Bimodal Condition Research Articles

The dissociating effects of fear and disgust on multisensory integration in autism: evidence from evoked potentials.

Deficits in Multisensory Integration (MSI) in ASD have been reported repeatedly and have been suggested to be caused by altered long-range connectivity. Here we investigate behavioral and ERP correlates of MSI in ASD using ecologically valid videos of emotional expressions. In the present study, we set out to investigate the electrophysiological correlates of audiovisual MSI in young autistic and neurotypical adolescents. We employed dynamic stimuli of high ecological validity (500 ms clips produced by actors) that depicted fear or disgust in unimodal (visual and auditory), and bimodal (audiovisual) conditions. We report robust MSI effects at both the behavioral and electrophysiological levels and pronounced differences between autistic and neurotypical participants. Specifically, neurotypical controls showed robust behavioral MSI for both emotions as seen through a significant speed-up of bimodal response time (RT), confirmed by Miller's Race Model Inequality (RMI), with greater MSI effects for fear than disgust. Adolescents with ASD, by contrast, showed behavioral MSI only for fear. At the electrophysiological level, the bimodal condition as compared to the unimodal conditions reduced the amplitudes of the visual P100 and auditory P200 and increased the amplitude of the visual N170 regardless of group. Furthermore, a cluster-based analysis across all electrodes revealed that adolescents with ASD showed an overall delayed and spatially constrained MSI effect compared to controls. Given that the variables we measured reflect attention, our findings suggest that MSI can be modulated by the differential effects on attention that fear and disgust produce. We also argue that the MSI deficits seen in autistic individuals can be compensated for at later processing stages by (a) the attention-orienting effects of fear, at the behavioral level, and (b) at the electrophysiological level via increased attentional effort.

Localization of Low- and High-Frequency Sounds in Cochlear Implant Recipients Using a Contralateral Hearing Aid.

The ability to localize sounds is partly recovered in patients using a cochlear implant (CI) in one ear and a hearing aid (HA) on the contralateral side. Binaural processing seems effective at least to some extent, despite the difference between electric and acoustic stimulation in each ear. To obtain further insights into the mechanisms of binaural hearing in these listeners, localization of low- and high-frequency sounds was tested. The study used a within-subject design, where participants were tasked with localizing sound sources in the horizontal plane. The experiment was conducted in an anechoic chamber, where an array of seven loudspeakers was mounted along the 24 azimuthal angle span from -90° to +90°. Stimuli were applied with different frequencies: broadband noise and high- and low-frequency noise. Ten CI recipients participated in the study. All had an asymmetric hearing loss with a CI in the poorer ear and an HA on the contralateral side. Accuracy of sound localization in terms of angular error and percentage of correct localization scores. The median angular error was 40° in bimodal conditions for both broadband noise and high-frequency noise stimuli. The angular error increased to 47° for low-frequency noise stimuli. In the unilaterally aided condition with an HA, only a median angular error of 78° was observed. Irrespective of the frequency composition of the stimuli, this group of bimodal listeners showed some ability to localize sounds. Angular errors were larger than those reported in the literature for bilateral CI users or single-sided deaf listeners with a CI. In the unilateral listening condition with HA, only localization of sounds was not possible for most subjects.

Unconscious multisensory integration: behavioral and neural evidence from subliminal stimuli.

The prevailing theories of consciousness consider the integration of different sensory stimuli as a key component for this phenomenon to rise on the brain level. Despite many theories and models have been proposed for multisensory integration between supraliminal stimuli (e.g., the optimal integration model), we do not know if multisensory integration occurs also for subliminal stimuli and what psychophysical mechanisms it follows. To investigate this, subjects were exposed to visual (Virtual Reality) and/or haptic stimuli (Electro-Cutaneous Stimulation) above or below their perceptual threshold. They had to discriminate, in a two-Alternative Forced Choice Task, the intensity of unimodal and/or bimodal stimuli. They were then asked to discriminate the sensory modality while recording their EEG responses. We found evidence of multisensory integration for supraliminal condition, following the classical optimal model. Importantly, even for subliminal trials participant's performances in the bimodal condition were significantly more accurate when discriminating the intensity of the stimulation. Moreover, significant differences emerged between unimodal and bimodal activity templates in parieto-temporal areas known for their integrative role. These converging evidences - even if preliminary and needing confirmation from the collection of further data - suggest that subliminal multimodal stimuli can be integrated, thus filling a meaningful gap in the debate about the relationship between consciousness and multisensory integration.

