Evidence for an across-frequency, between-channel process in asymptotic monaural temporal gap detection

Monaurally measured temporal gap detection (TGD) thresholds characteristically increase as the frequency difference is increased over a range of about half an octave to an octave between two sinusoids that mark the onset and offset of the silent gap. For greater sinusoidal frequency separations, the TGD thresholds often become asymptotic. This pattern probably reflects two different processes. The first process likely reflects within-channel processing within a single auditory filter or channel. The second process is less certain, but may reflect between-channel processing of the silent gap stimulus across two or more independent frequency channels. To evaluate the hypothesis that asymptotic monaural gap detection can be explained by a simple between-channel process, TGD thresholds were measured as a function of frequency separation between a pregap sinusoid presented to the left ear (channel 1) and a postgap sinusoid, of higher frequency, presented to the right ear (channel 2). The rationale for dichotic presentation of the sinusoidal markers and gap signal followed from the fact that the gap detection task must be performed between two independent channels by combining the outputs from each channel (ear) and recovering the gap information centrally. The resulting TGD thresholds for pregap sinusoids from 250 to 4000 Hz were relatively invariant and increased only slightly with increasing marker frequency separation. The average TGD thresholds for four listeners were in the range of 30 to 40 ms, which corresponded closely with their asymptotic TGD thresholds for the same set of stimulus conditions measured monaurally. This correspondence of the two data sets supports an across-frequency, between-channel process for asymptotic monaural gap detection at marker frequency separations greater than about half an octave.     

Effects of bilateral auditory cortical lesions on gap-detection thresholds in the ferret (Mustela putorius).

Ferrets were tested for their ability to detect temporal gaps in noise before and after bilateral lesions of the primary auditory cortex. Thresholds for gap detection were determined first for normal animals with band-pass noises at various center frequencies (0.5 to 32 kHz) and at 8 kHz with various sound pressure levels (-10 to 70 dB). Gap-detection ability improved steadily as sound pressure increased up to 70 dB. No systematic relation was found between threshold and center frequency. To determine the effects of brain damage, ferrets were tested with 8-kHz band-pass noise at 70 dBSPL. After bilateral lesions of auditory cortex, ferrets were still capable of detecting gaps, but the mean threshold was elevated from 10.1 to 20.1 ms. The data demonstrate that auditory cortex is important for perceptual tasks requiring fine temporal resolution. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transient auditory storage of acoustic details is associated with release of speech from informational masking in reverberant conditions.

Perceptual integration of the sound directly emanating from the source with reflections needs both temporal storage and correlation computation of acoustic details. We examined whether the temporal storage is frequency dependent and associated with speech unmasking. In Experiment 1, a break in correlation (BIC) between interaurally correlated wideband or narrowband noises was detectable even when an interaural interval (IAI) was introduced. The longest IAI, which varied markedly across participants, could be up to about 20 ms for wideband noise and decreased as the center frequency was increased for narrowband noises. In Experiment 2, when the interval between target speech and its single-reflection simulation (intertarget interval [ITI]) was reduced from 64 to 0 ms, intelligibility of target speech was markedly improved under speech-masking but not noise-masking conditions. The longest effective ITI correlated with the longest IAI for detecting the BIC only in the low-frequency (≤400 Hz) narrowband noise. Thus the ability to temporally store fine details contributes to perceptual integration of correlated leading and lagging sounds, which in turn, contributes to releasing speech from informational masking in noisy, reverberant environments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gap encoding by inferior collicular neurons is altered by minimal changes in signal envelope

