Spatial stimulus cue information supplying auditory saltation

Auditory saltation is a misperception of the spatial location of repetitive, transient stimuli. It arises when clicks at one location are followed in perfect temporal cadence by identical clicks at a second location. This report describes two psychophysical experiments designed to examine the sensitivity of auditory saltation to different stimulus cues for auditory spatial perception. Experiment 1 was a dichotic study in which six different six-click train stimuli were used to generate the saltation effect. Clicks lateralised by using interaural time differences and clicks lateralised by using interaural level differences produced equivalent saltation effects, confirming an earlier finding. Switching the stimulus cue from an interaural time difference to an interaural level difference (or the reverse) in mid train was inconsequential to the saltation illusion. Experiment 2 was a free-field study in which subjects rated the illusory motion generated by clicks emitted from two sound sources symmetrically disposed around the interaural axis, ie on the same cone of confusion in the auditory hemifield opposite one ear. Stimuli in such positions produce spatial location judgments that are based more heavily on monaural spectral information than on binaural computations. The free-field stimuli produced robust saltation. The data from both experiments are consistent with the view that auditory saltation can emerge from spatial processing, irrespective of the stimulus cue information used to determine click laterality or location.     

Lateralization of narrow-band noise by blind and sighted listeners

The effects of varying interaural time delay (ITD) and interaural intensity difference (IID) were measured in normal-hearing sighted and congenitally blind subjects as a function of eleven frequencies and at sound pressure levels of 70 and 90 dB, and at a sensation level of 25 dB (sensation level refers to the pressure level of the sound above its threshold for the individual subject). Using an 'acoustic' pointing paradigm, the subject varied the IID of a 500 Hz narrow-band (100 Hz) noise (the 'pointer') to coincide with the apparent lateral position of a 'target' ITD stimulus. ITDs of 0, +/-200, and +/-400 micros were obtained through total waveform delays of narrow-band noise, including envelope and fine structure. For both groups, the results of this experiment confirm the traditional view of binaural hearing for like stimuli: non-zero ITDs produce little perceived lateral displacement away from 0 IID at frequencies above 1250 Hz. To the extent that greater magnitude of lateralization for a given ITD, presentation level, and center frequency can be equated with superior localization abilities, blind listeners appear at least comparable and even somewhat better than sighted subjects, especially when attending to signals in the periphery. The present findings suggest that blind listeners are fully able to utilize the cues for spatial hearing, and that vision is not a mandatory prerequisite for the calibration of human spatial hearing.     

Temporal masking level differences for transients: Further evidence for a short-term integrator

Studies of binaural perception have indicated that subjects are able to use temporal information available in high-frequency regions of the spectrum to lateralize high-frequency waveforms but not to detect these waveforms in masking noise. The present experiments demonstrate that although high-frequency interaural difference cues are relatively ineffective in simultaneous and forward masking, they can be utilized in backward masking. In Experiment 1, large maskinglevel differences were found in backward masking for high-frequency transients presented either monaurally or with an interaural temporal delay. Experiments 2–4 examined fringe masking, effects of masker duration, and combined forward-backward masking for both high- and lowfrequency transients presented with interaural differences in phase and intensity. The results are interpreted as support for the view that the auditory system is organized into parallel shortand long-term integration systems specialized for processing transient and sustained aspects of acoustic stimulation. It is suggested that information from the two integrators is combined when analysis of interaural differences within each of the systems yields similar estimates of spatial location.     

Brief pitch-priming facilitates infants’ discrimination of pitch-evoking noise: Evidence from event-related potentials

Pitch is derived by the auditory system through complex spectrotemporal processing. Pitch extraction is thought to depend on both spectral cues arising from lower harmonics that are resolved by cochlear filters in the inner ear, and on temporal cues arising from the pattern of action potentials contained in the cochlear output. Adults are capable of extracting pitch in the absence of robust spectral cues, taking advantage of the temporal cues that remain. However, recent behavioral evidence suggests that infants have difficulty discriminating between stimuli with different pitches when resolvable spectral cues are absent. In the current experiments, we used the mismatch negativity (MMN) component of the event related potential derived from electroencephalographic (EEG) recordings to examine a cortical representation of pitch discrimination for iterated rippled noise (IRN) stimuli in 4- and 8-month-old infants. IRN stimuli are pitch-evoking sounds generated by repeatedly adding a segment of white noise to itself at a constant delay. We created IRN stimuli (delays of 5 and 6 ms creating pitch percepts of 200 and 167 Hz) and high-pass filtered them to remove all resolvable spectral pitch cues. In experiment 1, we did not find EEG evidence that infants could detect the change in the pitch of these IRN stimuli. However, in Experiment 2, after a brief period of pitch-priming during which we added a sine wave component to the IRN stimulus at its perceived pitch, infants did show significant MMN in response to pitch changes in the IRN stimuli with sine waves removed. This suggests that (1) infants can use temporal cues to process pitch, although such processing is not mature and (2) that a short amount of pitch-priming experience can alter pitch representations in auditory cortex during infancy.     