Online Processing Shows Advantages of Bimodal Listening‐While‐Reading for Vocabulary Learning: An Eye‐Tracking Study

AbstractChildren can learn words incidentally from stories. This kind of learning is enhanced when stories are presented both aurally and in written format, compared to just a written presentation. However, we do not know why this bimodal presentation is beneficial. This study explores two possible explanations: whether the bimodal advantage manifests online during story exposure, or later, at word retrieval. We collected eye‐movement data from 34 8‐to 9‐year‐old children exposed to two stories, one presented in written format (reading condition), and the second presented aurally and written at the same time (bimodal condition). Each story included six unfamiliar words (non‐words) that were repeated three times, as well as definitions and clues to their meaning. Following exposure, the learning of the new words' meanings was assessed. Results showed that, during story presentation, children spent less time fixating the new words in the bimodal condition, compared to the reading condition, indicating that the bimodal advantage occurs online. Learning was greater in the bimodal condition than the reading condition, which may reflect either an online bimodal advantage during story presentation or an advantage at retrieval. The results also suggest that the bimodal condition was more conducive to learning than the reading condition when children looked at the new words for a shorter amount of time. This is in line with an online advantage of the bimodal condition, as it suggests that less effort is required to learn words in this condition. These results support educational strategies that routinely present new vocabulary in two modalities simultaneously.

Contralateral hearing aid use in adult cochlear implant recipients: retrospective analysis of auditory outcomes

Objective To investigate retrospectively the frequency of usage of bimodal stimulation among cochlear implant (CI) users, as well its clinical benefit relative to unilateral use. Design All subjects had been monitored with the clinical Minimal Outcome Measurements test battery. Study samples 103 adults with bilateral postlingual profound sensorineural hearing loss and unilateral CI use were extracted from the local database. These were divided into two groups: those who only used a CI and those who used bimodal stimulation. Results The preoperative contralateral residual hearing in the bimodal group was significantly better than that of the CI-only group. In both groups, speech perception in quiet and in noise improved after CI, with no significant difference between postoperative unimodal conditions. For the bimodal group, an additional significant improvement was found for the bimodal condition compared to the unimodal. Conclusion Given the observed auditory benefit of bimodal stimulation in comparison to unimodal stimulation and given the finding that degree of residual hearing is not correlated with bimodal benefits, it is recommended to encourage CI recipients to continue contralateral HA use after CI. As a result of expanding CI criteria worldwide, the population of bimodal users is expected to grow in the near future.

Distributional learning of musical pitch despite tone deafness in individuals with congenital amusia

Congenital amusia is an innate and lifelong deficit of music processing. This study investigated whether adult listeners with amusia were still able to learn pitch-related musical chords based on stimulus frequency of statistical distribution, i.e., via distributional learning. Following a pretest-training-posttest design, 18 amusics and 19 typical, musically intact listeners were assigned to bimodal and unimodal conditions that differed in distribution of the stimuli. Participants' task was to discriminate chord minimal pairs, which were transposed to a novel microtonal scale. Accuracy rates for each test session were collected and compared between the two groups using generalized mixed-effects models. Results showed that amusics were less accurate than typical listeners at all comparisons, thus corroborating previous findings. Importantly, amusics-like typical listeners-demonstrated perceptual gains from pretest to posttest in the bimodal condition (but not the unimodal condition). The findings reveal that amusics' distributional learning of music remains largely preserved despite their deficient music processing. Implications of the results for statistical learning and intervention programs to mitigate amusia are discussed.

