Biomedical subjects

K N O'Connor

Publications and source records attributed to K N O'Connor.

5 recordsLinked to original sources

PubMed2000

Auditory scene analysis in dyslexics.

It has been argued that dyslexics suffer from temporal sensory processing deficits which affect their ability to discriminate speech in quiet environments. The impact of auditory deficits on non-language aspects of perception, however, is poorly understood. In almost every natural-listening environment, one must constantly construct scenes of the auditory world by grouping and analyzing sounds generated by multiple sources. We investigated whether dyslexics have difficulties grouping sounds. The results demonstrate that dyslexics have an impairment in grouping auditory objects that depends both on the sounds' frequency and presentation rate (i.e. the spectrotemporal context of the sound). We conclude that dyslexics have difficulty constructing scenes of the auditory world, and that these deficits can contribute to learning impairments.

Adolescent↗

PubMed2000

Global processing of spectrally complex sounds in macaques (Macaca mullata) and humans.

How nonhuman species perceive the world is a biological question of fundamental importance, and has major significance for establishing the validity and possible limitations of animal models of human sensory function and perception. Studies in comparative hearing have revealed that almost all animals, including monkeys, are worse than humans at discriminating tone frequencies. Less is known, however, about comparative differences in discriminating more spectrally complex sounds. We compared the capacity of macaques and humans to discriminate complex sound patterns by measuring spectral-contrast sensitivity using stimuli having sine-modulated power spectra, analogous to sine-wave gratings used in visual studies. We found that the auditory system of the macaque is far less sensitive than the human system over the sine-profile frequency range tested (0.5-2.0 cycles/octave). These results indicate that rhesus macaques hear at least some spectrally complex sounds with less fidelity than do humans, and demonstrate large differences in primate species' abilities to process low-resolution spectral patterns. These results cannot be accounted for by traditional, narrowband peripheral filter models of spectral analysis, but instead, imply the involvement of a central, frequency integration process that may differ significantly across species.

Animals↗

PubMed2000

Global spectral and location effects in auditory perceptual grouping.

An important problem in cognitive and systems neuroscience concerns the extent to which perceptual organization can be explained by "local," peripheral physiological mechanisms, or rather by more "global," central, and higher-level processes. Though central in vision research, this issue has received little attention in the field of audition. One claim is that auditory-perceptual grouping mechanisms, possibly related to visual figure-from-ground segregation or "pop-out," are low level, resulting from local processing in the frequency domain. However, no experiments have been performed specifically to test this question. We examined the effects of perceptual grouping on detection for reversal of two repeated target tones, one constant in frequency (1030 Hz), the other free to vary between trials (1045-8580 Hz). Detection was examined in the presence of a 1000-Hz background tone that repeated between target presentations. By varying the frequency of the high-target tone, this task was designed to modulate grouping between the background and low-target tones, thereby affecting reversal detection. We predicted that at large target frequency differences (deltaf), the high-target tone would segregate from the background and low-target tones, and so render the background and low-target tones less distinct. We found that reversal detection declined from optimal levels with increasing deltaf, and that performance was improved by spatially separating the location of the target and background sounds by at least 32 degrees. These results demonstrate that global frequency integration over at least three octaves occurs through grouping, and that grouping is affected by source location. This implies that auditory-perceptual grouping involves global neural processing, i.e., the participation of neurons with very broad frequency input that are also sensitive to spatial location.

Acoustic Stimulation↗

PubMed1999

Auditory temporal integration in the rhesus macaque (Macaca mulatta).

Temporal integration for pure tones was examined in two rhesus macaques. The subjects were required to respond to a brief sound (a tone burst) that deviated from a previous series of sounds (noise bursts) on a trial (a deviant-stimulus detection paradigm). Psychometric functions and thresholds were determined from correct detections (hit proportions) alone, and from d' scores. Two models describing the decline in threshold as a function of stimulus duration, one a power function the other an exponential, were tested against the data. When the decline (slope) in threshold per log stimulus duration is used as a rate measure, our results yield a lower estimate of temporal integration rate in rhesus than did a previous study [Clack, J. Acoust. Soc. Am. 40, 1140-1146 (1966)]. Both studies, however, gave slope estimates of integration rate that were higher than in most other species. Comparison of the models using data from several species, revealed that the exponential, but not the power model, could account for two sources of variation in threshold measurement. One source is due to the range across threshold as a function of duration (the linear rate component), and is described by the constant of proportionality Ik in the model. The other source of variation arises from the rate of decline within this range (the nonlinear rate component), and is described by the time constant tau. In terms of this model, differences in rate estimates between Clack's study and ours (and between rhesus and other species) are primarily due to the linear component. The nonlinear rate component was about equal for our study and Clack's (tau = approximately 150 ms): a time constant that is just slightly larger (indicating a rate of temporal integration slightly slower) than for most other species examined.

Animals↗

PubMed1997

Neural activity in the medial geniculate nucleus during auditory trace conditioning.

In classical trace conditioning the acquisition of a conditioned response (CR) is possible even though an interval (the trace interval) elapses between the conditioned stimulus (CS) and unconditioned stimulus (US). This implies that some neural representation of the CS (the stimulus trace) is able to support association between the two stimuli. The medial geniculate nucleus (MGN), particularly the medial division (mMGN), has been identified as one site in the auditory pathway where associative related changes in neural activity occur. If neurons in the MGN are involved in such a sensory trace and in acquisition of a CR, then it is expected that activity following an acoustic CS should be related to both stimulus and response. This study examined the extracellular activity of single units in the MGN during differential auditory trace conditioning of the rabbit nictitating membrane response (NMR). Two 150-ms tones (600 Hz and 1200 Hz) served as CS+ and CS-, and the US was periorbital electrostimulation. Changes in activity during the stimulus and trace interval were largest in the medial and dorsal MGN divisions on CS+ trials and on trials in which a CR was made. Examination of probe stimuli of short (50 ms) and long (600 ms) duration suggested that both CR latency and activity changes in the trace interval were related to stimulus duration and time-locked to stimulus offset. Comparisons of neural activity on the basis of fast or slow CR responses revealed different patterns of response--activity on fast CR trials was generally greater and tended to occur earlier. These results suggest that MGN neurons are involved in the maintenance of a sensory memory trace and possibly play a part in CR generation and timing.

Acoustic Stimulation↗