Sine-wave Stimuli Research Articles

The spatial properties of L- and M-cone inputs to electroretinograms that reflect different types of post-receptoral processing.

We studied the spatial arrangement of L- and M-cone driven electroretinograms (ERGs) reflecting the activity of magno- and parvocellular pathways. L- and M-cone isolating sine wave stimuli were created with a four primary LED stimulator using triple silent substitution paradigms. Temporal frequencies were 8 and 12 Hz, to reflect cone opponent activity, and 30, 36 and 48 Hz to reflect luminance activity. The responses were measured for full-field stimuli and for different circular and annular stimuli. The ERG data confirm the presence of two different mechanisms at intermediate and high temporal frequencies. The responses measured at high temporal frequencies strongly depended upon spatial stimulus configuration. In the full-field conditions, the L-cone driven responses were substantially larger than the full-field M-cone driven responses and also than the L-cone driven responses with smaller stimuli. The M-cone driven responses at full-field and with 70° diameter stimuli displayed similar amplitudes. The L- and M-cone driven responses measured at 8 and 12 Hz were of similar amplitude and approximately in counter-phase. The amplitudes were constant for most stimulus configurations. The results indicate that, when the ERG reflects luminance activity, it is positively correlated with stimulus size. Beyond 35° retinal eccentricity, the retina mainly contains L-cones. Small stimuli are sufficient to obtain maximal ERGs at low temporal frequencies where the ERGs are also sensitive to cone-opponent processing.

Stochastic resonance in visual sensitivity.

It is well known from psychophysical studies that stochastic resonance, in its simplest threshold paradigm, can be used as a tool to measure the detection sensitivity to fine details in noise contaminated stimuli. In the present manuscript, we report simulation studies conducted in the similar threshold paradigm of stochastic resonance. We have estimated the contrast sensitivity in detecting noisy sine-wave stimuli, with varying area and spatial frequency, as a function of noise strength. In all the cases, the measured sensitivity attained a peak at intermediate noise strength, which indicate the occurrence of stochastic resonance. The peak sensitivity exhibited a strong dependence on area and spatial frequency of the stimulus. We show that the peak contrast sensitivity varies with spatial frequency in a nonmonotonic fashion and the qualitative nature of the sensitivity variation is in good agreement with human contrast sensitivity function. We also demonstrate that the peak sensitivity first increases and then saturates with increasing area, and this result is in line with the results of psychophysical experiments. Additionally, we also show that critical area, denoting the saturation of contrast sensitivity, decreases with spatial frequency and the associated maximum contrast sensitivity varies with spatial frequency in a manner that is consistent with the results of psychophysical experiments. In all the studies, the sensitivities were elevated via a nonlinear filtering operation called stochastic resonance. Because of this nonlinear effect, it was not guaranteed that the sensitivities, estimated at each frequency, would be in agreement with the corresponding results of psychophysical experiments; on the contrary, close agreements were observed between our results and the findings of psychophysical investigations. These observations indicate the utility of stochastic resonance in human vision and suggest that this paradigm can be useful in psychophysical studies.

Phase-Locking Precision Is Enhanced by Multiquantal Release at an Auditory Hair Cell Ribbon Synapse

Sound-evoked spikes in the auditory nerve can phase-lock with submillisecond precision for prolonged periods of time. However, the synaptic mechanisms that enable this accurate spike firing remain poorly understood. Using paired recordings from adult frog hair cells and their afferent fibers, we show here that during sine-wave stimuli, synaptic failures occur even during strong stimuli. However, exclusion of these failures leads to mean excitatory postsynaptic current (EPSC) amplitudes that are independent of Ca(2+) current. Given the intrinsic jitter in spike triggering, evoked synaptic potentials and spikes had surprisingly similar degrees of synchronization to a sine-wave stimulus. This similarity was explained by an unexpected finding: large-amplitude evoked EPSCs have a significantly larger synchronization index than smaller evoked EPSCs. Large EPSCs therefore enhance the precision of spike timing. The hair cells' unique capacity for continuous, large-amplitude, and highly synchronous multiquantal release thus underlies its ability to trigger phase-locked spikes in afferent fibers.

