The precedence effect for signals moving in the horizontal plane

The precedence effect refers to a group of auditory phenomena related to the ability to locate sound sources in reverberant environments. In the present study, this phenomenon was investigated using two moving signals. The first signal was direct (lead) and the other was delayed (lag). The motion of the sound source was created by successive switching of ten loudspeakers. The continuity of the motion was created by simultaneously attenuating the stimulus in the previous loudspeaker and enhancing it in the next one. The length of the path of the lead and lag was 34°. The lead moved from 34° to 0° (to the right) and the lag moved –52° to –86° (to the left). The duration of the lead and the lag was 1 s. Lead–lag delays ranged from 1 to 40 ms. Subjects had to indicate the location of the lag. The results indicate that the lead signal dominated in the sound localization at short delay durations (up to 18 ms). In spite of the instructions, all the subjects pointed at the lead, which suggests that they perceived the lag in this location. Two distinct sounds were perceived at the longest delays. The mean echo threshold and its standard deviation in eight subjects was 9.6 ± 4.5 ms.     

Precedence effect at horizontal and vertical plane and moving lagging signal

The precedence effect refers to the fact that humans are able to localize sound sources in reverberant environments. In this study, sound localization was studied with dual sound source: stationary (lead) and moving (lag) for two planes: horizontal and vertical. Duration of lead and lag signals was 1s. Lead-lag delays ranged from 1-40 ms. Testing was conducted in free field, with broadband noise busts (5-18 kHz). The listeners indicated the perceived location of the lag signal. Results suggest that at delays above to 25 ms in horizontal plane and 40 ms in vertical plane subjects localized correctly the moving signal. At short delays (up to 8-10 ms), regardless of the instructions, all subjects pointed to the trajectory near the lead. The echo threshold varied dramatically across listeners. Mean echo thresholds were 7.3 ms in horizontal plane and 10.1 ms in vertical plane. Statistically significant differences were not observed for two planes [F(1, 5) = 5.52; p = 0.07].     

Estimating the Intended Sound Direction of the User: Toward an Auditory Brain-Computer Interface Using Out-of-Head Sound Localization

The auditory Brain-Computer Interface (BCI) using electroencephalograms (EEG) is a subject of intensive study. As a cue, auditory BCIs can deal with many of the characteristics of stimuli such as tone, pitch, and voices. Spatial information on auditory stimuli also provides useful information for a BCI. However, in a portable system, virtual auditory stimuli have to be presented spatially through earphones or headphones, instead of loudspeakers. We investigated the possibility of an auditory BCI using the out-of-head sound localization technique, which enables us to present virtual auditory stimuli to users from any direction, through earphones. The feasibility of a BCI using this technique was evaluated in an EEG oddball experiment and offline analysis. A virtual auditory stimulus was presented to the subject from one of six directions. Using a support vector machine, we were able to classify whether the subject attended the direction of a presented stimulus from EEG signals. The mean accuracy across subjects was 70.0% in the single-trial classification. When we used trial-averaged EEG signals as inputs to the classifier, the mean accuracy across seven subjects reached 89.5% (for 10-trial averaging). Further analysis showed that the P300 event-related potential responses from 200 to 500 ms in central and posterior regions of the brain contributed to the classification. In comparison with the results obtained from a loudspeaker experiment, we confirmed that stimulus presentation by out-of-head sound localization achieved similar event-related potential responses and classification performances. These results suggest that out-of-head sound localization enables us to provide a high-performance and loudspeaker-less portable BCI system.     

The precedence effect in the horizontal and vertical planes in experiments with a moving lagging signal

The precedence effect in the localization of a moving lagging sound source was studied in experiments on humans under the free field conditions in the presence of a stationary (lead) sound source. Broad-band noise (5–18 kHz) bursts 1 s in duration presented in the horizontal and vertical planes were used as signals. The lead-lag delays ranged from 1 to 40 ms. The results showed that, if the signals were presented in the horizontal plane, the probability of correct localization of the moving lagging signal was decreased for delays shorter than 25 ms; if the signals were presented in the vertical plane, it was decreased for delays shorter than 40 ms. If the delays were shorter than 8–10 ms, the subjects could not localize the moving lagging signal at all. In this interval of delays, the subjects could localize only the lead signal. The mean echo threshold for signals presented in the horizontal plane was smaller than for signals presented in the vertical plane (7.3 and 10.1 ms, respectively). However, comparison of these values across the sample of subject did not show significant differences [F(1, 5) = 5.52, p = 0.07]. The results of the study suggest that the precedence effect causes a tendency towards a stronger suppression of a moving lagging signal in the vertical plane than in the horizontal plane.     

