Suprathreshold Levels Research Articles

Impact of Forms of Visual Attenuation on Short-Term Eye Changes Under Controlled Reading Visibility.

Animal studies have suggested that visual degradation impacts eye growth due to the attenuation of high spatial frequencies. However, the influence of perceptual visibility remains unclear in humans. The aim of this study was to investigate the impact of visibility on visual attenuation-related eye changes during reading. Axial length (AxL) and choroidal thickness (ChT) changes associated with reading tasks were measured in two separate experiments. In the first experiment, the reading task was conducted under different forms of visual attenuation (contrast, resolution, defocus, noise, and crowding). For each form of visual attenuation, the text was set at a sub-threshold level of visibility, evaluated via prior measurement of reading performance, and kept constant via adaptive control of the intensity of the stimulation. Each sub-threshold reading condition was compared with a supra-threshold reading text, serving as control. In the second experiment, the effect of visibility on lens-induced defocus was further examined by comparing the effect of text stimulation with an equivalent dioptric of 5.5 D under sub- and supra-threshold levels of resolution. Near distance reading with supra-threshold texts caused eye elongation (AxL: +12.942 µm ± 2.147 µm; ChT: -3.192 µm ± 1.158 µm). Additional defocusing failed to exacerbate axial elongation under sub-threshold text visibility (mean difference: -0.135 µm ± 2.783 µm), revealing a clear inhibitory effect of lowering visibility on eye changes. Other forms of visual degradation, including crowding (mean difference: 6.153 µm ± 2.127 µm) and noise (mean difference: 5.02 µm ± 2.812 µm) also showed an inhibitory effect on eye elongation. The significant effect of crowding indicated that post-retinal mechanisms, involving attentional processes related to crowded characters, may play a role in the influence of visibility. Although the featural composition of visual stimulation can drastically influence eye changes, this study revealed an important mediating role of visibility, previously underscored in chick studies, which warrants further explorations of the impact of post-retinal processes in eye growth.

The roles of neural adaptation and sensitization in contact lens discomfort

PurposeTo investigate the roles of neural adaptation and sensitization in contact lens discomfort (CLD). MethodsCooling stimuli (20 °C) were applied to the cornea in a group comprising 24 symptomatic and 25 asymptomatic contact lens (CL) wearers as well as 15 non-CL wearing controls, using a computerized Belmonte esthesiometer. The adaptation paradigm consisted of 20 repetitive stimuli at threshold, sub- and supra-threshold levels. The sensitization paradigm involved five levels of suprathreshold stimuli ranging between 1x to 2x threshold. Following each stimulus, participants rated the sensation magnitude regarding intensity, coolness and irritation. Measurements were taken with habitual CL (BL_CL), after 2 weeks of no-CL (No_CL) and after restarting habitual CL wear (ReSt_CL). ResultsThe symptomatic subjects exhibited a lower threshold but reported enhanced sensations during the adaptation and sensitization paradigm, compared to the asymptomatic and control groups (all p ≤ 0.021). At the BL_CL and ReSt_CL visits, they showed increased ratings to repeated subthreshold stimuli (p = 0.025) and greater irritation during the sensitization paradigm (p ≤ 0.032). Ratings in asymptomatic and control groups were relatively unchanged over time (p ≥ 0.181). Logistic regression revealed a link between the augmented sensory responses and increased likelihood with CLD. ConclusionThe maladaptive sensory responses seen in CLD subjects, with reduced adaptation and heightened sensitization to ocular surface stimulation, suggest an imbalance between sensitization and adaptation in CLD. As CLD may represent a reversible subcategory of dry eye, it can serve as a human dry eye model for studying the neurosensory effect of ocular surface stimulation.

Using bioluminescence as a tool for studying diversity in marine zooplankton and dinoflagellates: an initial assessment.