Changes of calcium channel characteristics and its relationship with pancreatic islet β cell parasecretion in rat born small for gestational age

Method The animal model of small for gestation in rat was made under matemal calorie restriction by 50% from d1 of gestation until term, while the control groups named AGA rats, were obtained from normal pregnant rats. Both of SGA and AGA newborn rats were fed normally till 4 weeks and 8 weeks. Single islet b cell isolation and pancreatic tissue-slice technique were used to obtain b cells in neonatal rats and adult rats, respectively. Using whole cell patch clamp to record the characteristics of b cell voltage dependent calcium channel (such as current, reversal potential, I-V curve, activation curve, inactivation curve) in both SGA and AGA groups. Using capacitance measurement induced by a sequence of sine wave stimulus to reflect the insu lin secretion. In aw ord, study the tendency of calcium channel kinetics and secretion property by timing. Results The membrane capacitance of SGA was smaller than AGA rat after excluding the influence of whole cell membrane capacitance deviation both in neonatal rats, 4 weeks and 8 weeks (P 0.05). The same result was obtained in activation curve and inactivation curve of calcium channel, whose half activated voltage/ half inactivated voltage V1/2 and slope factor k between SGA and AGA both showed no significant difference (P>0.05) ; 2) adult rats: there was no statistical difference found in all average calcium current density (Id), including the total calcium, L-type and T-type. No significant difference was observed in the peak current density of I-V curve in SGA and AGA (P>0.05). However, the reversal potential in SGA group was much lower than control (P<0.05). The two group had the same shape of activation curve and inactivation curve of calcium channel, and 50% activated voltage between SGA and AGA had no significant difference, but the calcium channel of SGA was easily to be closed, the inactivated voltage in SGA group was much higher than control (P<0.01). Conclusion The effect of intrauterine malnourishment on pancreatic isletbcell last in postnatal life and the destroy of bcell tends to aggravate with time. Low calcium current density on b cell membrane devotes to the decrease of b cell secretion in SGA neonatal rat. However, the current of calcium channel returns to normal level in childhood. The kinetics of calcium channel is changed significantly,

Phase Distortion to Amplitude Conversion-Based Low-Cost Measurement of AM-AM and AM-PM Effects in RF Power Amplifiers

This work develops a simple, practical yet easily realizable method for low cost measurement of phase and amplitude distortions in radio frequency power amplifiers (RF PA). Amplitude-to-amplitude (AM-AM) and amplitude-to-phase (AM-PM) distortions are two significant distortion effects in PAs at high output power levels, causing out of band interference in the transmitted signal and bit errors in the received signal. Traditional measurements of amplitude and phase distortion in RF PAs require the use of expensive vector network analyzers. In this work, we propose the use of phase-to-amplitude conversion to develop a low cost and accurate test methodology for AM-AM and AM-PM measurement using simple load board test circuitry along with software based difference generation and peak detection mechanisms. Using either simple sine wave stimulus with power sweep or a single amplitude modulated RF stimulus, both distortion effects can be measured with high accuracy for nominal devices as well as over process and voltage variations, while allowing significant reduction in test cost.

Biological relevance of acoustic signal affects discrimination performance in a songbird

The fee-bee song of the black-capped chickadee (Poecile atricapillus) is a two-note, tonal song that can be sung at different absolute pitches within an individual. However, these two notes are produced at a consistent relative pitch. Moreover, dominant birds more reliably produce songs with this species-typical interval, compared to subordinate birds. Therefore, we asked whether presenting the species-typical relative pitch interval would aid chickadees in solving pitch interval discriminations. We found that species-typical relative pitch intervals selectively facilitated discrimination performance using synthetic sine-wave stimuli. Using shifted fee-bee song notes from recordings of naturally produced songs, birds learned the discrimination in fewer trials overall compared to synthetic stimuli. These results may reflect greater generalization among stimuli that occur outside species-typical production parameters. In addition, although sex differences in performance are rarely observed in acoustic discriminations in chickadees, female chickadees performed more accurately compared to males.

Use Spectrum Analysis to Test the Frequency-Domain Characteristics Parameters of ADCs

Many frequency-domain characteristics parameters can describe the dynamic behaviour of Analog to Digital Converters (ADCs). This paper researched how to use a sinewave stimulus and spectrum analysis to test those parameters. It analyzed the spectrum of coherent sampling and incoherent sampling of ADC response to a specified amplitude and frequency sinewave firstly. Incoherent sampling causes spectrum leakage. To reduce the errors in calculating parameters introduced by spectral leakage, this paper multiply the data record by a window function in the time domain prior to the DFT process. Simulate results demonstrate that window function can reduced the spectral leakage introduced by incoherent sampling and increase ADC parameters calculation accuracy.

