Behavioral auditory thresholds for sinusoidal electrical stimuli in the cat

Behavioral thresholds were measured in four cats by training them to respond behaviorally to acoustic auditory stimuli using food as a reward in an operant reinforcement paradigm. Following training, the subjects were implanted unilaterally with either a scaled-UCSF electrode containing four contacts or an electrode array containing eight intracochlear contacts and one extracochlear contact under temporalis muscle. Behavioral thresholds for electrical stimuli were obtained as a function of sinusoidal frequency, duration, and electrode configuration. Threshold functions for both electrode types and all animals had minima between 48 and 125 Hz and, in general, were relatively flat below this minima; functions increased at 3-6 dB/octave from 96 Hz to 1 kHz. Threshold varied predictably as a function of electrode configuration, with thresholds decreasing as much as 20 dB as electrode spacing was widened from a radial bipolar (200-microns separation) to a monopolar configuration (apical stimulating and temporalis return). With long-duration stimuli, increasing the electrode separation systematically increased the slope of the threshold-versus-frequency contours in all animals. Irrespective of electrode type or configuration, charge/phase thresholds for single-cycle sinusoids were relatively flat for stimulus periods up to 1-5 ms, approximating a constant charge/phase determination of threshold. At phase durations greater than 5 ms, charge thresholds increased at a rate slightly above 6 dB/octave (constant peak current), which was suggestive of neural accommodation. Thresholds for the cat share many features with those reported for implanted humans and monkeys.     

Gradient sensitivity to within-category variation in words and syllables.

Five experiments monitored eye movements in phoneme and lexical identification tasks to examine the effect of within-category subphonetic variation on the perception of stop consonants. Experiment 1 demonstrated gradient effects along voice-onset time (VOT) continua made from natural speech, replicating results with synthetic speech (B. McMurray, M. K. Tanenhaus, & R. N. Aslin, 2002). Experiments 2-5 used synthetic VOT continua to examine effects of response alternatives (2 vs. 4), task (lexical vs. phoneme decision), and type of token (word vs. consonant-vowel). A gradient effect of VOT in at least one half of the continuum was observed in all conditions. These results suggest that during online spoken word recognition, lexical competitors are activated in proportion to their continuous distance from a category boundary. This gradient processing may allow listeners to anticipate upcoming acoustic-phonetic information in the speech signal and dynamically compensate for acoustic variability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The missing fundamental in vowel height perception

Traunmüller (1981) suggested that the tonotopic distance between the first formant (F1) and the fundamental frequency (F0) is a major determinant of perceived vowel height. In the present study, subjects identified a vowel-height continuum ranging in formant pattern from /I/to/epsilon/, at five F0 values. Increasing F0 led to an increased probability of /I/responses (i.e., the phoneme boundary shifted toward the /epsilon/ end of the continuum). Various conditions of filtering out the lower harmonics of the stimuli caused only marginal shifts of the phoneme boundary. The experiments provide evidence against interpretations of Traunmüller's (1981) results that claim that vowel height is determined by the distance between F1 and the lowest harmonic that is present in the basilar membrane excitation pattern.     

Numerical analysis of a model of ligand-induced B-cell antigen-receptor clustering. Implications for simple models of B-cell activation in an immune network

Experimental measures of responsiveness to painful and non-painful stimuli as well as measures of typical and present clinical pain were assessed in 26 female patients with fibromyalgia and in an equal number of age-matched healthy women. Pressure pain thresholds, determined by means of a dolorimeter, were lower in the patients compared to the control subjects both at a tender point (trapezius) and at a non-tender control point (inner forearm). The same was true for the heat pain thresholds, measured using a contact thermode. In contrast, the pain thresholds for electrocutaneous stimuli were decreased only at the tender point. The detection thresholds for non-painful stimuli (warmth, cold and electrical stimuli) seemed to be less affected in the fibromyalgia patients, with only the detection threshold for cold being lower at both sites. Tender points were more sensitive than control points for mechanical pressure. The reverse was found for the other modalities which were tested. Although the 3 experimental pain thresholds showed patterns of either generalized or site-specific pain hyperresponsiveness, the between-methods correlations were not very high. While the correlations between the experimental pain thresholds and the various measures of clinical pain (Localized Pain Rating, McGill Pain Questionnaire) in the patients were generally low, there were significant negative correlations between pressure pain thresholds at the two sites and the level of present pain assessed by the Localized Pain Rating. We conclude that a pattern of pain hyperresponsiveness, generalized across the site of noxious stimulation and across the physical nature of the stressor, is associated with fibromyalgia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Integration of health care economics for addiction treatment in clinic care