Bioluminescence is light chemically produced by an organism. It is widespread across all major marine phyla and has evolved multiple times, resulting in a high diversity of spectral properties and first flash kinetic parameters (FFKP). The bioluminescence of a system is often a good proxy for planktonic biomass. The species-specific parameters of bioluminescent displays can be measured to identify species in situ and describe planktonic biodiversity. Most bioluminescent organisms will flash when mechanically stimulated i.e., when subjected to supra-threshold levels of shear stress. Here we compare first flash kinetic parameters such as flash duration, peak intensity, rise time, decay time, first-flash mechanically stimulated light and e-folding time obtained with the commercially available Underwater Bioluminescence Assessment Tool (UBAT). We provide descriptions of the first flash kinetic parameters of several species of dinoflagellates Pyrocystis fusiformis, Pyrocystis noctiluca, Pyrodinium bahamense, Lingulodinium polyedra, Alexandrium monilatum and two zooplankton (the ctenophore Mnemiopsis leidyi and the larvacean Oikopleura sp.). FFKPs are then compared and discussed using non-parametric analyses of variance (ANOVAs), hierarchical clustering and a linear discriminant analysis to assess the ability to use bioluminescence signatures for identification. Once the first flash kinetic parameters of a bioluminescent species have been described, it is possible to detect its presence using emissions collected by in situ bathyphotometers. Assessing abundance and diversity of bioluminescent species may therefore be possible.

Investigating the Effects of Level-Specific CE-Chirp on Auditory Brainstem Response Waves in Normal Hearing Infants.

Auditory brainstem response (ABR) to the level-specific (LS) CE-Chirp has been reported to provide optimum neural synchrony along cochlear partitions, theoretically improving ABR waveform resolution. Despite this promising finding, limited studies have been conducted to contrast the results between LS CE-Chirp and Click stimuli. The current study aimed to compare the results of ABR between the two stimuli (Click and LS CE-Chirp). Sixty-seven normal-hearing infants, both with and without risk factors, aged less than 7 months old, participated in this study. The ABR test was conducted at 70 dBnHL using 33.3 stimulus repetition rates with both Click and LS CE-Chirp stimuli. The signal averaging was stopped at a maximum fixed signal average of 2,500 sweeps. Data were statistically compared between the two stimuli using the Wilcoxon signed-rank test. The waves I and V ABRs elicited by LS CE-Chirp exhibited significantly larger amplitudes than the Click stimulus. However, the amplitude of wave III and absolute latencies were similar in both stimuli at a supra-threshold level. LS CE-Chirp has the advantage of larger amplitudes than the ABR from Click at the supra-threshold level (70 dBnHL) in normal-hearing infants.

Differences in time-intensity sensory profiles of sweet taste intensity of glucose between older and young adults.

To understand age-related changes in sweet taste perception in daily life, it is important to understand taste intensity at the suprathreshold level. Previous studies have attempted to characterize the temporal aspects of human taste perception in terms of time-intensity evaluations. The perception of dynamic taste intensity in older adults increases slowly for salty taste; however, there have been no previous studies on time-intensity sensory evaluation of sweet taste in older adults. We hypothesized that older adults perceive sweet taste intensity more slowly than young adults. Fifty young and 40 older adults participated in the study and glucose solutions of 0.6 M and 1.5 M were used as stimuli. The study comprised two experiments: (1) a cup tasting test (static taste perception in the mouth), and (2) a time-intensity sensory evaluation, in which the solutions were presented using a custom-made delivery system. The intra-oral device was made to fit each participant's dentition. Further, the level of gag reflex was taken into consideration for each participant in the design of the intra-oral device. A suction tube was placed across the posterior tongue near the throat to remove solution and saliva. The solution delivery system was controlled by an original computer program. Older adults presented significantly different maximum intensity timing and slope for both concentrations compared with young adults (slope for 1.5 M, p < 0.01; others, p < 0.05). No significant differences were found between the older and young adults for reaction timing and maximum intensity. We conclude that older adults perceived sweetness more slowly than young adults, and ultimately perceived almost the same intensity as young adults. This is the first reported characterization of the time-intensity profile of sweet taste intensity of glucose in older adults. Using a standardized system enabled us to assess and compare feedback on taste intensities among different age groups in real-time. Based on this, we recommend older adults "savor" to perceive sweet tastes at the same level experienced by young adults.