Neural correlates of temporal resolution in the central auditory system are currently under intense investigation. The gap detection paradigm offers a simple, yet important, test of temporal acuity because changes in behavioral gap thresholds have been correlated with deficits in complex stimulus processing, such as speech perception. In gap detection studies, silent gaps are typically shaped by rapid (< 1.0 ms) rise/fall (R/F) times, i.e., rapid decreases and increases in sound intensity. However, in nature, the envelopes surrounding silent periods can vary significantly in R/F time. Therefore, we investigated whether changes in the R/F time surrounding the silent gap affect neural processing by inferior collicular (IC) neurons. Gap R/F times were varied between 0.5 and 16 ms and the discharge pattern, response rate, and first spike latency of IC neurons were measured for gap widths up to 100 ms. Neurons were classified into phasic or tonic discharge patterns based on peri-stimulus time histograms elicited to 100 ms noise carriers. The results indicate that (1) minimal gap thresholds increased with R/F time regardless of response type, (2) first spike latency variance increased systematically with R/F time for units which had small first spike standard deviations at short R/F times, and (3) the response rate of some units (called 'gap-tuned') changed as a function of both R/F time and gap width. Gap-tuned units responded strongly to a particular gap width only when the envelope of the gap was shaped by a particular R/F time. For gap-tuned units, increases in R/F time shifted the tuning to larger gap widths and also broadened the response profile. These results show that temporal acuity of neurons in the IC, as measured by the gap detection paradigm, is sensitive to the envelope surrounding gaps embedded in noise carriers.     

Bis-naphthalimides 3: synthesis and antitumor activity of N,N''-bis[2-(1,8-naphthalimido)-ethyl] alkanediamines

Gap junctions regulate a variety of cell functions by creating a conduit between two apposing tissue cells. Gap junctions are unique among membrane channels. Not only do the constituent membrane channels span two cell membranes, but the intercellular channels pack into discrete cell-cell contact areas forming in vivo closely packed arrays. Gap junction membrane channels can be isolated either as two-dimensional crystals, individual intercellular channels, or individual hemichannels. The family of gap junction proteins, the connexins, create a family of gap junctions channels and structures. Each channel has distinct physiological properties but a similar overall structure. This review focuses on three aspects of gap junction structure: (1) the molecular structure of the gap junction membrane channel and hemichannel, (2) the packing of the intercellular channels into arrays, and (3) the ways that different connexins can combine into gap junction channel structures with distinct physiological properties. The physiological implications of the different structural forms are discussed.     

Perceptual interference between spatially separate sequential displays.

In an alphanumeric display, a spatially remote, temporally trailing probe interfered with identification of the contents of a multi-element, temporally leading target array. In the 1st of 3 experiments, perceptual interference diminished in 5 undergraduates with increasing stimulus-onset asynchrony (SOA) between target and probe, but the effect was still evident at an SOA of 1,000 msec. In the 2nd experiment, the strength and duration of the effect increased in 5 undergraduates with the number of items in the target array; the effect was more pronounced if probe and target letters were displayed in different cases. The 3rd experiment, with the same Ss as in Exp II, suggested that the locus of interference is probably at a postcategorical stage of processing. It is concluded that perceptual interference is a central phenomenon that requires attentional processes and differs in crucial respects from backward masking by superimposition of patterns. (French abstract) (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Changes in the perceived duration of a narrowband sound induced by a preceding stimulus.

The authors show that a narrowband noise (NBN) is perceived as longer when presented immediately after a wideband noise (WBN), compared to when the WBN is absent. This effect depended on the WBN’s frequency spectrum overlapping that of the NBN, and it increased as the duration of the WBN increased up to 300 ms. It decreased when a silent gap was introduced between the WBN and NBN, but remained significant for an easily detectable gap of 40 ms. A correlate of the effect was observed in the mismatch negativity (MMN) to a deviant stimulus, consisting of a WBN + NBN, presented in a sequence of more common isolated WBNs. The MMN latency was longer for an on-frequency than for an off-frequency WBN; and, more importantly, the size of this difference correlated across participants with the difference in perceived duration. A rhythm-adjustment experiment showed that the presence of an on-frequency WBN immediately preceding a tone caused that tone to be heard as starting earlier than when the WBN was absent. The results are discussed in relation to the continuity illusion and models of duration encoding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory perception of fractal contours.

