Two-month-old infants’ sensitivity to allophonic differences

The present study investigated 2-month-olds’ abilities to discriminate allophonic differences that are potentially useful in segmenting fluent speech. Experiment 1 investigated infants’ sensitivity to the kind of distinction that may signal the presence or absence of a word boundary. When tested with the high-amplitude sucking procedure, infants discriminated pairs of items, such as “nitrate” versus “night rate” and “nikrate” versus “nike rate.” By greatly reducing the potential contribution of prosodic differences to these contrasts, Experiment 2 evaluated whether the allophonic differences for /t/ and /r/ were sufficient for infants to distinguish the “nitrate” versus “night rate” pair. Infants distinguished “nitrate” from a cross-spliced version of “night rate,” which differed only in the allophones for /t/ and /r/ that it included. Thus, infants appear to possess one of the prerequisite capacities (i.e., the ability to discriminate allophonic distinctions) necessary to use allophonic information in segmenting fluent speech.     

Infants' sensitivity to allophonic cues for word segmentation

A series of four experiments was conducted to determine whether English-learning infants can use allophonic cues to word boundaries to segment words from fluent speech. Infants were familiarized with a pair of two-syllable items, such as nitrates and night rates and then were tested on their ability to detect these same words in fluent speech passages. The presence of allophonic cues to word boundaries did not help 9-month-olds to distinguish one of the familiarized words from an acoustically similar foil. Infants familiarized with nitrates were just as likely to listen to a passage about night rates as they were to listen to one about nitrates. Nevertheless, when the passages contained distributional cues that favored the extraction of the familiarized targets, 9-month-olds were able to segment these items from fluent speech. By the age of 10.5 months, infants were able to rely solely on allophonic cues to locate the familiarized target words in passages. We consider what implications these findings have for understanding how word segmentation skills develop.     

Infants’ sensitivity to allophonic cues for word segmentation

A series of four experiments was conducted to determine whether English-learning infants can use allophonic cues to word boundaries to segment words from fluent speech. Infants were familiarized with a pair of two-syllable items, such asnitrates andnight rates and then were tested on their ability to detect these same words in fluent speech passages. The presence of allophonic cues to word bound-aries did not help 9-month-olds to distinguish one of the familiarized words from an acoustically similar foil. Infants familiarized withnitrates were just as likely to listen to a passage aboutnight rates as they were to listen to one aboutnitrates. Nevertheless, when the passages contained distributional cues that favored the extraction of the familiarized targets, 9-month-olds were able to segment these items from fluent speech. By the age of 10.5 months, infants were able to rely solely on allophonic cues to locate the familiarized target words in passages. We consider what implications these findings have for understanding how word segmentation skills develop.

     

The Effect of Stress on Spontaneous Nest Leaving Behavior in the Mouse: An Improved Model of Stress-Induced Behavioral Pathology

The present experiments were conducted to develop a more sensitive and reliable model of stress-induced behavioral pathology in the mouse. Male mice were housed singly in nest cages connected to either a circular tunnel, a recreational cage or a large box with food foraging apparatus. Spontaneous nocturnal out of nest activity or food foraging behavior in these environments was continuously monitored for a two week period during which time the effects of stress were examined. It was found that both repeated restraint and aggression stress markedly and persistently reduced out of nest nocturnal activity or food foraging behavior in all 3 environments but did not alter activity in a novel open field or plus maze or food or saccharin intake in the nest cage. In a preliminary experiment the reduction in out of nest activity by stress was attenuated by prior chronic treatment with the antidepressant, desmethylimipramine. Plasma corticosterone was elevated immediately after aggression stress but reduced 5 hr after chronic aggression stress. The reduction in activity did not appear the result of increased anxiety as measured by spontaneous risk assessment behavior in the nest. It is concluded that the decrease in out of nest activity after stress in the present studies models a withdrawn behavioral state and may be due to either or both a decrease in appetitive motivation to leave the nest or an increased aversion to the external environment which does not apparently involve anxiety.