non-linguistic aspects of speech, such as who is talking? Here, we addressed this question by testing Canadian monolingual and bilingual 9-month-olds on their ability to learn to identify native Spanish-speaking females in a face-voice matching task. Importantly, neither group was familiar with Spanish prior to participating in the study. In line with our predictions, bilinguals succeeded in learning the face-voice pairings, whereas monolinguals did not. We consider multiple explanations for this finding, including the possibility that simultaneous bilingualism enhances perceptual attentiveness to talker-specific speech cues in infancy (even in unfamiliar languages), and that early bilingualism delays perceptual narrowing to language-specific talker recognition cues. This work represents the first evidence that multilingualism in infancy affects the processing of non-linguistic aspects of the speech signal, such as talker identity.

By 4.5 Months, Linguistic Experience Already Affects Infants' Talker Processing Abilities.

Contemporary models of adult speech perception acknowledge that the processing of linguistic and nonlinguistic aspects of the speech signal are interdependent. But when in development does this interdependence first emerge? In the adult literature, one way to demonstrate this relationship has been to examine how language experience affects talker identification. Thus, in this study, 4- to 5-month-old infants (N = 96) were tested on their ability to tell apart talkers in a familiar language (English) compared to unfamiliar languages (Polish or Spanish). Infants readily distinguished between talkers in the familiar language but not in the unfamiliar languages, supporting the hypothesis that the integrated processing of linguistic and nonlinguistic information in speech is early emerging and robust.

Resolving the (Apparent) Talker Recognition Paradox in Developmental Speech Perception.

The infant literature suggests that humans enter the world with impressive built-in talker processing abilities. For example, newborns prefer the sound of their mother's voice over the sound of another woman's voice, and well before their first birthday, infants tune in to language-specific speech cues for distinguishing between unfamiliar talkers. The early childhood literature, however, suggests that preschoolers are unable to learn to identify the voices of two unfamiliar talkers unless these voices are highly distinct from one another, and that adult-level talker recognition does not emerge until children near adolescence. How can we reconcile these apparently paradoxical messages conveyed by the infant and early childhood literatures? Here, we address this question by testing 16.5-month-old infants (N = 80) in three talker recognition experiments. Our results demonstrate that infants at this age have difficulty recognizing unfamiliar talkers, suggesting that talker recognition (associating voices with people) is mastered later in life than talker discrimination (telling voices apart). We conclude that methodological differences across the infant and early childhood literatures-rather than a true developmental discontinuity-account for the performance differences in talker processing between these two age groups. Related findings in other areas of developmental psychology are discussed.

Effects of language experience and task demands on talker recognition by children and adults.

Talker recognition is a language-dependent process, with listeners recognizing talkers better when the talkers speak a familiar versus an unfamiliar language. This language familiarity effect (LFE) is firmly established in adults, but its developmental trajectory in children is not well understood. Some evidence suggests that the effect already exists in infancy, but little is known about how it unfolds in childhood. The present study explored whether the strength of the LFE increases in early childhood. Adults and children were tested in their native language and a foreign language using a "same-different" talker discrimination task and a "voice line-up" talker recognition task. Results showed that adults and 6-year-olds, but not 5-year-olds, exhibit a robust LFE, suggesting that the effect strengthens as children's language competence increases. For both adults and older children, the emergence of an LFE moreover appeared to be task-dependent. This study contributes to a better understanding of how children develop mature talker recognition abilities and when children's processing of indexical and linguistic information in speech approaches adult-like levels. Furthermore, the findings reported here contribute to the debates regarding the origins of the LFE-a hallmark of adult talker recognition.

Input matters: Speed of word recognition in 2-year-olds exposed to multiple accents.

