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At least 1,315 records · Page 73Linked to original sources
PubMed1999

Localising awareness of action with transcranial magnetic stimulation.

Seven subjects reacted to an auditory stimulus by pressing a response key and judged their reaction time (RT) by reporting the position of a rotating clock-hand at which they pressed the key. Transcranial magnetic stimulation (TMS) was delivered either over primary motor cortex (MI) or more anteriorly (with the centre of the coil over FCz) 75 ms before each subject's median reaction time. TMS over MI produced substantial delays in actual RT, but much smaller delays in judged RT. TMS over FCz produced smaller delays in actual RT and relatively larger delays in judged RT. We conclude that awareness of responses is generated, at least in part, between premotor areas affected by stimulation over FCz and the primary motor cortex.

Adult↗
PubMed2000

Binaural interaction component and white-noise enhancement in middle latency responses: differential effects of anaesthesia in guinea pigs.

It is known that the response to binaural clicks is smaller in amplitude than the sum of two monaural responses. The difference is called the binaural interaction component (BIC). Also, an amplitude enlargement occurs in guinea pig middle latency responses (MLRs) to monaural clicks when white noise is applied to the other ear. This study was conducted to find out whether these two signs of binaural interaction result from the same mechanism. White noise enhancement (WNE) and BIC were computed from the evoked potential data simultaneously recorded in different phases of anaesthesia. WNE gradually decreased and disappeared with anaesthesia, but the relative amplitude of the BIC remained unchanged. This differential effect showed that different neural mechanisms must be responsible for BIC and WNE in guinea pig MLR.

Acoustic Stimulation↗
PubMed2002

Temporal modulation transfer functions in the barn owl (Tyto alba).

Barn owls (Tyto alba) have evolved several specializations in their auditory system to achieve the high sensory acuity required for prey capture, including superior processing of interaural time differences and phase coding in the auditory periphery. Here, we tested whether barn owls are capable of high temporal resolution that may be a prerequisite for the accuracy in binaural processing. Temporal resolution was measured psychoacoustically and demonstrated in temporal modulation transfer functions. Four barn owls were trained in an operant task with food reward to detect sinusoidal amplitude modulations within an 800-ms gated white-noise burst or 800-ms periods of modulation in continuous white noise (spectrum levels of -5 dB and 15 dB SPL). Within the range of tested amplitude modulation frequencies from 5 Hz to 1280 Hz, barn owls' detection thresholds were lowest at 10-20 Hz. This sensitivity corresponds to an intensity-difference limen of between 0.9 dB and 1.4 dB. For all conditions, temporal modulation transfer functions showed band-pass characteristics with a high-frequency cutoff in the range of 37 Hz to 92 Hz, corresponding to minimum integration times of 4.3 ms and 1.7 ms, respectively. In summary, these data indicate a temporal resolution in the owl's auditory system that is good, but not unusual, compared to other vertebrates.

Animals↗
PubMed2002

Neural representations of the axis of acoustic particle motion in nucleus centralis of the torus semicircularis of the goldfish, Carassius auratus.

Experiments examined differential coding of acoustic particle motion axis in the auditory midbrain of goldfish. Animals were exposed to vibratory stimuli varying in axis orientation as action potentials were recorded from single units in the central neuropil of nucleus centralis in the torus semicircularis. Response magnitudes as a function of stimulation axis were visualized in three dimensional plots called directional response profiles. These are generally comparable to directional responses observed among primary saccular afferents in having substantially vertical orientations. Distortions in shape from the peripheral patterns indicate neural information processing. A three-dimensional model was used to evaluate the hypothesis that responses in the auditory midbrain reflect the convergence of excitatory and inhibitory primary afferent-like responses. Model afferent inputs were generated and combined arithmetically. This analysis gives insight into the mechanisms of information processing that appear to occur in brainstem nuclei. The lack of diversity in best axis directions suggests that this mechanism alone cannot account for directional hearing abilities in this species. The roles that this directional representation and processing may play in directional hearing and sound source localization are not yet clear. Implications of these data on current models of fish directional hearing are discussed.

Acoustic Stimulation↗
PubMed2002

Effects of saccular otolith removal on hearing sensitivity of the sleeper goby (Dormitator latifrons).