A series of experiments examined auditory contour formation, investigating listeners' sensitivities to a family of random fractals known as fractional Brownian noises. Exps 1A and 1B looked at identification of contours when 3 different noises were portrayed using variations in the pitch, duration, or loudness of successive notes of a sequence. Listeners could categorize pitch and loudness encodings, but not duration mappings. Exp 2 looked at the effect of simultaneous presentation of pitch and loudness information, finding that these dimensions combined additively to increase identification of the noise distributions. Exp 3 looked at discrimination of pitch contours as a function of changing fractal dimension. Discrimination curves approximated an inverted U shape, a finding that is not understandable in terms of sensitivity to differences in fractal dimension per se, nor in terms of "tuned" perceptual sensitivity to statistical regularities of the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Coarse-to-fine encoding of spatial frequency information into visual short-term memory for faces but impartial decay.

Face perception studies investigated how spatial frequencies (SF) are extracted from retinal display while forming a perceptual representation, or their selective use during task-imposed categorization. Here we focused on the order of encoding low-spatial frequencies (LSF) and high-spatial frequencies (HSF) from perceptual representations into visual short-term memory (VSTM). We also investigated whether different SF-ranges decay from VSTM at different rates during a study-test stimulus-onset asynchrony. An old/new VSTM paradigm was used in which two broadband faces formed the positive set and the probes preserved either low or high SF ranges. Exposure time of 500 ms was sufficient to encode both HSF and LSF in the perceptual representation (experiment 1). Nevertheless, when the positive-set was exposed for 500 ms, LSF-probes were better recognized in VSTM compared with HSF-probes; this effect vanished at 800-ms exposure time (experiment 2). Backward masking the positive set exposed for 800 ms re-established the LSF-probes advantage (experiment 3). The speed of decay up to 10 seconds was similar for LSF- and HSF-probes (experiment 4). These results indicate that LSF are extracted and consolidated into VSTM faster than HSF, supporting a coarse-to-fine order, while the decay from VSTM is not governed by SF. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Neural correlates of gap detection and auditory fusion in cat auditory cortex

Responses were recorded from 130 single neurones in the primary auditory cortex of 12 ketamine-anaesthetized cats in response to double-click stimuli, to a /ba/-/pa/ phoneme continuum and to gaps inserted early (after 5 ms) and late (after 500 ms) in a 1 s duration noiseburst. Stimulus levels were between 45 and 75 dB SPL. Neural detection threshold for the 'late gap' was less than 5 ms. For the double click and 'early gap' stimuli thresholds were between 40 and 50 ms, whereas the phoneme continuum threshold for voice-onset-time (VOT) was between 10 and 25 ms. The 'late gap' and VOT thresholds are similar to psychophysical gap detection and the /ba/-/pa/ categorical perception boundary respectively.     

Diverse functions of vertebrate gap junctions

Gap junctions are clusters of intercellular channels between adjacent cells. The channels are formed by the direct apposition of oligomeric transmembrane proteins, permitting the direct exchange of ions and small molecules (< 1 kDa) between cells without involvement of the extracellular space. Vertebrate gap junction channels are composed of oligomers of connexins, an enlarging family of proteins consisting of perhaps > 20 members. This article reviews recent advances in understanding the structure of intercellular channels and describes the diverse functions attributable to gap junctions as a result of insights gained from targeted gene disruptions in mice and genetic disease in humans.     

Features of ipsilaterally evoked inhibition in the dorsal nucleus of the lateral lemniscus

