Biomedical subjects

Kelly L McDonald

Publications and source records attributed to Kelly L McDonald.

6 recordsLinked to original sources

PubMed2005

Left thalamo-cortical network implicated in successful speech separation and identification.

The separation of concurrent sounds is paramount to human communication in everyday settings. The primary auditory cortex and the planum temporale are thought to be essential for both the separation of physical sound sources into perceptual objects and the comparison of those representations with previously learned acoustic events. To examine the role of these areas in speech separation, we measured brain activity using event-related functional Magnetic Resonance Imaging (fMRI) while participants were asked to identify two phonetically different vowels presented simultaneously. The processing of brief speech sounds (200 ms in duration) activated the thalamus and superior temporal gyrus bilaterally, left anterior temporal lobe, and left inferior temporal gyrus. A comparison of fMRI signals between trials in which participants successfully identified both vowels as opposed to when only one of the two vowels was recognized revealed enhanced activity in left thalamus, Heschl's gyrus, superior temporal gyrus, and the planum temporale. Because participants successfully identified at least one of the two vowels on each trial, the difference in fMRI signal indexes the extra computational work needed to segregate and identify successfully the other concurrently presented vowel. The results support the view that auditory cortex in or near Heschl's gyrus as well as in the planum temporale are involved in sound segregation and reveal a link between left thalamo-cortical activation and the successful separation and identification of simultaneous speech sounds.

Acoustic Stimulation↗

PubMed2005

Contribution of harmonicity and location to auditory object formation in free field: evidence from event-related brain potentials.

The contribution of location and harmonicity cues in sound segregation was investigated using behavioral reports and source waveforms derived from the scalp-recorded evoked potentials. Participants were presented with sounds composed of multiple harmonics in a free-field environment. The third harmonic was either tuned or mistuned and could be presented from the same or different location from the remaining harmonics. Presenting the third harmonic at a different location than the remaining harmonics increased the likelihood of hearing the tuned or slightly (i.e., 2%) mistuned harmonic as a separate object. Partials mistuned by 16% of their original value "pop out" of the complex and were paralleled by an object-related negativity (ORN) that superimposed the N1 and P2 components. For the 2% mistuned stimuli, the ORN was present only when the mistuned harmonic was presented at a different location than the remaining harmonics. Presenting the tuned harmonic at a different location also yielded changes in neural activity between 150 and 250 ms after sound onset. The behavioral and electrophysiological results indicate that listeners can segregate sounds based on harmonicity or location alone. The results also indicate that a conjunction of harmonicity and location cues contribute to sound segregation primarily when harmonicity is ambiguous.

Acoustic Stimulation↗

PubMed2004

Aging: a switch from automatic to controlled processing of sounds?

In this article, the authors show that aging differentially affects peoples' ability to automatically and voluntarily process auditory information. Young, middle-aged, and older adults matched behaviorally in an auditory discrimination task showed similar patterns of neural activity indexing the voluntary and conscious detection of deviant (i.e., target) stimuli. In contrast, a negative wave indexing automatic processing (the mismatch negativity) was elicited only in young adults for near-threshold stimuli. These results indicate that aging affects the ability to automatically register small changes in a stream of homogeneous stimuli. However, this age-related decline in automatic detection of small change in the auditor environment can be compensated for by top-down controlled processes.

Adult↗

PubMed2003

Aging and the processing of sound duration in human auditory cortex.

Age-related declines in coding the fine temporal structure of acoustic signals is proposed to play a critical role in the speech perception difficulties commonly observed in older individuals. This hypothesis was tested by measuring auditory evoked potentials elicited by sounds of various durations in young, middle-aged and older adults. All stimuli generated N1 and P2 waves that peaked at about 104 and 200 ms post-stimulus onset. The N1 amplitude increased linearly with increases in the tonal duration in young, middle-aged, and older adults. The P2 amplitude also increased linearly with signal duration, but only in young and middle-aged adults. The results demonstrate that the N1 and P2 waves can resolve duration differences as short as 2-4 ms and that normal aging decreases the temporal resolving power for processing small differences in sound duration.

Adult↗

PubMed2002

Automatic and controlled processing of melodic contour and interval information measured by electrical brain activity.

Most work on how pitch is encoded in the auditory cortex has focused on tonotopic (absolute) pitch maps. However, melodic information is thought to be encoded in the brain in two different "relative pitch" forms, a domain-general contour code (up/down pattern of pitch changes) and a music-specific interval code (exact pitch distances between notes). Event-related potentials were analyzed in nonmusicians from both passive and active oddball tasks where either the contour or the interval of melody-final notes was occasionally altered. The occasional deviant notes generated a right frontal positivity peaking around 350 msec and a central parietal P3b peaking around 580 msec that were present only when participants focused their attention on the auditory stimuli. Both types of melodic information were encoded automatically in the absence of absolute pitch cues, as indexed by a mismatch negativity wave recorded during the passive conditions. The results indicate that even in the absence of musical training, the brain is set up to automatically encode music-specific melodic information, even when absolute pitch information is not available.

Adult↗

PubMed2002

Neural activity associated with distinguishing concurrent auditory objects.

The neural processes underlying concurrent sound segregation were examined by using event-related brain potentials. Participants were presented with complex sounds comprised of multiple harmonics, one of which could be mistuned so that it was no longer an integer multiple of the fundamental. In separate blocks of trials, short-, middle-, and long-duration sounds were presented and participants indicated whether they heard one sound (i.e., buzz) or two sounds (i.e., buzz plus another sound with a pure-tone quality). The auditory stimuli were also presented while participants watched a silent movie in order to evaluate the extent to which the mistuned harmonic could be automatically detected. The perception of the mistuned harmonic as a separate sound was associated with a biphasic negative-positive potential that peaked at about 150 and 350 ms after sound onset, respectively. Long duration sounds also elicited a sustained potential that was greater in amplitude when the mistuned harmonic was perceptually segregated from the complex sound. The early negative wave, referred to as the object-related negativity (ORN), was present during both active and passive listening, whereas the positive wave and the mistuning-related changes in sustained potentials were present only when participants attended to the stimuli. These results are consistent with a two-stage model of auditory scene analysis in which the acoustic wave is automatically decomposed into perceptual groups that can be identified by higher executive functions. The ORN and the positive waves were little affected by sound duration, indicating that concurrent sound segregation depends on transient neural responses elicited by the discrepancy between the mistuned harmonic and the harmonic frequency expected based on the fundamental frequency of the incoming stimulus.

Adult↗