Discrimination of Velocity and Spectral Composition of a Sound Stimulus during Its Movement in the Vertical Plane

Differential sensitivity to the velocity of a sound source image in the vertical plane was studied by using two signals with different spectral bandwidths: 0.25–4 kHz (signal 1) and 4–12.5 kHz (signal 2). Five subjects were tested. Sequential switching of loudspeakers with similar frequency characteristics simulated movement of a sound source. Differential velocity thresholds were determined for two reference velocities: 58 and 115°/s. Significant differences in the absolute values of these thresholds were found for signals with different spectral compositions. The threshold for signal 1 (0.25–4.0 kHz) exceeded that for signal 2 (4.0–12.5 kHz) twofold at 58°/s and 1.6-fold at 115°/s.     

Correlations between hearing and sound production in piranhas

Summary In order to determine whether correlations exist between hearing and the known soundproduction abilities in piranhas (Serrasalmus nattereri), behavioral auditory thresholds were obtained with continuous tones and tone pulses. A new avoidance conditioning method was developed, where fin movements of caged animals were taken as response to a tone. The mean values of the far-field audiogram ranged from –26 dB re. 0.1 Pa at 80 Hz to a low point of about –43 dB between 220–350 Hz and rose to –14 dB at 1500 Hz. The frequency spectrum of typical drumming sounds (barks) covers the range of best hearing (100–600 Hz).Piranhas are able to integrate temporally acoustic signals: in threshold investigations with repeated tone pulses, the thresholds rose approximately exponentially with decreasing pulse duration and repetition rate; thresholds of single pulses were higher with shorter pulses. The temporal patterning of the calls and the temporal integration ability are well correlated in piranhas, optimizing intraspecific detectability and total length of sound production with respect to the fatigue characteristics of drumming muscles and habituation of the neural pacemaker.The lagenae of the piranhas were found to face laterofrontally; this is thought to be a morphological adaptation to sound production, saving the lagenae from excessive strain during activation of the drumming muscles.Abbreviations Cl acoustic condition 1, where a board with the air loudspeaker rested on the experimental tank upon a layer of felt - C2 acoustic condition 2, where the loudspeaker was freely mounted 20 cm above the water surface - d _p pulse duration - f _p pulse repetition rate - D duty cycle     

Hearing in honeybees: operant conditioning and spontaneous reactions to airborne sound

Summary Airborne sound signals emitted by dancing bees (Apis mellifera) play an essential role in the bees' dance communication. It has been shown earlier that bees can learn to respond to airborne sounds in an aversive conditioning paradigm. Here we present a new training paradigm. A Y-choice situation was used to determine the frequency range and amplitude thresholds of hearing in bees. In addition, spontaneous reactions of bees to airborne sound were observed and used to determine thresholds of hearing. Both methods revealed that bees are able to detect sound frequencies up to about 500 Hz. The hearing threshold is 100–300 mm/s peak-to-peak velocity and is roughly constant over the range of detectable frequencies. The amplitude of the signals emitted in the dance language is 5 to 10 times higher, so we can conclude that bees can easily detect the dance sounds.     

Echo thresholds measured in the vertical and horizontal planes

The results of studying the precedence effect in the case where the direct and delayed (reflected) signals are located in the vertical and horizontal planes are considered. Loudspeakers emitting direct and reflected sounds were placed 45 deg to the left and right of the median line of the subject’s head in the horizontal plane and in front of and above the subject’s head, i.e., with 0 and 90 deg of elevation relative to the eye level, in the vertical plane. It has been shown that the time limits of the precedence effect of short (5-ms) signals are similar in the horizontal and vertical planes. For signals more than 10 ms in duration, the values of echo thresholds were higher in the vertical plane and significantly differed (p < 0.05) from the thresholds in the horizontal plane.     

