Infants' discrimination of consonant contrasts in the presence and absence of talker variability.

To learn speech-sound categories, infants must identify the acoustic dimensions that differentiate categories and selectively attend to them as opposed to irrelevant dimensions. Variability on irrelevant acoustic dimensions can aid formation of robust categories in infants through adults in tasks such as word learning (e.g., Rost and McMurray, 2009) or speech-sound learning (e.g., Lively et al., 1993). At the same time, variability sometimes overwhelms learners, interfering with learning and processing. Two prior studies (Kuhl & Miller, 1982; Jusczyk, Pisoni, & Mullennix, 1992) found that irrelevant variability sometimes impaired early sound discrimination. We asked whether variability would impair or facilitate discrimination for older infants, comparing 7.5-month-old infants' discrimination of an early acquired native contrast, /p/ vs. /b/ (in the word forms /pIm/ vs. /bIm/), in Experiment 1, with an acoustically subtle, non-native contrast, /n/ vs. /ŋ/ (in /nIm/ vs. /ŋIm/), in Experiment 2. Words were spoken by one or four talkers. Infants discriminated the native but not the non-native contrast, and there were no significant effects of talker condition. We discuss implications for theories of phonological learning and avenues for future research.

Neuroimaging findings of retroclival hemorrhage in children: a diagnostic conundrum.

BACKGROUND: Retroclival hemorrhage in children may occur in three compartments, namely epidural, subdural, and subarachnoid, frequently secondary to trauma. Retroclival epidural hematoma may be associated with ligamentous injury, which may further result in instability at the craniocervical junction. Retroclival subdural hematoma may indicate a sentinel event for traumatic injury elsewhere within the brain or posterior fossa. Retroclival subarachnoid hemorrhage may have severe clinical consequences related to vasospasm. OBJECTIVE: Neuroimaging is essential in the recognition, localization, and characterization of retroclival hemorrhage into various compartments and for evaluating potential severe clinical consequences such as craniocervical junction instability, underlying traumatic brain injury, and ischemia secondary to vasospasm. The goal of this paper is to discuss the anatomy and biomechanics of the craniocervical junction as well as the neuroimaging findings associated with various compartments of retroclival hemorrhage in children.