The Effect of Stimulation Intensity, Sampling Frequency, and Sample Synchronization in TMS-EEG on the TMS Pulse Artifact Amplitude and Duration.

Transcranial magnetic stimulation (TMS) coupled with electroencephalography (EEG) possesses diagnostic and therapeutic benefits. However, TMS provokes a large pulse artifact that momentarily obscures the cortical response, presenting a significant challenge for EEG data interpretation. We examined how stimulation intensity (SI), EEG sampling frequency (Fs) and synchronization of stimulation with EEG sampling influence the amplitude and duration of the pulse artifact. In eight healthy subjects, single-pulse TMS was administered to the primary motor cortex, due to its well-documented responsiveness to TMS. We applied two different SIs (90% and 120% of resting motor threshold, representing the commonly used subthreshold and suprathreshold levels) and Fs (conventional 5 kHz and high frequency 20 kHz) both with TMS synchronized with the EEG sampling and the conventional non-synchronized setting. Aside from removal of the DC-offset and epoching, no preprocessing was performed to the data. Using a random forest regression model, we identified that Fs had the largest impact on both the amplitude and duration of the pulse artifact, with median variable importance values of 1.444 and 1.327, respectively, followed by SI (0.964 and 1.083) and sampling synchronization (0.223 and 0.248). This indicated that Fs and SI are crucial for minimizing prediction error and thus play a pivotal role in accurately characterizing the pulse artifact. The results of this study enable focusing some of the study design parameters to minimize TMS pulse artifact, which is essential for both enhancing the reliability of clinical TMS-EEG applications and improving the overall integrity and interpretability of TMS-EEG data.

Reduced neural responses to pleasant odor stimuli after acute psychological stress is associated with cortisol reactivity

Acute stress alters olfactory perception. However, little is known about the neural processing of olfactory stimuli after acute stress exposure and the role of cortisol in such an effect. Here, we used an event-related olfactory fMRI paradigm to investigate brain responses to odors of different valence (unpleasant, pleasant, or neutral) in healthy young adults following an acute stress (Trier Social Stress Test, TSST) induction (N = 22) or a non-stressful resting condition (N = 22). We obtained the odor pleasantness, intensity, and familiarity ratings after the acute stress induction or resting condition. We also measured the participants' perceived stress and salivary cortisol at four time points during the procedure. We found a stress-related decrease in brain activation in response to the pleasant, but not to the neutral or unpleasant odor stimuli in the right piriform cortex extending to the right amygdala, the right orbitofrontal cortex, and the right insula. In addition, activation of clusters within the regions of interest were negatively associated with individual baseline-to-peak increase in salivary cortisol levels after stress. We also found increased functional connectivity between the right piriform cortex and the right insula after stress when the pleasant odor was presented. The strength of the connectivity was positively correlated with increased perceived stress levels immediately after stress exposure. These results provide novel evidence for the effects of acute stress in attenuating the neural processing of a pleasant olfactory stimulus. Together with previous findings, the effect of acute stress on human olfactory perception appears to depend on both the valence and the concentration (e.g., peri-threshold or suprathreshold levels) of odor stimuli.

How inhibitory and excitatory inputs gate output of the inferior olive.

