Search PubMed⌕ Search

Biomedical subjects

D Henderson

Publications and source records attributed to D Henderson.

At least 127 records · Page 7Linked to original sources
PubMed1995

Loosening the constraints on illusory conjunctions: assessing the roles of exposure duration and attention.

Illusory conjunctions are the incorrect combination of correctly perceived features, such as color and shape. They have been found to occur using a brief exposure (under 200 ms) and a dual task designed to divert attention. The present study investigated the roles of exposure duration and attention in obtaining illusory conjunctions. Several mathematical models of the feature integration task were also assessed. Experiment 1 tested participants' accuracy at combining features using a long exposure and an attention-diverting taks. Experiment 2 compared performance with and without the attention-diverting task. The final experiment compared performance using a brief (0.15 s) and a long (1.5 s) exposure duration without an attention-diverting task. Neither attention nor exposure duration had a significant effect on feature integration.

Attention↗
PubMed1995

Neurological side effects in two patients receiving gold injections for rheumatoid arthritis.

We describe two patients who developed neurological side effects as part of the spectrum of nitritoid reactions. Both reactions occurred late in the course of treatment. The first patient developed mild nitritoid symptoms and pain in a band-like distribution, corresponding to T10-T12 dermatomes, shortly after gold sodium thiomalate (GSTM) injection. Further injections were followed by similar symptoms in addition to paraesthesiae and altered pin-prick sensation of anterior thigh and legs with no residual deficit. She has had no further episodes since substitution of aurothioglucose. The second patient experienced mild nitritoid symptoms following several GSTM injections prior experiencing a cerebrovascular accident within several hours of her next injection. She subsequently haemorrhaged into the infarcted area with residual neurological deficits. These cases highlight that nitritoid reactions can be severe and may be heralded by milder symptoms. Patients who develop these reactions whilst receiving GSTM can be successfully changed to aurothioglucose.

Adult↗
PubMed1995

Effect of high-frequency interrupted noise exposures on evoked-potential thresholds, distortion-product otoacoustic emissions, and outer hair cell loss.

The effect of high-frequency interrupted noise exposures on evoked potential (EP) thresholds, distortion-product otoacoustic emissions (DPOAEs), and status of the outer hair cells was studied with the aim of understanding the correspondence among the three measures. Animal subjects were exposed to an octave band noise centered at 4 kHz at 85 dB SPL for 6 hr/day for 10 days. EP and DPOAE recordings were made before the exposure and on days 1, 2, 4, 6, 8, and 10 of exposure. A final set of measurements were made 5 days after the last exposure, following which the animals were sacrificed and their cochleas were examined using scanning electron microscopy. Both EPs and DPOAEs showed a worsening of auditory function after the first exposure and then showed a progressive recovery toward baseline. However, there was no consistent relationship between changes in EP thresholds and changes in DPOAEs nor were there any systematic changes in outer hair cells that corresponded with the changes in DPOAEs. Furthermore, EP thresholds often revealed considerable deficits in function while DPOAEs were normal.

Acoustic Stimulation↗
PubMed1995

Effects of noise exposure, race, and years of service on hearing in U.S. Army soldiers.

Over the last two decades the U.S. Army has instituted a comprehensive hearing conservation program (HCP) to reduce the prevalence of hearing loss in soldiers and civilian employees. As a component of this program, hearing threshold levels (HTLs) are stored in a central computerized Army-wide hearing conservation data registry. The aim of this study was to analyze the hearing threshold data to compare the hearing loss among soldiers representing different (1) race groups, (2) noise exposure groups, and (3) duration of military service. HTLs were age-corrected using data base B values from ISO 1999 (1990). As may be expected, soldiers exposed to high noise levels had significantly poorer hearing than the group of soldiers with limited noise exposure. On the average, results indicated a significant difference in HTLs among the race groups with black soldiers having the most sensitive hearing and white soldiers having the poorest. Also, subjects with greater durations of military service had the least sensitive hearing. Finally, race and years of service factors were found to interact in their effect on HTL. The findings are discussed in terms of implications of race differences, normative data, and effectiveness of the U.S. Army HCP.

Adolescent↗
PubMed1995

Pacemaker inhibition due to anodal ring electrode contact.

A 79-year-old patient with a permanent DDD pacemaker due to a complete AV block and severe bradycardia was seen with complaints of syncope. A surface ECG rhythm strip verified the loss of ventricular output with 6-second periods of asystole. Subsequent investigation using the pacemaker's annotated event markers and multiple polarity intracardiac electrograms indicated spurious signals arising from the anodal ring. On fluoroscopic examination intermittent contact was observed between the anodal ring of the pacing lead and the ring electrode of an abandoned lead. Reprogramming of the pulse generator's ventricular channel to the unipolar sensing configuration corrected the problem.

Aged↗
PubMed1994

Anatomical effects of impact noise.

Four groups of binaural chinchillas were exposed to impact noise (B-duration = 200 ms) ranging from 119 dB to 137 dB peak equivalent SPL at repetition rates of 1/s or 4/s. The duration of exposure was adjusted so that each exposure consisted of equal acoustic energy. Animals were then sacrificed immediately, 24 h or 30 days after the exposure and their cochleas subjected to scanning electron microscopy. For exposures of 119 dB or greater, there appeared to be direct mechanical damage, including large clefts between the third row of outer hair cells and Deiters' cells and fracture of tight cell junctions at the reticular lamina. There was also a progressive increase in cochlear damage over the 30 days of recovery. The patterns of cochlear pathology are compared with hearing losses and cochleograms of chinchillas previously subjected to similar exposures and with results of studies using higher level impulse noise. The results are discussed in terms of 'critical level' for impact and impulse noise.

