Effects of speech signal type and attention on acceptable noise level in elderly, hearing-impaired listeners

The primary objective of this study was to determine if acceptable noise levels (ANLs) in elderly, hearing-impaired listeners were dependent on speech intelligibility and listener attention levels. Acceptable noise levels (ANLs), expressed in decibels, is defined as the maximum background noise level that is acceptable while listening to and following a story. Connected speech test (CST) sentences were recorded with clear speech, conversational speech and temporally altered, fast-rate speech. Thirty-five, elderly, hearing-impaired individuals (61-97 years, M=75) with symmetrical, bilateral sensorineural hearing loss participated. Most comfortable listening levels (MCL) and background noise level (BNL) measurements were completed for each speech stimulus under conditions of attention and non-attention. ANLs were calculated and results were compared to a previous, similar study with younger, normal-hearing individuals. A significant main effect of stimulus type was found suggesting that ANL is dependent on the intelligibility of the target speech signal. Although a significant main effect of attention was not reached, a significant interaction between attention and stimulus type was found showing the condition of attention to produce lower mean ANLs for clear speech and higher ANLs for fast-rate speech. In comparison to the younger, normal-hearing group, the participants in this study had higher ANLs, overall. These findings are contradictory to previous findings. Knowledge of these results may guide clinical audiologists in counseling patients and family members on communication strategies

Effects of Speech Signal Type and Attention on Acceptable Noise Level in Elderly, Hearing-Impaired Listeners

The primary objective of this study was to determine if acceptable noise levels (ANLs) in elderly, hearing-impaired listeners were dependent on speech intelligibility and listener attention levels. Acceptable noise levels (ANLs), expressed in decibels, is defined as the maximum background noise level that is acceptable while listening to and following a story. Connected speech test (CST) sentences were recorded with clear speech, conversational speech and temporally altered, fast-rate speech. Thirty-five, elderly, hearing-impaired individuals (61-97 years, M=75) with symmetrical, bilateral sensorineural hearing loss participated. Most comfortable listening levels (MCL) and background noise level (BNL) measurements were completed for each speech stimulus under conditions of attention and non-attention. ANLs were calculated and results were compared to a previous, similar study with younger, normal-hearing individuals. A significant main effect of stimulus type was found suggesting that ANL is dependent on the intelligibility of the target speech signal. Although a significant main effect of attention was not reached, a significant interaction between attention and stimulus type was found showing the condition of attention to produce lower mean ANLs for clear speech and higher ANLs for fast-rate speech. In comparison to the younger, normal-hearing group, the participants in this study had higher ANLs, overall. These findings are contradictory to previous findings. Knowledge of these results may guide clinical audiologists in counseling patients and family members on communication strategies

Characterizing the postmortem human bone microbiome from surface-decomposed remains.

Microbial colonization of bone is an important mechanism of postmortem skeletal degradation. However, the types and distributions of bone and tooth colonizing microbes are not well characterized. It is unknown if microbial communities vary in abundance or composition between bone element types, which could help explain differences in human DNA preservation. The goals of the present study were to (1) identify the types of microbes capable of colonizing different human bone types and (2) relate microbial abundances, diversity, and community composition to bone type and human DNA preservation. DNA extracts from 165 bone and tooth samples from three skeletonized individuals were assessed for bacterial loading and microbial community composition and structure. Random forest models were applied to predict operational taxonomic units (OTUs) associated with human DNA concentration. Dominant bacterial bone colonizers were from the phyla Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes, and Planctomycetes. Eukaryotic bone colonizers were from Ascomycota, Apicomplexa, Annelida, Basidiomycota, and Ciliophora. Bacterial loading was not a significant predictor of human DNA concentration in two out of three individuals. Random forest models were minimally successful in identifying microbes related to human DNA concentration, which were complicated by high variability in community structure between individuals and body regions. This work expands on our understanding of the types of microbes capable of colonizing the postmortem human skeleton and potentially contributing to human skeletal DNA degradation

Soil elemental changes during human decomposition.

Mammalian decomposition provides pulses of organic matter to the local ecosystem creating ephemeral hotspots of nutrient cycling. While changes to soil biogeochemistry in these hotspots have been described for C and N, patterns associated with deposition and cycling of other elements have not received the same attention. The goal of our study was to evaluate temporal changes to a broad suite of dissolved elements in soils impacted by human decomposition on the soil surface including: 1) abundant mineral elements in the human body (K, Na, S, P, Ca, and Mg), 2) trace elements in the human body (Fe, Mn, Se, Zn, Cu, Co, and B), and 3) Al which is transient in the human body but common in soils. We performed a four-month human decomposition trial at the University of Tennessee Anthropology Research Facility and quantified elemental concentrations dissolved in the soil solution, targeting the mobile and bioavailable fraction. We identified three groups of elements based on their temporal patterns. Group 1 elements appeared to be cadaver-derived (Na, K, P, S) and their persistence in soil varied based upon soluble organic forms (P), the dynamics of the soil exchange complex (Na, K), and gradual releases attributable to microbial degradation (S). Group 2 elements (Ca, Mg, Mn, Se, B) included three elements that have greater concentrations in soil than would be expected based on cadaver inputs alone, suggesting that these elements partially originate from the soil exchange (Ca, Mg), or are solubilized as a result of soil acidification (Mn). Group 3 elements (Fe, Cu, Zn, Co, Al) increased late in the decomposition process, suggesting a gradual solubilization from soil minerals under acidic pH conditions. This work presents a detailed longitudinal characterization of changes in dissolved soil elements during human decomposition furthering our understanding of elemental deposition and cycling in these environments

Spatial impacts of a multi-individual grave on microbial and microfaunal communities and soil biogeochemistry.

Decomposing vertebrates, including humans, result in pronounced changes in surrounding soil biogeochemistry, particularly nitrogen (N) and carbon (C) availability, and alter soil micro- and macrofauna. However, the impacts of subsurface human decomposition, where oxygen becomes limited and microbial biomass is generally lower, are far less understood. The goals of this study were to evaluate the impact of human decomposition in a multi-individual, shallow (~70 cm depth) grave on soil biogeochemistry and soil microbial and nematode communities. Three individuals were interred and allowed to decay for four years. Soils were collected from two depths (0‒5 and 30‒35 cm) along linear transects radiating from the grave as well as from within and below (85‒90 cm depth) the grave during excavation to assess how decomposition affects soil properties. Along radiating surface transects, several extracellular enzymes rates and nematode richness increased with increasing distance from the grave, and likely reflect physical site disruption due to grave excavation and infill. There was no evidence of carcass-sourced C and N lateral migration from the grave, at least at 30‒35 cm depth. Within the grave, soils exhibited significant N-enrichment (e.g., ammonium, dissolved organic N), elevated electrical conductivity, and elevated respiration rates with depth. Soil biogeochemistry within the grave, particularly in the middle (30‒35 cm) and base (70‒75 cm depth), was significantly altered by human decomposition. Mean microbial gene abundances changed with depth in the grave, demonstrating increased microbial presence in response to ongoing decomposition. Human-associated Bacteroides were only detected at the base of the grave where anoxic conditions prevailed. Nematode community abundance and richness were reduced at 70‒75 cm and not detectable below 85‒90 cm. Further, we identified certain Plectus spp. as potential indicators of enrichment due to decomposition. Here we demonstrate that human decomposition influences soil biogeochemistry, microbes, and microfauna up to four years after burial