The underwater and airborne horizontal localization of sound by the northern fur seal

The accuracy of the underwater and airborne horizontal localization of different acoustic signals by the northern fur seal was investigated by the method of instrumental conditioned reflexes with food reinforcement. For pure-tone pulsed signals in the frequency range of 0.5-25 kHz the minimum angles of sound localization at 75% of correct responses corresponded to sound transducer azimuth of 6.5-7.5 degrees +/- 0.1-0.4 degrees underwater (at impulse duration of 3-90 ms) and of 3.5-5.5 degrees +/- 0.05-0.5 degrees in air (at impulse duration of 3-160 ms). The source of pulsed noise signals (of 3-ms duration) was localized with the accuracy of 3.0 degrees +/- 0.2 degrees underwater. The source of continuous (of 1-s duration) narrow band (10% of c.fr.) noise signals was localized in air with the accuracy of 2-5 degrees +/- 0.02-0.4 degrees and of continuous broad band (1-20 kHz) noise, with the accuracy of 4.5 degrees +/- 0.2 degrees.     

Discrimination of calling song models by the cricket,Teleogryllus oceanicus: the influence of sound direction on neural encoding of the stimulus temporal pattern and on phonotactic behavior

Summary Recordings were made from an identified auditory neuron, the omega neuron, in the cricketTeleogryllus oceanicus. Models of the conspecific calling song and of the song of another species were presented either singly or simultaneously, and the degree to which the temporal pattern of the conspecific model was encoded in the neuron's spike train was determined. When a single stimulus was presented alone, its temporal pattern was faithfully reflected by the cells's spiking activity, no matter what the azimuth of the broadcasting loudspeaker (Fig. 3). When two stimuli were presented simultaneously from opposite sides, encoding of the pattern ipsilateral to the recorded neuron was interfered with only slightly by the contralateral pattern, as long as the two loudspeakers were sufficiently separated (Figs. 2, 3, 4). When the loudspeakers were each 15° from the cricket's midline, however, the encoding of the temporal pattern of the ipsilateral song model was severely disrupted (Figs. 3, 4). Bilateral interactions are important in determining the response level of the neuron, but do not appear to contribute to the direction-selective encoding of the stimulus temporal pattern (Figs. 5, 6).Phonotactic steering movements of tethered, flying crickets were recorded under stimulus conditions similar to those used in the neurophysiological tests. Under one-stimulus conditions, crickets attempted to turn towards the conspecific model for all tested speaker locations. The heterospecific model elicited reliable steering behavior when it was broadcast from azimuths of 90° and 60°, but often failed to elicit consistent responses when the speaker was positioned closer to the cricket's midline (Figs. 7, 8A and 8B). Responses to the heterospecific pattern were smaller in amplitude than those to the conspecific song model (Figs. 7, 8B). Under two-stimulus conditions, the conspecific model was consistently preferred over the heterospecific song for all tested speaker locations in half the tested crickets. In the remaining animals, preference for the conspecific pattern was only evident for the larger loudspeaker azimuths (Figs. 7, 8C).These results demonstrate that simultaneouslypresented stimuli can be represented separately in the nervous system as a consequence of auditory directionality. It is postulated that the cricket's ability to choose between these stimuli may result from the interactions between two bilaterallypaired song recognizers, each of which may be driven primarily by sound stimuli from one side.     

Frequency discrimination by the bottle-nosed dolphin and the Northern fur seal depending on sound parameters and sound conduction pathways

Underwater differential frequency hearing thresholds in the Black Sea bottle-nosed dolphin (Tursiops truncatus p.) and the northern fur seal (Callorhinus ursinus) were measured depending on signal frequency and sound conduction pathways. The measurements were performed by the method of instrumental conditioned reflexes with food reinforcement under conditions of full and partial (with heads out of water at sound conduction through body tissues) submergence of animals into water. It was shown that in a frequency range of 5-100 kHz, underwater differential frequency hearing thresholds of the bottle-nosed dolphin changed from 0.46-0.60% to 0.21-0.34% and depended little on sound conduction pathways. The minimum underwater differential frequency hearing thresholds of the northern fur seal corresponded to the frequencies of maximum hearing sensitivity, changed from 1.7% to 1-2.3% in a frequency range of 1-20 kHz, sharply increased at the edges of the frequency hearing perception range, and depended little (in a range of 5-40 kHz) on sound conduction pathways. Thus, underwater sounds propagating through the body tissues of dolphin and fur seal reach the inner ear.     