An entropy-based method to measure phase-locking between LFP and spikes

Phase-locking between local field potential and spikes has been widely investigated through neurophysiological analysis. Two indices most frequently adopted traditionally include the mean resultant length and p of the Rayleigh test. However, the traditional method is found less reliable for cases with substantial sample sizes or with bimodal distribution. In this article, K we propose an entropy-based method to detect and measure phase-locking. Simulation results prove that the method can be effectively applied to cases with a relatively large sample size and it can effectively detect phase-locking even under bimodal conditions with two peaks of opposite phases. Furthermore, we propose thresholds to help measure the intensity of spike field phase-locking. We also apply the proposed method to our experimental data and find phase locking with two opposite phases, which would be left out in traditional phase-locking analysis.

Late integration of vision and proprioception during perturbed reaches.

The motor system corrects rapidly, but selectively, for perturbations to ongoing reaching movements, depending on the constraints of the task. To account for such sophistication, it has been postulated that corrections are based on an estimated limb state that integrates all sensory changes caused by the perturbation, taking into account their processing delays. Here, we asked if information from different sensory modalities is integrated immediately or processed separately in the early phase of a response. We perturbed the estimated state of the limb with both unimodal and bimodal visual and proprioceptive perturbations without changing the actual limb state. For visual perturbations, a cursor representing the hand was shifted to the left or the right relative to the true hand location. For proprioceptive perturbations, the biceps or triceps muscles were vibrated, which induced illusory limb-state changes to the right or the left. In the bimodal condition, the perturbations to vision and proprioception were either congruent or incongruent in their directions. Response latencies show that it takes ∼100 ms longer to respond to unimodal visual perturbations than to unimodal proprioceptive perturbations. Responses to bimodal perturbations show that it takes an additional ∼100 ms beyond the response to unimodal visual perturbations for intermodal consistency to impact the response. These results suggest that visual and proprioceptive signals are initially processed separately for state estimation and only combined at the level of the limb's motor output, instead of being immediately integrated into a single state estimate of the limb.NEW & NOTEWORTHY Both visual and proprioceptive signals provide information about arm state during reaching. By perturbing the perceived, but not the actual, position of the hand in both modalities using visual disturbances and muscle vibration, we examined multimodal integration and state estimation during reaching. Our results suggest that the early reach corrections are based on separate state estimates from the two sensory modalities and only later are based on a combined state estimate.

Integration of fundamental frequency and voice-onset-time to voicing categorization: Listeners with normal hearing and bimodal hearing configurations.

This study investigates the integration of word-initial fundamental frequency (F0) and voice-onset-time (VOT) in stop voicing categorization for adult listeners with normal hearing (NH) and unilateral cochlear implant (CI) recipients utilizing a bimodal hearing configuration [CI + contralateral hearing aid (HA)]. Categorization was assessed for ten adults with NH and ten adult bimodal listeners, using synthesized consonant stimuli interpolating between /ba/ and /pa/ exemplars with five-step VOT and F0 conditions. All participants demonstrated the expected categorization pattern by reporting /ba/ for shorter VOTs and /pa/ for longer VOTs, with NH listeners showing more use of VOT as a voicing cue than CI listeners in general. When VOT becomes ambiguous between voiced and voiceless stops, NH users make more use of F0 as a cue to voicing than CI listeners, and CI listeners showed greater utilization of initial F0 during voicing identification in their bimodal (CI + HA) condition than in the CI-alone condition. The results demonstrate the adjunctive benefit of acoustic hearing from the non-implanted ear for listening conditions involving spectrotemporally complex stimuli. This finding may lead to the development of a clinically feasible perceptual weighting task that could inform clinicians about bimodal efficacy and the risk-benefit profile associated with bilateral CI recommendation.

