Bilaterally independent (mismatched) hearing aids cannot replicate the natural timing and level cues between ears, and hence, may result in negative consequences for localization and speech perception in spatially-separated noise performance. Five gain reduction patterns were used to evaluate the impact of bilaterally mismatched gain reduction schemes on localization and speech perception performance in noise, compared to an unaltered bilaterally linear time-invariant amplification scheme (reference scheme), in which audibility was optimized. The bilaterally mismatched gain reduction schemes were later matched (synchronized) between ears to explore the possibility of restoring the deteriorated performance due to the mismatched schemes. Sound quality and listening-effort ratings among different gain reduction patterns were assessed, as well as the relationship between self-reported localization ability in daily life and measured localization performance in a laboratory setting. Twenty-four bilateral hearing aid users were enrolled in this study and tested in a virtual environment with insert earphones. The results indicated that bilaterally mismatched gain reduction schemes had a negative impact on localization, compared to the reference scheme; whereas matching gain reduction schemes between ears improved the deteriorated localization performance. In contrast, the use of bilaterally mismatched gain reductions did not negatively impact the speech perception performance in noise. Matching the gain reduction scheme between ears actually resulted in reduced speech perception performance, compared to the mismatched gain reductions. Self-reported localization abilities were not found to be strongly related to the measured localization performance in this study. Finally, these five different gain reduction patterns did not result in significantly different overall sound quality ratings and listening-effort ratings for hearing aid users. However, the use of gain reductions (mismatched or matched) reduced the perceived noise intrusiveness, compared to the use of reference schemes. It is unclear why there was a discrepancy between the results of the localization and speech perception performance in the present study. It is likely that hearing-impaired listeners do not use binaural cues in the localization task in the same manner as in the speech perception task.

<p>Humans are able to hear and detect small changes in sound across a wide dynamic range despite limited dynamic ranges of individual auditory nerve fibers. One mechanism that may adjust the dynamic range is the medial olivocochlear reflex (MOCR), a bilateral sound-activated system which decreases amplification of sound by the outer hair cells in the cochlea. Much of the previous physiological MOCR research has used long broadband noise elicitors. In behavioral measures of gain reduction, a fairly short elicitor has been found to be maximally effective for an on-frequency, tonal elicitor. However, the effect of the duration of broadband noise elicitors on behavioral tasks is unknown. Additionally, MOCR effects measured using otoacoustic emissions (OAEs), have not consistently shown a positive correlation with behavioral gain reduction tasks. This finding seems counterintuitive if both measurements share a common generation mechanism. The current study measured the effects of ipsilateral broadband noise elicitor duration on psychoacoustic gain reduction (Chapter 2) and transient-evoked OAEs (TEOAEs) (Chapter 3) estimated from a forward-masking paradigm. Changes in the TEOAE were measured in terms of magnitude and phase. When phase was accounted for in the TEOAEs, the time constants were approximately equal to the psychoacoustic time constants, and were relatively short (~80 ms). When only changes in TEOAE magnitude were measured, and phase was omitted, the average time constants were longer (~172-ms). Overall, the psychoacoustic and physiological data were consistent with the timecourse of gain reduction by the MOCR. However, when the magnitudes from these data were directly compared in a linear mixed-effects model (Chapter 4), no positive predictive relationship was found, and in some cases there was a significant negative association between the physiological and psychoacoustic measures of gain reduction as a function of elicitor duration. The multitude of factors involved in this relationship are discussed, as are the implications of dynamic range adjustment in everyday listening conditions (noisy backgrounds) in both normal and hearing impaired listeners (Chapter 5).</p>

The thesis deals with the topic of overheating of attic rooms during the summer period. In vast majority of family houses and apartment houses with inhabited attic spaces is the roof solved as lightweight. This kind of roof assembly is not able to sufficiently resist the summer boundary conditions and leads to increased heat gains in the interior. In this work, the attention is drawn entirely to the heat penetration through the roof. Different aspects of passive cooling were applied to the roof and the impact of each change was assessed. This concerns the color of the tiles, thermal accumulation, reflective surfaces and the ventilated air layer. The temperature and velocity profiles in the ventilated cavity were monitored and an analysis of the ventilated cavity efficiency was conducted. For individual analyses was used software – based on the principles of the Finite Element Method or the dynamic simulation software. Also other methods were employed: long-term measurement of temperatures on roof models; short-term measurement of surface temperature of various kinds of roof tiles; and laboratory measurement of reflexivity. Also the effect of insect grilles on the air flow is discussed; which was tested on a ventilator track. In this publication are explained the principles of natural convection; boundary layers and the theory of the coefficient of heat transfer. This work includes a standard of the precise calculation methodology for ventilated roofs which was developed for the purpose of creating a user-friendly guide. The results of individual analyses show, a definitely positive effect of the ventilated cavity on the heat gain reduction of attic rooms. The current technical solution of a roof ridge provides the exhaust of the water vapor from a roof assembly; but for providing ventilation for reducing heat gains is insufficient. This lead to a concept of an innovative roof ridge design which enhances the air exchange between the cavity and outdoor environment.