Auditory motion aftereffects of approaching and withdrawing sound sources

Auditory motion aftereffects of approaching and withdrawing sound sources were investigated in the free field. The approaching and withdrawing of a sound source were simulated by means of differently directed changes in the amplitude of impulses of broadband noise (from 20 Hz to 20 kHz) through two loudspeakers placed 1.1 and 4.5 m away from the listener. Presentation of the adapting approaching and withdrawing stimuli changed the perception of test signals following them: a stationary test signal was perceived by listeners as moving in the direction opposite to one of the movement of the adapting stimulus, whereas a test stimulus slowly moving in same direction as the adapting signal was perceived as stationary. The specific features of the auditory aftereffect of signals moving in a radial direction were similar to those of sound sources moving in a horizontal plane.     

The auditory aftereffects of radial sound source motion with different velocities

Auditory aftereffects were evaluated after short adaptation to radial sound source motion with different velocities. Approach and withdrawal of the sound source were simulated by means of rhythmical noise (from 20 Hz to 20 kHz) impulse sequences with an arising or diminishing amplitude. They were presented to an anechoic chamber through two loudspeakers placed at 1.1 and 4.5 m from the listener. The adapting stimulus velocities were 0.68, 3.43, 6.92, and 9.97 m/s with an adaptation duration of 5 s. At all motion velocities, the aftereffect manifested itself in divergence of psychometric functions upon approaching and withdrawing of adaptors. The direction of function displacements was opposite to that of the adaptor motion. Three parameters reflecting alteration of perception after motion adaptation were determined and compared with control data: the evaluation of stationary test stimuli; the velocity of moving test signal at the point of subjective equality (perceptually unmoving point); and the percentage of responses after averaging over all test signals. These parameters of auditory radial motion aftereffect similarly changed with the adaptor velocity. They demonstrated a significant effect at slow motion (0.68 and 3.43 m/s) and a small effect at a quick motion (6.92 and 9.97 m/s).     

Glutamate induces different neuronal conditioned responses than ACPD when used as a locally ionophoresed unconditioned stimulus in the cat motor cortex

Single unit recordings were made from the motor cortex of conscious cats with glass micropipettes that allowed ionophoretic application of 0.5 M glutamate in 2 M NaCl or 0.5 M ACPD (1S,3R-1-amino-cyclopentane-1,3-dicarboxylic acid, a mGluR agonist) in 2 M NaCl. Activity in response to a 70 dB click (1 ms rectangular pulse to loudspeaker) was studied before, during, and immediately after applying each agent locally as a paired US (90 nA current 570 ms after click for 300 ms in combination with glabella tap). A 70 dB hiss sound was presented 4.4 sec after the click as a discriminative stimulus (DS). CS and DS were presented 10 times initially (adaptation); then CS, US plus tap, and DS (approximately 10 times as conditioning); and then CS and DS (2-10 times to test post-conditioning). Glutamate potentiated the mean, early, 8-16 ms response to the click after conditioning (t=18.2, p<0.0001), but not the baseline activity which decreased from a mean of 17 spk/sec to 7 spk/sec (t=3.71, p<0.001). Baseline activity increased to 31 spk/sec when glutamate was applied during conditioning (t=3.30, p<0.005). ACPD reduced the intermediate, 64-72 ms response to the click after conditioning (t=8.18, p<0.0001), and potentiated the late 104-112 ms response (t=15.4, p<0.0001). Baseline activity was slightly increased after conditioning with ACPD. Saline did not potentiate the response to click. The results indicate that glutamate agonists that differ in their receptor affinities can induce different CRs when used as locally applied USs to condition neuronal responses to a click CS in the motor cortex of cats.     

