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Binaural reproduction can be used in listening experiments under real-life conditions to achieve a high realism and good reproducibility. In recent years a clear trend to more individual reproduction can be observed as the ability to measure individual head-related-transfer-functions (HRTFs) is becoming more widespread. The question of the accuracy and reproduction methods needed for a realistic playback however has not been sufficiently answered. To evaluate an appropriate approach for binaural reproduction via headphones different head-related-transfer-functions (HRTFs) and reproduction methods were compared in this paper. In a listening test eleven explicitly trained participants were asked to localize eleven sound sources positioned in the right hemisphere using the proximal pointing method. Binaural stimuli based on individually measured HRTFs were compared to those of an artificial head in a static reproduction of stimuli and in three dynamic reproduction methods of different resolutions (5°, 2.5° and 1°). Unsigned errors in azimuth and elevation as well as front-back-confusions and in-head-localization were observed. Dynamic reproduction of any resolution applied turned out fundamental for a reduction of undesired front-back-confusions and in-head-localization. Individually measured HRTFs showed a smaller effect on localization accuracy compared to the influence of dynamic sound reproduction. They were mainly observed to reduce the front-back-confusion rate.

This chapter examines the cognitive control mechanisms underlying auditory selective attention by considering the influence of variables that increase the complexity of the auditory scene concerning technical aspects such as dynamic binaural hearing, room acoustics, head movements, and interfering noise sources as well as those that influence the efficiency of cognitive processing. Classical research in auditory selective attention does not represent realistic or close to real-life listening experiences, of which room acoustics, distracting sources, as well as the dynamic reproduction of an acoustic scene including head movements, are essential parts. The chapter starts with an introduction to the subject of maintaining and switching attention from the standpoint of cognitive psychology. A paradigm suitable for the study of intentional switching of auditory selective attention is introduced through dichotic stimulus representation with different single number words (1–9, excluding 5) uttered by speakers of different gender presented simultaneously, one to the participant’s left ear and the other to the right ear. The listener is required to categorize, as quickly as possible, the target number as being either smaller or larger than five, with a visual cue indicating the listener’s task in each trial. This paradigm is gradually extended from dichotic reproduction to a complex dynamic acoustic scene to study the binaural effects in selective attention and attention switching, including different room acoustic conditions. Various technical possibilities are evaluated to validate the binaural reproduction of the spatial scene, minimizing errors on account of the acoustic virtual reality. Additionally, the influence of different binaural reproduction methods on the selective attention and attention switching model is carefully examined and compared to a natural listening condition using loudspeakers in an anechoic setting. The application of the binaural listening paradigm in anechoic conditions tests a listener’s ability to switch auditory attention in various setups intentionally. According to the results, intentional switching of the attention focus is associated with higher reaction times compared to maintaining the focus of attention on a single source. Also, particularly concerning the error rates, there is an observable effect of the stimulus category (i.e., stimuli spoken by target and distractor may evoke the same answer (congruent) or different answers (incongruent)). The congruency effect may be construed as an implicit performance measure of the degree to which task-irrelevant information is filtered out. The binaural paradigm has also been applied to older (slightly hearing-impaired) participants, with the results of which have been compared to experiments involving young normal-hearing participants, resulting in higher error rates and reaction times. Scenarios involving even more complex environments, including room acoustics (i.e., reverberation), have shown reaction times and error rates that rely significantly on reverberation time. Switch costs, in particular, reaction time differences between switch trials and repetition trials, can highly depend on the reverberation time.

An auditory attention-switching paradigm was combined with a judgment-switching paradigm to examine the interaction of a varying auditory attention component and a varying judgment component. Participants heard two dichotically presented stimuli-one spoken by a female speaker and one spoken by a male speaker. In each trial, the stimuli were a spoken letter and a spoken number. A visual explicit cue at the beginning of each trial indicated the auditory attention criterion (speaker sex/ear) to identify the target stimulus (Experiment 1) or the judgment that had to be executed (Experiment 2). Hence, the attentional selection criterion switched independently between speaker sexes (or between ears), while the judgment alternated between letter categorization and number categorization. The data indicate that auditory attention criterion and judgment were not processed independently, regardless of whether the attention criterion or the judgment was cued. The partial repetition benefits of the explicitly cued component suggested a hierarchical organization of the auditory attention component and the judgment component within the task set. We suggest that the hierarchy arises due to the explicit cuing of one component rather than due to a "natural" hierarchy of auditory attention component and judgment component.

