Spatial orientation in the bushcricket <Emphasis Type="Italic">Leptophyes punctatissima</Emphasis> (Phaneropterinae; Orthoptera): II. Phonotaxis to elevated sound sources on a walking compensator

The ability of the bushcricket Leptophyes punctatissima to orient to elevated sound sources was investigated. Males were placed on a walking compensator and oriented in response to a synthetic female reply, which was broadcast via one of five loudspeakers placed at elevations of 0°, 30°, 60°, 75° and 90°. Forward and backward movements were compensated, so that males remained at the same distance and elevation to the sound source. With increasing loudspeaker elevation, the males meandered more, and the ratio of the ideal path length to the actual path length decreased. The same was true for the correlation between stimulus angle and turn angle, and there were more turns to the wrong side with increasing loudspeaker elevation. Most males performed phonotaxis with a high acuity up to an elevation of 60°. Individuals varied strongly in their performance especially at a source elevation of 75°, where some were still very accurate in their approach, whereas the acuity of others decreased rapidly. We also describe a behaviour where males tilt their body axis to more anterior and sideward positions, both during walking and while calling on the spot. This behaviour is interpreted as a kind of directional scanning in order to actively induce changes in binaural cues.     

Binaural disparity cues available to the barn owl for sound localization

1. Bilateral recording of cochlear potentials was used to measure the variations in interaural time differences (ITDs) and interaural intensity differences (IIDs) as a free-field auditory stimulus was moved to different positions around a barn owl's head. 2. ITD varied smoothly with stimulus azimuth across a broad frequency range. 3. ITD varied minimally with stimulus elevation, except at extreme angles from the horizontal. 4. IID varied with both stimulus elevation and stimulus azimuth. Lower frequencies were more sensitive to variations in azimuth, whereas higher frequencies were more sensitive to variations in elevation. 5. The loci of spatial coordinates that form iso-IID contours and iso-ITD contours form a non-orthogonal grid that relates binaural disparity cues to sound location.     

Auditory lateralization in bushcrickets: a new dichotic paradigm

Pair formation in the bushcricket Gampsocleis gratiosa is achieved through acoustic signalling by the male and phonotactic approaches of the female towards the calling song. On a walking belt in the free sound field, females tracked the position of the speaker broadcasting the male calling song with a remarkable precision, deviating by no more than 10 cm in either direction from the ideal course. Starting with stimulus angles of 6–10° the females significantly turned to the correct side, and with stimulus angles greater than 25° no incorrect turns were made. Using neurophysiological data on the directionality of the ear we calculated that with such stimulus angles the available binaural intensity difference is in the order of 1–2 dB. We developed a dichotic ear stimulation device for freely moving females with a cross-talk barrier of about 50 dB, which allowed to precisely apply small binaural intensity differences. In such a dichotic stimulation paradigm, females on average turned to the tronger stimulated side starting with a 1 dB difference between both ears. The significance of such a reliable lateralization behaviour with small interaural intensity differences for phonotactic behaviour under natural conditions is discussed.     

Spatial orientation in the bushcricket <Emphasis Type="Italic">Leptophyes punctatissima</Emphasis> (Phaneropterinae; Orthoptera): I. Phonotaxis to elevated and depressed sound sources

Many species of acoustically interacting insects live in a complex, arboreal or semi-arboreal habitat. Thus mate finding by phonotaxis requires sound localization in the horizontal and vertical plane. Here we investigated the ability of the duetting bushcricket Leptophyes punctatissima to orient to one of three speakers, positioned at different levels in an artificial grid system, where each point in space could be reached by the male with almost equal probability. The system was designed analogous to a spherical calotte model of bismuth, where, once the male arrived at any nodal point had to decide between only three directions: either up or down and/or left and right. This design does not favour any phonotactic path of the males. All 12 males tested reached the three speaker positions (one in the horzontal plane, one elevated by 45°, one depressed by 45° relative to the starting position) with only little deviation from the shortest possible path. There was no significant difference with respect to the whole phonotactic time needed, the number of segments passed, or the number of stimuli received for the different speaker positions. This remarkable spatial orientation is achieved although the insects have no specialized external ear structures such as mammals, or some owls.     