The dorsal nucleus of the lateral lemniscus (DNLL) is a binaural nucleus whose neurons are excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. Here we report on several features of the ipsilaterally evoked inhibition in 95 DNLL neurons of the mustache bat. These features include its dependence on intensity, its tuning and the types of stimuli that are capable of evoking it. Inhibition was studied by evoking discharges with the iontophoretic application of glutamate, and then evaluating the strength and duration of the inhibition of the glutamate evoked background activity produced by stimulation of the ipsilateral ear. Excitatory responses were evoked by stimulation of the contralateral ear with best frequency (BF) tone bursts. Glutamate evoked discharges could be inhibited in all DNLL neurons and the inhibition often persisted for periods ranging from 10 to 50 ms beyond the duration of the tone burst that evoked it. The duration of the persistent inhibition increased with stimulus intensity. Stimulus duration had little influence on the duration of the persistent inhibition. Signals as short as 2 ms suppressed discharges for as long as 30 ms after the signal had ended. The frequency tuning of the total period of inhibition and the period of persistent inhibition were both closely matched to the tuning evoked by stimulation of the contralateral ear. Moreover, the effectiveness of complex signals for evoking persistent inhibition, such as brief FM sweeps and sinusoidally amplitude and frequency modulated signals, was comparable to that of tone bursts at the neuron's excitatory BF, so long as the complex signal contained frequencies at or around the neuron's excitatory BF. We also challenged DNLL cells with binaural paradigms. In one experiment, we presented a relatively long (40 ms) BF tone burst of fixed intensity to the contralateral ear, which evoked a sustained discharge, and a shorter, 10 ms signal of variable intensity to the ipsilateral ear. As the intensity of the 10 ms ipsilateral signal increased, it generated progressively longer periods of persistent inhibition and thus the discharges were suppressed for periods far longer than the 10 ms duration of the ipsilateral signal. With interaural time disparities, ipsilateral signals that led contralateral signals evoked a persistent inhibition that suppressed the responses to the trailing contralateral signals for periods of a least 15 ms. This suggests that an initial binaural sound that favors the ipsilateral ear should suppress the responses to trailing sounds that normally would be excitatory if they were presented alone. We hypothesize a circuit that generates the persistent inhibition and discuss how the results with binaural signals support that hypothesis.     

Masking with interaurally delayed stimuli: the use of "internal" delays in binaural detection

Detectability of 500-Hz tones was measured in the presence of broadband masking noise using three types of binaural conditions. In the first, the masker was presented diotically and the tone was interaurally delayed. In the second, the masker was interaurally delayed and the 500-Hz tone was presented either in phase (S0) or out of phase (S pi). In the third, the masker consisted of the sum of two independent noises having interaural delays of equal magnitude and opposite sign. The signal was, once more, presented either in phase (S0) or out of phase (S pi). Comparisons among the data and quantitative analyses assuming the use of compensatory "internal delays" suggested that internal delays are operative and compensate accurately for external delays of up to approximately 750 microseconds. The analyses also indicated that larger internal delays (i.e., up to 2 to 3 ms) are probably also operative. However, performance using such large internal delays appears to be degraded in accord with the hypothesis that their application introduces "noise" in the internal representation of the stimuli.     

Pitch perception in chinchillas (Chinchilla laniger): Stimulus generalization using rippled noise.

Rippled noises evoke the perception of pitch in human listeners. Infinitely iterated rippled noise (IIRN) is generated when wideband noise (WBN) is delayed, attenuated, and added to the original WBN through either a positive (+) or a negative (-) feedback loop. The pitch of IIRN[+] is matched to the reciprocal of the delay, whereas the pitch of IIRN[-] for the same delay is an octave lower. Chinchillas (Chinchilla laniger) were trained to discriminate IIRN[+] with a 4-ms delay from IIRN[+] with a 2-ms delay and then tested in a stimulus generalization paradigm with IIRN[+] at delays between 2 and 4 ms. Systematic gradients in behavioral response occurred along the dimension of delay, suggesting that a perceptual dimension corresponding to pitch exists for IIRN[+]. Behavioral responses to IIRN[-] test stimuli were more variable among chinchillas, suggesting that IIRN[-] did not evoke similar pitches relative to IIRN[+]. Systematic gradients in behavioral response were observed when IIRN[-] test stimuli were presented in the context of other IIRN[-] stimuli. Thus, other perceptual cues such as timbre may dominate the pitch cues when IIRN[-] test stimuli are presented in the context of IIRN[+] stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual learning reflects external noise filtering and internal noise reduction through channel reweighting

To investigate the nature of plasticity in the adult visual system, perceptual learning was measured in a peripheral orientation discrimination task with systematically varying amounts of external (environmental) noise. The signal contrasts required to achieve threshold were reduced by a factor or two or more after training at all levels of external noise. The strong quantitative regularities revealed by this novel paradigm ruled out changes in multiplicative internal noise, changes in transducer nonlinearites, and simple attentional tradeoffs. Instead, the regularities specify the mechanisms of perceptual learning at the behavioral level as a combination of external noise exclusion and stimulus enhancement via additive internal noise reduction. The findings also constrain the neural architecture of perceptual learning. Plasticity in the weights between basic visual channels and decision is sufficient to account for perceptual learning without requiring the retuning of visual mechanisms.     