Although studies investigating language abilities in young children exposed to more than one language have become common, there is still surprisingly little research examining language development in children exposed to more than one accent. Here, we report two looking-while-listening experiments examining the impact of routine home exposure to multiple accents on 2-year-olds' word recognition abilities. In Experiment 1, we found that monolingual English-learning 24-month-olds who routinely receive exposure to both Canadian English and a non-native variant of English are less efficient in their recognition of familiar words spoken in Canadian English than monolingual English-learning 24-month-olds who hear only Canadian English at home. In Experiment 2, we found that by 34months of age all children recognize words equally quickly regardless of their accent exposure at home. We conclude that monolingual toddlers in some locations may form a less homogeneous population than past work has assumed, a factor that should be considered when drawing generalizations about language development across different populations.

Input matters: Multi-accent language exposure affects word form recognition in infancy.

Early language input is far from uniform, even among children learning the same language. For instance, while some children are exposed to a single accent in their linguistic environment, others have routine exposure to multiple accents. Nonetheless, few studies have taken this into account when examining word recognition, and none has examined this issue in infants prior to the emergence of phonological constancy (∼18 months). This study demonstrates that daily exposure to multiple accents strongly impacts infants' performance in a laboratory word form recognition task. Accent variability in the input thus needs to be carefully considered when studying speech development.

Role of facial attractiveness in patients with slight-to-borderline treatment need according to the Aesthetic Component of the Index of Orthodontic Treatment Need as judged by eye tracking.

INTRODUCTION: Previous eye-tracking research has demonstrated that laypersons view the range of dental attractiveness levels differently depending on facial attractiveness levels. How the borderline levels of dental attractiveness are viewed has not been evaluated in the context of facial attractiveness and compared with those with near-ideal esthetics or those in definite need of orthodontic treatment according to the Aesthetic Component of the Index of Orthodontic Treatment Need scale. Our objective was to determine the level of viewers' visual attention in its treatment need categories levels 3 to 7 for persons considered "attractive," "average," or "unattractive." METHODS: Facial images of persons at 3 facial attractiveness levels were combined with 5 levels of dental attractiveness (dentitions representing Aesthetic Component of the Index of Orthodontic Treatment Need levels 3-7) using imaging software to form 15 composite images. Each image was viewed twice by 66 lay participants using eye tracking. Both the fixation density (number of fixations per facial area) and the fixation duration (length of time for each facial area) were quantified for each image viewed. Repeated-measures analysis of variance was used to determine how fixation density and duration varied among the 6 facial interest areas (chin, ear, eye, mouth, nose, and other). RESULTS: Viewers demonstrated excellent to good reliability among the 6 interest areas (intraviewer reliability, 0.70-0.96; interviewer reliability, 0.56-0.93). Between Aesthetic Component of the Index of Orthodontic Treatment Need levels 3 and 7, viewers of all facial attractiveness levels showed an increase in attention to the mouth. However, only with the attractive models were significant differences in fixation density and duration found between borderline levels with female viewers. Female viewers paid attention to different areas of the face than did male viewers. CONCLUSIONS: The importance of dental attractiveness is amplified in facially attractive female models compared with average and unattractive female models between near-ideal and borderline-severe dentally unattractive levels.

Audiovisual alignment of co-speech gestures to speech supports word learning in 2-year-olds.

Analyses of caregiver-child communication suggest that an adult tends to highlight objects in a child's visual scene by moving them in a manner that is temporally aligned with the adult's speech productions. Here, we used the looking-while-listening paradigm to examine whether 25-month-olds use audiovisual temporal alignment to disambiguate and learn novel word-referent mappings in a difficult word-learning task. Videos of two equally interesting and animated novel objects were simultaneously presented to children, but the movement of only one of the objects was aligned with an accompanying object-labeling audio track. No social cues (e.g., pointing, eye gaze, touch) were available to the children because the speaker was edited out of the videos. Immediately afterward, toddlers were presented with still images of the two objects and asked to look at one or the other. Toddlers looked reliably longer to the labeled object, demonstrating their acquisition of the novel word-referent mapping. A control condition showed that children's performance was not solely due to the single unambiguous labeling that had occurred at experiment onset. We conclude that the temporal link between a speaker's utterances and the motion they imposed on the referent object helps toddlers to deduce a speaker's intended reference in a difficult word-learning scenario. In combination with our previous work, these findings suggest that intersensory redundancy is a source of information used by language users of all ages. That is, intersensory redundancy is not just a word-learning tool used by young infants.

