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Atypical processing and integration of sensory inputs are hypothesized to play a role in unusual sensory reactions and social-cognitive deficits in autism spectrum disorder (ASD). Reports on the relationship between objective metrics of sensory processing and clinical symptoms, however, are surprisingly sparse. Here we examined the relationship between neurophysiological assays of sensory processing and (1) autism severity and (2) sensory sensitivities, in individuals with ASD aged 6-17. Multiple linear regression indicated significant associations between neural markers of auditory processing and multisensory integration, and autism severity. No such relationships were apparent for clinical measures of visual/auditory sensitivities. These data support that aberrant early sensory processing contributes to autism symptoms, and reveal the potential of electrophysiology to objectively subtype autism. [ABSTRACT FROM AUTHOR]

We assessed the role of alpha-band oscillatory activity during a task-switching design that required participants to switch between an auditory and a visual task, while task-relevant audiovisual inputs were simultaneously presented. Instructional cues informed participants which task to perform on a given trial and we assessed alpha-band power in the short 1.35-s period intervening between the cue and the task-imperative stimuli, on the premise that attentional biasing mechanisms would be deployed to resolve competition between the auditory and visual inputs. Prior work had shown that alpha-band activity was differentially deployed depending on the modality of the cued task. Here, we asked whether this activity would, in turn, be differentially deployed depending on whether participants had just made a switch of task or were being asked to simply repeat the task. It is well established that performance speed and accuracy are poorer on switch than on repeat trials. Here, however, the use of instructional cues completely mitigated these classic switch-costs. Measures of alpha-band synchronisation and desynchronisation showed that there was indeed greater and earlier differential deployment of alpha-band activity on switch vs. repeat trials. Contrary to our hypothesis, this differential effect was entirely due to changes in the amount of desynchronisation observed during switch and repeat trials of the visual task, with more desynchronisation over both posterior and frontal scalp regions during switch-visual trials. These data imply that particularly vigorous, and essentially fully effective, anticipatory biasing mechanisms resolved the competition between competing auditory and visual inputs when a rapid switch of task was required. [ABSTRACT FROM AUTHOR]

The frequency of environmental vibrations is sampled by two of the major sensory systems, audition and touch, notwithstanding that these signals are transduced through very different physical media and entirely separate sensory epithelia. Psychophysical studies have shown that manipulating frequency in audition or touch can have a significant cross-sensory impact on perceived frequency in the other sensory system, pointing to intimate links between these senses during computation of frequency. In this regard, the frequency of a vibratory event can be thought of as a multisensory perceptual construct. In turn, electrophysiological studies point to temporally early multisensory interactions that occur in hierarchically early sensory regions where convergent inputs from the auditory and somatosensory systems are to be found. A key question pertains to the level of processing at which the multisensory integration of featural information, such as frequency, occurs. Do the sensory systems calculate frequency independently before this information is combined, or is this feature calculated in an integrated fashion during preattentive sensory processing? The well characterized mismatch negativity, an electrophysiological response that indexes preattentive detection of a change within the context of a regular pattern of stimulation, served as our dependent measure. High-density electrophysiological recordings were made in humans while they were presented with separate blocks of somatosensory, auditory, and audio-somatosensory “standards” and “deviants,” where the deviant differed in frequency. Multisensory effects were identified beginning at ∼200 ms, with the multisensory mismatch negativity (MMN) significantly different from the sum of the unisensory MMNs. This provides compelling evidence for preattentive coupling between the somatosensory and auditory channels in the cortical representation of frequency [ABSTRACT FROM AUTHOR]

It is well established that sounds can enhance visual-target detection, but the mechanisms that govern these cross-sensory effects, as well as the neural pathways involved, are largely unknown. Here, we tested behavioral predictions stemming from the neurophysiologic and neuroanatomic literature. Participants detected near-threshold visual targets presented either at central fixation or peripheral to central fixation that were sometimes paired with sounds that originated from widely misaligned locations (up to 104° from the visual target). Our results demonstrate that co-occurring sounds improve the likelihood of visual-target detection (1) regardless of retinal eccentricity and (2) despite wide audiovisual misalignments. With regard to the first point, these findings suggest that auditory facilitation of visual-target detection is unlikely to operate through previously described corticocortical pathways from auditory cortex that predominantly terminate in regions of visual cortex that process peripheral visual space. With regard to the second point, auditory facilitation of visual-target detection seems to operate through a spatially non-specific modulation of visual processing. [ABSTRACT FROM AUTHOR]

