A comparison of the contrast effects in sound localization in the horizontal and vertical planes

The effect of a background sound on the auditory localization of a single sound source was examined. Nine loudspeakers were arranged crosswise in the horizontal and the median vertical plane. They ranged from -20 degrees to +20 degrees, with the center loudspeaker at 0 degree azimuth and elevation. Using vertical and horizontal centimeter scales, listeners verbally estimated the position of a 500-ms broadband noise stimulus being presented at the same time as a 2 s background sound, emitted by one of the four outer loudspeakers. When the background sound consisted of continuous broadband noise, listeners consistently shifted the apparent target positions away from the background sound locations. This auditory contrast effect, which is consistent with earlier findings, equally occurred in both planes. But when the background sound was changed to a pulse train of noise bursts, the contrast effect decreased in the horizontal plane and increased in the vertical plane. This discrepancy might be due to general differences in the processing of interaural and spectral localization information.     

The influence of stimulus bandwidth on localization of sound in space

The ability of listeners, deprived of prominent interaural time and intensity cues, to locate noise bands differing in width was investigated. To minimize binaural cues, we placed the sound source at various positions in the median sagittal plane. To eliminate binaural cues, we occluded one ear. The stimuli consisted of broadband noise and bands of noise centered at 8.0 kHz. The width of the latter ranged from 1.0 to 6.0 kHz. The results from seven listeners showed that localization proficiency for sounds in the median sagittal plane decreased with decreases in bandwidth for both binaural and monaural listening conditions. This function was less orderly for monaural localization of horizontally positioned sounds. Another consequence of a reduction in bandwidth was an increasing tendency of listeners to select certain loudspeakers over others as the source of the sound. A previous finding showing that localization of sound in the median sagittal plane is more accurate when listening binaurally rather than monaurally was confirmed.     

The time course of attention in a simple auditory detection task

What is the time course of human attention in a simple auditory detection task? To investigate this question, we determined the detectability of a 20-msec, 1000-Hz tone presented at expected and unexpected times. Twelve listeners who expected the tone to occur at a specific time after a 300-msec narrowband noise rarely detected signals presented 150-375 msec before or 100-200 msec after that expected time. The shape of this temporal-attention window depended on the expected presentation time of the tone and the temporal markers available in the trials. Further, though expecting the signal to occur in silence, listeners often detected signals presented at unexpected times during the noise. Combined with previous data, these results further clarify the listening strategy humans use when trying to detect an expected sound: Humans seem to listen specifically for that sound, while ignoring the background in which it is presented, around the time when the sound is expected to occur.     

Superordinate shape classification using natural shape statistics

This paper investigates the classification of shapes into broad natural categories such as animal or leaf. We asked whether such coarse classifications can be achieved by a simple statistical classification of the shape skeleton. We surveyed databases of natural shapes, extracting shape skeletons and tabulating their parameters within each class, seeking shape statistics that effectively discriminated the classes. We conducted two experiments in which human subjects were asked to classify novel shapes into the same natural classes. We compared subjects’ classifications to those of a naive Bayesian classifier based on the natural shape statistics, and found good agreement. We conclude that human superordinate shape classifications can be well understood as involving a simple statistical classification of the shape skeleton that has been “tuned” to the natural statistics of shape.     

Sound and the Korean Public: Sonic Citizenship in the Governance of Apartment Floor Noise Conflicts

Apartment floor noise is becoming a serious social problem in South Korea. Apartment floor noise conflicts arise from the disruption of neighbourhood community in Korean apartment complexes. To resolve the conflicts, the Korean government and apartment residents employ two modes of governance: technocratic and collaborative. These models of governance create legal and community standards of floor noise that constitute sonic citizenship—the status of residents as normal listeners with both the duty to reduce noise and the right to make noise. Using Sheila Jasanoff’s idea of ‘constitutive coproduction’, floor noise in the form of sonic knowledge is constitutively coproduced with sonic citizenship in the form of public knowledge. When apartment residents cannot bear normal sound, defined by the two modes of governance, they become abnormal listeners. If normal listeners cannot put up with the level of sound from upstairs, this sound becomes floor noise. Sonic knowledge is, therefore, vital to the construction of sonic citizenship. In technocratic governance, sonic citizenship emerges from the limits of endurance in governmental floor noise standards, based on results of an auditory perception test based on noise and vibration engineering. In collaborative governance, sonic citizenship results from voluntary agreements between apartment residents. Through such governances, governmental officials and apartment residents perceive a distinction between normal and abnormal residents or between normal and abnormal apartment life.     