Patients’ Perspectives on Electroconvulsive Therapy

In 2003, based on a review of 7 studies, Rose et al concluded that at least one third of patients report significant memory loss 6 months or more after electroconvulsive therapy (ECT). However, few details on the included studies were given. The present study evaluates factors that may have influenced the results. The 7 studies were scrutinized as to the 6-month assessment criterion, whether the data represent ECT-treated patients in general, specification and significance of the memory loss, stimulus type, and electrode placement. In 3 studies, the 6-month inclusion criterion was not met, including 1 study with 98% satisfied patients and 1 study with only 37% valid response rate. Two other studies selected individuals from user/advocacy groups generally biased against ECT and were probably overlapping. The significance of memory problems was not mentioned in any of the studies. Two studies reported that 30% and 55% of patients treated with bilateral ECT in the 1970s felt they had persistent memory gaps around the time of treatment, but the long-obsolete sine wave stimulus type was used. The results mostly concerned bilateral ECT, whereas unilateral ECT seemed to cause little complaints. Data used by Rose et al are severely flawed, making their results inconclusive and misleading.

Contextual coding of aggressive signals in weakly electric fish

Event Abstract Back to Event Contextual coding of aggressive signals in weakly electric fish Maurice Chacron1* 1 McGill University, Canada Although serotonergic pathways project unto many sensory brain areas, the consequences of such innervations on information processing are not well understood. We have previously shown that serotonin induces burst activity in pyramidal neurons of the electrosensory lateral line lobe (ELL) of weakly electric fish in vitro, which results in better detection of low frequency stimulus features. Here, to further investigate this effect under more natural conditions, we used an in vivo preparation and recorded from the same neurons in awake, behaving brown ghost fish. Extracellular and sharp electrode intracellular techniques were used to record responses of pyramidal neurons to serotonin after either focal application of serotonin to the molecular layer of ELL or electrical stimulation of raphe nuclei. Sine waves (2-256 Hz) were either applied locally to imitate prey or globally to imitate beats resulting from interaction between fish. Small chirps (i.e., aggressive signals) were produced by brief increases in the electric organ discharge frequency (EOD), whereas big chirps (i.e., courtship signals) were produced by long duration concomitant increases and decreases in EOD frequency and amplitude, respectively. In addition to an increased burst firing in ELL pyramidal neurons, serotonin application resulted in an increased phase locking of responses to low frequency (<64 Hz) sine wave stimuli. Further experiments revealed that serotonin did not alter coding of prey signal (i.e., local sinusoids). These results suggest that enhancement in phase locking during global communication is mediated by a feedback mechanism. Furthermore, serotonin application decreased the variability in timing of the first spike and improved the reliability of response to small chirp stimuli. Together, our findings indicate that serotonin, through burst generation in pyramidal neurons and modulation of a feedback pathway, improves the detection of same sex interactions through two mechanisms: increase reliability of coding of aggressive signals (i.e., small chirp) produced by dominant fish and better detection of low frequency beats generated during same sex interaction. Keywords: aggressive signals, Serotonin, weakly electric fish Conference: Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012. Presentation Type: Poster (but consider for student poster award) Topic: Neuromodulation Citation: Chacron M (2012). Contextual coding of aggressive signals in weakly electric fish. Conference Abstract: Tenth International Congress of Neuroethology. doi: 10.3389/conf.fnbeh.2012.27.00370 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: 01 May 2012; Published Online: 07 Jul 2012. * Correspondence: Dr. Maurice Chacron, McGill University, Montreal, Canada, maurice.chacron@mcgill.ca 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 Maurice Chacron Google Maurice Chacron Google Scholar Maurice Chacron PubMed Maurice Chacron 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.

Tracking vesicle fusion from hair cell ribbon synapses using a high frequency, dual sine wave stimulus paradigm

Recent experiments describe a technique for tracking membrane capacitance during depolarizations where membrane conductance is varying. This is a major advance over traditional technologies that can only monitor capacitance when conductance is constant because it gives direct information regarding release kinetics from single stimulations. Presented here is additional data supporting the use of this technology with multiple conductances being active including BK-Ca-activated potassium channels, SK Ca-activated potassium conductances and also the rapidly activating sodium conductance. It goes further to illustrate the ability to monitor rapid capacitative changes. And finally, it points out the need to evaluate single step responses because of the use-dependent movement of vesicles.

