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].     

Echo thresholds of the precedence effect in the vertical plane

Echo thresholds were measured for two configurations of loudspeakers in the vertical plane. The first configuration was characterized by the lead sound presentation from a loudspeaker placed in front of a subject, whereas the lag sound was presented from the loudspeaker above the subject's head. In the second configuration, the lead and lag sounds were presented from the same loudspeakers but in reverse order. All the stimuli were broadband noise bursts in the frequency range of 5-20 kHz. Burst durations were 5, 10, 20, and 100 ms. Average echo thresholds differences were significant only for the signals of 100 ms in duration (F (1, 16) = 6.28; p < 0.05). For the other signals (5, 10, 20 ms), there was no significant effect of location of lead and lag signals (p > 0.05).     

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.     

Direction of visual apparent motion driven solely by timing of a static sound

In temporal ventriloquism, auditory events can illusorily attract perceived timing of a visual onset [1-3]. We investigated whether timing of a static sound can also influence spatio-temporal processing of visual apparent motion, induced here by visual bars alternating between opposite hemifields. Perceived direction typically depends on the relative interval in timing between visual left-right and right-left flashes (e.g., rightwards motion dominating when left-to-right interflash intervals are shortest [4]). In our new multisensory condition, interflash intervals were equal, but auditory beeps could slightly lag the right flash, yet slightly lead the left flash, or vice versa. This auditory timing strongly influenced perceived visual motion direction, despite providing no spatial auditory motion signal whatsoever. Moreover, prolonged adaptation to such auditorily driven apparent motion produced a robust visual motion aftereffect in the opposite direction, when measured in subsequent silence. Control experiments argued against accounts in terms of possible auditory grouping, or possible attention capture. We suggest that the motion arises because the sounds change perceived visual timing, as we separately confirmed. Our results provide a new demonstration of multisensory influences on sensory-specific perception [5], with timing of a static sound influencing spatio-temporal processing of visual motion direction.     

Auditory event-related potentials to the apparent auditory image motion

Auditory event-related potentials (ERP) were registered to the dichotically presented white noise stimuli (duration 1500 ms, band 150-1200 Hz). Abrupt or gradual change ofinteraural time difference in the middle of stimuli (750 ms after sound offset) was perceived as an apparent auditory image (AI) instant relocation or motion from the midline to one of the ears. In responses these stimuli two ERPs were observed: one to the sound onset, and second--to the onset of motion or AI relocation. ERPs to AI relocation differed from those to sound onset in longer components latencies (123 ms versus 105 ms for N 1,227 ms versus 190 ms for P2). In responses to AI motion component latencies were even longer (N1: 137 ms, P2: 240 ms); N1 amplitude was greater at sites contralateral to the AI motion direction.     

Change in Auditory Image Movement Trajectories under Conditions of Direct Nonsimultaneous Masking

The authors studied fused auditory image (FAI) movement trajectories under conditions of direct nonsimultaneous masking. This movement was created by a gradual change in a dichotically presented series of clicks with interaural differences in stimulation from 0 to ±700 s or from ±700 to 0 s. Binaurally presented transmissions of wide-band noise served as maskers. The location and length of the trajectories were evaluated without a masker and with five values of the time lag between the signal beginning and masker end. When the test signal duration was 200 ms, the length of the trajectories was 33–44° without a masker. In the first test group, this trajectory lay close to the median line of the head without a masker (irrespective of the movement direction) and moved away from it under masking conditions. When the FAI moved from the median line towards the right or left ear, the initial part of the trajectory was masked; when the movement direction was opposite, the final part was masked. In the second group, the trajectories were located near the ears when the FAI moved from either ear and shifted towards the median line as a result of masking. When the movement direction was opposite, they were close to the median line and shifted towards the ear under masking conditions. When the FAI moved along all trajectories, their initial parts were masked.     