Acoustic Stimulation↗
PubMed1994

Frustration.

Explore the source record for details and available documents.

Attitude of Health Personnel↗
PubMed1994

The effect of 'conditioning' exposures on hearing loss from impulse noise.

Research has shown that prior noise exposures or 'conditioning' can moderate the amount of permanent threshold shift (PTS) from subsequent high intensity noise exposures. The aim of this experiment was to study the effect of 'conditioning' on subsequent exposure to high intensity impulse noise. The subjects were seven experimental and 14 control monaural chinchillas. Evoked potential (EVP) thresholds were measured before and after the noise exposures. Experimental animals received 10 days of exposure to an octave band noise (OBN) centered at 0.5 kHz OBN at 95 dB SPL (6 h on/18 h off) and allowed to recover for 5 days. The subjects were then exposed to an impulse noise at 150 dB SPL. The temporal spacing of the impulses consisted of a series of 50 pairs of impulses presented 50 ms apart with 1000 ms between the onset of each pair. The total duration of exposure was approximately 1 min. Control animals received only the impulse noise exposure. PTS was measured after 4 weeks. The threshold shift (TS) patterns during the 'conditioning' phase were consistent with previous research, with the greatest amount of TS occurring on the second day and decreasing with continued exposures. Four weeks after recovery from the impulse noise, the experimental animals showed significantly less PTS than the control animals. In addition, histological examination revealed significantly less hair cell loss in the experimental than in the control subjects. The results are discussed in the context of previous studies on 'toughening' and on the effects of impulse noise.

Acoustic Stimulation↗
PubMed1994

Localization of F-actin and fodrin along the organ of Corti in the chinchilla.

The distribution of the two cytoskeletal proteins, filamentous actin (F-actin) and fodrin, was investigated along the organ of Corti of the chinchilla using laser scanning confocal fluorescence microscopy. High intensity labeling of F-actin was seen in outer and inner hair cells, including the stereocilia. High intensity staining was also seen for fodrin in outer and inner hair cells, but not in their stereocilia. Staining intensity of both proteins along the lateral cell wall of the outer hair cells appeared to be greater in the middle and basal cochlear turns than in the apical turn. Pillars and Deiters cells also exhibited high intensity labeling of F-actin. The lack of significant differences in the distribution of fodrin between outer and inner hair cells makes the role of this protein in the active processes still unclear. Comparison of the distribution of F-actin and fodrin in the chinchilla with those reported in the guinea pigs suggest possible species differences.

Actins↗
PubMed1994

The role of middle ear muscles in the development of resistance to noise induced hearing loss.

The role of middle ear muscles (MEMs) in the development of increased resistance to noise induced hearing loss (NIHL) was studied using monaural chinchillas. Animals with severed MEMs as well as those with intact MEMs were exposed to an octave band noise (OBN) centered at 0.5 kHz at 95 dB for six hours/day for ten consecutive days. Results indicated that animals with severed MEMs showed greater initial threshold shifts (TS) than the animals with intact MEMs. Both the groups showed a decrease in TS over the ten days of exposure. The subjects were given five days of recovery and then re-exposed to the same noise at 106 dB for 48 h. Permanent threshold shifts (PTS) in each group was compared against those in a control group exposed to the noise only at the higher level. Interestingly, both the 'conditioned' groups incurred substantially less PTS than the control group exposed only to the higher level.

Animals↗
PubMed1994

Changes in distortion product otoacoustic emissions and outer hair cells following interrupted noise exposures.

Changes in distortion product otoacoustic emissions (DPOAEs) were examined during and after interrupted noise exposures and compared to the condition of the outer hair cells (OHCs) and inner hair cells (IHCs) as assessed by scanning electron microscopy (SEM). Binaural, adult chinchillas were exposed to a 95 dB SPL, octave band noise centered at 0.5 kHz for 15 days using a 3 h on/9 h off schedule. DPOAEs were measured before, during and after the exposures. DPOAE amplitudes decreased significantly during the first few days of the interrupted noise exposures and then began to recover. At most frequencies, the emission amplitudes recovered completely to pre-exposure baseline values by five days after the last exposure. The results of the present study indicate that the changes in DPOAE amplitude paralleled the recovery in the amplitude and threshold of the compound action potentials as reported previously (Boettcher et al., 1992). Although the DPOAEs completely recovered, considerable OHC loss and stereocilia disarray was evident even four weeks after exposure.

Acoustic Stimulation↗
PubMed1994

The relationship among distortion-product otoacoustic emissions, evoked potential thresholds, and outer hair cells following interrupted noise exposures.

Distortion-product otoacoustic emissions (DPOAEs) are gaining popularity as indicators of the status of the cochlea. The efficacy of DPOAEs as indicators of changes in thresholds and the status of outer hair cells (OHCs) were examined using an animal model. Monaural chinchillas were exposed to an octave band noise (OBN) centered at 0.5 kHz at 95 dB SPL for 6 hr/day for 10 days. DPOAEs and evoked potential thresholds were recorded before, during, and after the exposures. The animals were sacrificed 5 days after the last exposure, and the status of OHCs was assessed using scanning electron microscopy. Results indicate that both evoked potential thresholds and DPOAEs effectively track the temporary changes associated with interrupted noise exposures. However, DPOAEs often recovered to their baseline even when there was a threshold shift of > 25 dB. Furthermore, at 5 days postexposure, both evoked potential thresholds and DPOAEs were normal despite considerable OHC pathology. The findings suggest that normal DPOAEs may not guarantee normal cochlear status and, therefore, results of DPOAE measurements should be interpreted cautiously.

Acoustic Stimulation↗