Multisensory-driven facilitation within the peripersonal space is modulated by the expectations about stimulus location on the body

Compelling evidence from human and non-human studies suggests that responses to multisensory events are fastened when stimuli occur within the space surrounding the bodily self (i.e., peripersonal space; PPS). However, some human studies did not find such effect. We propose that these dissonant voices might actually uncover a specific mechanism, modulating PPS boundaries according to sensory regularities. We exploited a visuo-tactile paradigm, wherein participants provided speeded responses to tactile stimuli and rated their perceived intensity while ignoring simultaneous visual stimuli, appearing near the stimulated hand (VTNear) or far from it (VTFar; near the non-stimulated hand). Tactile stimuli could be delivered only to one hand (unilateral task) or to both hands randomly (bilateral task). Results revealed that a space-dependent multisensory enhancement (i.e., faster responses and higher perceived intensity in VTNear than VTFar) was present when highly predictable tactile stimulation induced PPS to be circumscribed around the stimulated hand (unilateral task). Conversely, when stimulus location was unpredictable (bilateral task), participants showed a comparable multisensory enhancement in both bimodal conditions, suggesting a PPS widening to include both hands. We propose that the detection of environmental regularities actively shapes PPS boundaries, thus optimizing the detection and reaction to incoming sensory stimuli.

Influence of Tactile Flow on Visual Heading Perception.

The integration of information from different sensory modalities is crucial for successful navigation through an environment. Among others, self-motion induces distinct optic flow patterns on the retina, vestibular signals and tactile flow, which contribute to determine traveled distance (path integration) or movement direction (heading). While the processing of combined visual-vestibular information is subject to a growing body of literature, the processing of visuo-tactile signals in the context of self-motion has received comparatively little attention. Here, we investigated whether visual heading perception is influenced by behaviorally irrelevant tactile flow. In the visual modality, we simulated an observer's self-motion across a horizontal ground plane (optic flow). Tactile self-motion stimuli were delivered by air flow from head-mounted nozzles (tactile flow). In blocks of trials, we presented only visual or tactile stimuli and subjects had to report their perceived heading. In another block of trials, tactile and visual stimuli were presented simultaneously, with the tactile flow within ±40° of the visual heading (bimodal condition). Here, importantly, participants had to report their perceived visual heading. Perceived self-motion direction in all conditions revealed a centripetal bias, i.e., heading directions were perceived as compressed toward straight ahead. In the bimodal condition, we found a small but systematic influence of task-irrelevant tactile flow on visually perceived headings as function of their directional offset. We conclude that tactile flow is more tightly linked to self-motion perception than previously thought.

Modality-specific and modality-general electrophysiological correlates of visual and auditory awareness: Evidence from a bimodal ERP experiment

To date, most studies on the event-related potential (ERP) correlates of conscious perception have examined a single perceptual modality. We compared electrophysiological correlates of visual and auditory awareness in the same experiment to test whether there are modality-specific and modality-general correlates of conscious perception. We used near threshold stimulation and analyzed event-related potentials in response to aware and unaware trials in visual, auditory and bimodal conditions. The results showed modality-specific negative amplitude correlates of conscious perception between 200 and 300 ms after stimulus onset. A combination of these auditory and visual awareness negativities was observed in the bimodal condition. A later positive amplitude difference, whose early part was modality-specific, possibly reflecting access to global workspace, and later part shared modality-general features, possibly indicating higher level cognitive processing involving the decision making, was also observed.

