Species specificity and temperature dependency of temporal processing by the auditory midbrain of two species of treefrogs.

Event Abstract Back to Event A Psychophysical and EEG Investigation of Cross-Modal Amplitude Modulation Justin R. Timora1* and Timothy W. Budd1 1 University of Newcastle, Australia It is well established that both auditory and tactile perceptual processing is dependent on the temporally dynamic features of sensory stimulation. Much less is known about how these temporal features are integrated across sensory modalities. According to the temporal principle of multisensory integration greater cross-modal temporal correspondence should enhance the integration of multisensory stimulation. Aim: Investigate how cross-modal temporal correspondence of amplitude modulation (AM) rate of multimodal presentations of acoustic and vibrotactile AM stimuli influence perceptual sensitivity for both psychophysical and EEG steady state measures of multisensory integration. Method: A psychophysical procedure was used to estimate auditory and vibrotactile AM detection thresholds for a 32 Hz AM target stimuli while the cross-modal modulation rate was varied across six conditions (0, 8, 16, 32, 64 and 128 Hz). In a separate session EEG activity was recorded while participants were presented with the same stimulus conditions. FFT was then used to measure EEG entrainment at the frequency corresponding to AM rate of stimulation. Results: Cross-modal AM rate significantly influenced auditory thresholds with polynomial contrasts indicating a significant quadratic trend. Cross-modal AM rate also significantly influenced vibrotactile thresholds with polynomial contrasts revealing a significant linear trend. Analysis of the 32 Hz SSR activity revealed no significant effect of cross-modal AM rate on the magnitude of 32 Hz SSR activity. Conclusions: Results of the psychophysical analysis suggest that perceptual sensitivity to AM stimuli varied with cross-modal AM rate. Contrary to prior literature, auditory sensitivity was worst when the cross-modal AM rates matched while sensitivity to vibrotactile AM stimuli decreased as the cross-modal AM rate increased. SSR activity was not influenced by cross-modal AM rate suggesting that the oscillatory activity as measured by the SSR may not reflect entrained activity involved in multisensory integration. Keywords: multisensory integration, steady-state responses, temporal processing, amplitude modulation, Temporal correspondence Conference: Australasian Society for Psychophysiology, Inc, Coffs Harbour, Australia, 26 Nov - 28 Nov, 2014. Presentation Type: Oral Presentation Topic: Psychophysiology Citation: Timora JR and Budd TW (2014). A Psychophysical and EEG Investigation of Cross-Modal Amplitude Modulation. Conference Abstract: Australasian Society for Psychophysiology, Inc. doi: 10.3389/conf.fnhum.2014.216.00008 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 20 Oct 2014; Published Online: 02 Dec 2014. * Correspondence: Mr. Justin R Timora, University of Newcastle, Newcastle, Australia, justin.timora@uon.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Justin R Timora Timothy W Budd Google Justin R Timora Timothy W Budd Google Scholar Justin R Timora Timothy W Budd PubMed Justin R Timora Timothy W Budd Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

We investigated the contribution of amplitude modulation (AM) rate and spectral separation to stream segregation of vocoder bandpass noises. Stimulus sequences were repeated pairs of A and B bursts, where bursts were white noise or vocoder bandpass noise carrying sinusoidal AM (100% modulation depth). Bursts differed either in the center frequency of the noise, or the AM rate, or both. Eight vocoder bands were used. The lowest four bands (1‐2‐3‐4) were combined into one bandpass noise (B bursts) and the higher three bands (3‐4‐5, 4‐5‐6, and 6‐7‐8) were combined to constitute the A bursts. Results show that stream segregation ability increases with greater spectral separation. Larger AM rate separations were associated with stronger segregation abilities, but not when A and B bursts were both white noise. Significant inter‐subject differences were noted. Results suggest that, while both spectral and AM rate separation separations could be cues for auditory stream segregation, stream segregation based on AM rate is more successful when combined with spectral separation. Correlations between segregation ability and understanding of vocoded speech will be discussed.