Using a well-established binaural-listening paradigm the ability to intentionally switch auditory selective attention was examined under anechoic, low reverberation (0.8 s) and high reverberation (1.75 s) conditions. Twenty-three young, normal-hearing subjects were tested in a within-subject design to analyze influences of the reverberation times. Spoken word pairs by two speakers were presented simultaneously to subjects from two of eight azimuth positions. The stimuli consisted of a single number word, (i.e., 1 to 9), followed by either the direction “UP” or “DOWN” in German. Guided by a visual cue prior to auditory stimulus onset indicating the position of the target speaker, subjects were asked to identify whether the target number was numerically smaller or greater than five and to categorize the direction of the second word. Switch costs, (i.e. reaction time differences between a position switch of the target relative to a position repetition), were larger under the high reverberation condition. Furthermore, the error rates were highly dependent on reverberant energy and reverberation interacted with the congruence effect, (i.e. stimuli spoken by target and distractor may evoke the same answer (congruent) or different answers (incongruent)), indicating larger congruence effects under higher reverberation times.

Using a binaural-listening paradigm, age-related differences in the ability to intentionally switch auditory selective attention between two speakers, defined by their spatial location, were examined. Therefore 40 normal-hearing participants (20 young, O 24.8 years; 20 older O 67.8 years) were tested. The spatial reproduction of stimuli was provided by headphones using head-related-transfer-functions of an artificial head. Spoken number words of two speakers were presented simultaneously to participants from two out of eight locations on the horizontal plane. Guided by a visual cue indicating the spatial location of the target speaker, the participants were asked to categorize the target's number word into smaller vs. greater than five while ignoring the distractor's speech. Results showed significantly higher reaction times and error rates for older participants. The relative influence of the spatial switch of the target-speaker (switch or repetition of speaker's direction in space) was identical across age groups. Congruency effects (stimuli spoken by target and distractor may evoke the same answer or different answers) were increased for older participants and depend on the target's position. Results suggest that the ability to intentionally switch auditory attention to a new cued location was unimpaired whereas it was generally harder for older participants to suppress processing the distractor's speech.

Major criteria for a successful binaural reproduction are not only a suitable localization performance, but also the authenticity and plausibility of the presented scene. It is therefore interesting to examine whether the binaural reproduction can be perceptually distinguished from a real source. The aim of the presented investigation is to compare the quality of the binaural reproduction via headphones with two different microphone setups (miniature microphone in Open-Dome and ear plug) for individual head-related-transfer-function (HRTF) and headphone-transfer-function (HpTF) measurements. Listening tests with a total of 80 subjects were carried out focusing on plausibility and authenticity. In the examination of plausibility detection rates showed that subjects were not able to match the reproduced pink noise to its reproduction system (real source vs. binaural reproduction via headphones). The authenticity of the static binaural reproduction was highly dependent on the stimulus. Pink noise could often be distinguished due to coloration in higher frequencies and small differences in location. A difference between microphone setups could not be found in neither of the listening tests.

In a two-component switching paradigm, in which participants switched between two auditory attention selection criteria (attention component: left vs. right ear) and two judgements (judgement component: number vs. letter judgement), we found high judgement switch costs in attention criterion repetitions, but low costs in attention criterion switches. This finding showed an interaction of components. Previous two-component switching studies observed differently emphasised interaction patterns. In the present study, we explored whether the strength of the interaction pattern reflects the strength of the binding of target location and judgement. Specifically, we investigated whether exogenous target location cueing led to weaker binding than endogenous cueing, and whether preparation for ear selection could influence the binding. Attention switches with auditory exogenous target location cues did not affect the component interaction pattern, whereas a prolonged preparation interval led to a more emphasised pattern. Binding between target location and judgement may therefore be rather automatic and may not necessarily require concurrent component processing. Sufficient time for target location switches with long preparation time may activate the previous trial’s episode or facilitate switches of the subsequent judgement.

In an auditory attention-switching paradigm, participants heard two simultaneously spoken number-words, each presented to one ear, and decided whether the target number was smaller or larger than 5 by pressing a left or right key. An instructional cue in each trial indicated which feature had to be used to identify the target number (e.g., female voice). Auditory attention-switch costs were found when this feature changed compared to when it repeated in two consecutive trials. Earlier studies employing this paradigm showed mixed results when they examined whether such cued auditory attention-switches can be prepared actively during the cue–stimulus interval. This study systematically assessed which preconditions are necessary for the advance preparation of auditory attention-switches. Three experiments were conducted that controlled for cue-repetition benefits, modality switches between cue and stimuli, as well as for predictability of the switch-sequence. Only in the third experiment, in which predictability for an attention-switch was maximal due to a pre-instructed switch-sequence and predictable stimulus onsets, active switch-specific preparation was found. These results suggest that the cognitive system can prepare auditory attention-switches, and this preparation seems to be triggered primarily by the memorised switching-sequence and valid expectations about the time of target onset.