The human auditory system has evolved to efficiently process individual streams of speech. However, obtaining temporally detailed responses to distinct continuous natural speech streams has hitherto been impracticable using standard neurophysiological techniques. Here a method is described which provides for the estimation of a temporally precise electrophysiological response to uninterrupted natural speech. We have termed this response AESPA (Auditory Evoked Spread Spectrum Analysis) and it represents an estimate of the impulse response of the auditory system. It is obtained by assuming that the recorded electrophysiological function represents a convolution of the amplitude envelope of a continuous speech stream with the to-be-estimated impulse response. We present examples of these responses using both scalp and intracranially recorded human EEG, which were obtained while subjects listened to a binaurally presented recording of a male speaker reading naturally from a classic work of fiction. This method expands the arsenal of stimulation types that can now be effectively used to derive auditory evoked responses and allows for the use of considerably more ecologically valid stimulation parameters. Some implications for future research efforts are presented. [ABSTRACT FROM AUTHOR]

This study used high-density mapping of human event-related potentials to examine the brain activity associated with selective information processing when subjects were cued on a trial-by-trial basis to perform a discrimination in either the visual or auditory modality. On each trial, word-cues (S1) instructed subjects to attend to features within one sensory-modality of an impending compound auditory-visual stimulus (S2) that arrived approximately 1-second following the cue. Subjects made a discrimination within the cued modality of the S2 stimulus. The spatio-temporal patterns of activity in response to the compound S2 stimulus were examined as a function of the sensory modality being attended. The earliest effects of intersensory attention on visual processing were seen subsequent to the initial activation of visual cortex, beginning at 80 ms and continuing into the P1 and N1 components of the visual ERP. The scalp-topography of this earliest modulation was consistent with modulation of activity in ventral visual stream areas. Thus, the locus of effects on visual S2 processing differed from the anticipatory parieto-occipital biasing activity that preceded S2 presentation. This pattern of effects strongly suggests that the anticipatory activity (following the cue) associated with sustaining the focus of attention during intersensory attention, at least in the context of this paradigm, does not operate as a simple gain mechanism in early visual sensory areas. Rather, attentional biasing can operate through a higher-order process whereby parieto-occipital cortices influence the subsequent flow of visual processing in the ventral stream. [ABSTRACT FROM AUTHOR]

Abstract: Multisensory experiences enhance perceptions and facilitate memory retrieval processes, even when only unisensory information is available for accessing such memories. Using fMRI, we identified human brain regions involved in discriminating visual stimuli according to past multisensory vs. unisensory experiences. Subjects performed a completely orthogonal task, discriminating repeated from initial image presentations intermixed within a continuous recognition task. Half of initial presentations were multisensory, and all repetitions were exclusively visual. Despite only single-trial exposures to initial image presentations, accuracy in indicating image repetitions was significantly improved by past auditory–visual multisensory experiences over images only encountered visually. Similarly, regions within the lateral–occipital complex–areas typically associated with visual object recognition processes–were more active to visual stimuli with multisensory than unisensory pasts. Additional differential responses were observed in the anterior cingulate and frontal cortices. Multisensory experiences are registered by the brain even when of no immediate behavioral relevance and can be used to categorize memories. These data reveal the functional efficacy of multisensory processing. [Copyright &y& Elsevier]

• We provide a publicly available spoken word stimulus set designed to evoke the N400. • Both semantic and syntactic errors can be assayed using this public stimulus set. • We provide 20 high-density neurotypical adult electrophysiological datasets. • The utility of these stimuli is demonstrated through robust evocation of the N400. • Cloze probability values for each stimulus are provided. During speech comprehension, the ongoing context of a sentence is used to predict sentence outcome by limiting subsequent word likelihood. Neurophysiologically, violations of context-dependent predictions result in amplitude modulations of the N400 event-related potential (ERP) component. While the N400 is widely used to measure semantic processing and integration, no publicly-available auditory stimulus set is available to standardize approaches across the field. Here, we developed an auditory stimulus set of 442 sentences that utilized the semantic anomaly paradigm, measured cloze probability for all stimuli, and was made for both children and adults. With 20 neurotypical adults, we validated that this set elicits robust N400′s, as well as two additional semantically-related ERP components: the recognition potential (∼ 250 ms) and the late positivity component (∼ 600 ms). This stimulus set (https://doi.org/10.5061/dryad.9ghx3ffkg) and the 20 high-density (128-channel) electrophysiological datasets (https://doi.org/10.5061/dryad.6wwpzgmx4) are made publicly available to promote data sharing and reuse. Future studies that use this stimulus set to investigate sentential semantic comprehension in both control and clinical populations may benefit from the increased comparability and reproducibility within this field of research. [ABSTRACT FROM AUTHOR]

