Biomedical subjects

Douglas E H Hartley

Publications and source records attributed to Douglas E H Hartley.

6 recordsLinked to original sources

PubMed2005

Effects of otitis media with effusion on auditory temporal resolution.

OBJECTIVE: There is mounting evidence to suggest that otitis media with effusion (OME) is associated with auditory processing deficits that persist beyond the resolution of the peripheral hearing loss. This study investigated the residual effects of OME on auditory temporal resolution. EXPERIMENT 1: METHODS: Experiment 1 measured detection thresholds for a brief tone presented either before (backward masking) or during (simultaneous masking) a masking noise, in 6- and 8-year-old children. Six-year-olds were selected from a prospectively studied group with a lifetime known history of OME. Eight-year-old children, with a retrospectively determined history of OME, were also recruited. All children were free of OME at the time of testing. RESULTS: Regardless of OME history, 6-year-old children had similar tone thresholds on all masking tasks. In contrast, 8-year-olds with a history of recurrent OME had 18 and 4dB higher mean thresholds for the backward and simultaneous masking conditions, respectively, compared with age-matched controls. Possible explanations for these results included (i) recruitment bias, rather than OME, contributed to differences in auditory processing abilities amongst 8-year-old children, or (ii) OME impaired performance at both ages, but this was not seen in 6-year-olds due to 'ceiling' effects. EXPERIMENT 2: METHODS: To distinguish between these possibilities, Experiment 2 measured temporal resolution, using backward masking and amplitude modulation detection, in the prospectively studied group of children when they were 8 years old. RESULTS: Regardless of OME history, these 8-year-olds had similar auditory temporal processing abilities. Results from Experiment 2 suggested that recruitment bias was the most likely explanation for the difference in auditory processing abilities between 8-year-old children with and without a history of OME found in Experiment 1. Consistent with previous data, associations were found between backward masking, age and cognitive ability. CONCLUSION: There is no evidence to suggest that OME effects temporal resolution after the recovery of normal pure-tone thresholds.

Age Factors↗

PubMed2004

Auditory processing efficiency and temporal resolution in children and adults.

Children have higher auditory backward masking (BM) thresholds than adults. One explanation for this is poor temporal resolution, resulting in difficulty separating brief or rapidly presented sounds. This implies that the auditory temporal window is broader in children than in adults. Alternatively, elevated BM thresholds in children may indicate poor processing efficiency. In this case, children would need a higher signal-to-masker ratio than adults to detect the presence of a signal. This would result in poor performance on a number of psychoacoustic tasks but would be particularly marked in BM due to the compressive nonlinearity of the basilar membrane. The objective of the present study was to examine the competing hypotheses of "temporal resolution" and "efficiency" by measuring BM as a function of signal-to-masker interval in children and adults. The children had significantly higher thresholds than the adults at each of the intervals. Subsequent modeling and analyses showed that the data for both children and adults were best fitted using the same, fixed temporal window. Therefore, the differences in BM threshold between adults and children were not due to differences in temporal resolution but to reduced detection efficiency in the children.

Acoustic Stimulation↗

PubMed2003

The auditory basis of language impairments: temporal processing versus processing efficiency hypotheses.

Claims have been made that language-impaired children have deficits processing rapidly presented or brief sensory information. These claims, known as the 'temporal processing hypothesis', are supported by demonstrations that language-impaired children have excess backward masking (BM). One explanation for these results is that BM is developmentally delayed in these children. However, little was known about how BM normally develops. Recently, we assessed BM in normally developing 6- and 8-year-old children and adults. Results showed that BM thresholds continue to improve over a comparatively protracted period (>10 years old). We also analysed reported deficits in BM in language-impaired and younger children, in terms of a model of temporal resolution. This analysis suggests that poor processing efficiency, rather than deficits in temporal resolution, can account for these results. This 'processing efficiency hypothesis' was recently tested in our laboratory. This experiment measured BM as a function of delays between the tone and the noise in children and adults. Results supported the processing efficiency hypothesis, and suggested that reduced processing efficiency alone could account for differences between adults and children. These findings provide a new perspective on the mechanisms underlying communication disorders, and imply that remediation strategies should be directed towards improving processing efficiency, not temporal resolution.