Forecast ability of the auditory system during perception of gradually or abruptly moving short sound images

The ability to localize endpoints of sound image trajectories was studied in comparison with stationary sound image positions. Sound images moved either gradually or abruptly to the left or right from the head midline. Different types of sound image movement were simulated by manipulating the interaural time delay. Subjects were asked to estimate the position of the virtual sound source, using the graphic tablet. It was revealed that the perceived endpoints of the moving sound image trajectories, like stationary stimulus positions, depended on the interaural time delay. The perceived endpoints of the moving sound images simulated by stimuli with the final interaural time delay lower than 200 micros were displaced further from the head midline as compared to stationary stimuli of the same interaural time delays. This forward displacement of the perceived position of the moving target can be considered as "representational momentum" and can be explained by mental extrapolation of the dynamic information, which is necessary for successive sensorimotor coordination. For interaural time delays above 400 micros, final positions of gradually and abruptly moving sound sources were closer to the head midline than corresponding stationary sound image position. When comparing the results of both duration conditions, it was shown that in case of longer stimuli the endpoints of gradually moving sound images were lateralized further from the head midline for interaural time delays above 400 micros.     

Independence of echo-threshold and echo-delay in the barn owl

Despite their prevalence in nature, echoes are not perceived as events separate from the sounds arriving directly from an active source, until the echo's delay is long. We measured the head-saccades of barn owls and the responses of neurons in their auditory space-maps while presenting a long duration noise-burst and a simulated echo. Under this paradigm, there were two possible stimulus segments that could potentially signal the location of the echo. One was at the onset of the echo; the other, after the offset of the direct (leading) sound, when only the echo was present. By lengthening the echo's duration, independently of its delay, spikes and saccades were evoked by the source of the echo even at delays that normally evoked saccades to only the direct source. An echo's location thus appears to be signaled by the neural response evoked after the offset of the direct sound.     

Temporal hierarchy of the visual perceptive systems in the Mondrian world.

Our earlier psychophysical work has shown that colour and motion are not perceived at the same time, with colour leading motion by about 50-100 ms. In pursuing this work, we thought it would be interesting to use a more complex colour stimulus, one in which the wavelength composition of the light reflected or emitted from surfaces changes continually, without entailing a change in the perceived colour (colour constancy). We therefore used a Mondrian figure--an abstract multi-coloured scene with no recognizable objects--against which squares (either red or green) moved up and down, changing colour from red to green in various phase differences with the change in direction of motion. The red and green squares changed continually in their spectral characteristics, as did every other patch on the Mondrian. The results showed that colour is still perceived before motion, by about 80 ms.     

楝星天牛胸部摩擦和鞘翅振动发声及其声学特性的研究*

楝星天牛Anoplophora horsfieldi(Hope)成虫可借两种不同的方式发声： 1.胸部摩擦发声;2.鞘翊振动发声。胸部摩擦发声可连续进行,具有抗拒敌害和种内通讯的生物学意义;鞘翅振动发声为断续产生,受外界刺激而诱发,主要与抗拒敌害有关。测定表明,胸部摩擦声由多个音组连续组成,每一音组的持续时间为1100-1 6000ms,依次由抬头声音节(持续384±22ms,含有250-350个脉冲列)、间隔1(270-600ms)、低头声音节(382±16ms,250-350个脉冲列)和间隔2(80-360ms)组成。 抬头声音节的功率谱由基本音及其分音组成,基本音为信号能量的主要部分,其主峰频率为742±30Hz(雄)和603±34HZ(雌)。鞘翅振动声由间隔不等的,7-9个脉冲列组成,脉冲列的振幅较大、频率较高,持续约7-10ms。功率谱图上虽然脉冲列的频率分布于0-3100Hz,但能量主要集中在850-1050Hz内。与胸部摩擦声相比,鞘翅振动声的能量更高、释放更突然,是一种更为有效的拒敌性行为。     

Spatial orientation in the bushcricket <Emphasis Type="Italic">Leptophyes punctatissima</Emphasis> (Phaneropterinae; Orthoptera): III. Peripheral directionality and central nervous processing of spatial cues