Categorical perception ( CP) is highly evident in audition when listeners' perception of speech sounds abruptly shifts identity despite equidistant changes in stimulus acoustics. While CP is an inherent property of speech perception, how (if) it is expressed in other auditory modalities (e.g., music) is less clear. Moreover, prior neuroimaging studies have been equivocal on whether attentional engagement is necessary for the brain to categorically organize sound. To address these questions, we recorded neuroelectric brain responses [event-related potentials ( ERPs)] from listeners as they rapidly categorized sounds along a speech and music continuum (active task) or during passive listening. Behaviorally, listeners' achieved sharper psychometric functions and faster identification for speech than musical stimuli, which was perceived in a continuous mode. Behavioral results coincided with stronger ERP differentiation between prototypical and ambiguous tokens (i.e., categorical processing) for speech but not for music. Neural correlates of CP were only observed when listeners actively attended to the auditory signal. These findings were corroborated by brain-behavior associations; changes in neural activity predicted more successful CP (psychometric slopes) for active but not passively evoked ERPs. Our results demonstrate auditory categorization is influenced by attention (active > passive) and is stronger for more familiar/overlearned stimulus domains (speech > music). In contrast to previous studies examining highly trained listeners (i.e., musicians), we infer that (i) CP skills are largely domain-specific and do not generalize to stimuli for which a listener has no immediate experience and (ii) categorical neural processing requires active engagement with the auditory stimulus. [ABSTRACT FROM AUTHOR]

There is growing interest in characterizing the neural basis of music perception and, in particular, assessing how similar, or not, it is to that of speech. To further explore this question, we employed an EEG adaptation paradigm in which we compared responses to short sounds belonging to the same category, either speech (pseudo-sentences) or music (piano or violin), depending on whether they were immediately preceded by a same- or different-category sound. We observed a larger reduction in the N100 component magnitude in response to musical sounds when they were preceded by music (either the same or different instrument) than by speech. In contrast, the N100 amplitude was not affected by the preceding stimulus category in the case of speech. For P200 component, we observed a diminution of amplitude when speech sounds were preceded speech, compared to music. No such decrease was found when we compared the responses to music sounds. These differences in the processing of speech and music are consistent with the proposal that some degree of category selectivity for these two classes of complex stimuli already occurs at early stages of auditory processing, possibly subserved by partly separated neuronal populations. [ABSTRACT FROM AUTHOR]

Summary: Multisensory information can be crucial, yet in many circumstances we have little, if any, awareness of the effects of multisensory inputs on what appear to be entirely unisensory perceptions. A recent study shows robust effects of auditory input on tactile frequency discriminations and that this auditory cross-sensory interference has specific tuning. [Copyright &y& Elsevier]

The superior colliculus (SC) is richly endowed with neurons that integrate cues from different senses to enhance their physiological responses and the overt behaviors they mediate. However, in the absence of experience with cross‐modal combinations (e.g., visual–auditory), they fail to develop this characteristic multisensory capability: Their multisensory responses are no greater than their most effective unisensory responses. Presumably, this impairment in neural development would be reflected as corresponding impairments in SC‐mediated behavioral capabilities such as detection and localization performance. Here, we tested that assumption directly in cats raised to adulthood in darkness. They, along with a normally reared cohort, were trained to approach brief visual or auditory stimuli. The animals were then tested with these stimuli individually and in combination under ambient light conditions consistent with their rearing conditions and home environment as well as under the opposite lighting condition. As expected, normally reared animals detected and localized the cross‐modal combinations significantly better than their individual component stimuli. However, dark‐reared animals showed significant defects in multisensory detection and localization performance. The results indicate that a physiological impairment in single multisensory SC neurons is predictive of an impairment in overt multisensory behaviors. [ABSTRACT FROM AUTHOR]