Effects of pulse separation on detection thresholds for electrical stimulation of the human cochlea

Effects of pulse separation on detection of electrical stimulation of the cochlea were studied in 12 profoundly deaf human subjects with Nucleus 22 cochlear implants. Biphasic symmetric pulses were used. Pulse separation is the time from offset of one biphasic pulse to the onset of the next biphasic pulse in the train. Effects of pulse separation were studied in the context of different covariables in four stages of the experiment. Effects of pulse separation seen in the different stages were similar, despite the different covariables. Both pulse separation and the total number of pulses per stimulus seem to be important variables affecting stimulus detection. For 0.5 ms/phase pulses, thresholds were lowest at the shortest pulse separations tested (0.2-1.1 ms) and increased as a function of pulse separation. For 2 ms/phase pulses, detection thresholds were lowest at pulse separations around 7.5 ms, in most cases, and higher at both longer and shorter pulse separations. These results suggest that interactions among adjacent pulses can either hinder or facilitate detection of the signal depending on the magnitudes of pulse separation and phase duration. Pulse separations at which thresholds measured for 2 ms/phase pulses were minimum were fairly consistent across subjects and did not correlate well with speech recognition scores. However, significant variation in this measure across species has been seen.     

Influence of polarity reversal on defibrillation success with biphasic shocks and a transvenous/subcutaneous defibrillator system in a porcine animal model

Clinical studies show that polarity reversal affects defibrillation success in transvenous monophasic defibrillators. Current devices use biphasic shocks for defibrillation. We investigated in a porcine animal model whether polarity reversal influences defibrillation success with biphasic shocks. In nine anesthetized, ventilated pigs, the defibrillation efficacy of biphasic shocks (14.3 ms and 10.8 ms pulse duration) with "initial polarity" (IP, distal electrode = cathode) and "reversed polarity" (RP, distal electrode = anode) delivered via a transvenous/subcutaneous lead system was compared. Voltage and current of each defibrillating pulse were recorded on an oscilloscope and impedance calculated as voltage divided by current. Cumulative defibrillation success was significantly higher for RP than for IP for both pulse durations (55% vs 44%, P = 0.019) for 14.3 ms (57% vs 45%, P < 0.05) and insignificantly higher for 10.8 ms (52% vs 42%, P = ns). Impedance was significantly lower with RP at the trailing edge of pulse 1 (IP: 44 +/- 8.4 vs RP: 37 +/- 9.3 with 14.3 ms, P < 0.001 and IP: 44 +/- 6.2 vs RP: 41 +/- 7.6 omega with 10.8 ms, P < 0.001) and the leading edge of pulse 2 (IP: 37 +/- 5 vs RP: 35 +/- 4.2 omega with 14.3 ms, P = 0.05 and IP: 37.5 +/- 3.7 vs RP: 36 +/- 5 omega with 10.8 ms, P = 0.02). In conclusion, in this animal model, internal defibrillation using the distal coil as anode results in higher defibrillation efficacy than using the distal coil as cathode. Calculated impedances show different courses throughout the shock pulses suggesting differences in current flow during the shock.     

