Infants Recognize Human Speech
The ability of infants to recognize speech is more sophisticated than previously known, according to New York University researchers. Their study, published in Developmental Psychology, showed that infants as young as 9 months old could make distinctions between speech and nonspeech sounds in humans and animals. Understanding when these abilities become instilled sheds new light on how early in life humans develop the ability to recognize speech.
To gauge aptitude to perceive speech at any early age, researchers examined the responses of 9-month-olds to recorded human and parrot speech and nonspeech sounds. Speech sounds by a parrot and an adult female included the words "truck," "treat," "dinner," and "two." The adult nonspeech sounds were whistles and a clearing of the throat, and the parrot nonspeech sounds were squawks and chirps.
Because infants cannot verbally communicate their recognition of speech, researchers used a commonly used method to measure this process: the infants' tendency to look longer at what they find interesting or unusual. Looking longer at a visual paired with a sound may be interpreted as a reflection of recognition. In this study, sounds were paired with a series of visuals: adult female faces, a checkerboard-like image, and a cup.
The results suggest that infants listened longer to human speech than human nonspeech sounds regardless of the visual stimulus, revealing the ability to recognize human speech independent of the context.
The findings on nonhuman speech were more nuanced. When paired with human-face visuals or human artifacts like cups, the infants listened to parrot speech longer than they did nonspeech, such that their preference for parrot speech was similar to their preference for human speech sounds. However, longer listening did not occur in the presence of other visual stimuli, suggesting the infants were able to distinguish animal speech from nonspeech, but only in some contexts. Search doi: 10.1037/a0029055.
Protein May Prevent Hearing Loss
Scientists have discovered a mechanism that helps protect sensory cells in the inner ear from permanent damage—a condition called earbud deafness syndrome—following acoustic noise exposure. The protein AMPK, which protects cells during a lack of energy, also activates a channel protein in the cell membrane that allows potassium to leave the cell. Study results, published online in FASEB Journal, could lead to new strategies and therapies to prevent and treat trauma resulting from extreme noise, especially in people with AMPK gene variants that may make them more vulnerable to hearing loss.
Researchers compared two groups of mice—one normal and another that lacked the AMPK protein—with similar hearing ability. They tested mice's hearing by measuring sound-induced brain activity, with all mice exposed to well-defined noise causing an acoustic trauma and leading to hearing impairment. After exposure, the hearing of the normal mice mostly recovered after two weeks, but the hearing in AMPK-deficient mice remained significantly impaired.
"When it comes to preventing hearing loss, keeping the volume down is still the best strategy," said Gerald Weissmann, FASEB Journal editor-in-chief. "This discovery does help explain why some people seem more likely to lose their hearing than others. At the same time, it also provides a target for new preventive strategies—and perhaps even a treatment—for earbud deafness syndrome." Search doi: 10.1096/fj.12-208132.