US Spending on Personal Health Care and Public Health, 1996-2013.

Importance: US health care spending has continued to increase, and now accounts for more than 17% of the US economy. Despite the size and growth of this spending, little is known about how spending on each condition varies by age and across time. Objective: To systematically and comprehensively estimate US spending on personal health care and public health, according to condition, age and sex group, and type of care. Design and Setting: Government budgets, insurance claims, facility surveys, household surveys, and official US records from 1996 through 2013 were collected and combined. In total, 183 sources of data were used to estimate spending for 155 conditions (including cancer, which was disaggregated into 29 conditions). For each record, spending was extracted, along with the age and sex of the patient, and the type of care. Spending was adjusted to reflect the health condition treated, rather than the primary diagnosis. Exposures: Encounter with US health care system. Main Outcomes and Measures: National spending estimates stratified by condition, age and sex group, and type of care. Results: From 1996 through 2013, $30.1 trillion of personal health care spending was disaggregated by 155 conditions, age and sex group, and type of care. Among these 155 conditions, diabetes had the highest health care spending in 2013, with an estimated $101.4 billion (uncertainty interval [UI], $96.7 billion-$106.5 billion) in spending, including 57.6% (UI, 53.8%-62.1%) spent on pharmaceuticals and 23.5% (UI, 21.7%-25.7%) spent on ambulatory care. Ischemic heart disease accounted for the second-highest amount of health care spending in 2013, with estimated spending of $88.1 billion (UI, $82.7 billion-$92.9 billion), and low back and neck pain accounted for the third-highest amount, with estimated health care spending of $87.6 billion (UI, $67.5 billion-$94.1 billion). The conditions with the highest spending levels varied by age, sex, type of care, and year. Personal health care spending increased for 143 of the 155 conditions from 1996 through 2013. Spending on low back and neck pain and on diabetes increased the most over the 18 years, by an estimated $57.2 billion (UI, $47.4 billion-$64.4 billion) and $64.4 billion (UI, $57.8 billion-$70.7 billion), respectively. From 1996 through 2013, spending on emergency care and retail pharmaceuticals increased at the fastest rates (6.4% [UI, 6.4%-6.4%] and 5.6% [UI, 5.6%-5.6%] annual growth rate, respectively), which were higher than annual rates for spending on inpatient care (2.8% [UI, 2.8%-2.8%] and nursing facility care (2.5% [UI, 2.5%-2.5%]). Conclusions and Relevance: Modeled estimates of US spending on personal health care and public health showed substantial increases from 1996 through 2013; with spending on diabetes, ischemic heart disease, and low back and neck pain accounting for the highest amounts of spending by disease category. The rate of change in annual spending varied considerably among different conditions and types of care. This information may have implications for efforts to control US health care spending.

Toddlers' Word Recognition in an Unfamiliar Regional Accent: The Role of Local Sentence Context and Prior Accent Exposure.

Adults are generally adept at recognizing familiar words in unfamiliar accents. However, studies testing young children's abilities to cope with accent-related variation in the speech signal have generated mixed results, with some work emphasizing toddlers' early competence and other work focusing more on their long-lasting difficulties in this domain. Here, we set out to unify these two perspectives and propose that task demands may play a crucial role in children's recognition of accented words. To this end, Canadian-English-learning 28-month-olds' looks to images on a screen were recorded while they were presented with a Scottish-accented speaker instructing them to find a depicted target object. To examine the effect of task demands, both local sentence context and prior accent exposure were manipulated. Overall, Canadian toddlers were found to recognize Scottish-accented words successfully, showing above-chance performance in the identification of words produced in an unfamiliar accent, even when target labels were presented in isolation. However, word recognition was considerably more robust when target words were presented in sentence context. Prior exposure to the unfamiliar Scottish accent in the laboratory did not modulate children's performance in this task. Taken together, these findings suggest that at least some task-related factors can affect children's recognition of accented words. Understanding unfamiliar accents, like understanding familiar accents, is thus not an isolated skill but, rather, is susceptible to contextual circumstances. Future models of spoken language processing in toddlerhood should incorporate these early effects of task demands.