The inferior olive provides the climbing fibers to Purkinje cells in the cerebellar cortex, where they elicit all-or-none complex spikes and control major forms of plasticity. Given their important role in both short-term and long-term coordination of cerebellum-dependent behaviors, it is paramount to understand the factors that determine the output of olivary neurons. Here, we use mouse models to investigate how the inhibitory and excitatory inputs to the olivary neurons interact with each other, generating spiking patterns of olivary neurons that align with their intrinsic oscillations. Using dual color optogenetic stimulation and whole-cell recordings, we demonstrate how intervals between the inhibitory input from the cerebellar nuclei and excitatory input from the mesodiencephalic junction affect phase and gain of the olivary output at both the sub- and suprathreshold level. When the excitatory input is activated shortly (~50 ms) after the inhibitory input, the phase of the intrinsic oscillations becomes remarkably unstable and the excitatory input can hardly generate any olivary spike. Instead, when the excitatory input is activated one cycle (~150 ms) after the inhibitory input, the excitatory input can optimally drive olivary spiking, riding on top of the first cycle of the subthreshold oscillations that have been powerfully reset by the preceding inhibitory input. Simulations of a large-scale network model of the inferior olive highlight to what extent the synaptic interactions penetrate in the neuropil, generating quasi-oscillatory spiking patterns in large parts of the olivary subnuclei, the size of which also depends on the relative timing of the inhibitory and excitatory inputs.

Intensity discrimination and neural representation of a masked tone in the presence of three types of masking release.

Hearing ability is usually evaluated by assessing the lowest detectable intensity of a target sound, commonly referred to as a detection threshold. Detection thresholds of a masked signal are dependent on various auditory cues, such as the comodulation of the masking noise, interaural differences in phase, and temporal context. However, considering that communication in everyday life happens at sound intensities well above the detection threshold, the relevance of these cues for communication in complex acoustical environments is unclear. Here, we investigated the effect of three cues on the perception and neural representation of a signal in noise at supra-threshold levels. First, we measured the decrease in detection thresholds produced by three cues, referred to as masking release. Then, we measured just-noticeable difference in intensity (intensity JND) to quantify the perception of the target signal at supra-threshold levels. Lastly, we recorded late auditory evoked potentials (LAEPs) with electroencephalography (EEG) as a physiological correlate of the target signal in noise at supra-threshold levels. The results showed that the overall masking release can be up to around 20 dB with a combination of these three cues. At the same supra-threshold levels, intensity JND was modulated by the masking release and differed across conditions. The estimated perception of the target signal in noise was enhanced by auditory cues accordingly, however, it did not differ across conditions when the target tone level was above 70 dB SPL. For the LAEPs, the P2 component was more closely linked to the masked threshold and the intensity discrimination than the N1 component. The results indicate that masking release affects the intensity discrimination of a masked target tone at supra-threshold levels, especially when the physical signal-to-noise is low, but plays a less significant role at high signal-to-noise ratios.

Cochlear synaptopathy impairs suprathreshold tone-in-noise coding in the cochlear nucleus.

Hearing impairment without threshold elevations can occur when there is damage to high-threshold auditory nerve fibre synapses with cochlear inner hair cells. Instead, cochlear synaptopathy produces suprathreshold deficits, especially in older patients, which affect conversational speech. Given that listening in noise at suprathreshold levels presents significant challenges to the ageing population, we examined the effects of synaptopathy on tone-in-noise coding on the central recipients of auditory nerve fibres, i.e. the cochlear nucleus neurons. To induce synaptopathy, guinea pigs received a unilateral sound overexposure to the left ears. A separate group received sham exposures. At 4weeks post-exposure, thresholds had recovered but reduced auditory brainstem response wave1 amplitudes and auditory nerve synapse loss remained on the left side. Single-unit responses were recorded from several cell types in the ventral cochlear nucleus to pure-tone and noise stimuli. Receptive fields and rate-level functions in the presence of continuous broadband noise were examined. The synaptopathy-inducing noise exposure did not affect mean unit tone-in-noise thresholds, nor the tone-in-noise thresholds in each animal, demonstrating equivalent tone-in-noise detection thresholds to sham animals. However, synaptopathy reduced single-unit responses to suprathreshold tones in the presence of background noise, particularly in the cochlear nucleus small cells. These data demonstrate that suprathreshold tone-in-noise deficits following cochlear synaptopathy are evident in the first neural station of the auditory brain, the cochlear nucleus neurons, and provide a potential target for assessment and treatment of listening-in-noise deficits in humans. KEY POINTS: Recording from multiple central auditory neurons can determine tone-in-noise deficits in animals with quantified cochlear synapse damage. Using this technique, we found that tone-in-noise thresholds are not altered by cochlear synaptopathy, whereas coding of suprathreshold tones-in-noise is disrupted. Suprathreshold deficits occur in small cells and primary-like neurons of the cochlear nucleus. These data provide important insights into the mechanisms underlying difficulties associated with hearing in noisy environments.