Changes in rainfall seasonality inferred from weathering and pedogenic trends in mid-Miocene paleosols of La Tatacoa, Colombia

The authigenic clay mineral assemblage of paleosol profiles and trends in their bulk geochemical evolution provide insight into the intensity of past chemical weathering regimes. These climate-sensitive weathering products can be used to interpret regional changes of the soil moisture regime, which in turn reflects upon the nature of rainfall seasonality (e.g., unimodal vs. bimodal). A conspicuous color change in the overbank deposits and paleosols of the mid-Miocene Honda Group of La Tatacoa, Colombia, is suggestive of a climatic transition which affected the fauna of La Venta - a mid-Miocene fossiliferous site and significant component of the South American Land Mammal Age (SALMA) classification. This study aims to determine how the paleopedology of this region records the climatic transition that modified the annual patterns of rainfall and soil moisture, forcing a change from the gray-colored paleosols hosted by the La Victoria Formation (~13.6 to ~13.1 Myr) to the red-beds of the Villavieja Formation (~13.1 to 12.0 Myr). In the La Victoria profile, the pedogenic fraction of the clay assemblage indicates that vermiculite, chlorite/HIV mixed-layered clays and high concentrations of base cations (Ca2+, Mg2+, Na+) developed in a poorly drained paleosol under reducing (low Eh) and above-neutral pH conditions. By contrast, the presence of kaolinite, goethite and hematite in the red-beds paleosols implies more oxidizing conditions (high Eh), whereas pedogenic vermiculite and smectite suggest a pH close to or mildly below neutral. A common detrital source (parent material) is inferred for both sets of paleosols. However, more intense chemical weathering towards aluminium rich clay in the Villavieja red-bed fossil soils indicates a change in soil humidity from a poorly drained soil environment of a seasonally flooded wetland system to an alternating regime of humidity and drought on a better drained floodplain. The variation in soil moisture is consistent with a change in seasonality from a unimodal rainfall regime in the case of the La Victoria paleosols to bimodal conditions in the case of the paleosols of the Villavieja Fm. After the establishment of a fully glaciated Antarctica and the global climate transition into the Mi-4 glacial stage at ~13.1 Ma, an increased rate of continental weathering along the paleotropical fringe could have been caused by a stronger temperature gradient between the equator and South Pole, shifting the Intertropical Convergence Zone northward and the rainfall patterns with it.

Differences in adults' spatial scaling based on visual or haptic information.

The present study examined differences in adults’ spatial-scaling abilities across three perceptual conditions: (1) visual, (2) haptic, and (3) visual and haptic. Participants were instructed to encode the position of a convex target presented in a simple map without a time limit. Immediately after encoding the map, participants were presented with a referent space and asked to place a disc at the same location from memory. All spaces were designed as tactile graphics. Positions of targets varied along the horizontal dimension. The referent space was constant in size while sizes of maps were systematically varied, resulting in three scaling factor conditions: 1:4, 1:2, 1:1. Sixty adults participated in the study (M = 21.18; SD = 1.05). One-third of them was blindfolded throughout the entire experiment (haptic condition). The second group of participants was allowed to see the graphics (visual condition); the third group were instructed to see and touch the graphics (bimodal condition). An analysis of participants’ absolute errors showed that participants produced larger errors in the haptic condition as opposed to the visual and bimodal conditions. There was also a significant interaction effect between scaling factor and perceptual condition. In the visual and bimodal conditions, results showed a linear increase in errors with higher scaling factors (which may suggest that adults adopted mental transformation strategies during the spatial scaling process), whereas, in the haptic condition, this relation was quadratic. Findings imply that adults’ spatial-scaling performance decreases when visual information is not available.

Effects of unintentional coordination on attentional load.

The goal of this study was to evaluate the impact of unintentional (spontaneous) coordination on high attentional visual load. More precisely, we wondered whether such coordination could free up some attentional resources and help improve performance in other more demanding attentional tasks. An experiment was performed in which participant attentional allocation was challenged by performing three tasks simultaneously while simultaneously being induced to unintentional entrain to an environmental rhythm. The first task was an interception task associated with a Stroop test to increase their attentional load. The second task was a reaction time test to alarms in different modalities (auditory, visual and bimodal) which was used to assess participant attentional load. The third task was a motor task in which participants were asked to swing their legs at a preferred frequency. The interface background brightness intensity was either synchronized in real time using a bidirectional coupling to participant leg movement or the background brightness was not changing at all. Our results on the reaction time task demonstrated that participants exhibited better reaction times for alarms in the bimodal condition than in the auditory condition and lastly for the visual condition. Also, participants exhibited a lower reaction time to alarms when the background brightness was synchronizing with their leg regardless the alarm modality. Overall, our study suggests a beneficial effect of unintentional environmental coordination on attentional resource allocation and highlights the importance of bidirectionality in interaction.