Acoustic intensity discrimination by the cichlid fish Astronotus ocellatus (Cuvier)

The acoustic intensity discrimination ability of the oscar (Astronotus ocellatus), a cichlid fish, was investigated using an automated positive reward method. Intensity discrimination thresholds (I, in dB) for 7-s continuous pure tone signals were measured both as functions of sound intensity above thresholds, i.e., sensation levels, (SL)(+10 dB, +20 dB and +30 dB) and frequency (200 Hz, 500 Hz, and 800 Hz). I at 500 Hz for +10 dB, +20 dB, and +30 dB SLs are 8.9, 5.5, and 3.3 dB, respectively. I (at+20 dB SL) for 200 Hz, 500 Hz, and 800 Hz are 4.5, 5.5, and 9.3 dB, respectively. Despite having poor auditory sensitivity (narrow frequency range and high thresholds), the intensity discrimination ability of the oscar follows the general trends of previously studied fish species, however, with higher thresholds.     

Temperature and auditory thresholds: Bioacoustic studies of the frogsRana r. ridibunda,Hyla a. arborea andHyla a. savignyi (Anura,amphibia)

Summary The auditory thresholds of three frogs-two subspecies of the genusHyla (H. a. arborea, H. a. savignyi) and one of the genusRana (R. r. ridibunda)—were measured at 5°, 12°, 20° and 28°C, by recording multi-unit activity from the torus semicircularis. In the tree frogs, the upper limit of the audible range is 7,000 Hz. At 5°C the best frequency is 3,000 Hz; the threshold (expressed in dB SPL in all cases) at this frequency is 49 dB (males) and 43 dB (females) forH. a. arborea and 42 dB (males) and 48 dB (females) forH. a. savignyi. At 12°C the thresholds are lower, and they are lower still at 20°, reaching a minimum, at 3,000 Hz, of 42 dB (males) and 38 dB (females) forH. a. arborea and 41 dB (males) and 40 dB (females) forH. a. savignyi. At frequencies of 1,000 Hz and lower, thresholds are high at 5°C; in part of this range they are considerably lowered at 20°C, whereas at 28°C there is a reduction in sensitivity to most frequencies inH. a. arborea, amounting to more than 10 dB in the males.H. a. savignyi differs in this regard; at 28° sensitivity is no less than at lower temperatures, and in fact is greater in the range 1,000–1,400 Hz. The audible range ofR. r. ridibunda is more restricted than that of the tree frogs, but it is more sensitive within this range. The highest frequency is 4,500 Hz. At 5°C the thresholds of the males are lowest at 500–600 Hz (42 dB) and 1,400–1,900 Hz (ca. 39 dB). The best frequencies of the females are 700 Hz (38 dB) and 1,400 Hz (36 dB). At 12°C the thresholds at 300 Hz and 1,000 Hz are markedly lowered, by 10–18 dB. The thresholds of the females at 20°C are still lower over almost the entire audible range, whereas in the males only part of the range is affected. This difference persists at 28°C, the threshold curve of the males being slightly raised, while that of the females is unchanged. Latencies are dependent upon temperature and sound pressure. With a rise in temperature from 5° to 20°C the latency falls by ca. 8 ms. An increase in sound pressure from 5 dB to 30 dB SPL shortens the latency by ca. 10 ms. These changes were found in all the frogs studied.     

R-weighting provides better estimation for rat hearing sensitivity

Since sounds may induce physiological and behavioural changes in animals, it is necessary to assess and define the acoustic environment in laboratory animal facilities. Sound studies usually express sound levels as unweighted linear sound pressure levels. However, because a linear scale does not take account of hearing sensitivity-which may differ widely both between and within species at various frequencies-the results may be spurious. In this study a novel sound pressure level weighting for rats, R-weighting, was calculated according to a rat's hearing sensitivity. The sound level of a white noise signal was assessed using R-weighting, with H-weighting tailored for humans, A-weighting and linear sound pressure level combined with the response curves of two different loudspeakers. The sound signal resulted in different sound levels depending on the weighting and the type of loudspeaker. With a tweeter speaker reproducing sounds at high frequencies audible to a rat, R- and A-weightings gave similar results, but the H-weighted sound levels were lower. With a middle-range loudspeaker, unable to reproduce high frequencies, R-weighted sound showed the lowest sound levels. In conclusion, without a correct weighting system and proper equipment, the final sound level of an exposure stimulus can differ by several decibels from that intended. To achieve reliable and comparable results, standardization of sound experiments and assessment of the environment in animal facilities is a necessity. Hence, the use of appropriate species-specific sound pressure level weighting is essential. R-weighting for rats in sound studies is recommended.     