Subclinical hearing loss associated with aging

ObjectiveContribute to clarifying the existence of subclinical hearing deficits associated with aging. DesignIn this work, we study and compare the auditory perceptual and electrophysiological performance of normal-hearing young and adult subjects (tonal audiometry, high-frequency tone threshold, a triplet of digits in noise, and click-evoked auditory brainstem response). Study sample45 normal hearing volunteers were evaluated and divided into two groups according to age. 27 subjects were included in the “young group” (mean 22.1 years), and 18 subjects (mean 42.22 years) were included in the “adult group.” ResultsIn the perceptual tests, the adult group presented significantly worse tonal thresholds in the high frequencies (12 and 16 kHz) and worse performance in the digit triplet tests in noise. In the electrophysiological test using the auditory brainstem response technique, the adult group presented significantly lower I and V wave amplitudes and higher V wave latencies at the supra-threshold level. At the threshold level, we observed a significantly higher latency in wave V in the adult group. In addition, in the partial correlation analysis, controlling for the hearing level, we observed a relationship (negative) between age and speech in noise performance and high-frequency thresholds. No significant association was observed between age and the auditory brainstem response. ConclusionThe results are compatible with subclinical hearing loss associated with aging.

Boothless audiometry: Ambient noise considerations

Ambient noise in the test environment will impact signal detection during hearing threshold measurements due to psychoacoustic masking effects. Technical standards specify the maximum permissible ambient noise levels (MPANLs) for use during audiometric testing. MPANLs are dependent on several factors, including transducer characteristics (supra-aural, circumaural, type of ear cushions or earphone enclosures, and insert earphones), the nature of the hearing test being performed (air conduction vs bone conduction and threshold test vs screen at a suprathreshold level), and measurement instrumentation. The nature of the ambient noise (spectrum and constant vs variable) at the test site must be determined and continually accounted for during the boothless hearing test procedure. Ambient noise monitoring procedures are reviewed and examples of ambient noise characteristics in real-world settings, where hearing testing might be performed outside of a sound-treated environment, are provided. Practical considerations are presented, including examples of available tools for ambient noise monitoring, selection of test locations, and transducer attenuation. These are discussed in the context of calculating MPANLs and how best to ensure that ambient noise levels are not negatively impacting the validity of hearing thresholds.

Comparison of verticality perception and postural sway induced by double temple-mastoidal and bipolar binaural 20 Hz sinusoidal galvanic vestibular stimulation.