Auditory Threshold↗

PubMed2003

Effects of otitis media with effusion (OME) on central auditory function.

Conductive hearing loss attenuates and delays sound passing through the middle ear. This impairs binaural hearing and other central auditory functions dependent on high fidelity sound transmission. Persistent conductive loss leads to central impairments that persist after the peripheral loss has resolved. For example, children who have had multiple episodes of otitis media with effusion (OME) in the first few years of life may have poor detection of sounds in noisy environments, evidenced by reduced binaural unmasking (BU). Recent research shows that a 'threshold' level of OME is required to produce impaired BU. Children who had OME in one or both ears for more than about 50% of the first 5 years had reduced BU. Animal research, using long-term ear plugging, suggests that total OME duration, rather than age at the time of having the disease, determines its effect on BU. Animals reared with bilateral (but not unilateral) ear plugs also have poor auditory temporal resolution, and reduced sensitivity to short tones in the presence of background noise, after plug removal. However, given time (6-24 months) and training, all animals regained normal temporal resolution.

Auditory Diseases, Central↗

PubMed2003

Effects of conductive hearing loss on temporal aspects of sound transmission through the ear.

Effects of conductive hearing loss on level and spectrum are well known. However, little is known about possible additional effects on temporal aspects of sound transmission. This study investigated effects of earplugs and middle ear effusions on amplitude and timing of cochlear microphonic (CM) responses in gerbils. Bilateral CM responses to pure tones (1-16 kHz) were monitored before and after (i). unilateral earplug insertion or (ii). injection of silicone oil, of various viscosities, into one middle ear. Earplugs produced flat hearing losses (mean 13 dB) and delayed CMs more at lower (mean 80 micros, 1-6 kHz) than at higher (20 micros, 8-16 kHz) frequencies. Effusions also produced flat hearing loss. On average, high viscosity effusions produced larger hearing losses (36 dB) than medium (25 dB) or low (20 dB) viscosity effusions. Low and medium viscosity effusions delayed responses to lower (mean 82 and 65 micros respectively, 1-6 kHz) more than to higher (mean 20 and 10 micros respectively, 8-16 kHz) frequencies. High viscosity effusions produced smaller delays across all frequencies (mean 31 micros, 1-16 kHz). In normal animals, CM responses were not delayed over a wide range of stimulus levels. Therefore, in addition to attenuation, conductive loss distorts acoustic temporal cues important for hearing.

Animals↗

PubMed2002

Auditory processing efficiency deficits in children with developmental language impairments.

The "temporal processing hypothesis" suggests that individuals with specific language impairments (SLIs) and dyslexia have severe deficits in processing rapidly presented or brief sensory information, both within the auditory and visual domains. This hypothesis has been supported through evidence that language-impaired individuals have excess auditory backward masking. This paper presents an analysis of masking results from several studies in terms of a model of temporal resolution. Results from this modeling suggest that the masking results can be better explained by an "auditory efficiency" hypothesis. If impaired or immature listeners have a normal temporal window, but require a higher signal-to-noise level (poor processing efficiency), this hypothesis predicts the observed small deficits in the simultaneous masking task, and the much larger deficits in backward and forward masking tasks amongst those listeners. The difference in performance on these masking tasks is predictable from the compressive nonlinearity of the basilar membrane. The model also correctly predicts that backward masking (i) is more prone to training effects, (ii) has greater inter- and intrasubject variability, and (iii) increases less with masker level than do other masking tasks. These findings provide a new perspective on the mechanisms underlying communication disorders and auditory masking.

Adult↗