Using an auditory variant of task switching, we examined the ability to intentionally switch attention in a dichotic-listening task. In our study, participants responded selectively to one of two simultaneously presented auditory number words (spoken by a female and a male, one for each ear) by categorizing its numerical magnitude. The mapping of gender (female vs. male) and ear (left vs. right) was unpredictable. The to-be-attended feature for gender or ear, respectively, was indicated by a visual selection cue prior to auditory stimulus onset. In Experiment 1, explicitly cued switches of the relevant feature dimension (e.g., from gender to ear) and switches of the relevant feature within a dimension (e.g., from male to female) occurred in an unpredictable manner. We found large performance costs when the relevant feature switched, but switches of the relevant feature dimension incurred only small additional costs. The feature-switch costs were larger in ear-relevant than in gender-relevant trials. In Experiment 2, we replicated these findings using a simplified design (i.e., only within-dimension switches with blocked dimensions). In Experiment 3, we examined preparation effects by manipulating the cueing interval and found a preparation benefit only when ear was cued. Together, our data suggest that the large part of attentional switch costs arises from reconfiguration at the level of relevant auditory features (e.g., left vs. right) rather than feature dimensions (ear vs. gender). Additionally, our findings suggest that ear-based target selection benefits more from preparation time (i.e., time to direct attention to one ear) than gender-based target selection.

The topic of the collaborative project is the exploration of cognitive control mechanisms underlying auditory selective attention. The aim is to examine the influence of variables that increase the complexity of the auditory scene with respect to technical aspects (dynamic binaural hearing with consideration of room acoustics and head movements) and that influence the efficiency of cognitive processing. Using a binaural-listening paradigm, the ability to intentionally shift auditory attention in various anechoic setups was tested. An anechoic reproduction fails to represent realistic listening experiences. The original paradigm is extended to use longer stimuli to offer more opportunities. Spoken phrases by two speakers were presented simultaneously to subjects from two of eight positions. The stimuli were phrases that consisted of a single number word followed by either the German direction “UP” or “DOWN”. Guided by a visual cue prior to auditory stimulus onset, subjects were asked to identify whether th...

Using a well-established binaural-listening paradigm, the ability to intentionally switch auditory selective attention was examined under anechoic, low reverberation (0.8 s) and high reverberation (1.75 s) conditions. Twenty-four young, normal-hearing subjects were tested in a within-subject design to analyze influences of the reverberation times. Spoken word pairs by two speakers were presented simultaneously to subjects from two of eight azimuth positions. The stimuli were word pairs that consisted of a single number word (i.e., 1 to 9) followed by either the German direction “UP” or “DOWN.” Guided by a visual cue prior to auditory stimulus onset indicating the position of the target speaker, subjects were asked to identify whether the target number was numerically smaller or greater than five and to categorize the direction of the second word. Switch costs (i.e., reaction time differences between a position switch of the target relative to a position repetition) were larger for the high reverberation c...

Binaural stimuli presented via headphones need to be plausible in localization and sound coloration for a successful reproduction of an acoustic scene, especially for experiments on auditory selective attention. The goal is to provide artificially generated acoustic scenes in a way that the difference between a real situation and an artificially generated situation has no influence in psychoacoustic experiments. The quality and reliability of binaural reproduction via headphones comparing two different microphone setups (miniature microphone in open dome and ear plug) used for individualized Head-Related Transfer Functions and headphone transfer function measurements is analyzed. Listening tests are carried out focusing on authenticity, naturalness and distinguishability in a direct comparison of real sources and binaural reproduction via headphones. Results for three different stimuli (speech, music, pink noise) are discussed.

A room-acoustic situation with many sources is one of the best examples for auditory selective attention – relevant information should be selectively observed and irrelevant information should be ignored. In a joint research project between Acoustics and Psychology at RWTH Aachen University the intentional switching of auditory selective attention is examined using dichotic and binaural presentation of the stimuli. The goal is to provide artificially generated acoustic scenes (e.g. typical classroom situation, open plan offices etc.), as in psychoacoustic experiments on auditory selective attention no differences between a real situation and an artificially generated situation occur. Therefore at first we investigate various binaural reproduction and equalization methods using experiments in auditory selective attention. Headphones must always be adequately equalized if they are to deliver high perceptual plausibility. However, the transfer function between headphones and ear drums varies between different persons. Because of this, individual equalizations with different microphone positions in the ear canal are measured. In listening tests the overall quality of the equalization methods is to be rated regarding localization and realism, envelopment as well as immersion. First results concerning the psychoacoustic experiments, the scene generation as well as headphone equalization will be presented.