Melanie Böhm | PubMed Health

PubMed2006

Complete genome of the mutualistic, N2-fixing grass endophyte Azoarcus sp. strain BH72.

Azoarcus sp. strain BH72, a mutualistic endophyte of rice and other grasses, is of agrobiotechnological interest because it supplies biologically fixed nitrogen to its host and colonizes plants in remarkably high numbers without eliciting disease symptoms. The complete genome sequence is 4,376,040-bp long and contains 3,992 predicted protein-coding sequences. Genome comparison with the Azoarcus-related soil bacterium strain EbN1 revealed a surprisingly low degree of synteny. Coding sequences involved in the synthesis of surface components potentially important for plant-microbe interactions were more closely related to those of plant-associated bacteria. Strain BH72 appears to be 'disarmed' compared to plant pathogens, having only a few enzymes that degrade plant cell walls; it lacks type III and IV secretion systems, related toxins and an N-acyl homoserine lactones-based communication system. The genome contains remarkably few mobile elements, indicating a low rate of recent gene transfer that is presumably due to adaptation to a stable, low-stress microenvironment.

Azoarcus↗

PubMed2005

Amplitude-mapping effects on speech intelligibility with unilateral and bilateral cochlear implants.

OBJECTIVE: A study was conducted examining the effects of amplitude-mapping adjustments on speech intelligibility with bilateral cochlear implant users, for both unilateral and bilateral device use. The main motivation for this study was the consideration that bilateral loudness summation may result in sounds becoming too loud if no adjustments are made to standard monaural amplitude-mapping functions (maps) when used bilaterally. In that case, reductions of the stimulation levels may be needed. The objective was to assess the impact of such adjustments on speech intelligibility in noise and in quiet. DESIGN: Four different maps were compared in eight bilateral users of the Nucleus 24 system. Each map variation was taken home for 1 week and used bilaterally. After each week, the map used was tested both unilaterally and bilaterally using an adaptive speech-in-noise test and bilaterally for low-level speech in quiet. For the tests in noise, both speech and noise were presented from the same loudspeaker placed directly in front of the listener (S0N0). One of the maps evaluated was a standard clinical map, fitted as if only one ear were to be used. The three other maps used stimulation levels that were reduced more near the maximal stimulation levels, near thresholds, or else by a similar amount over the entire dynamic range. RESULTS: The data showed a modest but statistically significant decrease in performance when stimulation levels were lowered. This was true both in noise and in quiet. For level reductions corresponding to binaural loudness summation effects, the performance decrease was on the order of 1 to 2 dB. Altering the slope of the map had relatively little effect on performance. Comparison of unilateral with bilateral performance using the same map (i.e., no compensation for bilateral loudness summation) and with speech and noise both presented from in front of the listeners showed a modest but statistically significant improvement in the bilateral condition. CONCLUSIONS: Using higher stimulation levels in amplitude-mapping functions can improve both monaural and binaural speech perception performance in quiet and in noise, even when the slope of the acoustic to electrical amplitude-mapping function is held constant (i.e., when the electrical signal-to-noise ratio remains constant). The results in noise can be understood if we assume that the relation between electrical stimulation levels and loudness grows faster at higher stimulation levels. When comparing the monaural better ear with binaural performance in noise (S0N0) by using the same map, that is to say, when no adjustments were made in the bilateral condition for bilateral loudness summation, an average signal-to-noise ratio benefit of 1.4 dB was found in the bilateral condition. These findings indicate that when fitting bilateral devices clinically, although binaural performance may decrease slightly if levels need to be reduced to compensate for binaural loudness summation, the binaural S0N0 advantage over the better ear will offset this. Consequently, performance with both ears after adjustment is likely to remain at least as good as for the better ear alone without level adjustment, even in the S0N0 condition where binaural advantages are minimized.

Acoustic Stimulation↗

PubMed2004

Benefits of bilateral electrical stimulation with the nucleus cochlear implant in adults: 6-month postoperative results.

OBJECTIVE: To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study, and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use. DESIGN: : Repeated single subject measures were carried out for each subject, with each subject serving as their own control. Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed. Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees, at S+45 degrees N45 degrees and at S-45 degrees N+45 degrees . Test materials included Freiburger monosyllabic words, Oldenburger sentences, and the Hochmair-Schulz-Moser sentences. Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality. The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately, classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions. For localization of sound, the binaural advantage was compared with left and right ears separately. Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student's t test to determine the statistical difference between the data sets. SETTING: Tertiary referral centers with a cochlear implant program. PATIENTS: Thirty-seven profoundly hearing-impaired adults were enrolled in the study, 22 simultaneously and 15 sequentially bilaterally implanted. All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3G speech processor, with the vast majority using the ACE speech coding strategy. RESULTS: For spatially separated speech in noise conditions, an interaural performance advantage for the ear closest to the speech source (i.e., with a superior signal to noise ratio) compared with that for the ear closest to the noise source (i.e., with an inferior signal to noise ratio) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal. This is referred to as a significant binaural head-shadow benefit, resulting in a mean improvement between -10 dB and -11.4 dB in the critical signal to noise ratio required for 50% speech comprehension for the Olden-burger sentences and a mean improvement in the maximum score of 42% to 55% for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences. Bilateral stimulation is always observed to provide a performance advantage over the unilateral listening condition for either ear when ipsilateral to the noise source. In addition, as demonstrated by approximately half the subjects tested in noise with the Hochmair-Schulz-Moser sentences, a performance advantage of bilateral stimulation may be observed over the better ear alone when positioned ipsilateral to the speech signal, which is referred to as a binaural squelch effect. On average, for the group, this resulted in a statistically significant improvement in speech comprehension scores of 8% in the bilateral listening condition compared with the scores for the better ear alone. Through assessment of comprehension of coincidental speech in noise and speech in quiet, a significant benefit of binaural redundancy was noted for the group for Oldenburger sentence scores in noise and in quiet compared with unilateral scores for either ear and for the Freiburger monosyllabic words in quiet in comparison with the better ear alone scores. Binaural stimulation also led to a significant improvement in localization ability over either monaural condition, with the root mean square degrees of error reduced by 38 degrees compared with that observed for unilateral stimulation. CONCLUSION: Similar to what has been observed for bilateral acoustic stimulation in the past, bilateral electrical stimulation provides the foundation for the potential advantages of the head-shadow effect, providing a binaural head-shadow benefit and binaural auditory processing such as binaural redundancy and binaural squelch effects, all of which combine to lead to improved speech comprehension over unilateral listening conditions. The combination of improved speech comprehension and improved localization ability made available through bilateral electrical stimulation provides the necessary foundation to further assist the hearing-impaired listener to better cope with communication in the everyday listening situation both in noise and in quiet.

Adolescent↗