Effects of the Configuration of Hearing Loss on Consonant Perception between Simulated Bimodal and Electric Acoustic Stimulation Hearing.

BACKGROUND: Cochlear implant technology allows for acoustic and electric stimulations to be combined across ears (bimodal) and within the same ear (electric acoustic stimulation [EAS]). Mechanisms used to integrate speech acoustics may be different between the bimodal and EAS hearing, and the configurations of hearing loss might be an important factor for the integration. Thus, differentiating the effects of different configurations of hearing loss on bimodal or EAS benefit in speech perception (differences in performance with combined acoustic and electric stimulations from a better stimulation alone) is important. PURPOSE: Using acoustic simulation, we determined how consonant recognition was affected by different configurations of hearing loss in bimodal and EAS hearing. RESEARCH DESIGN: A mixed design was used with one between-subject variable (simulated bimodal group vs. simulated EAS group) and one within-subject variable (acoustic stimulation alone, electric stimulation alone, and combined acoustic and electric stimulations). STUDY SAMPLE: Twenty adult subjects (10 for each group) with normal hearing were recruited. DATA COLLECTION AND ANALYSIS: Consonant perception was unilaterally or bilaterally measured in quiet. For the acoustic stimulation, four different simulations of hearing loss were created by band-pass filtering consonants with a fixed lower cutoff frequency of 100 Hz and each of the four upper cutoff frequencies of 250, 500, 750, and 1,000 Hz. For the electric stimulation, an eight-channel noise vocoder was used to generate a typical spectral mismatch by using fixed input (200-7,000 Hz) and output (1,000-7,000 Hz) frequency ranges. The effects of simulated hearing loss on consonant recognition were compared between the two groups. RESULTS: Significant bimodal and EAS benefits occurred regardless of the configurations of hearing loss and hearing technology (bimodal vs. EAS). Place information was better transmitted in EAS hearing than in bimodal hearing. CONCLUSION: These results suggest that configurations of hearing loss are not a significant factor for integrating consonant information between acoustic and electric stimulations. The results also suggest that mechanisms used to integrate consonant information may be similar between bimodal and EAS hearing.

Comparisons in Frequency Difference Limens Between Sequential and Simultaneous Listening Conditions in Normal-Hearing Listeners.

Purpose We compared frequency difference limens (FDLs) in normal-hearing listeners under two listening conditions: sequential and simultaneous. Method Eighteen adult listeners participated in three experiments. FDL was measured using a method of limits for comparison frequency. In the sequential listening condition, the tones were presented with a half-second time interval in between, but for the simultaneous listening condition, the tones were presented simultaneously. For the first experiment, one of four reference tones (125, 250, 500, or 750 Hz), which was presented to the left ear, was paired with one of four starting comparison tones (250, 500, 750, or 1000 Hz), which was presented to the right ear. The second and third experiments had the same testing conditions as the first experiment except with two- and three-tone complexes, comparison tones. The subjects were asked if the tones sounded the same or different. When a subject chose "different," the comparison frequency decreased by 10% of the frequency difference between the reference and comparison tones. FDLs were determined when the subjects chose "same" 3 times in a row. Results FDLs were significantly broader (worse) with simultaneous listening than with sequential listening for the two- and three-tone complex conditions but not for the single-tone condition. The FDLs were narrowest (best) with the three-tone complex under both listening conditions. FDLs broadened as the testing frequencies increased for the single tone and the two-tone complex. The FDLs were not broadened at frequencies > 250 Hz for the three-tone complex. Conclusion The results suggest that sequential and simultaneous frequency discriminations are mediated by different processes at different stages in the auditory pathway for complex tones, but not for pure tones.

Development and Evaluation of a Computer-Based ROPS Design Program.

Tractor overturn is the leading cause of agricultural fatalities in the U.S. Most of these fatalities can be eliminated using a rollover protective structure (ROPS) and a seatbelt. Unfortunately, not all agricultural tractors designed to support ROPS have ROPS designs. A computer-based ROPS design program (CRDP) was developed and successfully tested to provide quick and simple two-post, rear axle-mounted ROPS designs based on SAE Standard J2194. The program uses the tractor dimensions and mass to calculate the dimensions needed for ROPS components. Excel was used as the framework to provide the input, calculation, and ROPS drawing worksheets. Three ROPS (for Massey Ferguson 265, Long 460, and Allis Chalmers 5040 tractors) were designed and constructed using the CRDP. Static rear, side, and vertical tests were conducted based on SAE J2194 on two of the ROPS. All ROPS performance deflection (RPD) tests were less than the ROPS allowable deflection (RAD), indicating that the ROPS passed the static tests. The third ROPS was successfully mounted on the tractor axle housing within one hour, demonstrating the ease of installation using a bolted corner bracket design. Although the CRDP provided quick and simple ROPS designs, this program does not eliminate the requirement to conduct and pass the performance tests for ROPS designs specified in OSHA and SAE standards.