Galvanic vestibular stimulation (GVS) is believed to be one of the most valuable tools for studying the vestibular system. In our opinion, its combined effect on posture and perception needs to be examined more. The present study was conducted to investigate the effect of a 20 Hz sinusoidal Galvanic Vestibular Stimulation (sGVS) on the body sway and subjective visual vertical (SVV) deviation through two sets of electrode montages (bipolar binaural and double temple-mastoidal stimulation) during a three-stage experiment (baseline, threshold, and supra-threshold levels). While the individuals (32 normal individuals, 10 males, the mean age of 25.37±3.00 years) were standing on a posturography device and SVV goggles were put on, the parameters of the body sway and SVV deviation were measured simultaneously. Following the baseline stage (measuring without stimulation), the parameters were investigated during the threshold and supra-threshold stages (1 mA above the threshold) for 20 seconds. This was done separately for each electrode montage. Then, the results were compared between the three experimental stages and the two electrode montages. In both electrode montages, "the maximum amplitude" of the mediolateral (ML) and anteroposterior (AP) body sway decreased and increased in the threshold and supra-threshold stages, respectively, compared to the baseline stage. Comparison of the amount of "amplitude change" caused by each electrode montages showed that the double temple-mastoidal stimulation induced a significantly greater amplitude change in body sway during both threshold and supra-threshold stages (relative to the baseline stage).The absolute mean values of the SVV deviation were significantly different between the baseline and supra-threshold levels in both electrode montages. The SVV deviation in double temple-mastoidal stimulation was a bit greater than that in the bipolar binaural stimulation. Double temple-mastoidal stimulation has induced greater amount of change in the body sway and SVV deviation. This may be due to the more effective stimulation of the otoliths than semicircular canals.

Dependence of binaural gain for infrasound on interaural phase difference.

Increasing complaints about infrasound have generated interest in understanding its perception, including binaural effects. This study investigated the level difference between monaural and binaural presentation required for detection and equal loudness (binaural gain) for pure tones with frequencies of 8, 32, and 400 Hz and an 8 Hz sinusoidally amplitude-modulated tone with diotic 400 Hz carrier. Monaural stimuli were compared to binaural stimuli with interaural phase differences (IPDs) of 0°, 90°, and 180° in two experiments: absolute threshold measurements and loudness matching at 40 phons. The latter was repeated with transposed tones (400 Hz carrier multiplied by a half-wave-rectified 8 Hz sinusoid). When expressed as differences in sound pressure level, similar binaural gain was found across all stimulus types under the diotic condition. Confirming previous studies, the gain was larger at supra-threshold levels (40 phons) than at threshold. However, when the loudness-matching results were expressed as binaural gain with respect to the loudness level, they became 17.5, 11.2, and 5.8 phons for the 8, 32, and 400 Hz stimuli, respectively. Results for the 8 Hz pure tone and the transposed stimulus were IPD dependent.

The Relative and Combined Effects of Noise Exposure and Aging on Auditory Peripheral Neural Deafferentation: A Narrative Review.

Animal studies have shown that noise exposure and aging cause a reduction in the number of synapses between low and medium spontaneous rate auditory nerve fibers and inner hair cells before outer hair cell deterioration. This noise-induced and age-related cochlear synaptopathy (CS) is hypothesized to compromise speech recognition at moderate-to-high suprathreshold levels in humans. This paper evaluates the evidence on the relative and combined effects of noise exposure and aging on CS, in both animals and humans, using histopathological and proxy measures. In animal studies, noise exposure seems to result in a higher proportion of CS (up to 70% synapse loss) compared to aging (up to 48% synapse loss). Following noise exposure, older animals, depending on their species, seem to either exhibit significant or little further synapse loss compared to their younger counterparts. In humans, temporal bone studies suggest a possible age- and noise-related auditory nerve fiber loss. Based on the animal data obtained from different species, we predict that noise exposure may accelerate age-related CS to at least some extent in humans. In animals, noise-induced and age-related CS in separation have been consistently associated with a decreased amplitude of wave 1 of the auditory brainstem response, reduced middle ear muscle reflex strength, and degraded temporal processing as demonstrated by lower amplitudes of the envelope following response. In humans, the individual effects of noise exposure and aging do not seem to translate clearly into deficits in electrophysiological, middle ear muscle reflex, and behavioral measures of CS. Moreover, the evidence on the combined effects of noise exposure and aging on peripheral neural deafferentation in humans using electrophysiological and behavioral measures is even more sparse and inconclusive. Further research is necessary to establish the individual and combined effects of CS in humans using temporal bone, objective, and behavioral measures.