We examined peripheral and central nervous cues underlying the ability of the bushcricket Leptophyes punctatissima to orient to elevated and depressed sound sources broadcasting the female acoustic reply. The peripheral spatial directionality of the ear was measured physiologically using monaural preparations of an auditory interneuron (T-fibre). In the azimuth, maximal interaural intensity differences of 18 dB occur between ipsi- and contralateral stimulation. With increasing elevation or depression of the sound sources, IIDs decrease systematically and reach zero with the source exactly above or below the preparation. Bilateral, simultaneous recordings of the activity of the pair of interneurons allowed determining the binaural discharge differences which occur in response to the extremely short (1 ms) female reply. These discharge differences are large (four action potentials/stimulus) and reliable in the azimuth with lateral stimulation, and decrease gradually with more frontal stimulation. With elevation and depression of sound sources these differences again decrease to one action potential/stimulus at 60° or 75° elevation, and lateral stimulus angles of about 60°. We also calculated the reliability with which a receiver could correctly determine the location of the sound source. We discuss these quantitative measures in relation to the spatial phonotactic behaviour of male L. punctatissima.     

AUDIO CASSETTES REVIEW

ABSTRACT

Some animals emit sounds usable for acoustic monitoring of their population size. Such signals should be loud, omni-directional and easy to recognise and localise. Eurasian Bittern Botaurus stellaris mating calls (booms) are known to be loud and probably omni-directional but there is no data on acoustic localisation of this species. We made recordings of bittern booms with a 4-element GPS-linked microphone array, calibrated for absolute sound pressure level measurements. Receiver spacing was 65 to 294 m. The source level was 101 ± 3 dB re 20 μPa @ 1 m. The source level did not vary more than 7 dB for the same boom recorded at two different locations, with angular separations of 3°-27° as seen from the source. The geometric transmission loss was close to spherical, and the excess attenuation was much smaller than what was expected from the prevailing temperature and humidity conditions. The prevailing wind conditions caused sound velocity variations of up to 3%. The source location error was 104 ± 113 m (mean ± 1 s.d.). The prevalence of large location errors was probably caused by problems of discerning the direct path from multipath arrivals of the signal at the receivers and by sound velocity variations.     

Electrical activation in the coronary sinus branches as a guide to cardiac resynchronisation therapy: rationale for a coordinate system

Background

For successful cardiac resynchronisation therapy (CRT) a spatial and electrical separation of right and left ventricular electrodes is essential. The spatial distribution of electrical delays within the coronary sinus (CS) tributaries has not yet been identified.

Objective

Electrical delays within the CS are described during sinus rhythm (SR) and right ventricular pacing (RVP). A coordinate system grading the mitral ring from 0° to 360° and three vertical segments is proposed to define the lead positions irrespective of individual CS branch orientation.

Methods

In 13 patients undergoing implantation of a CRT device 6±2.5, (median 5) lead positions within the CS were mapped during SR and RVP. The delay to the onset and the peak of the local signal was measured from the earliest QRS activation or the pacing spike. Fluoroscopic positions were compared to localizations on a nonfluoroscopic electrode imaging system.

Results

During SR, electrical delays in the CS were inhomogenous in patients with or without left bundle branch block (LBBB). During RVP, the delays increased by 44±32 ms (signal onset from 36±33 ms to 95±30 ms; p<0.001, signal peak from 105±44 ms to 156±30 ms; p<0.001). The activation pattern during RVP was homogeneous and predictable by taking the grading on the CS ring into account: (% QRS) = 78−0.002 (grade−162)², p<0.0001. This indicates that 78% of the QRS duration can be expected as a maximum peak delay at 162° on the CS ring.

Conclusion

Electrical delays within the CS vary during SR, but prolong and become predictable during RVP. A coordinate system helps predicting the local delays and facilitates interindividual comparison of lead positions irrespective of CS branch anatomy.     

