Free‐field and virtual studies of the precedence effect in the median–sagittal plane: Duration effects

2000 ◽  
Vol 107 (5) ◽  
pp. 2849-2850
Author(s):  
Gerald Ng ◽  
Roberto Dizon ◽  
Ruth Litovsky ◽  
H. Steven Colburn
Keyword(s):  
Sagittal Plane ◽  
Free Field ◽  
Precedence Effect ◽  
Virtual Studies

scholarly journals Behavior and modeling of two-dimensional precedence effect in head-unrestrained cats

2015 ◽  
Vol 114 (2) ◽  
pp. 1272-1285
Author(s):  
Yan Gai ◽  
Janet L. Ruhland ◽  
Tom C. T. Yin
Keyword(s):  
Potassium Current ◽  
Horizontal Plane ◽  
Sagittal Plane ◽  
Precedence Effect ◽  
The Novel ◽  
Medial Superior Olive ◽  
Localization Dominance ◽  
Low Threshold ◽  
Spatial Locations ◽  
Auditory Illusion

The precedence effect (PE) is an auditory illusion that occurs when listeners localize nearly coincident and similar sounds from different spatial locations, such as a direct sound and its echo. It has mostly been studied in humans and animals with immobile heads in the horizontal plane; speaker pairs were often symmetrically located in the frontal hemifield. The present study examined the PE in head-unrestrained cats for a variety of paired-sound conditions along the horizontal, vertical, and diagonal axes. Cats were trained with operant conditioning to direct their gaze to the perceived sound location. Stereotypical PE-like behaviors were observed for speaker pairs placed in azimuth or diagonally in the frontal hemifield as the interstimulus delay was varied. For speaker pairs in the median sagittal plane, no clear PE-like behavior occurred. Interestingly, when speakers were placed diagonally in front of the cat, certain PE-like behavior emerged along the vertical dimension. However, PE-like behavior was not observed when both speakers were located in the left hemifield. A Hodgkin-Huxley model was used to simulate responses of neurons in the medial superior olive (MSO) to sound pairs in azimuth. The novel simulation incorporated a low-threshold potassium current and frequency mismatches to generate internal delays. The model exhibited distinct PE-like behavior, such as summing localization and localization dominance. The simulation indicated that certain encoding of the PE could have occurred before information reaches the inferior colliculus, and MSO neurons with binaural inputs having mismatched characteristic frequencies may play an important role.

Neural Correlates of the Precedence Effect in the Inferior Colliculus: Effect of Localization Cues

2002 ◽  
Vol 87 (2) ◽  
pp. 976-994 ◽  
Author(s):  
R. Y. Litovsky ◽  
B. Delgutte
Keyword(s):  
Inferior Colliculus ◽  
Time Course ◽  
Transfer Functions ◽  
Free Field ◽  
Field Studies ◽  
Suppressive Effect ◽  
Virtual Space ◽  
Precedence Effect ◽  
Excitatory Response ◽  
Accurate Localization

The precedence effect (PE) is an auditory phenomenon involved in suppressing the perception of echoes in reverberant environments, and is thought to facilitate accurate localization of sound sources. We investigated physiological correlates of the PE in the inferior colliculus (IC) of anesthetized cats, with a focus on directional mechanisms for this phenomenon. We used a virtual space (VS) technique, where two clicks (a “lead” and a “lag”) separated by a brief time delay were each filtered through head-related transfer functions (HRTFs). For nearly all neurons, the response to the lag was suppressed for short delays and recovered at long delays. In general, both the time course and the directional patterns of suppression resembled those reported in free-field studies in many respects, suggesting that our VS simulation contained the essential cues for studying PE phenomena. The relationship between the directionality of the response to the lead and that of its suppressive effect on the lag varied a great deal among IC neurons. For a majority of units, both excitation produced by the lead and suppression of the lag response were highly directional, and the two were similar to one another. For these neurons, the long-lasting inhibitory inputs thought to be responsible for suppression seem to have similar spatial tuning as the inputs that determine the excitatory response to the lead. Further, the behavior of these neurons is consistent with psychophysical observations that the PE is strongest when the lead and the lag originate from neighboring spatial locations. For other neurons, either there was no obvious relationship between the directionality of the excitatory lead response and the directionality of suppression, or the suppression was highly directional whereas the excitation was not, or vice versa. For these neurons, the excitation and the suppression produced by the lead seem to depend on different mechanisms. Manipulation of the directional cues (such as interaural time and level differences) contained in the lead revealed further dissociations between excitation and suppression. Specifically, for about one-third of the neurons, suppression depended on different directional cues than did the response to the lead, even though the directionality of suppression was similar to that of the lead response when all cues were present. This finding suggests that the inhibitory inputs causing suppression may originate in part from subcollicular auditory nuclei processing different directional cues than the inputs that determine the excitatory response to the lead. Neurons showing such dissociations may play an important role in the PE when the lead and the lag originate from very different directions.