Mechanisms of electrical coupling between pyramidal cells

Direct electrical coupling between neurons can be the result of both electrotonic current transfer through gap junctions and extracellular fields. Intracellular recordings from CA1 pyramidal neurons of rat hippocampal slices showed two different types of small-amplitude coupling potentials: short-duration (5 ms) biphasic spikelets, which resembled differentiated action potentials and long-duration (>20 ms) monophasic potentials. A three-dimensional morphological model of a pyramidal cell was employed to determine the extracellular field produced by a neuron and its effect on a nearby neuron resulting from both gap junctional and electric field coupling. Computations were performed with a novel formulation of the boundary element method that employs triangular elements to discretize the soma and cylindrical elements to discretize the dendrites. An analytic formula was derived to aid in computations involving cylindrical elements. Simulation results were compared with biological recordings of intracellular potentials and spikelets. Field effects produced waveforms resembling spikelets although of smaller magnitude than those recorded in vitro. Gap junctional electrotonic connections produced waveforms resembling small-amplitude excitatory postsynaptic potentials. Intracellular electrode measurements were found inadequate for ascertaining membrane events because of externally applied electric fields. The transmembrane voltage induced by the electric field was highly spatially dependent in polarity and wave shape, as well as being an order of magnitude larger than activity measured at the electrode. Membrane voltages because of electrotonic current injection across gap junctions were essentially constant over the cell and were accurately depicted by the electrode. The effects of several parameters were investigated: 1) decreasing the ratio of intra to extracellular conductivity reduced the field effects; 2) the tree structure had a major impact on the intracellular potential; 3) placing the gap junction in the dendrites introduced a time delay in the gap junctional mediated electrotonic potential, as well as deceasing the potential recorded by the somatic electrode; and 4) field effects decayed to one-half of their maximum strength at a cell separation of approximately 20 micron. Results indicate that the in vitro measured spikelets are unlikely to be mediated by gap junctions and that a spikelet produced by the electric field of a single source cell has the same waveshape as the measured spikelet but with a much smaller amplitude. It is hypothesized that spikelets are a manifestation of the simultaneous electric field effects from several local cells whose action potential firing is synchronized.     

Study on effect of baoyuan qiangshen tablet no. I in prolongating interval of hemodialysis in patients of terminal-stage of renal disease

BACKGROUND: The purpose of this study was to find out whether specific cortical potentials can be evoked and identified after word stimulation. The clinical relevance was to be investigated in patients with aphasic syndromes. MATERIALS AND METHODS: In 20 young adults with no signs of hearing impairment and in patients with manifest aphasic syndromes, word-evoked cortical potentials were compared with those after an equivalent noise stimulus. The test words were selected from the Freiburger Speech Comprehension Test. The duration of the words was between 450 and 640 ms. The stimulus was presented monaurally. The peak level was 70 dB HL. The noise stimulus was produced by modifying a low-band noise. Potentials were measured between the ipsilateral mastoid and the contralateral forehead. Data were analysed offline. RESULTS: In healthy persons, the potentials after word and noise stimulation did not differ until 100 ms after the stimulus onset. After noise stimulation a negative maximum could be seen 100 ms after the stimulus onset, and a positive maximum 200 ms after the stimulus onset. After word stimulation, a positive maximum of higher amplitude than after noise stimulation was measured 150 ms after the stimulus onset, and a negative maximum was measured 270 ms after the stimulus onset. In all test persons the difference curve of word-and noise-evoked potentials revealed a speech-specific component 170 ms (N 170) after the stimulus onset. The single-word analysis showed that the potentials depend on the phonemes of the test word. The potentials do not alter when the stimulus side is changed. In patients with aphasia the potentials depend on the grade of the disturbance of speech perception: global and Wernicke's aphasia show no significant difference of speech-and noise-evoked potentials, whereas in Broca's aphasia a speech specific maximum is apparent. CONCLUSION: The speech-specific component may be regarded as a paradigm of cortical speech detection processes. Electrophysiological speech audiometry by means of word-evoked cortical potentials seems possible and may be used for clinical purposes.     

Age-related changes in temporal resolution: Envelope and intensity effects.

Gap-detection thresholds were determined for 10 younger and 10 older adults (mean age 23 yrs and 68 yrs, respectively) at 2 sensation levels (40 and 60 dB SL) for tone pips with Gaussian amplitude envelopes whose standard deviations were 0.5, 1, 1.5, and 2 msec. Gap-detection thresholds were larger for the older participants under all conditions. For all participants, gap-detection thresholds increased with the standard deviation of the Gaussian amplitude envelope, were relatively independent of sensation level, and were independent of the degree of hearing loss. Because spectral splatter decreases with increasing standard deviation of the Gaussian amplitude envelope, the age-related differences in gap detection cannot be attributed to differences between how young and old listeners are affected by off-frequency cues. Furthermore, the consistent age difference in gap detection at all amplitude envelope standard deviations was shown to be incompatible with the hypothesis that temporal integration time is longer for older listeners. (PsycINFO Database Record (c) 2010 APA, all rights reserved)