Optical study of spatiotemporal inhibition evoked by two-tone sequences in the guinea pig auditory cortex

Spatiotemporal response patterns in the anterior and dorsocaudal fields of the guinea pig auditory cortex after two-tone sequences were studied in anesthetized animals (Nembutal 30 mg kg⁻¹) using an optical recording method (voltage-sensitive dye RH795, 12 × 12 photodiode array). Each first (masker) and second (probe) tone was 30 ms long with a 10-ms rise-fall time. Masker-probe pair combinations of the same or different frequencies with probe delays of 30–150 ms were presented to the ear contralateral to the recording side. With same-frequency pairs, responses to the probe were inhibited completely after probe delays of less than 50 ms and the inhibition lasted for more than 150 ms, and the inhibition magnitudes in different isofrequency bands of the anterior field were essentially the same. With different-frequency (octave-separated) pairs, responses to the probe were not inhibited completely even after probe delays as short as 30 ms, and the inhibition lasted only for 110–130 ms. Inhibition magnitudes were different from location to location. Accepted: 4 August 1997     

Electromechanical delay in the vastus lateralis muscle during dynamic isometric contractions

Electromechanical delay (EMD) values were obtained using a cross-correlation technique for a series of 14 repetitive submaximal dynamic isometric contractions of the vastus lateralis performed by five subjects. To avoid a phase lag, which is introduced with one-way filtering, the EMG was processed with a bi-directional application of a second-order Butterworth filter. A mean EMD value of 86 ms (SD = 5.1 ms) was found. Moreover, contraction and relaxation delays were computed and compared. There was a significant difference between the contraction and relaxation delays (P less than 0.005). The mean contraction delay was 81.9 ms and the mean relaxation delay was 88.8 ms. Despite this significant difference, the computed contraction and relaxation delay values lie in the same range as the total phase lag, calculated with the cross-correlation technique. The magnitude of EMD values found supports the need to account for this delay when interpreting temporal aspects of patterns of intermuscular coordination.     

Sluggishness of auditory perception during localization of short moving sound images

During localization of a moving sound source, a shift of the perceived position relative to the actual one of the starting point is an expression of the perception of sluggishness of the auditory system. In this study, the human ability to localize starting points during a gradual or abrupt movement of fused auditory images (FAIs) was compared with the ability to localize the position of a stationary sound image. Sound images moved from the midline of the head in the direction of each of the ears. The subject’s responses were recorded using a graphics table. There was a tendency to shift the starting point of the trajectory in the direction of the movement. This tendency was stronger for gradual rather than for abrupt FAI movement and for shorter stimuli (100 ms) than for long ones (200 ms). The value of the starting point’s displacement depended on the final interaural time delay. The results obtained are discussed in terms of the “snapshots” and “movement detector” theories, as well as in terms of the sluggish and anticipatory ability of auditory perception.     

The Contribution of Head Movement to the Externalization and Internalization of Sounds

Background

When stimuli are presented over headphones, they are typically perceived as internalized; i.e., they appear to emanate from inside the head. Sounds presented in the free-field tend to be externalized, i.e., perceived to be emanating from a source in the world. This phenomenon is frequently attributed to reverberation and to the spectral characteristics of the sounds: those sounds whose spectrum and reverberation matches that of free-field signals arriving at the ear canal tend to be more frequently externalized. Another factor, however, is that the virtual location of signals presented over headphones moves in perfect concert with any movements of the head, whereas the location of free-field signals moves in opposition to head movements. The effects of head movement have not been systematically disentangled from reverberation and/or spectral cues, so we measured the degree to which movements contribute to externalization.

Methodology/Principal Findings

We performed two experiments: 1) Using motion tracking and free-field loudspeaker presentation, we presented signals that moved in their spatial location to match listeners’ head movements. 2) Using motion tracking and binaural room impulse responses, we presented filtered signals over headphones that appeared to remain static relative to the world. The results from experiment 1 showed that free-field signals from the front that move with the head are less likely to be externalized (23%) than those that remain fixed (63%). Experiment 2 showed that virtual signals whose position was fixed relative to the world are more likely to be externalized (65%) than those fixed relative to the head (20%), regardless of the fidelity of the individual impulse responses.