It is not known to what extent the entire saccule contributes to overall hearing sensitivity in any fish species. Here we report directional and frequency sensitivity in a teleost fish (Dormitator latifrons) and effects of unilateral and bilateral removal of saccular otoliths on its hearing sensitivity. The fish had different hearing thresholds in the horizontal (-54.4 to -50.3 dB re: 1 micro m) and mid-sagittal (-58.6 to -53.1 dB) planes. At 100 Hz, unilateral otolith removal did not significantly change hearing sensitivity in the mid-sagittal plane, but caused selective reductions of auditory sensitivity by 3-7 dB in the azimuthal axes that are consistent with the longitudinal axis of the damaged saccule. Along the fish's longitudinal axis, unilateral otolith removal significantly decreased auditory sensitivity at 50 Hz and 400 Hz, but not at 100 Hz, 200 Hz, and 345 Hz. At 100 Hz, bilateral otolith removal resulted in robust hearing loss of 27-35 dB at different axes in both horizontal and mid-sagittal planes. Along the fish's longitudinal axis, the bilateral removal reduced auditory sensitivity by 13-27 dB at the different frequencies. Therefore, these results demonstrate that the saccule plays important roles in directional hearing and frequency responses.

Acoustic Stimulation↗
PubMed2002

Directionality and frequency tuning of primary saccular afferents of a vocal fish, the plainfin midshipman (Porichthys notatus).

While particle motion is thought to directly stimulate the inner ear of most fish species, it is difficult to measure and might not be predictable from pressure measurements in a small tank. It is therefore important to replicate experiments conducted relative to pressure measurements using stimuli of known particle motion, to ensure that unmeasured components of the stimulus field do not produce misleading frequency response profiles. The frequency sensitivity of the inner ear of the plainfin midshipman fish, Porichthys notatus, in response to isopressure stimuli has been described. This study now examines the frequency and directional response properties of midshipman saccular afferents in response to whole-body displacements simulating acoustic particle motion. Best frequencies were distributed bimodally, with peaks at 50 Hz and 100 Hz. Most units had cosinusoidally shaped directional response profiles in the horizontal and vertical planes, though some units showed slight deviations from this pattern. A few units (probably saccular efferents) had omnidirectional directional response profiles and did not phase lock to the stimulus waveform. These results are consistent with responses of the midshipman saccular nerve to isopressure stimuli, and strengthen the hypothesis that the frequency sensitivity of the midshipman ear matches the frequency content of behaviorally relevant vocalizations.

Acoustic Stimulation↗
PubMed2004

Phonotaxis in Hyla versicolor (Anura, Hylidae): the effect of absolute call amplitude.

The influence of call amplitude on phonotaxis in female Hyla versicolor was studied using a no-choice paradigm. One set of experiments estimated effects of stimulus amplitude on phonotaxis toward a synthetic model of a conspecific call. The response strength increased with amplitude from the behavioral threshold (37-43 dB SPL) up to 79 dB SPL and then decreased at higher amplitudes. Females approached the loudspeaker with short walking bouts (approximately 1 s duration) occurring immediately after call presentations. Increase in response strength was attributed to an increasing proportion of calls that elicited such walking bouts, whereas the decrease at high amplitudes resulted from decreasing distance covered per bout. The quality of orientation remained constant for all above-threshold amplitudes. A second set of experiments tested the selectivity for interval duration and pulse duration at amplitudes of 55, 70, and 85 dB SPL. Selectivity for both parameters was similar at 70 and 85 dB SPL, but tended to increase at 55 dB SPL. The results suggest that selective phonotaxis in H. versicolor is not adapted for long-distance communication. This finding differs from those of comparable studies of acoustic insects.

Acoustic Stimulation↗
PubMed2004

Coding of acoustic particle motion by utricular fibers in the sleeper goby, Dormitator latifrons.

It is unknown whether the fish utricle contributes to directional hearing. Here, we report response properties of single utricular fibers in a teleost fish ( Dormitator latifrons) to linear accelerations at various stimulus frequencies and axes. Characteristic frequencies ranged from < or =50-400 Hz (median=80 Hz), and best frequencies shifted from 50 to 250 Hz with stimulus level. Best sensitivity of utricular fibers was distributed from -70 to -40 dB re: 1 g (mean=-52 dB), which is about 30 dB less sensitive than saccular fibers. Q50% fell between 0.16 and 11.50 (mean=2.04) at 15 dB above threshold. We observed temporal response patterns of entrained phase-locking, double phase-locking, phase-locked bursting, and non-phase-locked bursting. Most utricular fibers were directionally selective with various directional response profiles, and directional selectivity was stimulus-level dependent. Horizontal best-response axes were distributed in a 152 degrees range while mid-sagittal best-response axes were clustered around the fish longitudinal axis, which is consistent with the horizontal orientation of the utricle and morphological polarizations of utricular hair cells. Therefore, results of this study indicate that the utricle in this vertebrate plays an auditory role in azimuth and that utricular fibers extend the response dynamic range of this species in directional hearing.