Interaural time vs. interaural intensity in a lateralization paradigm

In a two-interval lateralization procedure, observers judged whether a stimulus presented with an interaural intensive difference was right or left in lateral space of the same stimulus presented with only an interaural temporal difference. The stimuli were pure tones of 500 and 1,000 Hz and 1,000-Hz low-pass noise. All stimuli were presented at both 65 and 55 dB SPL. For each of several values of interaural time (ranging from 0 to 1,000 microsec across all stimuli), a function was determined which related proportion of “right” relative position judgments to the value of the interaural intensive difference. The intercepts of these functions indicated that a progressively smaller amount of interaural intensive difference was required for the two stimuli to occupy a similar lateral location as the interaural temporal difference was increased. The slopes of the function suggested that the images associated with larger values of the interaural temporal differences are less distinct and blend together more than the images associated with small values of the temporal difference. Thus, the procedure provided a means for comparing the lateral location of images produced by interaural differences of time and intensity.     

Weber’s law,the “near miss,” and binaural detection

Weber functions (ΔI/I in dB) for gated 250-Hz tones were studied for monaural and several binaural stimulus configurations (homophasic, and antiphasic with varying phase angle for addition of signal to masker). The various cues for discrimination of signal plus masker from masker alone are functions of intensity increments at one or both ears, an intensity increment at one ear coupled with a decrement at the other, or the introduction of a phase difference between the ears. The decline of the Weber fraction with increasing masker level (the “near miss” to Weber’s law) was confirmed for monaural discrimination over the entire 40-dB range, and a similar rate of decline was found for various binaural stimuli over the lower half of that range. The data also confirm the individual differences found in other studies for sensitivity favoring either interaural amplitude or interaural phase shifts.     

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.     

Brief pitch-priming facilitates infants’ discrimination of pitch-evoking noise: Evidence from event-related potentials

Pitch is derived by the auditory system through complex spectrotemporal processing. Pitch extraction is thought to depend on both spectral cues arising from lower harmonics that are resolved by cochlear filters in the inner ear, and on temporal cues arising from the pattern of action potentials contained in the cochlear output. Adults are capable of extracting pitch in the absence of robust spectral cues, taking advantage of the temporal cues that remain. However, recent behavioral evidence suggests that infants have difficulty discriminating between stimuli with different pitches when resolvable spectral cues are absent. In the current experiments, we used the mismatch negativity (MMN) component of the event related potential derived from electroencephalographic (EEG) recordings to examine a cortical representation of pitch discrimination for iterated rippled noise (IRN) stimuli in 4- and 8-month-old infants. IRN stimuli are pitch-evoking sounds generated by repeatedly adding a segment of white noise to itself at a constant delay. We created IRN stimuli (delays of 5 and 6 ms creating pitch percepts of 200 and 167 Hz) and high-pass filtered them to remove all resolvable spectral pitch cues. In experiment 1, we did not find EEG evidence that infants could detect the change in the pitch of these IRN stimuli. However, in Experiment 2, after a brief period of pitch-priming during which we added a sine wave component to the IRN stimulus at its perceived pitch, infants did show significant MMN in response to pitch changes in the IRN stimuli with sine waves removed. This suggests that (1) infants can use temporal cues to process pitch, although such processing is not mature and (2) that a short amount of pitch-priming experience can alter pitch representations in auditory cortex during infancy.     

Visual grouping by motion precedes the relative localization between moving and flashed stimuli

A flashed stimulus is perceived as spatially lagging behind a moving stimulus when they are spatially aligned. When several elements are perceptually grouped into a unitary moving object, a flash presented at the leading edge of the moving stimulus suffers a larger spatial lag than a flash presented at the trailing edge (K. Watanabe. R. Nijhawan. B. Khurana, & S. Shimojo. 2001). By manipulation of the flash onset relative to the motion onset, the present study investigated the order of perceptual operations of visual motion grouping and relative visual localization. It was found that the asymmetric mislocalization was observed irrespective of physical and/or perceptual temporal order between the motion and flash onsets. Thus, grouping by motion must be completed to define the leading-trailing relation in a moving object before the visual system explicitly represents the relative positions of moving and flashed stimuli.     