Sound localization by the bottlenose porpoise Tursiops truncatus.

1. Sound localization was measured behaviourally for the Atlantic bottlenose porpoise (Tursiops truncatus) using a wide range of pure tone pulses as well as clicks simulating the species echolocation click. 2. Measurements of the minimum audible angle (MAA) on the horizontal plane give localization discrimination thresholds of between 2 and 3 degrees for sounds from 20 to 90 kHz and thresholds from 2-8 to 4 degrees at 6, 10 and 100 kHz. With the azimuth of the animal changed relative to the speakers the MAAs were 1-3-1-5 degrees at an azimuth of 15 degrees and about 5 degrees for an azimuth of 30 degrees. 3. MAAs to clicks were 0-7-0-8 degrees. 4. The animal was able to do almost as well in determining the position of vertical sound sources as it could for horizontal localization. 5. The data indicate that at low frequencies the animal may have been localizing by using the region around the external auditory meatus as a detector, but at frequencies about 20 kHz it is likely that the animal was detecting sounds through the lateral sides of the lower jaw. 6. Above 20 kHz, it is likely that the animal was localizing using binaural intensity cues. 7. Our data support evidence that the lower jaw is an important channel for sound detection in Tursiops.     

The time scale of adaptation in tonal sequence processing by the mouse auditory midbrain neurons

The time course of poststimulatory adaptation of the inferior colliculus central nucleus (ICC) of CBB6F₁ hybrid mice to sound sequences, specifically, series of four tonal stimuli presented at intervals of 0, 2, 4, 10, 20, 50, 100, 200, 500, 700, 1000, and 1500 ms were studied. Assessment of the adaptation of the entire neuronal population have shown that, at an interstimulus interval of 0–200 ms, the response to the first tone in a series is significantly stronger than those to the second to fourth tones, the strengths of the latter three responses not differing significantly from one another. If the interstimulus interval is 500 ms or longer, the response to none of the tones in a series differs significantly in strength from the others. The role of adaptation of midbrain neurons to the grouping of components of bioacoustic stimuli is discussed.     

Sound and vibration sensitivity of VIIIth nerve fibers in the grassfrog, Rana temporaria

We have studied the sound and vibration sensitivity of 164 amphibian papilla fibers in the VIIIth nerve of the grassfrog, Rana temporaria. The VIIIth nerve was exposed using a dorsal approach. The frogs were placed in a natural sitting posture and stimulated by free-field sound. Furthermore, the animals were stimulated with dorso-ventral vibrations, and the sound-induced vertical vibrations in the setup could be canceled by emitting vibrations in antiphase from the vibration exciter. All low-frequency fibers responded to both sound and vibration with sound thresholds from 23 dB SPL and vibration thresholds from 0.02 cm/s². The sound and vibration sensitivity was compared for each fiber using the offset between the rate-level curves for sound and vibration stimulation as a measure of relative vibration sensitivity. When measured in this way relative vibration sensitivity decreases with frequency from 42 dB at 100 Hz to 25 dB at 400 Hz. Since sound thresholds decrease from 72 dB SPL at 100 Hz to 50 dB SPL at 400 Hz the decrease in relative vibration sensitivity reflects an increase in sound sensitivity with frequency, probably due to enhanced tympanic sensitivity at higher frequencies. In contrast, absolute vibration sensitivity is constant in most of the frequency range studied. Only small effects result from the cancellation of sound-induced vibrations. The reason for this probably is that the maximal induced vibrations in the present setup are 6–10 dB below the fibers' vibration threshold at the threshold for sound. However, these results are only valid for the present physical configuration of the setup and the high vibration-sensitivities of the fibers warrant caution whenever the auditory fibers are stimulated with free-field sound. Thus, the experiments suggest that the low-frequency sound sensitivity is not caused by sound-induced vertical vibrations. Instead, the low-frequency sound sensitivity is either tympanic or mediated through bone conduction or sound-induced pulsations of the lungs.Abbreviations AP amphibian papilla - BF best frequency - PST peristimulus time