Auditory event perception: The source—perception loop for posture in human gait

There is a small but growing literature on the perception of natural acoustic events, but few attempts have been made to investigate complex sounds not systematically controlled within a laboratory setting. The present study investigates listeners’ ability to make judgments about the posture (upright—stooped) of the walker who generated acoustic stimuli contrasted on each trial. We use a comprehensive three-stage approach to event perception, in which we develop a solid understanding of the source event and its sound properties, as well as the relationships between these two event stages. Developing this understanding helps both to identify the limitations of common statistical procedures and to develop effective new procedures for investigating not only the two information stages above, but also the decision strategies employed by listeners in making source judgments from sound. The result is a comprehensive, ultimately logical, but not necessarily expected picture of both the source—sound—perception loop and the utility of alternative research tools.     

Effects of glide slope, noise intensity, and noise duration on the extrapolation of FM glides through noise.

Listeners are quite adept at maintaining integrated perceptual events in environments that are frequently noisy. Three experiments were conducted to assess the mechanisms by which listeners maintain continuity for upward sinusoidal glides that are interrupted by a period of broadband noise. The first two experiments used stimulus complexes consisting of three parts: prenoise glide, broadband noise interval, and postnoise glide. For a given prenoise glide and noise interval, the subject's task was to adjust the onset frequency of a same-slope postnoise glide so that, together with the prenoise glide and noise, the complex sounded as "smooth and continuous as possible." The slope of the glides (1.67, 3.33, 5, and 6.67 Bark/sec) as well as the duration (50, 200, and 350 msec) and relative level of the interrupting noise (0, -6, and -12 dB S/N) were varied. For all but the shallowest glides, subjects consistently adjusted the offset portion of the glide to frequencies lower than predicted by accurate interpolation of the prenoise portion. Curiously, for the shallowest glides, subjects consistently selected postnoise glide onset-frequency values higher than predicted by accurate extrapolation of the prenoise glide. There was no effect of noise level on subjects' adjustments in the first two experiments. The third experiment used a signal detection task to measure the phenomenal experience of continuity through the noise. Frequency glides were either present or absent during the noise for stimuli like those use in the first two experiments as well as for stimuli that had no prenoise or postnoise glides. Subjects were more likely to report the presence of glides in the noise when none occurred (false positives) when noise was shorter or of greater relative level and when glides were present adjacent to the noise.     

Effects of glide slope,noise intensity,and noise duration on the extrapolation of FM glides through noise

Listeners are quite adept at maintaining integrated perceptual events in environments that are frequently noisy. Three experiments were conducted to assess the mechanisms by which listeners maintain continuity for upward sinusoidal glides that are interrupted by a period of broadband noise. The first two experiments used stimulus complexes consisting of three parts: prenoise glide, broadband noise interval, and postnoise glide. For a given prenoise glide and noise interval, the subject’s task was to adjust the onset frequency of a same-slope postnoise glide so that, together with the prenoise glide and noise, the complex sounded as “smooth and continuous as possible.” The slope of the glides (1.67, 3.33, 5, and 6.67 Bark/sec) as well as the duration (50, 200, and 350 msec) and relative level of the interrupting noise (0, ?6, and ?12 dB S/N) were varied. For all but the shallowest glides, subjects consistently adjusted the offset portion of the glide to frequencies lower than predicted by accurate interpolation of the prenoise portion. Curiously, for the shallowest glides, subjects consistently selected postnoise glide onset-frequency values higher than predicted by accurate extrapolation of the prenoise glide. There was no effect of noise level on subjects’ adjustments in the first two experiments. The third experiment used a signal detection task to measure the phenomenal experience of continuity through the noise. Frequency glides were either present or absent during the noise for stimuli like those used in the first two experiments as well as for stimuli that had no prenoise or postnoise glides. Subjects were more likely to report the presence of glides in the noise when none occurred (false positives) when noise was shorter or of greater relative level and when glides were present adjacent to the noise.     