A detection-theoretic model of echo inhibition

A detection-theoretic analysis of the auditory localization of dual-impulse stimuli is described, and a model for the processing of spatial cues in the echo pulse is developed. Although for over 50 years "echo suppression" has been the topic of intense theoretical and empirical study within the hearing sciences, only a rudimentary understanding of its mechanisms has emerged. In this article, psychometric functions and results from matching studies are used in developing a model that specifies the perceived position of the echo pulse as a normal deviate, with an expectation that is a logistic function of the echo delay and a variance that depends on interaural time difference. Loss of information in the echo event is quantified as a decline in the efficiency with which the binaural system receives information from the lag impulse.     

Selective attentional delays and attentional capture among simultaneous visual onset elements

Visual discrimination and detection responses to a single stimulus presented simultaneously with noise stimuli are slower and less accurate than are responses to a single stimulus presented alone. This occurs even though the location of the relevant stimulus (target) is known or visually indicated with stimuli onset. Results showed that noise elements delay focal attending and processing of a target. Furthermore, precuing the target location reduces, and can eliminate, target processing delays. Processing delays were not due to response competition or to random attentional capture by noise. It is suggested that simultaneous stimuli are perceived initially as a single object, and delays in processing a single stimulus are due to difficulties in perceptually segregating this stimulus from noise. Precuing is assumed to facilitate this segregation process.     

Inhibition of the cutaneous eyeblink reflex by unilateral and bilateral acoustic input: the persistence of contralateral antagonism in auditory processing

The eyeblink reflex elicited by a cutaneous stimulus is inhibited by weak auditory stimuli that are heard just before the blink. It has been shown that monaural prestimuli produce more reflex depression than binaural prestimuli do, suggesting that reflex modification is sensitive to the outcome of antagonistic connections between contralateral auditory inputs. We examined the time course of this antagonism by giving unilateral versus bilateral pairs of noise pips 100 msec before the reflex eyeblink, with the noise pips separated by 0, 1, 4, or 8 msec. Unilateral stimuli were more effective in every condition, but their advantage diminished with increased delay between the two components. The extended bilateral and unilateral trends of increasing reflex depression with increased delay meet at about 15 msec; if this extrapolation is valid, 15 msec represents the upper limit on this system's retention of the location of a brief noise impulse. The rate of convergence of the two temporal functions reflects the decay of the antagonistic effect of one noise on its contralateral counterpart.     

Fast Fourier-based DSP algorithm for auditory motion experiments

A digital signal-processing (DSP) technique for rapid generation of complex auditory motion stimuli based on dynamic linear changes in interaural delay is described. In this technique, a pair of comple-mentary discrete Fourier transforms (DFTs) for which the component spacing in one series is different than that of the other is used. The appeal of this technique is its wide applicability, since it can generate real-time motion stimuli of any velocity and starting interaural delay for complex broadband or filtered noise waveforms and nonstationary sounds such as speech, music, and other natural sounds.     

The role of binaural and fundamental frequency difference cues in the identification of concurrently presented vowels

The relative importance of voice pitch and interaural difference cues in facilitating the recognition of both of two concurrently presented synthetic vowels was measured. The interaural difference cues used were an interaural time difference (400 μsec ITD), two magnitudes of interaural level difference (15 dB and infinite ILD), and a combination of ITD and ILD (400 μsec plus 15 dB). The results are analysed separately for those cases where both vowels are identical and those where they are different. When the two vowels are different, a voice pitch difference of one semitone is found to improve the percentage of correct reports of both vowels by 35.8% on average. However, the use of interaural difference cues results in an improvement of 11.5% on average when there is a voice pitch difference of one semitone, but only a non-significant 0.1% when there is no voice pitch difference. When the two vowels are identical, imposition of either a voice pitch difference or binaural difference reduces performance, in a subtractive manner. It is argued that the smaller size of the interaural difference effect is not due to a “ceiling effect” but is characteristic of the relative importance of the two kinds of cues in this type of experiment. The possibility that the improvement due to interaural difference cues may in fact be due to monaural processing is discussed. A control experiment is reported for the ITD condition, which suggests binaural processing does occur for this condition. However, it is not certain whether the improvement in the ILD condition is due to binaural processing or use of the improvement in signal-to-noise ratio for a single vowel at each ear.     

Binaural processing of temporal and intensity cues: Suggestions for a one-system model

Summary Models of auditory localization-lateralization assume either a single or different neural systems for the processing of binaural time delay and intensity differences. An experiment was conducted, making use of the effect of sensory adaptation. The results are in favour of assuming a single system which processes both temporal and intensity cues in binaural stimulation.     