Visceral pain is a substantial, clinical problem but unfortunately few experimental models are available to study this phenomenon in man. In the present study we inserted a stimulation catheter 5-10 cm into the ileo-sigmoidostomy of nine patients. The catheter contained six small, flexible electrodes separated by 4 mm. The gut was stimulated by single burst, repeated burst (five stimuli delivered at 2 Hz), or continuous burst stimuli (4 Hz for 30, 60, 90, and 120 s). The sensation (ST), pain detection (PDT), and pain tolerance (PTT) thresholds to single/repeated burst stimuli were determined. The location/size/sensitivity of referred pain after repeated/continuous stimulation were characterized. The brain potentials to single burst stimuli and to increasing stimulus intensity were measured. ST to single burst stimuli was easy to determine (8 mA) and to reproduce. The patients found it difficult to determine the PDT and PTT to single burst stimuli, however both thresholds were easily determined for repeated burst stimuli. The pain thresholds to single burst stimuli were twice as high as the thresholds to repeated burst stimuli, indicating the importance of central temporal summation for visceral pain. Minor changes in the stimulus location resulted in changes of the referred pain projection site. The words most frequently selected (78%) from the McGill Pain Questionnaire to describe repeated burst stimulations were shooting, pricking, flashing, and boring. The amplitude of the brain potentials increased at increasing stimulus intensity. A stimulus intensity giving an initial pain rating of around 5 on a 0-10 visual analog scale (VAS) was used for continuous stimulation. A general increase of the pain intensity and the area of referred pain was found during this stimulation. It was concluded that electrical stimulation of the human gut provokes pain and especially long sequences of visceral stimuli are adequate to evoke referred pain mimicking pain profiles of pathologic origin.     

Detection of silent intervals between noises activating different perceptual channels: some properties of "central" auditory gap detection

This article describes four experiments on gap detection by normal listeners, with the general goal being to examine the consequences of using noises in different perceptual channels to delimit a silent temporal gap to be detected. In experiment 1, subjects were presented with pairs of narrow-band noise sequences. The leading element in each pair had a center frequency of 2 kHz and the trailing element's center frequency was parametrically varied. Gap detection thresholds became increasingly poor, sometimes by up to an order of magnitude, as the spectral disparity was increased between the noise bursts that marked the gap. These data suggested that gap-detection performance is impoverished when the underlying perceptual timing operation requires a comparison of activity in different perceptual channels rather than a discontinuity detection within a given channel. In experiment 2, we assessed the effect of leading-element duration in within-channel and between-channel gap detection tasks. Gap detection thresholds rose when the duration of the leading element was less than about 30 ms, but only in the between-channel case. In experiment 3, the gap-detection stimulus was redesigned so that we could probe the perceptual mechanisms that might be involved in stop consonant discrimination. The leading element was a wideband noise burst, and the trailing element was a 300-ms bandpassed noise centered on 1.0 kHz. The independent variable was the duration of the leading element, and the dependent variable was the smallest detectable gap between the elements. When the leading element was short in duration (5-10 ms), gap thresholds were close to 30 ms, which is close to the voice onset time that parses some voiced from unvoiced stop consonants. In experiment 4, the generality of the leading-element duration effect in between-channel gap detection was examined. Spectrally identical noises defining the leading and trailing edges of the gap were presented to the same or to different ears. There was a leading-element duration effect only for the between channel case. The mean gap threshold was again close to 30 ms for short leading-element durations. Taken together, the data suggest that gap detection requiring a temporal correlation of activity in different perceptual channels is a fundamentally different task to the discontinuity detection used to execute gap detection performance in the traditional, within-channel paradigm.     

Attention modulates both primary and second somatosensory cortical activities in humans: a magnetoencephalographic study

To clarify the role of primary and second somatosensory cortex (SI and SII) in somatosensory discrimination, we recorded somatosensory evoked magnetic fields during a stimulus strength discrimination task. The temporal pattern of cortical activation was analyzed by dipole source model coregistered with magnetic resonance image. Stimulus intensity was represented in SI as early as 20 ms after the stimulus presentation. The later components of SI response (latency 37.7 and 67.9 ms) were enhanced by rarely presented stimuli (stimulus deviancy) during passive and active attention. This supports an early haptic memory mechanism in human primary sensory cortex. Contra- and ipsilateral SII responses followed the SI responses (latency 124.6 and 138.3 ms, respectively) and were enhanced by attention more prominently than the SI responses. Active attention increased SII but not SI activity. These results are consistent with the concept of ventral somatosensory pathway that SI and SII are hierarchically organized for passive and active detection of discrete stimuli.     

