Further tests of the local nonlinear interaction-based mechanism for simultaneous suppression of tone burst-evoked otoacoustic emissions

Tone burst-evoked otoacoustic emission (TBOAE) components measured in response to a 1kHz tone burst (TB1) are suppressed by the simultaneous presence of an additional tone burst (TB2). This "simultaneous suppression of TBOAEs" has been explained in terms of a mechanism based on local nonlinear interactions between the basilar membrane (BM) travelling waves caused by TB1 and TB2. A test of this local nonlinear interaction (LNI)-based mechanism, as a function of the frequency separation (δf, expressed in kHz) between TB1 and TB2, has previously been reported by Killan etal. (2012) using a simple mathematical model [Killan etal., Hear. Res. 285, 58-64 (2012)]. The two experiments described in this paper add additional data on the extent to which the LNI-based mechanism can account for simultaneous suppression, by testing two further hypotheses derived from the model predictions. Experiment I tested the hypothesis that TBOAE suppression is directly linked to TBOAE amplitude nonlinearity where ears that exhibit a higher degree of amplitude nonlinearity yield greater suppression than more linear ears, and this relationship varies systematically as a function of δf. In order to test this hypothesis simultaneous suppression at a range of values of δf at 60dB peak-equivalent sound pressure level (p.e. SPL) and TBOAE amplitude nonlinearity from normal human ears was measured. In Experiment II the hypothesis that suppression will also increase progressively as a function of increasing tone burst level was tested by measuring suppression for a range of δf and tone burst levels at 40, 50, 60 and 70dB p.e. SPL. The majority of the findings from both experiments provide support for the LNI-based mechanism being primarily responsible for simultaneous suppression. However, some data were inconsistent with this view. Specifically, a breakdown in the relationship between suppression and TBOAE amplitude nonlinearity at δf=1 (i.e. when TB2 was reasonably well separated from, and had a higher frequency than TB1) and unexpected level-dependence, most notably at δf=1, but also where δf=-0.5, was observed. Either the LNI model is too simple or an alternative explanation, involving response components generated at basal regions of the basilar membrane, is required to account for these findings

Occupational Noise, Smoking, and a High Body Mass Index are Risk Factors for Age-related Hearing Impairment and Moderate Alcohol Consumption is Protective: A European Population-based Multicenter Study

A multicenter study was set up to elucidate the environmental and medical risk factors contributing to age-related hearing impairment (ARHI). Nine subsamples, collected by nine audiological centers across Europe, added up to a total of 4,083 subjects between 53 and 67 years. Audiometric data (pure-tone average [PTA]) were collected and the participants filled out a questionnaire on environmental risk factors and medical history. People with a history of disease that could affect hearing were excluded. PTAs were adjusted for age and sex and tested for association with exposure to risk factors. Noise exposure was associated with a significant loss of hearing at high sound frequencies (>1 kHz). Smoking significantly increased high-frequency hearing loss, and the effect was dose-dependent. The effect of smoking remained significant when accounting for cardiovascular disease events. Taller people had better hearing on average with a more pronounced effect at low sound frequencies (<2 kHz). A high body mass index (BMI) correlated with hearing loss across the frequency range tested. Moderate alcohol consumption was inversely correlated with hearing loss. Significant associations were found in the high as well as in the low frequencies. The results suggest that a healthy lifestyle can protect against age-related hearing impairment

An ecological future for weed science to sustain crop production and the environment. A review

Sustainable strategies for managing weeds are critical to meeting agriculture's potential to feed the world's population while conserving the ecosystems and biodiversity on which we depend. The dominant paradigm of weed management in developed countries is currently founded on the two principal tools of herbicides and tillage to remove weeds. However, evidence of negative environmental impacts from both tools is growing, and herbicide resistance is increasingly prevalent. These challenges emerge from a lack of attention to how weeds interact with and are regulated by the agroecosystem as a whole. Novel technological tools proposed for weed control, such as new herbicides, gene editing, and seed destructors, do not address these systemic challenges and thus are unlikely to provide truly sustainable solutions. Combining multiple tools and techniques in an Integrated Weed Management strategy is a step forward, but many integrated strategies still remain overly reliant on too few tools. In contrast, advances in weed ecology are revealing a wealth of options to manage weedsat the agroecosystem levelthat, rather than aiming to eradicate weeds, act to regulate populations to limit their negative impacts while conserving diversity. Here, we review the current state of knowledge in weed ecology and identify how this can be translated into practical weed management. The major points are the following: (1) the diversity and type of crops, management actions and limiting resources can be manipulated to limit weed competitiveness while promoting weed diversity; (2) in contrast to technological tools, ecological approaches to weed management tend to be synergistic with other agroecosystem functions; and (3) there are many existing practices compatible with this approach that could be integrated into current systems, alongside new options to explore. Overall, this review demonstrates that integrating systems-level ecological thinking into agronomic decision-making offers the best route to achieving sustainable weed management

Simultaneous suppression of tone burst-evoked otoacoustic emissions: Two and three-tone burst combinations.

Previous investigations have shown that components of a tone burst-evoked otoacoustic emission (TBOAE) evoked by a 1 kHz tone burst (TB1) can be suppressed by the simultaneous presence of a 2 kHz tone burst (TB2) or a pair of tone bursts at 2 and 3 kHz (TB2 and TB3 respectively). No previous study has measured this "simultaneous suppression of TBOAEs" for both TB2 alone and TB2 and TB3 from the same ears, so that the effect of the additional presence of TB3 on suppression caused by TB2 is not known. In simple terms, three outcomes are possible; suppression increases, suppression is reduced or suppression is not affected. Comparison of previously reported simultaneous suppression data suggests TB3 causes a reduction in suppression, though it is not clear if this is a genuine effect or simply reflects methodological and ear differences between studies. This issue has implications for previously proposed mechanisms of simultaneous suppression of TBOAEs and the interpretation of clinical data, and is clarified by the present study. Simultaneous suppression of TBOAEs was measured for TB1 and TB2 as well as TB1, TB2 and TB3 at 50, 60 and 70 dB p.e. SPL from nine normal human ears. Results showed no significant difference between mean suppression obtained for the two and three-tone burst combinations, indicating the reduction of suppression inferred from comparison of previous data is likely a result of methodological and ear differences rather than a genuine effect

Speech identification under simulated hearing-aid frequency response characteristics in relation to sensitivity, frequency resolution, and temporal resolution

Word identification in noise was measured adaptively under flat and rising frequency response conditions to represent basic alternatives for a hearing-aid characteristic. The speech test results were compared with measures of sensitivity, loudness tolerance, frequency resolution, and temporal resolution in 23 hearing-aid users with mild or moderate sensorineural hearing losses. Subjects also rated the two frequency responses for preference and subjective quality. A paradoxical relationship was found whereby superior speech performance under the flat condition was associated with preference for the rising condition, and vice versa. No combinations of psychoacoustic variables satisfactorily explained either relative performance or preference, although high-frequency sensitivity and upward spread of masking were implicated. Absolute speech performance was related to sensitivity at 2 kHz, age, and sex, but not to frequency resolution once other factors were partialed. Temporal resolution was also a factor, but this was due largely to the influence of extreme values in two subjects. It is concluded that, for moderate degrees of hearing loss, speech identification in noise can be predicted from age, sex, and sensitivity with little advantage from recourse to measurement of frequency or temporal resolution