Perceptual weighting of acoustic cues for word stress in normal hearing listeners and cochlear implant users

Accurate perception of word stress is key to segmenting and understanding speech. We examined perception of four acoustic cues to word stress in English—vowel quality (VQ), pitch, syllable duration, and intensity—and how perception of these cues is affected by specific kinds of signal degradation. Cochlear implants (CIs) severely degrade VQ and pitch, which could demand different relative reliance on these cues. We tested NH listeners in unprocessed, vocoded, and simulated bimodal (unprocessed low frequencies, vocoded high frequencies) conditions as well as CI users. Stimuli included stress-contrastive word pairs (DESert versus dessERT, SUBject versus subJECT) with orthogonal manipulations of each cue. For both NH and CI listeners, there were strikingly different patterns of cue weighting between these word pairs, highlighting how stress cue weighting is flexible across words rather than being absolute. Vocoding the stimuli led to a downweighting of VQ and pitch cues and a compensatory upweighting of duration and intensity; perception of pitch and VQ were largely restored in the bimodal conditions with 250 and 800 Hz bands preserved, respectively. CI users relied on duration more than the NH controls in any condition, while also showing a surprising ability to use VQ and pitch cues.

Seeming confines: Electrophysiological evidence of peripersonal space remapping following tool-use in humans

The peripersonal space (PPS) is a special portion of space immediately surrounding the body, where the integration between tactile stimuli delivered on the body and auditory or visual events emanating from the environment occurs. Interestingly, PPS can widen if a tool is employed to interact with objects in the far space. However, electrophysiological evidence of such tool-use dependent plasticity in the human brain is scarce. Here, in a series of three experiments, participants were asked to respond to tactile stimuli, delivered to their right hand, either in isolation (unimodal condition) or combined with auditory stimulation, which could occur near (bimodal-near) or far from the stimulated hand (bimodal-far). According to multisensory integration spatial rule, when bimodal stimuli are presented at the same location, we expected a response enhancement (response time – RT – facilitation and event-related potential – ERP – super-additivity). In Experiment 1, we verified that RT facilitation was driven by bimodal input spatial congruency, independently from auditory stimulus intensity. In Experiment 2, we showed that our bimodal task was effective in eliciting the magnification of ERPs in bimodal conditions, with significantly larger responses in the near as compared to far condition. In Experiment 3 (main experiment), we explored tool-use driven PPS plasticity. Our audio-tactile task was performed either following tool-use (a 20-min reaching task, performed using a 145 cm-long rake) or after a control cognitive training (a 20-min visual discrimination task) performed in the far space. Following the control training, faster RTs and greater super-additive ERPs were found in bimodal-near as compared to bimodal-far condition (replicating Experiment 2 results). Crucially, this far-near differential response was significantly reduced after tool-use. Altogether our results indicate a selective effect of tool-use remapping in extending the boundaries of PPS. The present finding might be considered as an electrophysiological evidence of tool-use dependent plasticity in the human brain.

Cochlear Implant Performance in Candidates With Moderate Hearing Loss Qualifying in Noise.