Physiological studies of timbre encoding in the auditory midbrain

Perceived timbre, especially brightness, is influenced by the spectral peaks of sounds. We hypothesize that spectral peaks are reliably encoded in the inferior colliculus (IC) due to capture and off-characteristic frequency (CF) inhibition. Capture occurs when a component near CF saturates the inner-hair-cell response, reducing the amplitude of neural fluctuations, the low-frequency changes in auditory-nerve firing rate that arise from the interaction of components within complex sounds. IC neurons are sensitive to amplitude modulation and respond to neural fluctuations with enhanced or suppressed rates. Extracellular single-unit recordings were made in the IC of awake rabbits in response to synthetic harmonic stimuli with triangular-shaped spectral magnitudes and zero-phase. Stimuli were presented at 40–80 dB SPL to test for robust encoding over a range of suprathreshold levels. Responses were compared to the output of an auditory-nerve model that exhibits capture followed by a modulation-tuned midbrain model. Results were generally consistent with model predictions, especially for cells suppressed by modulations. Dependent on the modulation transfer function type, responses show dips or peaks in average rate over many levels when the peak harmonic frequency matches CF. This work fills a gap in neural timbre research by investigating spectral peak encoding in the auditory midbrain.

Effects of electrical pulse polarity shape on intra cochlear neural responses in humans: Triphasic pulses with anodic and cathodic second phase

Modern cochlear implants employ charge-balanced biphasic and triphasic pulses. However, the effectiveness of electrical pulse shape and polarity is still a matter of debate. For this purpose, a previous study (Bahmer & Baumann, 2013) conducted electrophysiological and psychophysical measurements following triphasic pulse stimulation with constant cathodic second phase and varying anodic first and third phases. Pulse stimulation with constant anodic second phase was not investigated.Therefore, in this study, pulse stimulation with cathodic and anodic second phase was applied for the recording of electrically evoked compound action potentials (ECAPs) as well as for psychophysical thresholds in cochlear implant (CI) recipients. First it was investigated whether the temporal polarity distribution has a different effect on neuronal stimulation when the second phase is cathodic or anodic; second, whether the electrophysiological and psychophysical results show a comparable difference between triphasic stimulation with anodic and cathodic second phases.The results showed that variation of the temporal polarity distribution of the triphasic pulse had a smaller effect on the ECAP response when the second phase was anodic compared to when it was cathodic, whereas for psychophysical detection thresholds this variation had a similar effect for both polarities. While electrophysiological responses and psychophysical detection thresholds showed a high correlation for variations of the triphasic pulse with cathodic second phase, the results for variations of the triphasic pulse with anodic second phase showed only moderate correlation. Furthermore, the difference between triphasic stimulation with cathodic and anodic second phases did not correlate between the electrophysiological and psychophysical results.In summary, after stimulation with different configurations of triphasic pulses used in the present study, the polarity of the second phase has an effect on electrophysiological response at suprathreshold level but not on the psychophysical detection thresholds. Thus, at different stimulation levels a possible substitution of the psychophysical test by an electrophysiological measurement (e.g. neural health measurement of the cochlea) could not be corroborated by the present results.

Effects of modulator shape at thresholds and supra-thresholds spectral modulation perception