Background: Cystinosis, a rare lysosomal storage disease, is characterized by cystine crystallization and accumulation within tissues and organs, including the kidneys and brain. Its impact on neural function appears mild relative to its effects on other organs, but therapeutic advances have led to substantially increased life expectancy, necessitating deeper understanding of its impact on neurocognitive function in adulthood. We previously demonstrated intact auditory sensory processing, accompanied by mild sensory memory difficulties, in children and adolescents with cystinosis.Methods: We investigated whether further progressive decrements in these processes would be observed in adults with cystinosis, comparing high-density auditory-evoked potential (AEP) recordings from adults with cystinosis (N = 15; ages: 19-38 years) to those of age-matched controls (N = 17). We employed a duration oddball paradigm with different stimulation rates, in which participants passively listened to regularly occurring standard tones interspersed with infrequently occurring deviant tones. Analyses focused on AEP components reflecting auditory sensory-perceptual processing (N1 and P2), sensory memory (mismatch negativity, MMN), and attentional orienting (P3a).Results: Overall, adults with cystinosis produced highly similar sensory-perceptual AEP responses to those observed in controls suggesting intact early auditory cortical processing. However, significantly increased P2 and P3a amplitudes and reduced MMN at slower stimulation rates were observed, suggesting mild-to-moderate changes in auditory sensory memory and attentional processing. While cognitive testing revealed lower scores on verbal IQ and perceptual reasoning in cystinosis, these did not correlate with the AEP measures.Conclusions: These neurophysiological data point to the emergence of subtle auditory processing deficits in early adulthood in cystinosis, warranting further investigation of memory and attentional processes in this population, and of their consequences for perceptual and cognitive function. [ABSTRACT FROM AUTHOR]

• Operating in a multisensory context inextricably linked to intersensory attention. • Task switching and mixing costs account for the redundant signals effect. Individuals respond faster to presentations of bisensory stimuli (e.g. audio-visual targets) than to presentations of either unisensory constituent in isolation (i.e. to the auditory-alone or visual-alone components of an audio-visual stimulus). This well-established multisensory speeding effect, termed the redundant signals effect (RSE), is not predicted by simple linear summation of the unisensory response time probability distributions. Rather, the speeding is typically faster than this prediction, leading researchers to ascribe the RSE to a so-called co-activation account. According to this account, multisensory neural processing occurs whereby the unisensory inputs are integrated to produce more effective sensory-motor activation. However, the typical paradigm used to test for RSE involves random sequencing of unisensory and bisensory inputs in a mixed design, raising the possibility of an alternate attention-switching account. This intermixed design requires participants to switch between sensory modalities on many task trials (e.g. from responding to a visual stimulus to an auditory stimulus). Here we show that much, if not all, of the RSE under this paradigm can be attributed to slowing of reaction times to unisensory stimuli resulting from modality switching, and is not in fact due to speeding of responses to AV stimuli. As such, the present data do not support a co-activation account, but rather suggest that switching and mixing costs akin to those observed during classic task-switching paradigms account for the observed RSE. [ABSTRACT FROM AUTHOR]

Enhanced detection and discrimination, along with faster reaction times, are the most typical behavioural manifestations of the brain's capacity to integrate multisensory signals arising from the same object. In this study, we examined whether multisensory behavioural gains are observable across different components of the localization response that are potentially under the command of distinct brain regions. We measured the ability of ferrets to localize unisensory (auditory or visual) and spatiotemporally coincident auditory-visual stimuli of different durations that were presented from one of seven locations spanning the frontal hemifield. During the localization task, we recorded the head movements made following stimulus presentation, as a metric for assessing the initial orienting response of the ferrets, as well as the subsequent choice of which target location to approach to receive a reward. Head-orienting responses to auditory-visual stimuli were more accurate and faster than those made to visual but not auditory targets, suggesting that these movements were guided principally by sound alone. In contrast, approach-to-target localization responses were more accurate and faster to spatially congruent auditory-visual stimuli throughout the frontal hemifield than to either visual or auditory stimuli alone. Race model inequality analysis of head-orienting reaction times and approach-to-target response times indicates that different processes, probability summation and neural integration, respectively, are likely to be responsible for the effects of multisensory stimulation on these two measures of localization behaviour. [ABSTRACT FROM AUTHOR]

Extracting temporal periodicities and envelope shapes of sounds is important for listening within complex auditory scenes but declines behaviorally with age. Here, we recorded local field potentials ( LFPs) and spikes to investigate how ageing affects the neural representations of different modulation rates and envelope shapes in the inferior colliculus of rats. We specifically aimed to explore the input-output ( LFP-spike) response transformations of inferior colliculus neurons. Our results show that envelope shapes up to 256-Hz modulation rates are represented in the neural synchronisation phase lags in younger and older animals. Critically, ageing was associated with (i) an enhanced gain in onset response magnitude from LFPs to spikes; (ii) an enhanced gain in neural synchronisation strength from LFPs to spikes for a low modulation rate (45 Hz); (iii) a decrease in LFP synchronisation strength for higher modulation rates (128 and 256 Hz) and (iv) changes in neural synchronisation strength to different envelope shapes. The current age-related changes are discussed in the context of an altered excitation-inhibition balance accompanying ageing. [ABSTRACT FROM AUTHOR]