To determine postcochlear implantation performance for patients qualifying on preimplant testing in noise. Retrospective chart review of cochlear implant recipients. Performance on word and sentence testing in the implanted ear and bimodal condition were compared between pre- and postimplantation time points. At 2-years postimplantation, CNC testing in quiet in the implanted ear improved from an average percent correct score of 14.0 ± 12.1% to 54.9 ± 14.8% (n = 20, p < 0.0001, d = 3.0) for those qualifying at +8, and from 23.4 ± 15.6% to 55.5 ± 19.4% (n = 28, p < 0.0001, d = 1.8) for those qualifying at +5. Likewise, AzBio in quiet in the implanted ear improved from an average % correct score of 19.9 ± 16.0% to 75.1 ± 11.8% (n = 20, p < 0.0001, d = 4.0) for those qualifying at +8, and from 46.2 ± 21.7% to 74.1 ± 21.3% (n = 27, p < 0.0001, d = 1.4) for those qualifying at +5. CNC and AzBio performance in quiet in the bimodal condition also improved with those qualifying at +8 and +5 having similar average scores at 2-years post activation. For those qualifying at +8, performance improved on CNC and AzBio in the implanted ear in 95% of patients and in the bimodal condition in 89% of patients. The proportion of patients improving on both tests for those qualifying at +5 at 2 years was 85% in the implanted ear, and 72% in the bimodal condition. The majority of patients qualifying for cochlear implantation with the addition of noise showed improved speech perception in quiet. These data provide useful counseling tools for patients considering cochlear implantation who do not meet traditional eligibility requirements when tested in quiet.

Encoding of vestibular and optic flow cues to self-motion in the posterior superior temporal polysensory area.

Neurons in the posterior superior temporal polysensory area (STPp) showed significant directional selectivity in response to vestibular, optic flow and combined visual-vestibular stimuli. By comparison to the dorsal medial superior temporal area, the visual latency was slower in STPp but the vestibular latency was faster. Heading preferences under combined stimulation in STPp were usually dominated by visual signals. Cross-modal enhancement was observed in STPp when both vestibular and visual cues were presented together at their heading preferences. Human neuroimaging data implicated that the superior temporal polysensory area (STP) might be involved in vestibular-visual interaction during heading computations, but the heading selectivity has not been examined in the macaque. Here, we investigated the convergence of optic flow and vestibular signals in macaque STP by using a virtual-reality system and found that 6.3% of STP neurons showed multisensory responses, with visual and vestibular direction preferences either congruent or opposite in roughly equal proportion. The percentage of vestibular-tuned cells (18.3%) was much smaller than that of visual-tuned cells (30.4%) in STP. The vestibular tuning strength was usually weaker than the visual condition. The visual latency was significantly slower in STPp than in the dorsal medial superior temporal area (MSTd), but the vestibular latency was significantly faster than in MSTd. During the bimodal condition, STP cells' response was dominated by visual signals, with the visual heading preference not affected by the vestibular signals but the response amplitudes modulated by vestibular signals in a subadditive way.

Modeling Crossing Random Seas by Fully Non-Linear Numerical Simulations

Bimodal spectrum wave conditions, known as crossing seas, can produce extreme waves which are hostile to humans during oceanic activities. This study reports some new findings of the probability of extreme waves in deep crossing random seas in response to the variation of spectral bandwidth through fully non-linear numerical simulations. Two issues are addressed, namely (i) the impacts of the spectral bandwidth on the changes of extreme wave statistics, i.e., the kurtosis and crest exceedance probability, and (ii) the suitability of theoretical distribution models for accurately describing the wave crest height exceedance probability in crossing seas. The numerical results obtained by simulating a large number of crossing sea conditions on large spatial-temporal scale with a variety of spectral bandwidth indicate that the kurtosis and crest height exceedance probability will be enhanced when the bandwidth of each wave train becomes narrower, suggesting a higher probability of encountering extreme waves in narrowband crossing seas. Meanwhile, a novel empirical formula is suggested to predict the kurtosis in crossing seas provided the bandwidth is known in advance. In addition, the Rayleigh and second-order Tayfun distribution underestimate the crest height exceedance probability, while the third-order Tayfun distribution only yields satisfactory predictions for cases with relatively broader bandwidth regarding the wave conditions considered in this study. For crossing seas with narrower bandwidth, all the theoretical distribution models failed to accurately describe the crest height exceedance probability of extreme waves.