Cochlear-implant (CI) users struggle to understand speech in difficult listening environments partly because they have limited access to auditory cues that allow for perceptual segregation between target and competing sounds. Because CI speech coding strategies optimize the encoding of envelope cues to promote better speech intelligibility, envelope may be an important cue for source segregation in CI users. Recent work has suggested that access to amplitude modulation (AM) depth and rate varies according to location of electrodes in the cochlea, and that turning off electrodes that yield poorer AM sensitivity may improve speech reception. The purpose of this study was to investigate the role of AM sensitivity in the ability of listeners to use AM rate information in multiple electrodes. It was hypothesized that electrodes with higher AM thresholds, which were simulated in normal-hearing listeners, would limit listeners’ ability to segregate AM rates. Subjects discriminated between pairs of stimuli that varied in AM rate relative to a reference rate. Stimulus pairing was within- or across-ears. Results suggest that AM insensitive electrodes impair CI users’ ability to discriminate AM rates, which may limit source segregation using envelope cues in complex listening environments. [This work was supported by NIH-NIDCD R01 DC003083 (Litovsky).]

Directing attention to sounds of different frequencies allows listeners to perceive a sound of interest, like a talker, in a mixture. Whether cortically generated frequency-specific attention affects responses as low as the auditory brainstem is currently unclear. Participants attended to either a high- or low-frequency tone stream, which was presented simultaneously and tagged with different amplitude modulation (AM) rates. In a replication design, we showed that envelope-following responses (EFRs) were modulated by attention only when the stimulus AM rate was slow enough for the auditory cortex to track—and not for stimuli with faster AM rates, which are thought to reflect ‘purer’ brainstem sources. Thus, we found no evidence of frequency-specific attentional modulation that can be confidently attributed to brainstem generators. The results demonstrate that different neural populations contribute to EFRs at higher and lower rates, compatible with cortical contributions at lower rates. The results further demonstrate that stimulus AM rate can alter conclusions of EFR studies.

The sound-producing muscles of frogs and toads are interesting because they have been selected to produce high-power outputs at high frequencies. The two North American species of gray tree frog, Hyla chrysoscelis and Hyla versicolor, are a diploid-tetraploid species pair. They are morphologically identical, but differ in the structure of their advertisement calls. H. chrysoscelis produces very loud pulsed calls by contracting its calling muscles at approximately 40 Hz at 20 degrees C, whereas, H. versicolor operates the homologous muscles at approximately 20 Hz at this temperature. This study examined the matching of the intrinsic contractile properties of the calling muscles to their frequency of use. I measured the isotonic and isometric contractile properties of two calling muscles, the laryngeal dilator, which presumably has a role in modulating call structure, and the external oblique, which is one of the muscles that provides the mechanical power for calling. I also examined the properties of the sartorius as a representative locomotor muscle. The calling muscles differ greatly in twitch kinetics between the two species. The calling muscles of H. chrysoscelis reach peak tension in a twitch after approximately 15 ms, compared with 25 ms for the same muscles in H. versicolor. The muscles also differ significantly in isotonic properties in the direction predicted from their calling frequencies. However, the maximum shortening velocities of the calling muscles of H. versicolor are only slightly lower than those of the comparable muscles of H. chrysoscelis. The calling muscles have similar maximum shortening velocities to the sartorius, but have much flatter force-velocity curves, which may be an adaptation to their role in cyclical power output. I conclude that twitch properties have been modified more by selection than have intrinsic shortening velocities. This difference corresponds to the differing roles of shortening velocity and twitch kinetics in determining power output at differing frequencies.

Individuals with cochlear implants (CIs) attain lower speech reception scores in noise relative to normal-hearing (NH) listeners. Poorer performance in CI users is partly due to reduced access to cues used to segregate sound sources, which may be limited by poor electrode-neuron interface in the auditory periphery. Poor electrode-neuron interface reduces sensitivity to temporal information at specific cochlear sites. This study investigated the influence of the periphery on discriminating differences in amplitude modulation (AM) rates presented simultaneously in two different cochlear channels. In each trial, one interval was presented and subjects chose whether AM rates were the same or different. AM rates were paired within- or across-ears. It was hypothesized that, if sensitivity to AM rate was reduced in one channel due to poor transduction of AM rate, then across-channel sensitivity would decrease. Both CI users and NH listeners participated in this experiment. Results suggest that when temporal enco...

