Studies of auditory looming bias have shown that sources increasing in intensity are more salient than sources decreasing in intensity. Researchers have argued that listeners are more sensitive to approaching sounds compared with receding sounds, reflecting an evolutionary pressure. However, these studies only manipulated overall sound intensity; therefore, it is unclear whether looming bias is truly a perceptual bias for changes in source distance, or only in sound intensity. Here we demonstrate both behavioral and neural correlates of looming bias without manipulating overall sound intensity. In natural environments, the pinnae induce spectral cues that give rise to a sense of externalization; when spectral cues are unnatural, sounds are perceived as closer to the listener. We manipulated the contrast of individually tailored spectral cues to create sounds of similar intensity but different naturalness. We confirmed that sounds were perceived as approaching when spectral contrast decreased, and perceived as receding when spectral contrast increased. We measured behavior and electroencephalography while listeners judged motion direction. Behavioral responses showed a looming bias in that responses were more consistent for sounds perceived as approaching than for sounds perceived as receding. In a control experiment, looming bias disappeared when spectral contrast changes were discontinuous, suggesting that perceived motion in distance and not distance itself was driving the bias. Neurally, looming bias was reflected in an asymmetry of late eventrelated potentials associated with motion evaluation. Hence, both our behavioral and neural findings support a generalization of the auditory looming bias, representing a perceptual preference for approaching auditory objects.auditory looming bias | electroencephalography | distance motion perception | sound externalization | head-related transfer functions I magine yourself alone in the wilderness. Suddenly, a threatening sound permeates the darkness. Is it approaching? This is a critical question when it comes to your survival because approaching objects usually pose a greater threat than receding objects (1). The phenomenon that approaching sounds are more salient than receding sounds is commonly termed "auditory looming bias." Looming bias is reflected in a broad variety of psychophysical tasks related to salience and alertness: bias in loudness-change estimates (2-4) and judgments of duration (5), improved discriminability of motion speed (6), underestimated distances for egocentrically moving (4) or bypassing sounds (7,8), and reduced reaction time for auditory (3, 9) and visual (3) targets preceded by looming sounds. In animals, looming biases result in faster learning speed during associative conditioning (10) and longer duration of attention (11). This list shows that looming bias triggers a variety of percepts across a wide range of psychoacoustic tasks. Despite its broad behavioral significance, the mechanisms underlying auditory looming bias are still poorly ...

The auditory brainstem response (ABR) is an evoked potential that reflects the responses to sound by brainstem neural centers. The binaural interaction component (BIC) is obtained by subtracting the sum of the monaural ABR responses from the binaural response. Its latency and amplitude change in response to variations in binaural cues. The BIC is thus thought to reflect the activity of binaural nuclei and is used to non-invasively test binaural processing. However, any conclusions are limited by a lack of knowledge of the relevant processes at the level of individual neurons. The aim of this study was to characterize the ABR and BIC in the barn owl, an animal where the ITD-processing neural circuits are known in great detail. We recorded ABR responses to chirps and to 1 and 4 kHz tones from anesthetized barn owls. General characteristics of the barn owl ABR were similar to those observed in other bird species. The most prominent peak of the BIC was associated with nucleus laminaris and is thus likely to reflect the known processes of ITD computation in this nucleus. However, the properties of the BIC were very similar to previously published mammalian data and did not reveal any specific diagnostic features. For example, the polarity of the BIC was negative, which indicates a smaller response to binaural stimulation than predicted by the sum of monaural responses. This is contrary to previous predictions for an excitatory-excitatory system such as nucleus laminaris. Similarly, the change in BIC latency with varying ITD was not distinguishable from mammalian data. Contrary to previous predictions, this behavior appears unrelated to the known underlying neural delay-line circuitry. In conclusion, the generation of the BIC is currently inadequately understood and common assumptions about the BIC need to be reconsidered when interpreting such measurements.

OCR often performs poorly on degraded documents. One approach to improving performance is to determine a good filter to improve the appearance of the document image before sending it to the OCR engine. Quality metrics have been measured in document images to determine what type of filtering would most likely improve the OCR response for that document image. In this paper those same quality metrics are measured for several word images degraded by known parameters in a document degradation model. The correlation between the degradation model parameters and the quality metrics is measured. High correlations do appear in many places that were expected. They are also absent in some expected places and offer a comparison of quality metric definitions proposed by different authors.