On the selective activation of unmyelinated C-fibers using sinusoidal electrical stimulation: An ERP study

Objective To verify the possibility of selective activation of C-fibers by a 5-Hz transcutaneous electrical stimulus. Methods Because Aβ-, Aδ- and C-fibers have different conduction velocities, we verified the selective activation of A- and C-fibers on the basis of evoked potential latencies. We tested whether a 5-Hz sinusoidal electric stimulus could selectively activate C-fibers and consequently generate ultra-late N2/P2 components in the 750–1200 ms range. Results We found that a 5-Hz sine wave stimulus, whether of high or low intensity, elicited N2/P2 complexes only in the late latencies (160–390 ms), suggesting that A-fibers were concomitantly activated along with C-fibers. Conclusions These findings are in agreement with those of previous simulation studies suggesting that activation of fibers of diameter less than 2.5 μm (i.e., C-fibers) at the 5-Hz frequency requires accompanying activity from Aβ- and Aδ-fibers. Significance Transcutaneous electrical stimulation with sine wave currents of different frequencies does not seem to be a reliable method for the selective assessment of somatosensory pathways.

A new interpretation of components in the ERG signals to sine wave luminance stimuli at different temporal frequencies and contrasts

Full-field electroretinograms were recorded from five normal human subjects using white light (mean luminance: 250 cd/m2) sine wave stimuli at different frequencies and contrasts. In agreement with previous studies, we found that the amplitude of the fundamental component displayed a dip at about 12 Hz, coinciding with a maximum in the second harmonic component, indicating frequency doubling of the responses. By including measurements at different contrasts, we were able to recognize two (sine-like and transient) response components. We found that the waveform of the transient response was relatively frequency independent. An algorithm to separate the two components was developed. The interaction between these two components can explain the frequency-doubled responses around 12 Hz. The sine-like component is more linear and prominent in the low-frequency region, whereas the transient seems to be more nonlinear and prominent in the high-frequency region.

Chirping response of weakly electric knife fish (Apteronotus leptorhynchus) to low-frequency electric signals and to heterospecific electric fish

Brown ghost knife fish (Apteronotus leptorhynchus) can briefly increase their electric organ discharge (EOD) frequency to produce electrocommunication signals termed chirps. The chirp rate increases when fish are presented with conspecific fish or high-frequency (700-1100 Hz) electric signals that mimic conspecific fish. We examined whether A. leptorhynchus also chirps in response to artificial low-frequency electric signals and to heterospecific electric fish whose EOD contains low-frequency components. Fish chirped at rates above background when presented with low-frequency (10-300 Hz) sine-wave stimuli; at 30 and 150 Hz, the threshold amplitude for response was 1 mV cm(-1). Low-frequency (30 Hz) stimuli also potentiated the chirp response to high-frequency ( approximately 900 Hz) stimuli. Fish increased their chirp rate when presented with two heterospecific electric fish, Sternopygus macrurus and Brachyhypopomus gauderio, but did not respond to the presence of the non-electric fish Carassius auratus. Fish chirped to low-frequency (150 Hz) signals that mimic those of S. macrurus and to EOD playbacks of B. gauderio. The response to the B. gauderio playback was reduced when the low-frequency component (<150 Hz) was experimentally filtered out. Thus, A. leptorhynchus appears to chirp specifically to the electric signals of heterospecific electric fish, and the low-frequency components of heterospecific EODs significantly influence chirp rate. These results raise the possibility that chirps function to communicate to conspecifics about the presence of a heterospecific fish or to communicate directly to heterospecific fish.

