Diotic and dichotic detection with reproducible chimeric stimuli.

Subject responses were measured for individual narrow-band reproducible stimuli in a low-frequency tone-in-noise detection task. Both N0S0 and N0Spi conditions were examined. The goal of the experiment was to determine the relative importance of envelope and fine-structure cues. Therefore, chimeric stimuli were generated by recombining envelopes and fine structures from different reproducible stimuli. Detection judgments for noise-alone or tone-plus-noise stimuli that had common envelopes but different fine structures or common fine structures but different envelopes were compared. The results showed similar patterns of responses to stimuli that shared envelopes, indicating the importance of envelope cues; however, fine-structure cues were also shown to be important. The relative weight assigned to envelope and fine-structure cues varied across subjects and across interaural conditions. The results also indicated that envelope and fine-structure information are not processed independently. Implications for monaural and binaural models of masking are discussed.

An evaluation of models for diotic and dichotic detection in reproducible noises.

Several psychophysical models for masked detection were evaluated using reproducible noises. The data were hit and false-alarm rates from three psychophysical studies of detection of 500-Hz tones in reproducible noise under diotic (N0S0) and dichotic (N0Spi) conditions with four stimulus bandwidths (50, 100, 115, and 2900 Hz). Diotic data were best predicted by an energy-based multiple-detector model that linearly combined stimulus energies at the outputs of several critical-band filters. The tone-plus-noise trials in the dichotic data were best predicted by models that linearly combined either the average values or the standard deviations of interaural time and level differences; however, these models offered no predictions for noise-alone responses. The decision variables of more complicated temporal models, including the models of Dau et al. [(1996a). J. Acoust. Soc. Am. 99, 3615-3622] and Breebaart et al. [(2001a). J. Acoust. Soc. Am. 110, 1074-1088], were weakly correlated with subjects' responses. Comparisons of the dependencies of each model on envelope and fine-structure cues to those in the data suggested that dependence upon both envelope and fine structure, as well as an interaction between them, is required to predict the detection results.

Detection of tones in reproducible noise maskers by rabbits and comparison to detection by humans.

Processing mechanisms used for detection of tones in noise can be revealed by using reproducible noise maskers and analyzing the pattern of results across masker waveforms. This study reports detection of a 500-Hz tone in broadband reproducible noise by rabbits using a set of masker waveforms for which human results are available. An appetitive-reinforcement, operant-conditioning procedure with bias control was used. Both fixed-level and roving-level noises were used to explore the utility of energy-related cues for detection. An energy-based detection model was able to partially explain the fixed-level results across reproducible noise waveforms for both rabbit and human. A multiple-channel energy model was able to explain fixed-level results, as well as the robust performance observed with roving-level noises. Further analysis using the energy model indicated a difference between species: human detection was influenced most by the noise spectrum surrounding the tone frequency, whereas rabbit detection was influenced most by the noise spectrum at frequencies above that of the tone. In addition, a temporal envelope-based model predicted detection by humans as well as the single-channel energy model did, but the envelope-based model failed to predict detection by rabbits. This result indicates that the contributions of energy and temporal cues to auditory processing differ across species. Overall, these findings suggest that caution must be used when evaluating neural encoding mechanisms in one species on the basis of behavioral results in another.

Visual search performance with 3-D auditory cues: effects of motion, target location, and practice.

OBJECTIVES: We evaluate visual search performance in both static (nonmoving) and dynamic (moving) search environments with and without spatial (3-D) auditory cues to target location. Additionally, the effects of target trajectory, target location, and practice are assessed. BACKGROUND: Previous research on aurally aided visual search has shown a significant reduction in response times when 3-D auditory cues are displayed, relative to unaided search. However, the vast majority of this research has examined only searches for static targets in static visual environments. The present experiment was conducted to examine the effect of dynamic stimuli upon aurally aided visual search performance. METHOD: The 8 participants conducted repeated searches for a single visual target hidden among 15 distracting stimuli. The four main conditions of the experiment consisted of the four possible combinations of 3-D auditory cues (present or absent) and search environment (static or dynamic). RESULTS: The auditory cues were comparably effective at reducing search times in dynamic environments (-25%) as in static environments (-22%). Audio cues helped all participants. The cues were most beneficial when the target appeared at large eccentricities and on the horizontal plane. After a brief initial exposure to 3-D audio, no training or practice effects with 3-D audio were found. CONCLUSION: We conclude that 3-D audio is as beneficial in environments comprising moving stimuli as in those comprising static stimuli. APPLICATION: Operators in dynamic environments, such as aircraft cockpits, ground vehicles, and command-and-control centers, could benefit greatly from 3-D auditory technology when searching their environments for visual targets or other time-critical information.

Binaural detection with narrowband and wideband reproducible noise maskers. III. Monaural and diotic detection and model results.

A single-interval, yes-no, tone-in-noise detection experiment was conducted to measure the proportion of "tone present" responses to each of 25 reproducible noise-alone and tone-plus-noise waveforms under narrowband (100 Hz), wideband (2900 Hz), monotic, and diotic stimulus conditions. Proportions of "tone present" responses (estimates of the probabilities of hits and false alarms) were correlated across masker bandwidths and across monotic and diotic conditions. Two categories of models were considered; one based on stimulus energy or neural counts, and another based on temporal structure of the stimulus envelope or neural patterns. Both categories gave significant correlation between decision variables and data. A model based on a weighted combination of energy in multiple critical bands performed best, predicting up to 90% of the variance in the reproducible-noise data. However, since energy-based models are unable to successfully explain detection under a roving-level paradigm without substantial modification, it is argued that other variations of detection models must be considered for future study. Temporal models are resistant to changes in threshold under roving-level conditions, but explained at most only 67% of the variance in the reproducible-noise data.

Binaural detection with narrowband and wideband reproducible noise maskers: I. Results for human.

This study investigated binaural detection of tonal targets (500 Hz) using sets of individual masker waveforms with two different bandwidths. Previous studies of binaural detection with wideband noise maskers show that responses to individual noise waveforms are correlated between diotic (N0S0) and dichotic (N0S(pi)) conditions [Gilkey et al., J. Acoust. Soc. Am. 78, 1207-1219 (1985)]; however, results for narrowband maskers are not correlated across interaural configurations [Isabelle and Colburn, J. Acoust. Soc. Am. 89, 352-359 (1991)]. This study was designed to allow direct comparison, in detail, of responses across bandwidths and interaural configurations. Subjects were tested on a binaural detection task using both narrowband (100-Hz bandwidth) and wideband (100 Hz to 3 kHz) noise maskers that had identical spectral components in the 100-Hz frequency band surrounding the tone frequency. The results of this study were consistent with the previous studies: N0S0 and N0S(pi) responses were more strongly correlated for wideband maskers than for narrowband maskers. Differences in the results for these two bandwidths suggest that binaural detection is not determined solely by the masker spectrum within the critical band centered on the target frequency, but rather that remote frequencies must be included in the analysis and modeling of binaural detection with wideband maskers. Results across the set of individual noises obtained with the fixed-level testing were comparable to those obtained with a tracking procedure which was similar to the procedure used in a companion study of rabbit subjects [Zheng et al., J. Acoust. Soc. Am. 111, 346-356 (2002)].