Seeing structure: Shape skeletons modulate perceived similarity

An intrinsic part of seeing objects is seeing how similar or different they are relative to one another. This experience requires that objects be mentally represented in a common format over which such comparisons can be carried out. What is that representational format? Objects could be compared in terms of their superficial features (e.g., degree of pixel-by-pixel overlap), but a more intriguing possibility is that they are compared on the basis of a deeper structure. One especially promising candidate that has enjoyed success in the computer vision literature is the shape skeleton—a geometric transformation that represents objects according to their inferred underlying organization. Despite several hints that shape skeletons are computed in human vision, it remains unclear how much they actually matter for subsequent performance. Here, we explore the possibility that shape skeletons help mediate the ability to extract visual similarity. Observers completed a same/different task in which two shapes could vary either in their skeletal structure (without changing superficial features such as size, orientation, and internal angular separation) or in large surface-level ways (without changing overall skeletal organization). Discrimination was better for skeletally dissimilar shapes: observers had difficulty appreciating even surprisingly large differences when those differences did not reorganize the underlying skeletons. This pattern also generalized beyond line drawings to 3-D volumes whose skeletons were less readily inferable from the shapes’ visible contours. These results show how shape skeletons may influence the perception of similarity—and more generally, how they have important consequences for downstream visual processing.

     

Sudden changes in spectrum of an echo cause a breakdown of the precedence effect

The effect of changing the frequency components of an echo relative to the sound source was examined in a two-choice discrimination task. Subjects sat in an anechoic chamber and discriminated the direction of the lag noise burst within a lead-lag pair presented over loudspeakers. The leading noise burst was broadband, and the lagging burst was either high- or low-pass filtered. On some conditions, this test burst pair was preceded by a conditioning train of burst pairs, which also had a broadband lead and either a high- or low-frequency lag. When the frequency content of the echo was held constant across the conditioning train and test burst pair, echo suppression that was built up during the repeating train was maintained for the test burst pair, shown by the subjects’ poor performance in detecting the location of the lagging burst. By comparison, subjects had little difficulty in localizing the lagging burst when the frequency content of the echo changed between the conditioning train and the test burst, indicating that any buildup of suppression during the train was broken when the lagging burst’s spectrum shifted. The data are consistent with an interpretation in which echo suppression is temporarily broken when listeners’ built-up expectations about room acoustics are violated.     

Do video sounds interfere with auditory event-related potentials?

To make the electroencephalogram (EEG) recording procedure more tolerable, listeners have been allowed in some experiments to watch an audible video while their auditory P1, NI, P2, and mismatch negativity (MMN) event-related potentials (ERPs) to experimental sounds have been measured. However, video sounds may degrade auditory ERPs to experimental sounds. This concern was tested with 19 adults who were instructed to ignore standard and deviant tones presented through headphones while they watched a video with the soundtrack audible in one condition and silent in the other. Video sound impaired the size, latency, and split-half reliability of the MMN, and it decreased the size of the P2. However, it had little effect on the P1 or N1 or on the split-half reliability of the P1—N1—P2 waveform, which was significantly more reliable than the MMN waveform regardless of whether the video sound was on or off. The impressive reliability of the P1 and N1 components allows for the use of video sound during EEG recording, and they may prove useful for assessing auditory processing in listeners who cannot tolerate long testing sessions.     

The effects of attenuation of frequency segments on binaural localization of sound

Perceived location of tonal stimuli d narrow noise bands presented in two-dimensional space varies in an orderly manner with changes in stimulus frequency. Hence, frequency has a referent in space that is most apparent during monaural listening. The assumption underlying the present study is that maximum sound pressure level measured at the ear canal entrance for the various frequencies serves as a prominent spectral cue for their spatial referents. Even in binaural localization, location judgments in the vertical plane are strongly influenced by spatial referents. We measured sound pressure levels at the left ear canal entrance for 1.0-kHz-wide noise bands, centered from 4.0 kHz through 10.0 kHz, presented at locations from 60° through ?45° in the vertical plane; the horizontal plane coordinate was fixed at ?90°. On the basis of these measurements, we fabricated three different band-stop stimuli in which differently centered 2.0-kHz-wide frequency segments were filtered from a broadband noise. Unfiltered broadband noise served as the remaining stimulus. Localization accuracy differed significantly among stimulus conditions (p<.01). Where in the vertical plane most errors were made depended on which frequency segment was filtered from the broadband noise.     

Localizing Localization: The Role of Working Memory in Auditory Localization

It is unclear from current accounts of working memory which, if any, of its components might be involved in our ability to specify the location of a sound source. A series of studies were performed to assess the degree of interference in localization of broadband noise, by a concurrent articulatory suppression (articulatory loop—Experiment 1), serial recall (phonological store and articulatory loop—Experiment 2), and Paced Visual Serial Addition Test (central executive—Experiment 3). No significant disruption of auditory localization was revealed by the first two experiments, ruling out a role for the phonological loop in auditory localization. In Experiment 3, a large degree of error was exhibited in localization, when performed concurrently with the addition task, indicating a requirement for central resources. This suggestion is confirmed by comparison of localization performance across all three studies, which demonstrates a clear deterioration in performance as the demand of concurrent tasks on central resources increases. Finally, concurrent localization was shown to disrupt the primacy portion of the serial position curve, as well as performance on the Paced Visual Serial Addition Test.     

