Response to auditory stimuli in 6- and 9-week-old human infants
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Newborn infants show developmental changes in their response to sound. Cardiac orienting responses to sound emerge by 9 weeks of age, indicating auditory development in early infancy.
Area of Science:
- Developmental psychology
- Auditory perception
- Infant behavior
Background:
- Infants' responses to auditory stimuli are crucial for understanding early sensory development.
- Previous research has explored infant responses, but age-related changes in orienting responses require further investigation.
Purpose of the Study:
- To investigate age-related changes in cardiac and non-cardiac responses to auditory stimuli in young infants.
- To differentiate between orienting and startle responses in infants at 6 and 9 weeks of age.
Main Methods:
- Cardiac and non-cardiac responses (sucking, eye-opening, eye-movement) were measured in 48 infants (24 at 6 weeks, 24 at 9 weeks).
- Infants were exposed to 5-second, 75-dB complex sounds under conditions designed to elicit orienting responses.
Main Results:
- No significant cardiac orienting response was observed at 6 weeks of age.
- A significant decelerative cardiac response, indicative of orienting, emerged by 9 weeks of age.
- Sucking suppression was identified as a component of orienting, while eye-movement responses were linked to startle.
Conclusions:
- Age-related changes in auditory orienting responses occur in infants as young as 9 weeks, even when controlling for state.
- The type of auditory stimulus influences the probability and nature of infant orienting responses.
- These findings contribute to understanding the developmental trajectory of auditory processing and attention in early infancy.
Abstract:
Response to 5-sec, 75-dB complex sounds was studied in groups of 24 infants each at 6 and 9 weeks of age. Under conditions appropriate for eliciting orienting, no significant cardiac response appeared at 6 weeks, but a significantly decelerative response did appear at 9weeks. Measurement of noncardiac responses suggested that sucking suppression is also a component of orienting to sound, that the status of eye-opening is equivocal, and that previously reported eye-movement responses are probably a component of startle. We concluded that age changes in orienting may occur in young infants, even when state is controlled, and that the probability of orienting varies with the kind of stimuli employed.