幼年蝙蝠下丘神经元的听空间特性

实验分别在出生后４周龄的幼年和成年鲁氏菊头蝠（Ｒｈｉｎｏｌｏｐｈｕｓｒｏｕｘｉ）上进行。使用移动声刺激装置,高频喇叭可在动物头部前方水平方向１８０度、垂直方向６０度的范围内移动。玻璃微电极记录单个神经元的听反应。实验考察了幼年和成年动物下丘神经元的听空间特性,共观察了３０１个神经元,其中幼年动物１４８个,成年动物１５３个。结果表明,４周龄的幼年动物下丘听神经元已表现出方向敏感性,即每个听神经元均有一个特定的最佳反应中心和反应域。但神经元听反应中心在听空间的分布相当弥散,大多数位于对侧水平方向２０—８０度、垂直方向上下１５度范围内。而成年动物听神经元反应中心的分布则相当集中,局限地分布于对侧水平方向２８－５０度,垂直方向０—１０度范围内,两者构成明显差异。     

Target-approaching behavior of barn owls (Tyto alba): influence of sound frequency

We studied the influence of frequency on sound localization in free-flying barn owls by quantifying aspects of their target-approaching behavior to a distant sound source during ongoing auditory stimulation. In the baseline condition with a stimulus covering most of the owls hearing range (1–10 kHz), all owls landed within a radius of 20 cm from the loudspeaker in more than 80% of the cases and localization along the azimuth was more accurate than localization in elevation. When the stimulus contained only high frequencies (>5 kHz) no changes in striking behavior were observed. But when only frequencies from 1 to 5 kHz were presented, localization accuracy and precision decreased. In a second step we tested whether a further border exists at 2.5 kHz as suggested by optimality models. When we compared striking behavior for a stimulus having energy from 2.5 to 5 kHz with a stimulus having energy between 1 and 2.5 kHz, no consistent differences in striking behavior were observed. It was further found that pre-takeoff latency was longer for the latter stimulus than for baseline and that center frequency was a better predictor for landing precision than stimulus bandwidth. These data fit well with what is known from head-turning studies and from neurophysiology.     

Spatial distribution and temporal dynamics of high‐elevation forest stands in southern Siberia

Aim To evaluate the hypothesis that topographic features of high‐elevation mountain environments govern spatial distribution and climate‐driven dynamics of the forest. Location Upper mountain forest stands (elevation range 1800–2600 m) in the mountains of southern Siberia. Methods Archive maps, satellite and on‐ground data from1960 to 2002 were used. Data were normalized to avoid bias caused by uneven distribution of topographic features (elevation, azimuth and slope steepness) within the analysed area. Spatial distribution of forest stands was analysed with respect to topography based on a digital elevation model (DEM). Results Spatial patterns in mountain forests are anisotropic with respect to azimuth, slope steepness and elevation. At a given elevation, the majority of forests occupied slopes with greater than mean slope values. As the elevation increased, forests shifted to steeper slopes. The orientation of forest azimuth distribution changed clockwise with increase in elevation (the total shift was 120°), indicating a combined effect of wind and water stress on the observed forest patterns. Warming caused changes in the forest distribution patterns during the last four decades. The area of closed forests increased 1.5 times, which was attributed to increased stand density and tree migration. The migration rate was 1.5 ± 0.9 m year^–1, causing a mean forest line shift of 63 ± 37 m. Along with upward migration, downward tree migration onto hill slopes was observed. Changes in tree morphology were also noted as widespread transformation of the prostrate forms of Siberian pine and larch into erect forms. Main conclusions The spatial pattern of upper mountain forests as well as the response of forests to warming strongly depends on topographic relief features (elevation, azimuth and slope steepness). With elevation increase (and thus a harsher environment) forests shifted to steep wind‐protected slopes. A considerable increase in the stand area and increased elevation of the upper forest line was observed coincident with the climate warming that was observed. Warming promotes migration of trees to areas that are less protected from winter desiccation and snow abrasion (i.e. areas with lower values of slope steepness). Climate‐induced forest response has significantly modified the spatial patterns of high‐elevation forests in southern Siberia during the last four decades, as well as tree morphology.     

