Biomedical subjects

R N Desjardins

Publications and source records attributed to R N Desjardins.

5 recordsLinked to original sources

PubMed2001

Measuring temporal resolution in infants using mismatch negativity.

We show that the mismatch negativity (MMN) component of the event-related potential can be used to measure auditory temporal resolution in human infants. Infrequent stimuli with silent gaps of 4, 8, or 12 ms modulated the P2 component, generated MMN, and produced a P3a-like positivity. The data indicate that within-channel gap detection thresholds at 6 months are essentially at adult levels under conditions of little adaptation. Since MMN is elicited without attention and does not require a behavioural response, it can be measured similarly across the lifespan. We are now in a position to study the development of cross-channel temporal resolution and adaptation effects in infancy, and to examine how these abilities in infancy relate to later language acquisition.

Acoustic Stimulation↗

PubMed2000

Is infant-directed speech prosody a result of the vocal expression of emotion?

Many studies have found that infant-directed (ID) speech has higher pitch, has more exaggerated pitch contours, has a larger pitch range, has a slower tempo, and is more rhythmic than typical adult-directed (AD) speech. We show that the ID speech style reflects free vocal expression of emotion to infants, in comparison with more inhibited expression of emotion in typical AD speech. When AD speech does express emotion, the same acoustic features are used as in ID speech. We recorded ID and AD samples of speech expressing love-comfort, fear, and surprise. The emotions were equally discriminable in the ID and AD samples. Acoustic analyses showed few differences between the ID and AD samples, but robust differences across the emotions. We conclude that ID prosody itself is not special. What is special is the widespread expression of emotion to infants in comparison with the more inhibited expression of emotion in typical adult interactions.

Adult↗

PubMed1999

Using mismatch negativity to measure auditory temporal resolution thresholds.

It has been hypothesized that poor auditory temporal resolution is related to language-learning problems in children as well as problems with speech perception in noise in the elderly. We show that the presence of occasional silent gaps between short tone pips elicits mismatch negativity (MMN) in young adults. We also measured gap-detection thresholds with MMN that agree well with behavioural thresholds. Near threshold, the MMN increases as the gap size increases millisecond by millisecond. The MMN methodology for measuring temporal resolution is not only robust, but can be applied identically across the life span as it does not require the attention of participants or a behavioural response. We are now in a position to examine temporal resolution in infancy.

Acoustic Stimulation↗

PubMed1997

An exploration of why preschoolers perform differently than do adults in audiovisual speech perception tasks.

Preschoolers' perception of audiovisual speech is considerably less influenced by visual information than adults'. We test the hypothesis that experience correctly producing consonants plays a role in developing the underlying representation which mediates the perception of visible speech. We divided preschoolers into two groups: those who made substitution errors and those who did not. Using a newly developed methodology, we tested substituters, nonsubstituters, and adults in an auditory-only condition, a visual-only condition, and an audiovisual condition. There were no differences among groups in the auditory-only condition. Overall, children still showed less visual influence than adults. Among the children, substituters were poorer at lip-reading in the visual-only condition and showed less visual influence on the incongruent audiovisual tokens than did nonsubstituters. These results support our hypothesis that experience correctly producing consonants plays a role in the elaboration of the underlying representation.

Adult↗

PubMed1996

Infants' reliance on a social criterion for establishing word-object relations.

The language children hear presents them with a multitude of co-occurrences between words and things in the world, and they must repeatedly determine which among these manifold co-occurrences is relevant. Social factors--such as cues regarding the speaker's referential intent--might serve as one guide to whether word-object covariation should be registered. In 2 studies, infants (15-20 months and 18-20 months in Studies 1 and 2, respectively) heard novel labels at a time when they were investigating a single novel object; in one case the label was uttered by a speaker seated within the infant's view and displaying concurrent attention to the novel toy (coupled condition), whereas in the other case the label emanated from a speaker seated out of the infant's view (decoupled condition). In both studies, subsequent comprehension questions indicated that infants of 18-20 months registered a stable link between label and object in the coupled conditions, but not in the decoupled condition, despite the fact that covariation between label and object was equivalent in the 2 conditions. Thus, by 18-20 months children are inclined to establish a mapping between word and object only when a speaker displays signs of referring to that object.

Age Factors↗