Global, regional, and national incidence and mortality for HIV, tuberculosis, and malaria during 1990-2013: a systematic analysis for the Global Burden of Disease Study 2013.

BACKGROUND: The Millennium Declaration in 2000 brought special global attention to HIV, tuberculosis, and malaria through the formulation of Millennium Development Goal (MDG) 6. The Global Burden of Disease 2013 study provides a consistent and comprehensive approach to disease estimation for between 1990 and 2013, and an opportunity to assess whether accelerated progress has occured since the Millennium Declaration. METHODS: To estimate incidence and mortality for HIV, we used the UNAIDS Spectrum model appropriately modified based on a systematic review of available studies of mortality with and without antiretroviral therapy (ART). For concentrated epidemics, we calibrated Spectrum models to fit vital registration data corrected for misclassification of HIV deaths. In generalised epidemics, we minimised a loss function to select epidemic curves most consistent with prevalence data and demographic data for all-cause mortality. We analysed counterfactual scenarios for HIV to assess years of life saved through prevention of mother-to-child transmission (PMTCT) and ART. For tuberculosis, we analysed vital registration and verbal autopsy data to estimate mortality using cause of death ensemble modelling. We analysed data for corrected case-notifications, expert opinions on the case-detection rate, prevalence surveys, and estimated cause-specific mortality using Bayesian meta-regression to generate consistent trends in all parameters. We analysed malaria mortality and incidence using an updated cause of death database, a systematic analysis of verbal autopsy validation studies for malaria, and recent studies (2010-13) of incidence, drug resistance, and coverage of insecticide-treated bednets. FINDINGS: Globally in 2013, there were 1·8 million new HIV infections (95% uncertainty interval 1·7 million to 2·1 million), 29·2 million prevalent HIV cases (28·1 to 31·7), and 1·3 million HIV deaths (1·3 to 1·5). At the peak of the epidemic in 2005, HIV caused 1·7 million deaths (1·6 million to 1·9 million). Concentrated epidemics in Latin America and eastern Europe are substantially smaller than previously estimated. Through interventions including PMTCT and ART, 19·1 million life-years (16·6 million to 21·5 million) have been saved, 70·3% (65·4 to 76·1) in developing countries. From 2000 to 2011, the ratio of development assistance for health for HIV to years of life saved through intervention was US$4498 in developing countries. Including in HIV-positive individuals, all-form tuberculosis incidence was 7·5 million (7·4 million to 7·7 million), prevalence was 11·9 million (11·6 million to 12·2 million), and number of deaths was 1·4 million (1·3 million to 1·5 million) in 2013. In the same year and in only individuals who were HIV-negative, all-form tuberculosis incidence was 7·1 million (6·9 million to 7·3 million), prevalence was 11·2 million (10·8 million to 11·6 million), and number of deaths was 1·3 million (1·2 million to 1·4 million). Annualised rates of change (ARC) for incidence, prevalence, and death became negative after 2000. Tuberculosis in HIV-negative individuals disproportionately occurs in men and boys (versus women and girls); 64·0% of cases (63·6 to 64·3) and 64·7% of deaths (60·8 to 70·3). Globally, malaria cases and deaths grew rapidly from 1990 reaching a peak of 232 million cases (143 million to 387 million) in 2003 and 1·2 million deaths (1·1 million to 1·4 million) in 2004. Since 2004, child deaths from malaria in sub-Saharan Africa have decreased by 31·5% (15·7 to 44·1). Outside of Africa, malaria mortality has been steadily decreasing since 1990. INTERPRETATION: Our estimates of the number of people living with HIV are 18·7% smaller than UNAIDS's estimates in 2012. The number of people living with malaria is larger than estimated by WHO. The number of people living with HIV, tuberculosis, or malaria have all decreased since 2000. At the global level, upward trends for malaria and HIV deaths have been reversed and declines in tuberculosis deaths have accelerated. 101 countries (74 of which are developing) still have increasing HIV incidence. Substantial progress since the Millennium Declaration is an encouraging sign of the effect of global action. FUNDING: Bill & Melinda Gates Foundation.