A neural network model of ventriloquism effect and aftereffect

Presenting simultaneous but spatially discrepant visual and auditory stimuli induces a perceptual translocation of the sound towards the visual input, the ventriloquism effect. General explanation is that vision tends to dominate over audition because of its higher spatial reliability. The underlying neural mechanisms remain unclear. We address this question via a biologically inspired neural network. The model contains two layers of unimodal visual and auditory neurons, with visual neurons having higher spatial resolution than auditory ones. Neurons within each layer communicate via lateral intra-layer synapses; neurons across layers are connected via inter-layer connections. The network accounts for the ventriloquism effect, ascribing it to a positive feedback between the visual and auditory neurons, triggered by residual auditory activity at the position of the visual stimulus. Main results are: i) the less localized stimulus is strongly biased toward the most localized stimulus and not vice versa; ii) amount of the ventriloquism effect changes with visual-auditory spatial disparity; iii) ventriloquism is a robust behavior of the network with respect to parameter value changes. Moreover, the model implements Hebbian rules for potentiation and depression of lateral synapses, to explain ventriloquism aftereffect (that is, the enduring sound shift after exposure to spatially disparate audio-visual stimuli). By adaptively changing the weights of lateral synapses during cross-modal stimulation, the model produces post-adaptive shifts of auditory localization that agree with in-vivo observations. The model demonstrates that two unimodal layers reciprocally interconnected may explain ventriloquism effect and aftereffect, even without the presence of any convergent multimodal area. The proposed study may provide advancement in understanding neural architecture and mechanisms at the basis of visual-auditory integration in the spatial realm.     

Directionality of auditory nerve fiber responses to pure tone stimuli in the grassfrog, Rana temporaria. II. Spike timing

We studied the directionality of spike timing in the responses of single auditory nerve fibers of the grass frog, Rana temporaria, to tone burst stimulation. Both the latency of the first spike after stimulus onset and the preferred firing phase during the stimulus were studied. In addition, the directionality of the phase of eardrum vibrations was measured. The response latency showed systematic and statistically significant changes with sound direction at both low and high frequencies. The latency changes were correlated with response strength (spike rate) changes and were probably the result of directional changes in effective stimulus intensity. Systematic changes in the preferred firing phase were seen in all fibers that showed phaselocking (i.e., at frequencies below 500–700 Hz). The mean phase lead for stimulation from the contralateral side was approximately 140° at 200 Hz and decreased to approximately 100° at 700 Hz. These phaseshifts correspond to differences in spike timing of approximately 2 ms and 0.4 ms respectively. The phaseshifts were nearly independent of stimulus intensity. The phase directionality of eardrum vibrations was smaller than that of the nerve fibers. Hence, the strong directional phaseshifts shown by the nerve fibers probably reflect the directional characteristics of extratympanic pathways. Accepted: 23 November 1996     

A Dominance Hierarchy of Auditory Spatial Cues in Barn Owls

Background

Barn owls integrate spatial information across frequency channels to localize sounds in space.