Conclusions/Significance

Head movements play a significant role in the externalization of sound sources. These findings imply tight integration between binaural cues and self motion cues and underscore the importance of self motion for spatial auditory perception.     

Alternation of Sound Location Induces Visual Motion Perception of a Static Object

Background

Audition provides important cues with regard to stimulus motion although vision may provide the most salient information. It has been reported that a sound of fixed intensity tends to be judged as decreasing in intensity after adaptation to looming visual stimuli or as increasing in intensity after adaptation to receding visual stimuli. This audiovisual interaction in motion aftereffects indicates that there are multimodal contributions to motion perception at early levels of sensory processing. However, there has been no report that sounds can induce the perception of visual motion.

Methodology/Principal Findings

A visual stimulus blinking at a fixed location was perceived to be moving laterally when the flash onset was synchronized to an alternating left-right sound source. This illusory visual motion was strengthened with an increasing retinal eccentricity (2.5 deg to 20 deg) and occurred more frequently when the onsets of the audio and visual stimuli were synchronized.

Conclusions/Significance

We clearly demonstrated that the alternation of sound location induces illusory visual motion when vision cannot provide accurate spatial information. The present findings strongly suggest that the neural representations of auditory and visual motion processing can bias each other, which yields the best estimates of external events in a complementary manner.     

Response characteristics of wide-field non-habituating non-directional motion detecting neurons in the optic lobe of the locust,Locusta migratoria

1. Extracellular recordings from wide-field nonhabituating non-directional (ND) motion detecting neurons in the second optic chiasma of the locust Locusta migratoria are presented. The responses to various types of stepwise moving spot and bar stimuli were monitored (Fig. 1)
2. Stepwise motion in all directions elicited bursts of spikes. The response is inhibited at stimulus velocities above 5°/s. At velocities above 10°/s the ND neurons are slightly more sensitive to motion in the horizontal direction than to motion in the vertical direction (Fig. 2). The ND cells have a preference for small moving stimuli (Fig. 3).
3. The motion response has two peaks. The latency of the second peak depends on stimulus size and stimulus velocity. Increasing the height from 0.1 to 23.5° of a 5°/s moving bar results in a lowering of this latency time from 176 to 130 ms (Fig. 4). When the velocity from a single 0.1° spot is increased from 1 to 16°/s, the latency decreases from 282 to 180 ms (Figs. 5–6).
4. A change-of-direction sensitivity is displayed. Stepwise motion in one particular direction produces a continuous burst of spike discharges. Reversal or change in direction leads to an inhibition of the response (Fig. 7).
5. It shows that non-directional motion perception of the wide-field ND cells can simply be explained by combining self-and lateral inhibition.

     

Freezing-induced xylem cavitation and the northern limit of Larrea tridentata

We investigated the occurrence of freezing-induced cavitation in the evergreen desert shrub Larrea tridentata and compared it to co-occurring, winter-deciduous Prosopis velutina. Field measurements indicated that xylem sap in L. tridentata froze at temperatures below c. –5°C, and that this caused no measurable cavitation for minimum temperatures above –7°C. During the same period P. velutina cavitated almost completely. In the laboratory, we cooled stems of L. tridentata to temperatures ranging from –5 to –20°C, held them at temperature for 1 or 12 h, thawed the stems at a constant rate and measured cavitation by the decrease in hydraulic conductivity of stem segments. As observed in the field, freezing exotherms occurred at temperatures between –6.5 and –9°C and as long as temperatures were held above –11°C there was no change in hydraulic conductivity after thawing. However, when stems were cooled to between –11°C and –20°C, stem hydraulic conductivity decreased linearly with minimum temperature. Minimum temperatures between –16 and –20°C were sufficient to completely eliminate hydraulic conductance. Record (>20 year) minimum isotherms in this same range of temperatures corresponded closely with the northern limit of L. tridentata in the Mojave and Sonoran deserts.