Pitch perception in chinchillas (Chinchilla laniger): stimulus generalization using rippled noise

Rippled noises evoke the perception of pitch in human listeners. Infinitely iterated rippled noise (IIRN) is generated when wideband noise (WBN) is delayed, attenuated, and added to the original WBN through either a positive (+) or a negative (-) feedback loop. The pitch of IIRN[+] is matched to the reciprocal of the delay, whereas the pitch of IIRN[-] for the same delay is an octave lower. Chinchillas (Chinchilla laniger) were trained to discriminate IIRN[+] with a 4-ms delay from IIRN[+] with a 2-ms delay and then tested in a stimulus generalization paradigm with IIRN[+] at delays between 2 and 4 ms. Systematic gradients in behavioral response occurred along the dimension of delay, suggesting that a perceptual dimension corresponding to pitch exists for IIRN[+]. Behavioral responses to IIRN[-] test stimuli were more variable among chinchillas, suggesting that IIRN[-] did not evoke similar pitches relative to IIRN[+]. Systematic gradients in behavioral response were observed when IIRN[-] test stimuli were presented in the context of other IIRN[-] stimuli. Thus, other perceptual cues such as timbre may dominate the pitch cues when IIRN[-] test stimuli are presented in the context of IIRN[+] stimuli.     

Contextual influences of dimension, speed, and direction of motion on subjective time perception

Research has indicated that the direction of motion and the speed of motion can influence the subjective estimates of temporal duration of two-dimensional (2-D) stimuli expanding and contracting within the picture plane. In this study, we investigated whether the contextual cues of stimulus/movement-plane dimensionality (2-D stimuli with implied movement in the picture plane or depth-rendered “3-D” stimuli with implied movement in the depth plane) influence and interact with speed and implied movement direction during interval estimation. Participants viewed a series of standard stimulus durations followed by a test stimulus duration and determined whether the test and standard durations differed. The results indicated that moving stimuli were overestimated relative to stationary stimuli, regardless of the direction of motion or dimensionality. Also, faster-moving stimuli were overestimated relative to slower-moving stimuli. Importantly, an interaction between movement direction and dimensional cues indicated that the loom/recede distinction occurs for 2-D but not for 3-D stimuli. It is possible that the loom/recede distinction for the 2-D condition may be an artifact arising from reduced or from a lack of perceived motion in 2-D “recede” conditions, rather than a specific overestimation for looming stimuli.     

The dynamics of the visual system in combining conflicting KDE and binocular stereopsis cues

The dynamics of the visual system in combining multiple depth cues were investigated by measuring the temporal change in the perceived 3-D shape of a random-dot stimulus with conflicting kinetic depth effect (KDE) and binocular stereopsis cues. The KDE shape perception dominated for the first few seconds, and then was gradually supplanted by the stereo shape perception. The effects of various pre-adaptation stimuli suggested that the temporal change in the perceived shape resulted from a self-adaptation of the KDE mechanism that occurs mainly at the levels of motion and relative motion detection.     

Binaural release from temporal induction

This study examined the effects of interaural phase difference (IPhD) relations in temporal induction (TI)—that is, the perceived continuity of a fainter sound (inducee) through an interrupting higher amplitude sound (inducer). The extent of TI was measured both directly as the upper amplitude level for continuity and indirectly as the loudness reduction of the inducer. It was found that TI was inhibited when the IPhD of the inducer and the IPhD of the inducee differed. It was also found that the extent of induction was positively related to the masking potential of the inducer as measured by the binaural masking level difference procedure. These results suggest that TI involves processes that are affected by interaural phase differences and that the masking potential rule, shown by previous studies to apply in the frequency domain, applies also in the IPhD domain. The present findings are consistent with the hypothesis that TI results from allocation of a portion of the neural excitation produced by the inducer over to the inducee if the inducer has the appropriate masking potential. As a consequence, obliterated signals can be selectively restored on the basis of both frequency-specific monaural cues and azimuth-related binaural cues, abilities that can enhance detection of signals under the noisy conditions of everyday life.     

Attentional zooming and the global-dominance phenomenon: Effects of level-specific cueing and abrupt visual onset

Summary In four experiments level-specific cueing of hierarchically structured stimuli was used to test the hypothesis that valid cues can reduce the global-dominance phenomenon. Compound stimuli (Experiments 1 and 2) or simple geometric forms (Experiments 3 and 4) were presented with different SOAs after a valid, an invalid, or a neutral level-specific cue (cue validity 80%). Costs for invalid cues and benefits for valid cues were produced in all experiments. However, a reduction of the global-local RT difference to about zero was achieved only after the reduction of the abrupt visual onset accompanying stimulus presentation in Experiments 2 (with compound stimuli) and 4 (with simple geometric forms). In addition, there was no longer the typical asymmetric-interference pattern (i. e., features of the global level interfere with local identification, but not vice versa) that was one of Navon's (1977) main arguments for assuming a perceptual precedence. It is concluded that the RT that is longer for local than for global identifications is produced by the time needed to refocus visual attention intentionally from the global level, which is focussed at first unintentionally, to the local level.