Methodology/Principal Findings

We presented barn owls with synchronous sounds that contained different bands of frequencies (3–5 kHz and 7–9 kHz) from different locations in space. When the owls were confronted with the conflicting localization cues from two synchronous sounds of equal level, their orienting responses were dominated by one of the sounds: they oriented toward the location of the low frequency sound when the sources were separated in azimuth; in contrast, they oriented toward the location of the high frequency sound when the sources were separated in elevation. We identified neural correlates of this behavioral effect in the optic tectum (OT, superior colliculus in mammals), which contains a map of auditory space and is involved in generating orienting movements to sounds. We found that low frequency cues dominate the representation of sound azimuth in the OT space map, whereas high frequency cues dominate the representation of sound elevation.

Conclusions/Significance

We argue that the dominance hierarchy of localization cues reflects several factors: 1) the relative amplitude of the sound providing the cue, 2) the resolution with which the auditory system measures the value of a cue, and 3) the spatial ambiguity in interpreting the cue. These same factors may contribute to the relative weighting of sound localization cues in other species, including humans.     

Neuronal responses to turtle head rotation in vitro

Extracellular recordings were made during vestibular stimulation from an in vitro turtle brain stem in which the temporal bones remained attached. Under visual control, microelectrodes were slowly advanced into the vestibular nucleus (VN) while we rotated the brain and searched for a single isolated unit whose spike activity was modulated by the lateral semicircular canals. In some experiments, responses were shown to be due to stimulation of the lateral canals, either by positioning the brains in forward or backward pitch during horizontal rotation or by plugging the vertical canals with wax. VN neurons usually had low spontaneous activity and rectified sinusoidal responses to sinusoidal stimulation. Spike response histograms were averaged from many stimulus cycles and were then fit to a sine function. The fitted phase and amplitude parameters were plotted relative to stimulus frequency and amplitude. The sample of VN cells were quite heterogeneous. Using stimuli at 1 Hz, however, each cell's response phase was weakly correlated with the slope of the plots of response amplitude versus frequency so that a cell could be categorized as sensitive to velocity or acceleration and as sensitive to ipsiversive or contraversive rotation, depending on whether its phase was near −180°, −90°, 0°, or 90°, and whether the gain exceeded 0.4 spikes/s per °/s. The properties of these VN cells suggest that there is substantial complexity in the vestibular responses at this first site of central vestibular processing. These data are compared to that of other species where such vestibular signals play an important role in oculomotor and spinal reflexes. © 1997 John Wiley & Sons, Inc. J Neurobiol 33: 99–177, 1997     

Evidence for acoustic communication in the parasitoid wasp Glyptapanteles flavicoxis

Females of the parasitoid wasp Glyptapanteles flavicoxis (Marsh) (Hymenoptera: Braconidae) deposit sex pheromone on substrate that elicits attraction and wing fanning in conspecific males. We tested the hypothesis that wing fanning sound induces a behavioral response from females which, in turn, affects the males’ orientation toward them. Females exposed to playback of the males’ wing fanning sound engaged in short flights, with sound characteristics different from those of the males’ wing fanning sound. In two‐choice bioassays, playback of the females’ flight sound attracted significantly more males than a silent control stimulus, and in combination with pheromone‐containing body extract of females it attracted more males than female body extract alone. Our data support the conclusion that the males’ wing fanning induces sound and visual reply signals from females that help males orient toward them.     

Cues for male phonotaxis in the duetting bushcricketLeptophyes punctatissima

Summary A computer controlled setup is introduced which allows the song analysis of both male and femaleLeptophyes punctatissima during duetting in a laboratory situation. The essential acoustical parameters for the initiation of the male's phonotactic approach towards the stationary female are described. The female responds reflex-like to the male song after a remarkably short delay time of about 28 ms. The male only performs phonotaxis if he perceives the female reply above an intensity value of about 50 dB SPL and if the female response falls within a critical time window from 25 to a maximum of 55 ms after the onset of his song (Figs. 3 and 5). The sound intensity and overall time delay of the female response can be varied independently, so that the relationship between both parameters and their limitations for maximum phonotaxis distance can be described.     