Physiological Studies of the Precedence Effect in the Inferior Colliculus of the Cat. II. Neural Mechanisms

1998 ◽  
Vol 80 (3) ◽  
pp. 1302-1316 ◽  
Author(s):  
Ruth Y. Litovsky ◽  
Tom C. T. Yin
Keyword(s):  
Inferior Colliculus ◽  
Free Field ◽  
Neural Mechanisms ◽  
Precedence Effect ◽  
Medial Superior Olive ◽  
Mixed Effect ◽  
Source Level ◽  
Physiological Studies ◽  
Interaural Differences ◽  
Lead Location

Litovsky, Ruth Y. and Tom C. T. Yin. Physiological studies of the precedence effect in the inferior colliculus of the cat. II. Neural mechanisms. J. Neurophysiol. 80: 1302–1316, 1998. We studied the responses of neurons in the inferior colliculus (IC) of cats to stimuli known to evoke the precedence effect (PE). This paper focuses on stimulus conditions that probe the neural mechanisms underlying the PE but that are not usually encountered in a natural situation. Experiments were conducted under both free-field (anechoic chamber) and dichotic (headphones) conditions. We found that in free field the amount of suppression of the lagging response depended on the location of the leading source. With stimuli in the azimuthal plane, the majority (84%) of units showed stronger suppression of the lagging response for a leading stimulus placed in the cell's responsive area as compared with a lead in the unresponsive field. A smaller number of units showed stronger suppression for a lead placed in the unresponsive field, and a few showed little effect of the lead location. In the elevational plane, there was less sensitivity of the leading source to changes in location, but for those cells in which there was sensitivity, suppression was always stronger when the lead was in the cell's responsive area. Studies on stimulus locations also were conducted under dichotic conditions by varying the interaural differences in time (ITD) of the leading source. Results were consistent with those obtained in free field, suggesting that ITDs play an important role in determining the amount of suppression that was observed as a function of leading stimulus location. In addition to location and ITD, we also studied the effect of varying the relative levels of the lead and lag as well as stimulus duration. For all units studied, increasing the level of the leading stimulus while holding the lagging stimulus constant resulted in increased suppression. Similar effects of leading source level were observed in azimuth and elevation. The effect of varying the duration of the leading source also showed that longer duration stimuli produce stronger suppression; this finding was observed both in azimuth and elevation. We also compared the suppression observed under binaural and monaural contralateral conditions and found a mixed effect: some neurons show stronger suppression under binaural conditions, others to monaural contralateral conditions, and still others show no effect. The results presented here support the hypothesis that the PE reflects a long-lasting inhibition evoked by the leading stimulus. Five possible sources for the inhibition are considered: the auditory nerve, intrinsic circuits in the cochlear nucleus, medial and lateral nuclei of the trapezoid body inhibition to the medial superior olive, dorsal nucleus of the lateral lemniscus (DNLL) inhibition to the ICC, and intrinsic circuits in the ICC itself.

scholarly journals Physiological Studies of the Precedence Effect in the Inferior Colliculus of the Cat. I. Correlates of Psychophysics