This study investigated the extent to which flat-spectrum harmonic complexes could be identified as one of six vowels when three pairs of successive harmonics, located at the first, second, and third formant frequency values, were amplitude modulated. In experiment 1, the amplitude modulation (AM) rate was at or close to 10 Hz. In condition 1, all components were added in cosine phase, and the 10-Hz AM was in phase for all "formants." Performance improved monotonically with increasing modulation index, m. In condition 2, m was fixed at 0.5 and the level of each background harmonic was varied randomly (roved) from stimulus to stimulus. Even a rove range of only +/- 2 dB reduced scores considerably. Condition 3 was like condition 1, but with components added in random phase. Performance was very poor for all modulation indices. This suggests that subjects were unable to use momentary differences in level between formant and background harmonics, and supports the idea that, for cosine-phase stimuli, they were using information from the low-amplitude portions ("valleys") of the cochlea-filtered waveforms. In further conditions, the components were added in cosine phase and the AM had a different phase and/or different rate (10, 16, and 24 Hz) on the different formants. Scores were very similar to those obtained when the AM was identical for all formants. In experiment 2, the AM rate was at or close to 2 Hz. When all formants were modulated in phase at 2 Hz, very good performance was found for components added in cosine phase, and performance was essentially unaffected by making the AM different in rate and/or phase across formants. When the components were added in random phase, performance was well above chance when the formants were modulated in-phase at 2-Hz, but worsened markedly when the modulation differed in rate and/or phase across formants. Randomizing the level of each background harmonic caused performance to deteriorate and to become similar for cosine-phase and random-phase stimuli. Performance deteriorated further when the AM differed in phase across formants. The results suggest that, for a 2-Hz modulation rate, and when information from the valleys is not available, performance depends on momentary increases in level of the formant harmonics relative to the background.

1. Recordings were made from single units in the torus semicircularis ofBufo americanus andBufo fowleri. Using sinusoidally amplitude-modulated (AM) white noise as a stimulus, the temporal selectivity of these neurons could be described by five response categories: ‘AM nonselective’ (40%); ‘AM high-pass’ (8%); ‘AM low-pass’ (9%); ‘AM band-suppression’ (9%); and ‘AM tuned’ (34%). 2. The degree to which the stimulus modulation rate was coded in the periodicity of spiking of each toral neuron (i.e., synchronization of a unit's spikes to a particular phase of the modulation waveform) was calculated for modulation rates ranging from 10 to 150 Hz. The synchronization characteristics of toral neurons generally failed to reveal the temporal selectivity of these cells. In fact, those units which were most sharply AM-tuned rarely exhibited significant response synchronization at any modulation rate tested. 3. The distribution of ‘best rates of AM’ is different for the two species of toads; AM-tuned neurons recorded from the torus semicircularis of Fowler's toad were, on the average, tuned to higher rates, relative to those recorded from the American toad. These findings constitute positive evidence for the existence of ‘matched temporal filters’ in the anuran central auditory system. 4. Synthetic stimuli differing only in the rate at which they were amplitude modulated were used to evoke advertisement calls from maleBufo americanus. Modulation rates of 7.5 Hz, 15 Hz, 30 Hz, 60 Hz and 120 Hz were used. In these field studies males responded best to 30 Hz AM; lower or higher modulation rates were less effective. The AM-tuned neurons in the torus semicircularis of this species are well suited to process AM rates of 30 Hz.