Mismatch negativity as a characteristic of the distinguishing locating capacity of the human auditory system

Mismatch negativity has been studied under the conditions of dichotic stimulation by deviant stimuli that either changed their azimuth from zero to 4.5°, 13.5°, and 22.5° or moved with small velocities from the head midline to one of the ears. The reference stimuli were located along the head midline. Our experiments have shown that both a discontinuous increase in the azimuth and an increase in the velocity of moving stimuli are accompanied by an increase in the amplitude of mismatch negativity. This process is more pronounced in the cases of (1) an instantaneous change in the deviant azimuth compared to its movement, (2) a longer duration of the deviant sound, (3) action of the deviant in the right hemisphere, and (4) the frontal derivation. The correlations of changes in the mismatch negativity with psychophysical data on the resolution of the human auditory system are considered.     

大棕蝠下丘听神经元频率调谐的方向敏感性

实验在8只大棕蝠(Eptesicusfuscus)上进行.选取了5个声源方位记录部位对侧80°(C-80°)、40°(C-40°)、0°和同侧40°(I-40°)、80°(I-80°).下丘听神经元的频率调谐曲线的形状有三种V型、封闭型和U型.以C-40°的频率调谐曲线为对照,声源方位改变时,多数神经元频率调谐曲线的形状和最佳频率不变.多数神经元在声源方位由记录部位对侧转向同侧时,频率调谐曲线的锐度(以QndB值为指标)由小变大;神经元在I-80°、I-40°的QndB值显著高于C-80°、C-40°、0°的QndB值.在所观察的47个神经元中,5个声源方位的最低阈值的平均值有显著差异,由高到低的分布为MTI-80°＞MTI-40°＞MT0°＞MTc-80°＞MTc-40°.我们推测,声源方位对神经元频率调谐特性影响的机制,可能是抑制性和兴奋性输入的比例不同而相互整合的结果.     

In search of differences between the two types of sensory cells innervating spider slit sensilla (<Emphasis Type="Italic">Cupiennius salei</Emphasis> Keys.)

The metatarsal lyriform organ of the spider Cupiennius salei is a vibration detector consisting of 21 cuticular slits supplied by two sensory cells each, one ending in the outer and the other at the inner slit membrane. In search of functional differences between the two cell types due to differences in stimulus transmission, we analyzed (1) the adaptation of responses to electrical stimulation, (2) the thresholds for mechanical stimulation and (3) the representation of male courtship vibrations using intracellular recording and staining techniques. Single- and multi-spiking receptor neurons were found among both cell types, which showed high-pass filter characteristics. Below 100-Hz threshold, tarsal deflections were between 1° and 10°. At higher frequencies, they decreased down to values as small as 0.05°, corresponding to 4.5-nm tarsal deflection in the most sensitive cases. Different slits in the organ and receptor cells with slow or fast adaptation did not differ in this regard. When stimulated with male courtship vibrations, both types of receptor cells again did not differ significantly regarding number of action potentials, latency and synchronization coefficients. Surprisingly, the differences in dendrite coupling were not reflected by the physiological responses of the two cell types innervating the slits.     

Responses of neurons in the electrosensory lateral line lobe of the weakly electric fish <Emphasis Type="Italic">Gnathonemus petersii</Emphasis> to simple and complex electrosensory stimuli

Mormyrid fish use active electrolocation to detect and analyze objects. The electrosensory lateral line lobe in the brain receives input from electroreceptors and an efference copy of the command to discharge the electric organ. In curarized fish, we recorded extracellularly from neurons of the electrosensory lateral line lobe while stimulating in the periphery with either a local point stimulus or with a more natural whole-body stimulus. Two classes of neurons were found: (1) three types of E-cells, which were excited by a point stimulus; and (2) two types of I-cells, which were inhibited by point stimulus and responded with excitation to the electric organ corollary discharge. While all neurons responded to a point stimulus, only one out of two types of I-units and two of the three types of E-units changed their firing behavior to a whole-body stimulus or when an object was present. In most units, the responses to whole-body stimuli and to point stimuli differed substantially. Many electrosensory lateral line lobe units showed neural plasticity after prolonged sensory stimulation. However, plastic effects during whole body stimulation were often unlike those occurring during point stimuli, suggesting that under natural conditions electrosensory lateral line lobe network effects play an important role in shaping neural plasticity.     