Spectral cues which influence monaural Localization in the horizontal plane

An extensive series of behavioral tests was carried out to determine what region, or regions, of the sound spectrum were critical for locating sounds monaurally in the horizontal plane. Seven subjects were requested to locate narrow bands of noise centered at different frequencies, combinations of these noise bands, low-pass, high-pass, and broadband noise. As observed in an earlier study, increasing bandwidth did not necessarily lead to improved localization performance until the band became broad, including, for example, all frequencies above 4.0 kHz. What seems to be happening is that listeners perceive narrow bands of noise originating from restricted places in the horizontal plane which may differ one from another depending on the frequency composition of the stimulus. In several instances, if two noise bands were presented simultaneously, the resulting stimulus was located with reasonable accuracy provided each component, when presented singly, was perceived as emanating from clearly separate azimuthal positions. If, however, two noise bands, which were perceived to originate from approximately the same azimuthal position when presented singly, were now presented simultaneously, the resulting stimulus still was perceived to originate from the same region of the horizontal plane. This, then, is a case where augmenting the spectral content of the stimulus does not bring about improved performance. We suggest that the expression of judgmental biases in the apparent location of a band of noise may prove useful for understanding why some stimuli of specified width and center frequency are localizable while others are not.     

Coherence masking protection in speech sounds: The role of formant synchrony

Three experiments were performed to examine listeners’ thresholds for identifying stimuli whose spectra were modeled after the vowels /i/ and /ε/, with the differences between these stimuli restricted to the frequency of the first formant. The stimuli were presented in a low-pass masking noise that spectrally overlapped the first formant but not the higher formants. Identification thresholds were lower when the higher formants were present than when they were not, even though the first formant contained the only distinctive information for stimulus identification. This indicates that listeners were more sensitive in identifying the first formant energy through its contribution to the vowel than as an independent percept; this effect is given the namecoherence masking protection. The first experiment showed this effect for synthetic vowels in which the distinctive first formant was supported by a series of harmonics that progressed through the higher formants. In the second two experiments, the harmonics in the first formant region were removed, and the first formant was simulated by a narrow band of noise. This was done so that harmonic relations did not provide a basis for grouping the lower formant with the higher formants; coherence masking protection was still observed. However, when the temporal alignment of the onsets and offsets of the higher and lower formants was disrupted, the effect was eliminated, although the stimuli were still perceived as vowels. These results are interpreted as indicating that general principles of auditory grouping that can exploit regularities in temporal patterns cause acoustic energy belonging to a coherent speech sound to stand out in the auditory scene.     

Negative congruence effects in letter and pseudo-letter recognition: the role of similarity and response conflict

Letters and pseudo-letters were presented in three experiments using a sequential same-different task. While first items were always presented in isolation, the second item was either presented in isolation or surrounded by geometrical non-target shapes that could be congruent or incongruent to the target. In two experiments, a physical sameness criterion was used. In Experiment 1, in one condition, different pairs were always distinct in shape, in another they were similar in shape. Negative congruence effects were obtained for different pairs that are similar. In Experiment 2, this effect is replicated within participants. In this experiment, similar and dissimilar stimuli were mixed. The results were explained in terms of the difficulty of responding different to stimuli that are similar in shape: when the second item is surrounded by a congruent shape, the similarity is emphasized, making this response even more difficult. In Experiment 3, the same stimuli were presented using a categorical sameness criterion. This reduces the role of physical similarity and thus eliminates the response conflict. As a result, negative congruence effects were no longer observed. Taken together, the three experiments identify another source of negative congruence effects besides the ones recently reported in the literature.     