Effect of rimonabant, the cannabinoid CB1 receptor antagonist, on peripheral nerve in streptozotocin-induced diabetic rat

The aim of this study is to investigate the effect of rimonabant, which has antiatherosclerotic and antiinflammatory properties, on peripheral neuropathy in a diabetic rat. Diabetic rat models were induced by treatment with streptozotocin and then either normal or diabetic rats were treated with an oral dose of 10mg/kg/day rimonabant or placebo for 24 weeks. We quantified the densities of intraepidermal (PGP9.5+) nerve fiber and total skin (RECA-1+) capillary length. We also measured the current perception threshold, as defined by the intensity of sine-wave stimulus, skin blood flow after treadmill running and TNF-alpha level in spinal cord tissue or plasma. After 24 weeks, rimonabant reduced the body weight and food intake in both diabetic and normal rats, but it had no effect on blood sugar levels. In addition, rimonabant treatment significantly improved the decreased intraepidermal nerve fiber density (5.53+/-0.12 vs. 4.36+/-0.27/mm, P<0.05) and alleviated the increased current perception threshold in rimonabant-treated versus control diabetic rats. These responses were closely associated with the attenuation of skin capillary loss (1.98+/-0.07 vs. 1.67+/-0.10 mm/mm(2), P<0.05), increase in skin blood flow (14.93+/-1.08 vs. 12.07+/-0.87 TPU, P<0.05) and reduction in TNF-alpha level in tissue (70.10+/-4.99 vs. 91.18+/-3.34 pg/mg, P<0.05) in rimonabant-treated diabetic rats compared with placebo. These findings suggest that rimonabant can be beneficial for treatment of diabetic peripheral neuropathy, possibly due to its potential role in micro- and macrovessel protection and its anti-inflammatory properties.

An integrator-like circuit in cerebellar cortex

Event Abstract Back to Event An integrator-like circuit in cerebellar cortex Reinoud Maex1* 1 University of Hertfordshire, Science and Technology Research Institute, United Kingdom The brain builds dynamic models of the body and the outside world in order to predict the consequences of stimuli and actions. Dynamic models require a component that mathematically integrates signals with respect to time. A well known example is the oculomotor integrator, which calculates eye position from eye velocity commands to counteract the elasticity forces that destabilize gaze direction. Many models for neural integration have been proposed, based on feedback excitation, lateral inhibition, or intrinsic neuronal nonlinearities. We here draw the attention to the presence of an integrator-like circuit in the cerebellar cortex, an organ thought to implement dynamic models. Our computer simulations of a model of the cerebellar cortex demonstrate that the output neurons, Purkinje cells, can integrate their parallel-fiber inputs. Their responses to pulse, step and sinewave stimuli are found to have components with time-constants greater than 10 seconds. Both neuronal and network mechanisms contribute. A bi-stability of the Purkinje cell dynamics (phenomenologically the transition to an ON state) generates a slow response tail following pulse stimulation, whose amplitude and time-constant strongly depend on the pre-stimulus baseline spike rate, vanishing at low and high rates. Reciprocal inhibition among the Purkinje cells via their recurrent axon collaterals further prolongs the slow response component to step and sinewave stimuli. This model explains how a fast circuit like the cerebellar cortex may learn the timing of slow processes. Modulation of the baseline spike rate by inhibitory synapses may be a mechanism of plasticty of the response time-course independently of the response amplitude. Keywords: computational neuroscience Conference: Bernstein Conference on Computational Neuroscience, Berlin, Germany, 27 Sep - 1 Oct, 2010. Presentation Type: Presentation Topic: Bernstein Conference on Computational Neuroscience Citation: Maex R (2010). An integrator-like circuit in cerebellar cortex. Front. Comput. Neurosci. Conference Abstract: Bernstein Conference on Computational Neuroscience. doi: 10.3389/conf.fncom.2010.51.00099 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: 03 Sep 2010; Published Online: 23 Sep 2010. * Correspondence: Dr. Reinoud Maex, University of Hertfordshire, Science and Technology Research Institute, Hertfordshire, United Kingdom, r.maex1@herts.ac.uk 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 Reinoud Maex Google Reinoud Maex Google Scholar Reinoud Maex PubMed Reinoud Maex 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.

A modular gradient‐sensing network for chemotaxis in Escherichia coli revealed by responses to time‐varying stimuli

The Escherichia coli chemotaxis-signaling pathway computes time derivatives of chemoeffector concentrations. This network features modules for signal reception/amplification and robust adaptation, with sensing of chemoeffector gradients determined by the way in which these modules are coupled in vivo. We characterized these modules and their coupling by using fluorescence resonance energy transfer to measure intracellular responses to time-varying stimuli. Receptor sensitivity was characterized by step stimuli, the gradient sensitivity by exponential ramp stimuli, and the frequency response by exponential sine-wave stimuli. Analysis of these data revealed the structure of the feedback transfer function linking the amplification and adaptation modules. Feedback near steady state was found to be weak, consistent with strong fluctuations and slow recovery from small perturbations. Gradient sensitivity and frequency response both depended strongly on temperature. We found that time derivatives can be computed by the chemotaxis system for input frequencies below 0.006 Hz at 22 degrees C and below 0.018 Hz at 32 degrees C. Our results show how dynamic input-output measurements, time honored in physiology, can serve as powerful tools in deciphering cell-signaling mechanisms.