Vision and electroreception: Integration of sensory information in the optic tectum of the weakly electric fishApteronotus albifrons

Summary The responses of single neurons to visual and electrosensory stimulation were studied in the optic tectum of the weakly electric fishApteronotus albifrons. Most of the cells recorded in the region of the tectum studied, the anterior medial quadrant, were poorly responsive or completely insensitive to flashes of light or to bursts of AC electrical stimuli applied to the entire fish. However, these cells gave vigorous responses to moving visual or electrosensory stimuli. Most cells showed differences in their response contingent upon the direction of the stimulus movement and most received input from both the visual and electrosensory systems. Electrosensory responses to moving stimuli were depressed by jamming stimuli, 4 Hz amplitude modulation of the animal's electric organ discharge, presented simultaneously with the moving stimulus. However, the jamming signal presented alone typically evoked no response. Moving visual stimuli, presented simultaneously with the electrosensory, were usually able to restore the magnitude of a response toward its value in the unjammed situation. For most of the cells studied the receptive fields for vision and electroreception were in register. In some cases the visual and electrosensory components could be separated by presenting the two types of stimuli separately, or by presenting both simultaneously but with some amount of spatial separation, which causes the two to be misaligned relative to the fish. In other cases the individual responses could not be separated by spatial manipulations of the two stimuli and in these cases differences in the alignment of the two types of stimuli could cause changes in the intensity of the cells' responses.Abbreviations AM amplitude modulation - EOD electric organ discharge - PLLL posterior lateral line lobe     

螽斯(Deracantha onos)的趋声性与定位精度

本文研究雌硕螽(Deracantha onos)对正在鸣叫的同种雄螽斯的趋声运动的特征,并依据其行走路径测算出定位精度。只有同种雄螽斯的叫声才能诱发雌螽斯作趋声反应。雌螽斯趋声运动的速度约比非趋声行走高十倍。趋声路径呈“之”字形。用极性方位图表示螽斯趋声运动的方向性。有叫声时,相对于声源为零度的方向上的权最大,介于0.34与0.69之间。极性方位图的质心的方位角代表声定位的精度,小于3°。趋声路径的平均方位角为0.4°,标准离差10°左右。     

Frequency filter properties of lobster chemoreceptor cells determined with high-resolution stimulus measurement

1. We developed a high resolution, on-line stimulus measurement system for accurate control of chemical stimulus applications for Homarus americanus lateral antennule chemoreceptors. Focal stimulus presentations in an electrophysiological preparation with the receptor sensilla intact were measured at small spatial (30 μm) and time (5 ms) scales.
2. We tested 15 receptor cells with ten 100 ms pulses of 10⁴ M hydroxyproline at 0.5, 1, 2 and 4 Hz and with a single 8 s square pulse. Individual cells showed differences in their capabilities to resolve pulses (“flicker fusion”). At 2 Hz stimulation, some cells could follow stimulus pulses while others could not. At 4 Hz, 3 cells could still encode individual stimulus pulses accurately. The population resolved pulses up to 2 Hz; at 4 Hz, the population response to a pulse series approximated the response to a square pulse.
3. Repetitive stimulation caused a gradual decrease in the number of spikes and a gradual increase in first spike latency (“cumulative adaptation”). Increased stimulation frequency resulted in greater cumulative adaptation.
4. Since individual differences in adaptation and disadaptation rates of the receptor cells could not be attributed to measured stimulus variability in situ, lobster chemoreceptor cell populations have intrinsic temporal diversity which, we hypothesize, could be used to analyze pulsatile stimuli that occur in natural turbulent odor plumes.