Mismatch negativity and auditory sensory memory evaluation: a new faster paradigm

A new faster paradigm to measure the duration of auditory sensory memory, as indexed by mismatch negativity (MMN) suppression to stimuli presented at increasing inter-stimulus intervals (ISI), is proposed. Trains of three stimuli were delivered at very short ISI (300 ms). The inter-train interval varied according to the memory probe interval (MPI) tested. Trains started randomly with a deviant or standard stimulus (50% each), with their event-related brain potentials subtracted to obtain the MMN. The new paradigm provided MMNs identical to the conventional one at MPIs of 0.4 and 4.0 s in young subjects, and revealed MMN suppression when the MPI was increased to 5.0 s in older subjects. The new paradigm estimates auditory sensory memory duration in one-third the time of conventional MMN.     

Locus of selective adaptation in speech perception.

Used the interaural transfer technique in 2 experiments with 19 Ss (aged 18–45 yrs) and 9 Ss (aged 19–34 yrs), respectively, to determine the relative locus of selective adaptation in speech perception. Findings show that voiced (/ba/ or /da/) and voiceless (/pa/ or /ta/) consonants seemed to affect different auditory system loci. On a voice-onset-time continuum (/ba/ to /pa/ or /da/ to /ta/) the selective adaptation effects produced by voiceless consonants were largely ear independent and endured over delays of at least 1 min. However, voiced adapters produced selective adaptation effects that were highly ear specific and relatively short lived (     

Attention within auditory word perception: Insights from the phonemic restoration illusion.

Conducted 2 experiments to determine the extent to which attention plays a role in the phonemic restoration illusion and to infer from this the nature of attention in auditory word perception. Exp I examined the effect of training on the magnitude of the phonemic restoration illusion. 24 Ss received training with the potentially restorable stimuli (972 trials with feedback); in addition, the presence or absence of an attentional cue, contained in a visual prime preceeding each trial, was varied between groups of Ss. Findings reveal that cuing the identity and location of the critical phoneme of each test word allowed Ss to attend to the critical phoneme, thereby inhibiting the illusion, but only when the prime also identified the test word itself. Exp II was a 2-part replication of Exp I, using 92 Ss and some modifications of the conditions. Results show that when the prime provided only the identity or location of the critical phoneme, or only the identity of the word, Ss performed identically to those Ss for whom the prime contained no information at all about the test word. Training did not produce any generalized learning about the types of stimuli used. Results indicate that attention is necessary to perceive phonemic units selectively and is focused through the level that has primacy in the perception of spoken words, the mental lexicon. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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.     

The use of isolated vowels as auditory stimuli in eliciting the verbal transformation effect.

Determined the effectiveness of single isolated vowels as auditory stimuli in eliciting perceptual illusory changes in ss, a phenomenon referred to by R. M. Warren (see pa, vol. 36:3gh49w) as the "verbal transformation effect." 3 vowels, /i/, /ae/, and /u/, were individually presented to a group of 24 19-24 yr. Old normal listeners in a single experimental session. Each vowel was repeatedly presented by means of headphones for a period of 5 min. Results indicate that single isolated vowels are capable of eliciting verbal transformations in normal listeners. However, the transformations reported often differed from those obtained in previous studies which used more phonetically complex auditory stimuli. The nature of the verbal transformations, average number of alternate forms perceived and transitions employed, and average number of repetitions of the stimuli prior to the onset of the ss' 1st verbal transformations are discussed. Comparisons with findings of previous investigations are provided. (french summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Musical duplex perception: Perception of figurally good chords with subliminal distinguishing tones.

In a variant of duplex perception with speech, phoneme perception is maintained when distinguishing components are presented below intensities required for separate detection, forming the basis for the claim that a phonetic module takes precedence over nonspeech processing. This finding is replicated with music chords (C major and minor) created by mixing a piano 5th with a sinusoidal distinguishing tone (E or E flat). Individual threshold intensities for detecting E or E flat in the context of the fixed piano tones are established. Chord discrimination thresholds defined by distinguishing tone intensity were determined. Exp 2 verified masked detection thresholds and subliminal chord identification for experienced musicians. Accurate chord perception was maintained at distinguishing tone intensities nearly 20 dB below the threshold for separate detection. Speech and music findings are argued to demonstrate general perceptual principles. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time course of simultaneous masking in the starling's auditory forebrain