1998 ◽  
Vol 80 (3) ◽  
pp. 1285-1301 ◽  
Author(s):  
Ruth Y. Litovsky ◽  
Tom C. T. Yin
Keyword(s):  
Inferior Colliculus ◽  
Free Field ◽  
Median Plane ◽  
Stimulus Level ◽  
Central Nucleus ◽  
Precedence Effect ◽  
Discharge Rates ◽  
Physiological Studies ◽  
Echo Suppression ◽  
Maximal Suppression

Litovsky, Ruth Y. and Tom C. T. Yin. Physiological studies of the precedence effect in the inferior colliculus of the cat. I. Correlates of psychophysics. J. Neurophysiol. 80: 1285–1301, 1998. The precedence effect (PE) is experienced when two spatially separated sounds are presented with such a brief delay that only a single auditory image at or toward the location of the leading source is perceived. The responses of neurons in the central nucleus of the inferior colliculus (ICC) of cats were studied using stimuli that are known to elicit the PE, focusing on the effects of changes in stimulus conditions that a listener might encounter in a natural situation. Experiments were conducted under both free-field (anechoic chamber) and dichotic (headphones) conditions. In free field, the PE was simulated by presenting two sounds from different loudspeakers with one sound delayed relative to the other. Either click or noise stimuli (2- to 10-ms duration) were used. Dichotically, the same conditions were simulated by presenting two click or noise pairs separated by an interstimulus delay (ISD) with interaural time differences (ITDs) imposed separately for each pair. At long ISDs, all neurons responded to both leading and lagging sources as if they were delivered alone. As the ISDs were shortened, the lagging response became suppressed. The ISD of half-maximal suppression varied considerably within the population of neurons studied, ranging from 2 to 100 ms, with means of 35 and 38 ms for free field and dichotic conditions, respectively. Several correlates of psychophysical findings were observed in ICC neurons: suppression was usually stronger with lower overall stimulus level and longer duration stimuli. Suppression also was compared along the azimuth and elevation in free field by placing the lagging source at (0°,0°), which is common to both axes, and the leading sources at locations along either plane that generated similar discharge rates. All neurons that showed suppression along the azimuth also did so in the elevation. In addition, there was a high correlation in the ISD of half-maximal suppression along the two planes ( r = 0.87). These findings suggest that interaural difference cues, which are robust along the horizontal axis but minimal in the median plane, are not necessary for neural correlates of the PE to be manifested. Finally, single-neuron responses did not demonstrate a correlate of build-up of suppression, a phenomenon whereby echo suppression accumulates with ongoing stimulation. This finding adds credibility to theories about the PE that argue for a “higher order” component of the PE.

Receptive Fields and Binaural Interactions for Virtual-Space Stimuli in the Cat Inferior Colliculus

1999 ◽  
Vol 81 (6) ◽  
pp. 2833-2851 ◽  
Author(s):  
Bertrand Delgutte ◽  
Philip X. Joris ◽  
Ruth Y. Litovsky ◽  
Tom C. T. Yin
Keyword(s):  
Inferior Colliculus ◽  
Sound Localization ◽  
Transfer Functions ◽  
Sagittal Plane ◽  
Free Field ◽  
Receptive Fields ◽  
Field Studies ◽  
Contralateral Side ◽  
Virtual Space ◽  
Acoustic Cues