The interaural level difference (ILD) of a lateralized target source may be effectively reduced when the target is presented together with background noise containing zero ILD. It is not certain whether listeners perceive a position congruent with the reduced ILD or the actual target ILD in a lateralization task. Two sets of behavioral experiments revealed that many listeners perceived a position at or even larger than that corresponding to the presented target ILD when a temporal onset/offset asynchrony between the broadband target and the broadband background noise was present. When no temporal asynchrony was present, however, the perceived lateral position indicated a dependency on the coherence of the background noise for several listeners. With interaurally correlated background noise, listeners reported a reduced ILD resulting from the combined target and background noise stimulus. In contrast, several of the listeners made a reasonable estimate of the position corresponding to the target ILD for interaurally uncorrelated, broadband, background noise. No obvious difference in performance was seen between low- or high-frequency stimuli. Extension of a weighting template to the output of a standard equalization-cancellation model was shown to remove a lateral bias on the predicted target ILD resulting from the presence of background noise. Provided that an appropriate weighting template is applied based on knowledge of the background noise coherence, good prediction of the behavioral data is possible.

A study by Tóth, Kocsis, Háden, Szerafin, Shinn-Cunningham, and Winkler [Neuroimage 141, 108 − 119 (2016)] reported that spatial cues (such as interaural differences or ITDs) that differentiate the perceived sound source directions of a target tone sequence (figure) from simultaneous distracting tones (background) did not improve the ability of participants to detect the target sequence. The present study aims to investigate more systematically whether spatially separating a complex auditory “figure” from the background auditory stream may enhance the detection of a target in a cluttered auditory scene. Results of the presented experiment suggest that the previous negative results arose because of the specific experimental conditions tested. Here the authors find that ITDs provide a clear benefit for detecting a target tone sequence amid a mixture of other simultaneous tone bursts.

A temporally acute binaural system can help to resolve inherent fluctuations in binaural information that are often present in complex auditory scenes. Using a broadband noise stimulus that rapidly alternates between two different values of interaural time difference (ITD), the ability of the binaural system to hear the lateral position resulting from one of the ITD values was investigated. Results show that listeners are able to accurately lateralize brief noise tokens of only 3-7 ms in duration. In two subsequent experiments, the role of an amplitude modulation (AM) imposed on the ITD-switching stimulus used in the first experiment was tested. For wideband stimuli, the temporal position of the ITD target relative to the phase of the AM did not influence absolute lateralization or detection performance. When the stimuli were narrowband, however, detection of the ITD target was best when temporally positioned in the rising portion of the AM. These experiments illustrate that the auditory system is capable of making accurate lateral estimates of very brief moments of ITD information. Furthermore, for these instantaneous changes in ITD information, the stimulus bandwidth can influence the role of envelope cues for the readout of binaural information.

We recently reported that detecting a “figure” of repeated chords amidst “background” tones was worse when the figure was spatially separated from the background, a counterintuitive result given the published studies of spatial unmasking. Because of the way we blocked trials and provided instructions/feedback, listeners may have directed attention to the front where most figures appeared. Here, we investigated whether spatial cues would improve figure detection when listeners were instructed that spatial cues could aid performance. Figure detection was recorded for a condition where both the background and figure were presented diotically and for two binaural conditions. In one binaural condition, the figure occurred as a brief token at a lateral position separated from the background. In the other binaural condition, the background was composed of both a diotic stream and a lateralized stream, which contained the target (if present). Figure detection accuracy was better for both binaural conditions than for the diotic condition. Accuracy was best for the binaural condition in which the background was diotic and the figure was a brief lateralized token. These results reinforce the idea that binaural cues can be used to direct attentional focus, enhancing detectability of a target object amidst competing sounds.

For realistic listening conditions, interaural cues will fluctuate due to the presence of multiple active sources. If it is assumed that the binaural system is sluggish, then the perceived location of the sound input would be an average of the varying interaural cues. If, however, the binaural system is fast enough to assess the rapidly changing interaural differences, then it could be possible for the binaural system to properly identify the spatial position of a target source. Using a continuous, broadband noise stimulus that contained periodically alternating interaural time differences (ITD) and, notably, no monaural cues, we investigated the binaural system's ability to lateralize brief durations of the target ITD. Results show that listeners can lateralize targets for durations of 3–6 ms indicating that the binaural system allows for a segregation and lateralization of the target and interfering noise streams. Furthermore, results indicate that the binaural system mediates the buildup of a modulated stream. A second experiment investigating whether the salience of the target ITD in the aforementioned stimulus depends on the temporal position of the target within the phase of an amplitude modulated envelope revealed that this was not the case.