Simultaneous masking of pure tones was studied in the primary auditory forebrain of a songbird species, the European starling (Sturnus vulgaris). The responses of 32 multi-unit clusters in the input layer of the auditory neostriatum (field L2a) were recorded via radiotelemetry from freely moving birds. The probe was a 10-ms tone burst at the units' characteristic-frequency (CF) presented 20 dB above the threshold. The masker was an 80-ms tone burst presented either at the units' CF (excitatory masker) or at a frequency located in inhibitory side-bands (inhibitory masker) of the units' tuning curves. The probe was presented either 3 ms or 63 ms after masker onset. Probes presented at a 3-ms delay were influenced at significantly lower levels of an excitatory masker than probes presented at a 63-ms delay. The mean difference in masker level at the detection thresholds for both probe delays was 8 dB. No difference in masker level was observed for inhibitory-frequency maskers. The observed neural masking effects may be explained by at least four mechanisms: (1) swamping of the probe response by the response to the masker, (2) a reduction of the probe response during neural adaptation of the response to the masker, (3) a reduction of the probe response during side-band inhibition in the central nervous system, and (4) suppression originating in the cochlea.     

Time course of forward masking tuning curves in cat primary auditory cortex

Nonsimultaneous two-tone interactions were studied in the primary auditory cortex of anesthetized cats. Poststimulatory effects of pure tone bursts (masker) on the evoked activity of a fixed tone burst (probe) were investigated. The temporal interval from masker onset to probe onset (stimulus onset asynchrony), masker frequency, and intensity were parametrically varied. For all of the 53 single units and 58 multiple-unit clusters, the neural activity of the probe signal was either inhibited, facilitated, and/or delayed by a limited set of masker stimuli. The stimulus range from which forward inhibition of the probe was induced typically was centered at and had approximately the size of the neuron's excitatory receptive field. This "masking tuning curve" was usually V shaped, i.e., the frequency range of inhibiting masker stimuli increased with the masker intensity. Forward inhibition was induced at the shortest stimulus onset asynchrony between masker and probe. With longer stimulus onset asynchronies, the frequency range of inhibiting maskers gradually became smaller. Recovery from forward inhibition occurred first at the lower- and higher-frequency borders of the masking tuning curve and lasted the longest for frequencies close to the neuron's characteristic frequency. The maximal duration of forward inhibition was measured as the longest period over which reduction of probe responses was observed. It was in the range of 53-430 ms, with an average of 143 +/- 71 (SD) ms. Amount, duration and type of forward inhibition were weakly but significantly correlated with "static" neural receptive field properties like characteristic frequency, bandwidth, and latency. For the majority of neurons, the minimal inhibitory masker intensity increased when the stimulus onset asynchrony became longer. In most cases the highest masker intensities induced the longest forward inhibition. A significant number of neurons, however, exhibited longest periods of inhibition after maskers of intermediate intensity. The results show that the ability of cortical cells to respond with an excitatory activity depends on the temporal stimulus context. Neurons can follow higher repetition rates of stimulus sequences when successive stimuli differ in their spectral content. The differential sensitivity to temporal sound sequences within the receptive field of cortical cells as well as across different cells could contribute to the neural processing of temporally structured stimuli like speech and animal vocalizations.     

Electrically evoked auditory brainstem response in peripherally myelin-deficient mice

The integrity of the myelin sheath is important for normal electrophysiological function and survival of neurons that make up the auditory nerve. It is hypothesized that myelin deficiency of the auditory nerve may change the electrophysiologic characteristics of the auditory system, especially the temporal properties. In this study, the electrically evoked auditory brainstem response (EABR) was systematically evaluated in TrJ and Po-DT-A mice. Both of these mice have a deficit of their peripheral myelin. Correlation between the EABR and degree of myelin deficiency was also evaluated. The EABR in both strains of poorly myelinated mice exhibited prolonged latency, decreased amplitude, elevated threshold of wave I evoked by short-duration stimuli (20 microseconds/phase). A 2-pulse stimulation paradigm was used to evaluate refractory properties. Myelin-deficient mice exhibited slower recovery from the refractory state than controls. Long-duration stimuli (4 ms/phase) were used to assess integration properties. Myelin-deficient mice demonstrated prolonged wave I latency and more gradual latency changes with current level. Myelin thickness showed a strong correlation with EABR threshold for short-duration stimulation (r = -0.784), maximum wave I latency (r = -0.778) and the time constant of the wave I latency-current level function (r = -0.736) for long-duration stimulation and normalized wave I recovery functions (r = -0.718). These findings suggest that EABR measurement may be a promising tool to assess the electrically stimulated properties of auditory neurons, particularly related to the status of myelin sheath.     