National health accounts data from 1996 to 2010: a systematic review.

OBJECTIVE: To collect, compile and evaluate publicly available national health accounts (NHA) reports produced worldwide between 1996 and 2010. METHODS: We downloaded country-generated NHA reports from the World Health Organization global health expenditure database and the Organisation for Economic Co-operation and Development (OECD) StatExtract website. We also obtained reports from Abt Associates, through contacts in individual countries and through an online search. We compiled data in the four main types used in these reports: (i) financing source; (ii) financing agent; (iii) health function; and (iv) health provider. We combined and adjusted data to conform with OECD's first edition of A system of health accounts manual, (2000). FINDINGS: We identified 872 NHA reports from 117 countries containing a total of 2936 matrices for the four data types. Most countries did not provide complete health expenditure data: only 252 of the 872 reports contained data in all four types. Thirty-eight countries reported an average not-specified-by-kind value greater than 20% for all data types and years. Some countries reported substantial year-on-year changes in both the level and composition of health expenditure that were probably produced by data-generation processes. All study data are publicly available at http://vizhub.healthdata.org/nha/. CONCLUSION: Data from NHA reports on health expenditure are often incomplete and, in some cases, of questionable quality. Better data would help finance ministries allocate resources to health systems, assist health ministries in allocating capital within the health sector and enable researchers to make accurate comparisons between health systems.

Vaccine resource tracking systems.

BACKGROUND: From 1999 to 2010, annual disbursements of development assistance for health for vaccinations increased from $0.5 billion to $2.0 billion (all financial values USD 2010). In its 2012 Global Vaccine Action Plan (GVAP), the World Health Assembly recommended establishing a comprehensive vaccination resource tracking system to better understand the source and recipients of these funds, and ultimately their impact on outcomes. This systematic review aims to respond to the GVAP recommendation in reviewing and assessing the state of the data and literature on vaccination resource tracking. METHODS: We scrutinized all relevant vaccination resource tracking systems identified in the literature and by practitioners in the field. We examined schemes used elsewhere in the health sector and by other sectors. Informant interviews were also conducted to determine what data exists and how it might be utilized. With this information, we completed a qualitative assessment of existing approaches to vaccination resources tracking. RESULTS: Tracking systems provide information about some vaccine-related activity in the majority of low- and middle-income countries. Data are generally available for the period of 2006-2010. Levels of granularity vary. Interviewees were concerned about the degree of rigor used to validate the data and the lack of verification. Data are often presented in tabular form, which may be unwieldy for non-technical audiences. CONCLUSIONS: The schemes currently in place to track the resources available for vaccinations were fairly advanced relative to other mechanisms in the health sector. Nonetheless, the coverage, validity, and accessibility of vaccination resource tracking data could be ameliorated. Establishing improved feedback loops and verification mechanisms that connect country-level administrators and the international organizations that support reporting efforts would enhance data quality.

Learning to identify talkers: Do 4.5-month-old infants distinguish between unfamiliar males?

Vocal recognition of socially relevant conspecifics is an important skill throughout the animal kingdom. Human infants recognize their own mother at birth, and they distinguish between unfamiliar female talkers by 4.5 months of age. Can 4.5-month-olds also distinguish between unfamiliar male talkers? To date, no adequately powered study has addressed this question. Here, a visual fixation procedure demonstrates that, unlike adults, 4.5-month-olds (N = 48) are worse at telling apart unfamiliar male voices than they are at telling apart unfamiliar female voices. This result holds despite infants' equal attentiveness to unfamiliar male and female voices.