Receptive fields and binaural interactions for virtual-space stimuli in the cat inferior colliculus. Sound localization depends on multiple acoustic cues such as interaural differences in time (ITD) and level (ILD) and spectral features introduced by the pinnae. Although many neurons in the inferior colliculus (IC) are sensitive to the direction of sound sources in free field, the acoustic cues underlying this sensitivity are unknown. To approach this question, we recorded the responses of IC cells in anesthetized cats to virtual space (VS) stimuli synthesized by filtering noise through head-related transfer functions measured in one cat. These stimuli not only possess natural combinations of ITD, ILD, and spectral cues as in free field but also allow precise control over each cue. VS receptive fields were measured in the horizontal and median vertical planes. The vast majority of cells were sensitive to the azimuth of VS stimuli in the horizontal plane for low to moderate stimulus levels. Two-thirds showed a “contra-preference” receptive field, with a vigorous response on the contralateral side of an edge azimuth. The other third of receptive fields were tuned around a best azimuth. Although edge azimuths of contra-preference cells had a broad distribution, best azimuths of tuned cells were near the midline. About half the cells tested were sensitive to the elevation of VS stimuli along the median sagittal plane by showing either a peak or a trough at a particular elevation. In general receptive fields for VS stimuli were similar to those found in free-field studies of IC neurons, suggesting that VS stimulation provided the essential cues for sound localization. Binaural interactions for VS stimuli were studied by comparing responses to binaural stimulation with responses to monaural stimulation of the contralateral ear. A majority of cells showed either purely inhibitory (BI) or mixed facilitatory/inhibitory (BF&I) interactions. Others showed purely facilitatory (BF) or no interactions (monaural). Binaural interactions were correlated with azimuth sensitivity: most contra-preference cells had either BI or BF&I interactions, whereas tuned cells were usually BF. These correlations demonstrate the importance of binaural interactions for azimuth sensitivity. Nevertheless most monaural cells were azimuth-sensitive, suggesting that monaural cues also play a role. These results suggest that the azimuth of a high-frequency sound source is coded primarily by edges in azimuth receptive fields of a population of ILD-sensitive cells.

Psychophysical and Physiological Evidence for a Precedence Effect in the Median Sagittal Plane

1997 ◽  
Vol 77 (4) ◽  
pp. 2223-2226 ◽  
Author(s):  
Ruth Y. Litovsky ◽  
Brad Rakerd ◽  
Tom C. T. Yin ◽  
William M. Hartmann
Keyword(s):  
Inferior Colliculus ◽  
Sagittal Plane ◽  
Precedence Effect ◽  
Single Neurons ◽  
Spectral Cues ◽  
Physiological Evidence ◽  
True Location

Litovsky, Ruth Y., Brad Rakerd, Tom C. T. Yin, and William M. Hartmann. Psychophysical and physiological evidence for a precedence effect in the median sagittal plane. J. Neurophysiol. 77: 2223–2226, 1997. A listener in a room is exposed to multiple versions of any acoustical event, coming from many different directions in space. The precedence effect is thought to discount the reflected sounds in the computation of location, so that a listener perceives the source near its true location. According to most auditory theories, the precedence effect is mediated by binaural differences. This report presents evidence that the precedence effect operates in the median sagittal plane, where binaural differences are virtually absent and where spectral cues provide information regarding the location of sounds. Parallel studies were conducted in psychophysics by measuring human listeners' performance, and in neurophysiology by measuring responses of single neurons in the inferior colliculus of cats. In both experiments the precedence effect was found to operate similarly in the azimuthal and sagittal planes. It is concluded that precedence is mediated by binaurally based and spectrally based localization cues in the azimuthal and sagittal planes, respectively. Thus,models that attribute the precedence effect entirely to processes that involve binaural differences are no longer viable.

Psychophysical Investigation of an Auditory Spatial Illusion in Cats: The Precedence Effect

2003 ◽  
Vol 90 (4) ◽  
pp. 2149-2162 ◽  
Author(s):  
Daniel J. Tollin ◽  
Tom C.T. Yin
Keyword(s):  
Horizontal Plane ◽  
Sagittal Plane ◽  
Source Location ◽  
Precedence Effect ◽  
Search Coil ◽  
Localization Dominance ◽  
Reverberant Environments ◽  
Echo Threshold ◽  
Search Coil Technique

The precedence effect (PE) describes several spatial perceptual phenomena that occur when similar sounds are presented from two different locations and separated by a delay. The mechanisms that produce the effect are thought to be responsible for the ability to localize sounds in reverberant environments. Although the physiological bases for the PE have been studied, little is known about how these sounds are localized by species other than humans. Here we used the search coil technique to measure the eye positions of cats trained to saccade to the apparent locations of sounds. To study the PE, brief broadband stimuli were presented from two locations, with a delay between their onsets; the delayed sound meant to simulate a single reflection. Although the cats accurately localized single sources, the apparent locations of the paired sources depended on the delay. First, the cats exhibited summing localization, the perception of a “phantom” sound located between the sources, for delays < ±400 μs for sources positioned in azimuth along the horizontal plane, but not for sources positioned in elevation along the sagittal plane. Second, consistent with localization dominance, for delays from 400 μs to about 10 ms, the cats oriented toward the leading source location only, with little influence of the lagging source, both for horizontally and vertically placed sources. Finally, the echo threshold was reached for delays >10 ms, where the cats first began to orient to the lagging source on some trials. These data reveal that cats experience the PE phenomena similarly to humans.