Perception of auditory–visual temporal synchrony in human infants.

Using a habituation/test procedure, the author investigated adults' and infants' perception of auditory–visual temporal synchrony. Participants were familiarized with a bouncing green disk and a sound that occurred each time the disk bounced. Then, they were given a series of asynchrony test trials where the sound occurred either before or after the disk bounced. The magnitude of the auditory visual temporal asynchrony threshold differed markedly in adults and infants. The threshold for the detection of asynchrony created by a sound preceding a visible event was 65 ms in adults and 350 ms in infants and for the detection of asynchrony created by a sound following a visible event was 112 ms in adults and 450 ms in infants. Also, infants did not respond to asynchronies that exceeded intervals that yielded reliable discrimination. Infants' perception of auditory–visual temporal unity is guided by a synchrony and an asynchrony window, both of which become narrower in development. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Stereoacuity and colour contrast

We have measured the contrast dependence of stereoacuity using both horizontally and vertically oriented, isoluminant (red-green) and isochromatic (yellow-black), 0.5 c/deg Gabor patches. For comparison, contrasts were computed in multiples of detection threshold, where detection threshold was defined as the contrast required for the stimulus to be simultaneously detectable in each eye. Disparity thresholds (1/stereoacuity) for vertical chromatic Gabors were higher than those for vertical luminance Gabors by a factor of between 4 and 9 depending on contrast, and declined less steeply with contrast. Disparity thresholds for horizontal chromatic Gabors were very high (130-210 min arc) compared with horizontal luminance Gabors (by a factor of between 9 and 17) and were only measurable at contrasts above 10 times simultaneous monocular detection threshold. These results support the view that chromatic stereoscopic processing is less precise than luminance stereoscopic processing, and that there is a special deficit in the processing of disparity with horizontally oriented chromatic stimuli. The implications of these results for the role of colour vision in stereopsis are discussed.     

Conditioned facilitation of brain reward function after repeated cocaine administration.

Cocaine lowers brain reward thresholds, reflecting increased brain reward function. The authors investigated whether, similar to acute cocaine administration, cocaine-predictive conditioned stimuli would lower intracranial self-stimulation (ICSS) thresholds. Rats received a saline injection for 5 days, a cocaine injection (10 mg/kg) for 20 consecutive days, then saline for 5 additional days. Thresholds were measured immediately before and 10 min after each injection. The initial 5 saline injections had no effect on thresholds, whereas cocaine significantly lowered thresholds for 20 days. There was no tolerance or sensitization to this effect of cocaine over days. During the last 5 days when cocaine administration was substituted with saline, rats demonstrated a conditioned lowering of thresholds during the 2nd daily ICSS session. These data demonstrate that cocaine-predictive conditioned stimuli induce a conditioned facilitation of brain reward function. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Middle latency responses to electrical stimulation of the auditory nerve in unanaesthetized guinea pigs

Middle latency responses (MLR) to sinusoidal and pulsatile electrical stimulation (ES) of the cochlea and to acoustical stimulation (AS) were evaluated in awake guinea pigs with chronically implanted electrodes. The ear, which was later electrically stimulated, was deafened by local intracochlear application of gentamicin, the opposite ear was left intact. Waveforms and P1-P2 interpeak intervals of the electrically evoked MLR (ES-MLR) were similar to those evoked by acoustical stimulation of the intact ear (AS-MLR) and the latencies of the ES-MLR were shorter by about 1-3 ms. Thresholds of ES-MLR in the frequency range 0.5-32 kHz increased with increasing ES frequency (slope 3.2 dB/octave), thresholds were 3.5-9.5 dB lower for intracochlear than for extracochlear ES. Dynamic ranges for ES-MLR varied between 6-20 dB. MLR amplitude-intensity functions for ES were steeper (slope 2-12 microV/dB) than those for AS (slope 0.2-2 microV/dB). Maximal ES-MLR amplitudes exceeded usually 1.5-3 times the amplitudes of the acoustically evoked MLR. Both types of stimulations evoked larger MLR amplitudes to contralateral stimulation than to ipsilateral stimulation (average ratio = 4.1 +/- 2.2 for AS and 3.3 +/- 2.2 for ES). Because of the relatively long latency and therefore insensitivity to electrical artifact, the ES-MLR can be used for the evaluation of different strategies of the electrical stimulation of the cochlea in awake guinea pig.