Acceleration↗
PubMed2004

Long-distance, low-frequency elephant communication.

The production, transmission, and reception of and the behavioral response to long-distance, low-frequency sound by elephants is reviewed. The structure of low-frequency calls generated by elephants is separated into the "source" and the "filter" roles played by the lungs, larynx and vocal track, the composition of the expired air and the ambient air temperature. Implications regarding the size, age, sex, sexual and physical status follow from the call structure and detection. Reception of the signal is discussed in terms of the characteristics of the elephant's ear with particular attention to the determination of the threshold of hearing and the ability to locate the source of low-frequency sounds. Factors which influence the transmission of near infrasound are related to atmospheric structure. The critical role played by the thermal stratification and vertical gradient and magnitude of the wind in determining both the range and the detection of a signal are discussed for open and closed elephant habitats. Infrasound plays a pervasive role in reproduction, resource utilization, avoidance of predation and other social interactions. Current and future technology can be expected to contribute to the detection and interpretation of elephant communication. This will aid in the understanding of behavior and in efforts to sustain the species.

Animal Communication↗
PubMed2005

Sharpening of directional responses along the auditory pathway of the oyster toadfish, Opsanus tau.

Our previous studies have shown that the peripheral auditory system of the toadfish encodes the direction of a sound source. Here, we compare directional responses of peripheral saccular afferents, cells in the descending octaval nucleus (DON) of the medulla, and the torus semicircularis (TS) of the midbrain. Recording locations in the brain were labeled with neurobiotin to confirm the site. To compare directional responses among cells, we calculated an index [sharpening ratio (SR)] that weights the relative strength of responses to the best direction for that cell and to the adjacent stimulus angles tested. Unsharpened saccular afferents tend to have a cosinusoidal directional response pattern (DRP) with an expected SR of 0.87. In DON, more than 60% of the cells exhibited directional sharpening (defined as SR <0.8). In TS, more than 80% of the cells exhibited directional sharpening. We conclude that directional auditory sharpening first occurs in DON and some additional sharpening occurs in the ascending pathway to the midbrain, particularly in azimuth. The sharpening of directional selectivity is likely to be an important component of the neural computations underlying directional hearing.

Animals↗
PubMed2005

Temporal resolution of the Risso's dolphin, Grampus griseus, auditory system.

Toothed whales and dolphins (Odontocetes) are known to echolocate, producing short, broadband clicks and receiving the corresponding echoes, at extremely rapid rates. Auditory evoked potentials (AEP) and broadband click stimuli were used to determine the modulation rate transfer function (MRTF) of a neonate Risso's dolphin, Grampus griseus, thus estimating the dolphin's temporal resolution, and quantifying its physiological delay to sound stimuli. The Risso's dolphin followed sound stimuli up to 1,000 Hz with a second peak response at 500 Hz. A weighted MRTF reflected that the animal followed a broad range of rates from 100 to 1,000 Hz, but beyond 1,250 Hz the animal's hearing response was simply an onset/offset response. Similar to other mammals, the dolphin's AEP response to a single stimulus was a series of waves. The delay of the first wave, PI, was 2.76 ms and the duration of the multi-peaked response was 4.13 ms. The MRTF was similar in shape to other marine mammals except that the response delay was among the fastest measured. Results predicted that the Risso's dolphin should have the ability to follow clicks and echoes while foraging at close range.

Animal Communication↗
PubMed2005

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 degrees the females significantly turned to the correct side, and with stimulus angles greater than 25 degrees 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.

Acoustic Stimulation↗
PubMed2005

Directionality of the pressure-difference receiver ears in the northern leopard frog, Rana pipiens pipiens.

We studied the directional response of the coupled-eardrum system in the northern leopard frog, Rana pipiens pipiens. Eardrum behavior closely approximates a linear time-invariant system, with a highly correlated input-output relationship between the eardrum pressure difference and the eardrum velocity. Variations in the eardrum transfer function at frequencies below 800 Hz indicate the existence of an extratympanic sound transmission pathway which can interfere with eardrum motions. The eardrum velocity was shown to shift in phase as a function of sound incident angle, which was a direct result of the phase-shift of the eardrum pressure difference. We used two laser-Doppler vibrometers to measure the interaural vibration time difference (IVTD) and the interaural vibration amplitude difference (IVAD) between the motions of the two eardrums. The coupled-eardrum system enhanced the IVTD and IVAD by a factor of 3 and 3 dB, respectively, when compared to an isolated-eardrum system of the same size. Our findings are consistent with the time-delay sensitivity of other coupled-eardrum systems such as those found in crickets and flies.