Event Abstract Back to Event Multisensory integration of temporal processing in the auditory and somatosensory modalities: A psychophysical and EEG study. Justin Timora1* and Timothy Budd1 1 University of Newcastle, Australia Prior research examining multisensory integration has established the importance of the cross modal correspondence of temporal information. In the present study we examine the perceptual and neurophysiological impact of cross modal variations in amplitude modulation (AM) rate of acoustic and vibrotactile stimulation. To achieve this 33 participants completed separate psychophysical and EEG recording sessions where the cross modal correspondence of AM rate was varied. For the psychophysical session AM detection thresholds were estimated for 21 and 40 Hz auditory and vibrotactile stimuli where AM rate varied across modalities in one of three different cross modal correspondence (CMC) conditions, being either the SAME, DIFFERENT or NONE (i.e. unmodulated). For the EEG session identical stimulation conditions were presented and an FFT analysis carried out to determine whether EEG entrainment at each AM rate varied according to cross modal correspondence of temporal stimulation. The psychophysical results showed significant decreases in AM detection thresholds for conditions where the non-target modality was amplitude modulated at the same rate as the target modality (i.e. SAME), indicating reduced perceptual sensitivity when stimuli in both modalities were amplitude modulated. In contrast the results of the EEG analysis showed the opposite relationship, where EEG activity at the stimulation rate (i.e. entrainment) showed increases in EEG power for stimulus conditions where cross modal correspondence for AM stimulation was the same (i.e. SAME). These results suggest a potential dissociation between perception and EEG activity and are discussed in terms of the relationship between oscillatory neural activity and multisensory integration. Keywords: multisensory integration, multisensory processing, steady state, amplitude modulation, temporal processing Conference: ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012. Presentation Type: Poster Presentation Topic: Sensation and Perception Citation: Timora J and Budd T (2012). Multisensory integration of temporal processing in the auditory and somatosensory modalities: A psychophysical and EEG study.. Conference Abstract: ACNS-2012 Australasian Cognitive Neuroscience Conference. doi: 10.3389/conf.fnhum.2012.208.00173 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 14 Oct 2012; Published Online: 17 Nov 2012. * Correspondence: Mr. Justin Timora, University of Newcastle, Newcastle, Australia, justin.timora@uon.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Justin Timora Timothy Budd Google Justin Timora Timothy Budd Google Scholar Justin Timora Timothy Budd PubMed Justin Timora Timothy Budd Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Response characteristics of 130 single neurons in the superior olivary nucleus of the northern leopard frog (Rana pipiens pipiens) were examined to determine their selectivity to various behaviorally relevant temporal parameters [rise-fall time, duration, and amplitude modulation (AM) rate] of acoustic signals. Response functions were constructed with respect to each of these variables. Neurons with different temporal firing patterns such as tonic, phasic or phasic-burst firing patterns, participated in time domain analysis in specific manners. Phasic neurons manifested preferences for signals with short rise-fall times, thus possessing low-pass response functions with respect to this stimulus parameter; conversely, tonic and phasic-burst units were non-selective and possessed all-pass response functions. A distinction between temporal firing patterns was also observed for duration coding. Whereas phasic units showed no change in the mean spike count with a change in stimulus duration (i.e., all-pass duration response functions), tonic and phasic-burst units gave higher mean spike counts with an increase in stimulus duration (i.e., primary-like high-pass response functions). Phasic units manifested greater response selectivity for AM rate than did tonic or phasic-burst units, and many phasic units were tuned to a narrow range of modulation rates (i.e., band-pass). The results suggest that SON neurons play an important role in the processing of complex acoustic patterns; they perform extensive computations on AM rate as well as other temporal parameters of complex sounds. Moreover, the response selectivities for rise-fall time, duration, and AM rate could often be shown to contribute to the differential responses to complex synthetic and natural sounds.

Recent investigation of memory-related functions in the auditory system have capitalized on the use of memory-modulating molecules to probe the relationship between memory and substrates of memory in auditory system coding. For example, epigenetic mechanisms, which regulate gene expression necessary for memory consolidation, are powerful modulators of learning-induced neuroplasticity and long-term memory (LTM) formation. Inhibition of the epigenetic regulator histone deacetylase 3 (HDAC3) promotes LTM, which is highly specific for spectral features of sound. The present work demonstrates for the first time that HDAC3 inhibition also enables memory for temporal features of sound. Adult male rats trained in an amplitude modulation (AM) rate discrimination task and treated with a selective inhibitor of HDAC3 formed memory that was highly specific to the AM rate paired with reward. Sound-specific memory revealed behaviorally was associated with a signal-specific enhancement in temporal coding in the auditory system; stronger phase locking that was specific to the rewarded AM rate was revealed in both the surface-recorded frequency following response and auditory cortical multiunit activity in rats treated with the HDAC3 inhibitor. Furthermore, HDAC3 inhibition increased trial-to-trial cortical response consistency (relative to naive and trained vehicle-treated rats), which generalized across different AM rates. Stronger signal-specific phase locking correlated with individual behavioral differences in memory specificity for the AM signal. These findings support that epigenetic mechanisms regulate activity-dependent processes that enhance discriminability of sensory cues encoded into LTM in both spectral and temporal domains, which may be important for remembering spectrotemporal features of sounds, for example, as in human voices and speech. SIGNIFICANCE STATEMENT Epigenetic mechanisms have recently been implicated in memory and information processing. Here, we use a pharmacological inhibitor of HDAC3 in a sensory model of learning to reveal the ability of HDAC3 to enable precise memory for amplitude-modulated sound cues. In so doing, we uncover neural substrates for memory's specificity for temporal sound cues. Memory specificity was supported by auditory cortical changes in temporal coding, including greater response consistency and stronger phase locking. HDAC3 appears to regulate effects across domains that determine specific cue saliency for behavior. Thus, epigenetic players may gate how sensory information is stored in long-term memory and can be leveraged to reveal the neural substrates of sensory details stored in memory.