Noise induced amplification of sub-threshold pulses in multi-thread excitable semiconductor ‘neurons’

We report on the transmission of electrical pulses through a semiconductor structure which emulates biological neurons. The ‘neuron’ emits bursts of electrical spikes whose coherence we study as a function of the amplitude and frequency of a sine wave stimulus and noise. Noise is found to enhance the transmission of pulses below the firing threshold of the neuron. We demonstrate stochastic resonance when the power of the output signal passes through a maximum at an optimum noise value. Under appropriate conditions, we observe coherence resonance and stochastic synchronization. Data are quantitatively explained by modelling the FitzHugh–Nagumo equations derived from the electrical equivalent circuit of the soma. We have therefore demonstrated a physically realistic neuron structure that provides first principles feedback on mathematical models and that is well suited to building arborescent networks of pulsing neurons.

Children need coherence masking protection.

Listeners can recognize speech targets at poorer signal-to-noise levels when more signal components are present, even if the additional components are spectrally distant and contribute no new information, but only if all components can be grouped together. [P. C. Gordon, Percept. Psychophys. 59, 232–242 (1997)]. This phenomenon (coherence masking release) was studied in adults and children using the first formant (F1) of [ε] and [ɪ] as targets. Formants were presented in low-pass white noise for vowel labeling, with and without a consistent F2/F3 component above the noise cutoff. Synthetic-speech and sine-wave stimuli were used. Thresholds for accurate labeling were obtained with an adaptive procedure for F1-only and for all 3-formants. For synthetic speech, adults had 3.3 dB of masking release for 3-formants compared to F1-only. Children showed a 6.5-dB effect in the same direction, due to higher thresholds for F1-only. All listeners heard sine waves as non-speech, showed similar thresholds, and had reduced masking release (1.5 dB), but in this case F1-only had the advantage over the 3-formant condition. Conclusions were as follows: (1) children need coherent signals to recognize speech in noise and (2) when combined with Gordon’s results, it seems masking release for speech signals likely has a phonetic explanation.

Does harmonicity explain children’s cue weighting of fricative-vowel syllables?

When labeling syllable-initial fricatives, children have been found to weight formant transitions more and fricative-noise spectra less than adults, prompting the suggestion that children attend more to the slow vocal-tract movements that create syllabic structure than to the rapid gestures more closely aligned with individual phonetic segments. That explanation fits well with linguistic theories, but an alternative explanation emerges from auditory science: Perhaps children attend to formant transitions because they are found in voiced signal portions, and so formants share a common harmonic structure. This work tested that hypothesis by using two kinds of stimuli lacking harmonicity: sine-wave and whispered speech. Adults and children under 7 years of age were asked to label fricative-vowel syllables in each of those conditions, as well as natural speech. Results showed that children did not change their weighting strategies from those used with natural speech when listening to sine-wave stimuli, but weighted formant transitions less when listening to whispered stimuli. These findings showed that it is not the harmonicity principle that explains children's preference for formant transitions in phonetic decisions. It is further suggested that children are unable to recover formant structure when those formants are not spectrally prominent and/or are noisy.

Sensibilidade ao contraste de crianças surdas e ouvintes para grades senoidais em condições mesópicas

The aim of this study was to compare the contrast sensitivity (CSF) of deaf children and hearing children to spatial frequency of 0.25 to 2.0 cpd (cycles per degree of visual angle) at mesopic luminance level (0.7 cd/m2), using the psychophysical forced-choice method. Twenty children (7-12 years old) participated in this research, ten with prelingual deafness and ten with normal hearing. All participants had normal or corrected visual acuity. The ANOVA showed significant difference between the two groups [F(1, 238) = 15.487; p 0.05). The results suggest alterations in CSF to sine-wave gratings stimuli of deaf children at mesopic luminance level.