Acoustic Stimulation↗
PubMed2006

The role of pressure difference reception in the directional hearing of budgerigars (Melopsittacus undulatus).

In many birds, the middle ears are connected through an air-filled interaural pathway. Sound transmission through this pathway may improve directional hearing. However, attempts to demonstrate such a mechanism have produced conflicting results. One reason is that some species of birds develop a lower static air pressure in the middle ears when anaesthetized, which reduces eardrum vibrations. In anaesthetized budgerigars with vented interaural air spaces and presumed normal eardrum vibrations, we find that sound propagating through the interaural pathway considerably improves cues to the directional hearing. The directional cues in the received sound combined with amplitude gain and time delay of sound propagating through the interaural pathway quantitatively account for the observed dependence of eardrum vibration on direction of sound incidence. Interaural sound propagation is responsible for most of the frontal gradient of eardrum vibration (i.e. when a sound source is moved from a small contralateral angle to the same ipsilateral angle). Our study confirms that at low frequencies the interaural sound propagation may cause vibrations of the eardrum to differ much in time, thus providing a possible cue for directional hearing. The acoustically effective size of the head of our birds (diameter 28 mm) is much larger than expected from the dimensions of the skull, so apparently the feathers on the head have a considerable acoustical effect.

Acoustic Stimulation↗
PubMed2006

Sensitivity to interaural time difference and representation of azimuth in central nucleus of inferior colliculus in the barn owl.

Standard electrophysiology and virtual auditory stimuli were used to investigate the influence of interaural time difference on the azimuthal tuning of neurons in the core and the lateral shell of the central nucleus of the inferior colliculus of the barn owl. The responses of the neurons to virtual azimuthal stimuli depended in a periodic way on azimuth. Fixation of the interaural time difference, while leaving all other spatial cues unchanged, caused a loss of periodicity and a broadening of azimuthal tuning. This effect was studied in more detail in neurons of the core. The azimuthal range tested and the frequency selectivity of the neurons were additional parameters influencing the changes induced by fixating the interaural time difference. The addition of an interaural time difference to the virtual stimuli resulted in a shift of the tuning curves that correlated with the interaural time difference added. In this condition, tuning strength did not change. These results suggest that interaural time difference is an important determinant of azimuthal tuning in all neurons of the core and lateral shell of the central nucleus of the inferior colliculus, and is the only determinant in many of the neurons from the core.

Acoustic Stimulation↗
PubMed2000

Direction-dependent corticofugal modulation of frequency-tuning curves of inferior collicular neurons in the big brown bat, Eptesicus fuscus.

This study examined if corticofugal modulation of subcortical frequency-tuning curves varied with sound direction. Both excitatory and inhibitory frequency tuning curves of inferior collicular neurons of the big brown bat, Eptesicus fuscus were plotted before and during electrical stimulation in the auditory cortex at two sound directions (contra-40 degrees and ipsi-40 degrees). Most collicular neurons had broader excitatory frequency-tuning curves at contra-40 degrees but had broader inhibitory frequency-tuning curves at ipsi-40 degrees. Cortical electrical stimulation changed the excitatory minimum thresholds of most collicular neurons at a greater degree at ipsi-40 degrees than at contra-40 degrees. However, cortical electrical stimulation produced a greater increase in the sharpness of excitatory frequency-tuning curves of most corticofugally inhibited collicular neurons at contra-40 degrees but produced a greater decrease in the sharpness of excitatory frequency-tuning curves of most corticofugally facilitated collicular neurons at ipsi-40 degrees. Cortical electrical stimulation also produced a greater change in the sharpness of inhibitory frequency-tuning curves of most corticofugally inhibited collicular neurons at contra-40 degrees than at ipsi-40 degrees. Possible mechanisms for this direction-dependent corticofugal modulation of frequency-tuning curves of collicular neurons are discussed.

Animals↗
PubMed1997

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 degrees at 200 Hz and decreased to approximately 100 degrees 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.

Acoustic Stimulation↗
PubMed1997

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 x 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.

Acoustic Stimulation↗