The Effect of Nonlinear Amplitude Growth on the Speech Perception Benefits Provided by a Single-Sided Vocoder

2019 ◽  
Vol 62 (3) ◽  
pp. 745-757 ◽  
Author(s):  
Jessica M. Wess ◽  
Joshua G. W. Bernstein
Keyword(s):  
Transfer Functions ◽  
Spatial Configuration ◽  
Free Field ◽  
Spatial Separation ◽  
Compression And Expansion ◽  
Interaural Difference ◽  
Interaural Differences ◽  
Single Sided Deafness ◽  
Perceptual Separation ◽  
Loudness Growth

PurposeFor listeners with single-sided deafness, a cochlear implant (CI) can improve speech understanding by giving the listener access to the ear with the better target-to-masker ratio (TMR; head shadow) or by providing interaural difference cues to facilitate the perceptual separation of concurrent talkers (squelch). CI simulations presented to listeners with normal hearing examined how these benefits could be affected by interaural differences in loudness growth in a speech-on-speech masking task.MethodExperiment 1 examined a target–masker spatial configuration where the vocoded ear had a poorer TMR than the nonvocoded ear. Experiment 2 examined the reverse configuration. Generic head-related transfer functions simulated free-field listening. Compression or expansion was applied independently to each vocoder channel (power-law exponents: 0.25, 0.5, 1, 1.5, or 2).ResultsCompression reduced the benefit provided by the vocoder ear in both experiments. There was some evidence that expansion increased squelch in Experiment 1 but reduced the benefit in Experiment 2 where the vocoder ear provided a combination of head-shadow and squelch benefits.ConclusionsThe effects of compression and expansion are interpreted in terms of envelope distortion and changes in the vocoded-ear TMR (for head shadow) or changes in perceived target–masker spatial separation (for squelch). The compression parameter is a candidate for clinical optimization to improve single-sided deafness CI outcomes.

Underlying Structure of Auditory-Visual Consonant Perception by Hearing-Impaired Children and the Influences of Syllabic Compression

1988 ◽  
Vol 31 (2) ◽  
pp. 156-165 ◽  
Author(s):  
P. A. Busby ◽  
Y. C. Tong ◽  
G. M. Clark
Keyword(s):  
Hearing Aids ◽  
Free Field ◽  
Acoustic Parameter ◽  
Hearing Impaired ◽  
Visual Signal ◽  
Underlying Structure ◽  
Choice Procedure ◽  
Release Times ◽  
Impaired Children ◽  
Hearing Impaired Children

The identification of consonants in a/-C-/a/nonsense syllables, using a fourteen-alternative forced-choice procedure, was examined in 4 profoundly hearing-impaired children under five conditions: audition alone using hearing aids in free-field (A),vision alone (V), auditory-visual using hearing aids in free-field (AV1), auditory-visual with linear amplification (AV2), and auditory-visual with syllabic compression (AV3). In the AV2 and AV3 conditions, acoustic signals were binaurally presented by magnetic or acoustic coupling to the subjects' hearing aids. The syllabic compressor had a compression ratio of 10:1, and attack and release times were 1.2 ms and 60 ms. The confusion matrices were subjected to two analysis methods: hierarchical clustering and information transmission analysis using articulatory features. The same general conclusions were drawn on the basis of results obtained from either analysis method. The results indicated better performance in the V condition than in the A condition. In the three AV conditions, the subjects predominately combined the acoustic parameter of voicing with the visual signal. No consistent differences were recorded across the three AV conditions. Syllabic compression did not, therefore, appear to have a significant influence on AV perception for these children. A high degree of subject variability was recorded for the A and three AV conditions, but not for the V condition.

Sign in / Sign up

Export Citation Format

Share Document