Effect of cochlear damage on the detection of complex temporal envelopes

Acoustic limitations on propagation of low-frequency complex communication sounds make the amplitude modulation (AM) rate an important auditory feature for both aquatic larval (tadpole) and partly terrestrial (adult) bullfrogs. Phase-locked responses to AM signals were recorded from neurons in the auditory midbrain during metamorphic and postmetamorphic development. The best modulation frequency (BMF) and maximal significant AM rate are significantly negatively correlated with the developmental stage. Pre- and early prometamorphic tadpoles show phase locking to higher AM rates than postmetamorphic animals. Late prometamorphic (deaf period) tadpoles show a substantial reduction in auditory sensitivity, lower BMFs, reduced bandwidths of modulation transfer functions (MTF), and loss of significant phase locking. By the onset of the metamorphic climax, there is a recovery of auditory sensitivity and phase-locked responding, with late climax tadpoles showing auditory sensitivity similar to that of postmetamorphic frogs. The changes in neural responding across metamorphosis are correlated with morphological changes in the auditory periphery and central auditory nuclei, and match differences in the acoustic environment as the animal shifts from an aquatic to a more terrestrial lifestyle. [Research supported in part by an NIH research Grant NS28565 (AMS) and an NSF Graduate Fellowship (SBH).]

Auditory responses were recorded from single units in the eighth nerve and in the midbrain torus semicircularis of the leopard frog (Rana pipiens). Acoustic stimuli included sinusoidally amplitude-modulated (AM) tones and noise, as well as pure tones. Mean spike rates were measured at various rates of AM, and the degree to which a unit's spikes were restricted to a particular phase of the modulation cycle was described by a synchronization coefficient. The firing rate of eighth-nerve fibers was largely independent of the rate of AM over the modulation range 10 to 150 Hz. Further, the general shape of the spike rate vs. AM-rate function was invariant with either depth of modulation or sound-pressure level (SPL). Although virtually all eighth-nerve fibers exhibited significant synchronization to the envelope of AM, the shape of the synchronization function depended on the unit's best-excitatory frequency (BEF). Fibers with highest BEF's, presumed to innervate the basilar papilla, generally showed greater synchronization as the AM rate was increased (up to 100-150 Hz). Fibers tuned to the low-and midfrequency region, which innervate the amphibian papilla, exhibited low-pass synchronization characteristics. As the depth of modulation was reduced, the degree of synchronization of eighth-nerve fibers decreased. For a given depth of modulation an increase in sound level tended to decrease the degree of synchronization, but significant synchronization could still be observed at stimulus intensities at least 65 dB above threshold. On the basis of the spike rate vs. AM-rate functions, the temporal selectivity of single cells in the torus could be characterized by five response types: AM nonselective (spike rate was largely independent of the AM rate); AM high-pass (activity increased as the AM rate was increased); AM low-pass (response was greatest for slow AM rates and decreased at high rates); AM band-suppression (these neurons responded well to low and high AM rates, but responded weakly to intermediate rates); and AM-tuned (spike rate was greatest over a narrow range of modulation rates). In these measurements the depth of modulation was held constant at 100%. The five response categories are not discrete, but rather reflect representative examples along a continuum with regard to temporal selectivity. The temporal selectivity exhibited by toral units in their firing rates was not evident in their AM-synchronization functions.(ABSTRACT TRUNCATED AT 400 WORDS)

Single units in the auditory midbrain nucleus (torus semicircularis) were recorded in leopard frogs Rana pipiens. Acoustic stimuli consisted of pure tones, sinusoidal amplitude-modulated (AM) tones, or sinusoidal amplitude-modulated white noise. On the basis of iso-intensity curves (sound pressure level is held constant while the rate of amplitude modulation is varied), the temporal selectivity of cells in the torus fall into four categories: Nonselective (response is independent of rate of AM); low-pass (response is greatest to low rates of AM); high-pass (response is greatest to high rates of AM); and tuned (response is best to a particular rate of AM). For both amplitude modulated tones and amplitude modulated noise the predominant response type is the tuned class. By using white noise as the carrier source, spectral factors can be eliminated as a source of tuning so that the selectivity of these cells is due exclusively to the temporal features of the stimulus. Those units which show temporal tuning respond maximally when the degree of modulation is 100%. Thus a “temporal tuning curve” could be constructed by determining, for various rates of AM, the percentage modulation required to give a criterion (threshold) number of spikes. The rate of AM at which this criterion threshold could be reached using the lowest percentage modulation is considered to be the best rate of amplitude modulation for that unit. [Supported by NINCDS grant NS-09244.]