Spectral modulation detection is common method to assess spectral envelope perception in research and clinical settings. Prior investigations into spectral modulation (SM) detection have used two different modulator shapes: a sinusoidal envelope on a logarithmic amplitude scale or a sinusoidal envelope on a linear amplitude scale. The former creates a sinusoidally shaped excitation pattern, while the latter creates an excitation pattern with broad peaks and sharp valleys. What impact, if any, modulator shape has on SM perception at detection threshold or at supra-threshold levels is unknown. To investigate potential perceptual differences between waveform shapes: (1) SM detection was measured for modulation frequencies ranging from 0.5 to 8.0 cycles/octave; (2) Spectral modulation masking was measured for SM frequencies of 0.5 and 2.0 cycles/octave. The SM phase of the masker was manipulated (0, 90, or 180 degrees) so that maskers had a peak, a midpoint, or a valley at 1147 Hz. Tone detection (1147 Hz) was measured for the logarithmic and linear sinusoidal SM envelope shapes for each of the three phases. Results revealed significant differences between the two spectral envelope shapes for both spectral modulation detection and for spectral modulation masking. [Work supported by NIH R01DC015051].

The Effect of Odour Valence and Odour Detection Threshold on the Withholding and Cancellation of Reach-to-Press Responses

IntroductionWithholding uninitiated actions and cancelling ongoing ones are two main components of response inhibition, a key element of the executive control. Inhibitory performance is sensitive to emotional contexts elicited by subliminal and supraliminal visual material. However, whether stimuli from other sensory modalities, such as odours, would equally modulate response inhibition remains unclear. Here, we aimed to assess the effect of task-irrelevant odours as a function of their valence and threshold on both action withholding and action cancellation of reach-to-press movements.MethodThirty-two healthy participants performed a Go/No-Go task that included the presentation of pleasant (orange) and unpleasant (trimethyloxazole) odour primes at supra- and sub-threshold levels; clean air was included as a control condition. The reach-to-press responses were composed of an initial release phase and a subsequent reaching phase.ResultsOnly the supra-threshold pleasant (vs. control) odour impaired action withholding. Moreover, the pleasant (vs. control) odour—presented at both sub- and supra-threshold levels—elicited more accurate Go responses, whereas the sub- and supra-threshold pleasant and unpleasant (vs. control) odours triggered faster responses in the release phase. Additionally, only the supra-threshold pleasant (vs. unpleasant) odour impaired action cancellation in the reaching phase. Furthermore, reaching responses were slower following the supra-threshold unpleasant (vs. control) odour.ConclusionsOur findings extend the sparse literature on the impact of odour stimuli on goal-directed behaviour, highlighting the role of both odour valence and threshold in the modulation of response inhibition.ImplicationsDetermining the mechanisms by which odour stimuli modulate response inhibition lays the foundations for research on odour-triggered disinhibition.

Nearby contours abolish the binocular advantage

That binocular viewing confers an advantage over monocular viewing for detecting isolated low luminance or low contrast objects, has been known for well over a century; however, the processes involved in combining the images from the two eyes are still not fully understood. Importantly, in natural vision, objects are rarely isolated but appear in context. It is well known that nearby contours can either facilitate or suppress detection, depending on their distance from the target and the global configuration. Here we report that at close distances collinear (but not orthogonal) flanking contours suppress detection more under binocular compared to monocular viewing, thus completely abolishing the binocular advantage, both at threshold and suprathreshold levels. In contrast, more distant flankers facilitate both monocular and binocular detection, preserving a binocular advantage up to about four times the detection threshold. Our results for monocular and binocular viewing, for threshold contrast discrimination without nearby flankers, can be explained by a gain control model with uncertainty and internal multiplicative noise adding additional constraints on detection. However, in context with nearby flankers, both contrast detection threshold and suprathreshold contrast appearance matching require the addition of both target-to-target and flank-to-target interactions occurring before the site of binocular combination. To test an alternative model, in which the interactions occur after the site of binocular combination, we performed a dichoptic contrast matching experiment, with the target presented to one eye, and the flanks to the other eye. The two models make very different predictions for abutting flanks under dichoptic conditions. Interactions after the combination site predict that the perceived contrast of the flanked target will be strongly suppressed, while interactions before the site predict the perceived contrast will be more or less veridical. The data are consistent with the latter model, strongly suggesting that the interactions take place before the site of binocular combination.