The effect of vibrato on the recognition of masked vowels

Five experiments on the identifiability of synthetic vowels masked by wideband sounds are reported. In each experiment, identification thresholds (signal/masker ratios, in decibels) were measured for two versions of four vowels: a vibrated version, in which FO varied sinusoidally around 100 Hz; and a steady version, in which F0 was fixed at 100 Hz. The first three experiments were performed on naive subjects. Experiment 1 showed that for maskers consisting of bursts of pink noise, vibrato had no effect on thresholds. In Experiment 2, where the maskers were periodic pulse trains with an F0 randomly varied between 120 and 140 Hz from trial to trial, vibrato slightly improved thresholds when the sound pressure level of the maskers was 40 dB, but had no effect for 65-dB maskers. In Experiment 3, vibrated rather than steady pulse trains were used as maskers; when these maskers were at 40 dB, the vibrated versions of the vowels were slightly less identifiable than their steady versions; but, as in Experiment 2, vibrato had no effect when the maskers were at 65 dB. Experiment 4 showed that the unmasking effect of vibrato found in Experiment 2 disappeared in subjects trained in the identification task. Finally, Experiment 5 indicated that in trained listeners, vibrato had no influence on identification performance even when the maskers and the vowels had synchronous onsets and offsets. We conclude that vibrating a vowel masked by a wideband sound can affect its identification threshold, but only for tonal maskers and in untrained listeners. This effect of vibrato should probably be considered as a Gestalt phenomenon originating from central auditory mechanisms.     

Lexical Mediation Between Sight and Sound in Speechreading

In two experiments, we investigated whether simultaneous speech reading can influence the detection of speech in envelope-matched noise. Subjects attempted to detect the presence of a disyllabic utterance in noise while watching a speaker articulate a matching or a non-matching utterance. Speech detection was not facilitated by an audio-visual match, which suggests that listeners relied on low-level auditory cues whose perception was immune to cross-modal top-down influences. However, when the stimuli were words (Experiment 1), there was a (predicted) relative shift in bias, suggesting that the masking noise itself was perceived as more speechlike when its envelope corresponded to the visual information. This bias shift was absent, however, with non-word materials (Experiment 2). These results, which resemble earlier findings obtained with orthographic visual input, indicate that the mapping from sight to sound is lexically mediated even when, as in the case of the articulatory-phonetic correspondence, the cross-modal relationship is non-arbitrary.     

Binaural and monaural localization of sound in two-dimensional space

Two experiments were conducted. In experiment 1, part 1, binaural and monaural localization of sounds originating in the left hemifield was investigated. 104 loudspeakers were arranged in a 13 x 8 matrix with 15 degrees separating adjacent loudspeakers in each column and in each row. In the horizontal plane (HP), the loudspeakers extended from 0 degrees to 180 degrees; in the vertical plane (VP), they extended from -45 degrees to 60 degrees with respect to the interaural axis. Findings of special interest were: (i) binaural listeners identified the VP coordinate of the sound source more accurately than did monaural listeners, and (ii) monaural listeners identified the VP coordinate of the sound source more accurately than its HP coordinate. In part 2, it was found that foreknowledge of the HP coordinate of the sound source aided monaural listeners in identifying its VP coordinate, but the converse did not hold. In experiment 2, part 1, localization performances were evaluated when the sound originated from consecutive 45 degrees segments of the HP, with the VP segments extending from -22.5 degrees to 22.5 degrees. Part 2 consisted of measuring, on the same subjects, head-related transfer functions by means of a miniature microphone placed at the entrance of their external ear canal. From these data, the 'covert' peaks (defined and illustrated in text) of the sound spectrum were extracted. This spectral cue was advanced to explain why monaural listeners in this study as well as in other studies performed better when locating VP-positioned sounds than when locating HP-positioned sounds. It is not claimed that there is inherent advantage for localizing sound in the VP; rather, monaural localization proficiency, whether in the VP or HP, depends on the availability of covert peaks which, in turn, rests on the spatial arrangement of the sound sources.     

On the role of eye movements and saccade preparation in generating auditory inhibition of return.

In three experiments, listeners were required to either localize or identify the second of two successive sounds. The first sound (the cue) and the second sound (the target) could originate from either the same or different locations, and the interval between the onsets of the two sounds (Stimulus Onset Asynchrony, SOA) was varied. Sounds were presented out of visual range at 135 azimuth left or right. In Experiment 1, localization responses were made more quickly at 100 ms SOA when the target sounded from the same location as the cue (i.e., a facilitative effect), and at 700 ms SOA when the target and cue sounded from different locations (i.e., an inhibitory effect). In Experiments 2 and 3, listeners were required to monitor visual information presented directly in front of them at the same time as the auditory cue and target were presented behind them. These two experiments differed in that in order to perform the visual task accurately in Experiment 3, eye movements to visual stimuli were required. In both experiments, a transition from facilitation at a brief SOA to inhibition at a longer SOA was observed for the auditory task. Taken together these results suggest that location-based auditory IOR is not dependent on either eye movements or saccade programming to sound locations.