Hearing loss is a hallmark sign in the elderly population. Decline in auditory perception provokes deficits in the ability to localize sound sources and reduces speech perception, particularly in noise. In addition to a loss of peripheral hearing sensitivity, changes in more complex central structures have also been demonstrated. Related to these, this study examines the auditory directional maps in the deep layers of the superior colliculus of the rat. Hence, anesthetized Sprague-Dawley adult (10 months) and aged (22 months) rats underwent distortion product of otoacoustic emissions ( DPOAEs) to assess cochlear function. Then, auditory brainstem responses ( ABRs) were assessed, followed by extracellular single-unit recordings to determine age-related effects on central auditory functions. DPOAE amplitude levels were decreased in aged rats although they were still present between 3.0 and 24.0 kHz. ABR level thresholds in aged rats were significantly elevated at an early (cochlear nucleus - wave II) stage in the auditory brainstem. In the superior colliculus, thresholds were increased and the tuning widths of the directional receptive fields were significantly wider. Moreover, no systematic directional spatial arrangement was present among the neurons of the aged rats, implying that the topographical organization of the auditory directional map was abolished. These results suggest that the deterioration of the auditory directional spatial map can, to some extent, be attributable to age-related dysfunction at more central, perceptual stages of auditory processing. [ABSTRACT FROM AUTHOR]

Natural auditory scenes possess highly structured statistical regularities, which are dictated by the physics of sound production in nature, such as scale-invariance. We recently identified that natural water sounds exhibit a particular type of scale invariance, in which the temporal modulation within spectral bands scales with the centre frequency of the band. Here, we tested how neurons in the mammalian primary auditory cortex encode sounds that exhibit this property, but differ in their statistical parameters. The stimuli varied in spectro-temporal density and cyclo-temporal statistics over several orders of magnitude, corresponding to a range of water-like percepts, from pattering of rain to a slow stream. We recorded neuronal activity in the primary auditory cortex of awake rats presented with these stimuli. The responses of the majority of individual neurons were selective for a subset of stimuli with specific statistics. However, as a neuronal population, the responses were remarkably stable over large changes in stimulus statistics, exhibiting a similar range in firing rate, response strength, variability and information rate, and only minor variation in receptive field parameters. This pattern of neuronal responses suggests a potentially general principle for cortical encoding of complex acoustic scenes: while individual cortical neurons exhibit selectivity for specific statistical features, a neuronal population preserves a constant response structure across a broad range of statistical parameters. [ABSTRACT FROM AUTHOR]

Oscillatory entrainment mechanisms are invoked during attentional processing of rhythmically occurring stimuli, whereby their phase alignment regulates the excitability state of neurons coding for anticipated inputs. These mechanisms have been examined in the delta band (1-3 Hz), where entrainment frequency matches the stimulation rate. Here, we investigated entrainment for subdelta rhythmic stimulation, recording from intracranial electrodes over human auditory cortex during an intersensory audiovisual task. Audiovisual stimuli were presented at 0.67 Hz while participants detected targets within one sensory stream and ignored the other. It was found that entrainment operated at twice the stimulation rate (1.33 Hz), and this was reflected by higher amplitude values in the FFT spectrum, cyclic modulation of alpha-amplitude, and phase-amplitude coupling between delta phase and alpha power. In addition, we found that alpha-amplitude was relatively increased in auditory cortex coincident with to-be-ignored auditory stimuli during attention to vision. Thus, the data suggest that entrainment mechanisms operate within a delimited passband such that for subdelta task rhythms, oscillatory harmonics are invoked. The phase of these delta-entrained oscillations modulates alpha-band power. This may in turn increase or decrease responsiveness to relevant and irrelevant stimuli, respectively. [ABSTRACT FROM AUTHOR]

Watching a speaker's facial movements can dramatically enhance our ability to comprehend words, especially in noisy environments. From a general doctrine of combining information from different sensory modalities (the principle of inverse effectiveness), one would expect that the visual signals would be most effective at the highest levels of auditory noise. In contrast, we find, in accord with a recent paper, that visual information improves performance more at intermediate levels of auditory noise than at the highest levels, and we show that a novel visual stimulus containing only temporal information does the same. We present a Bayesian model of optimal cue integration that can explain these conflicts. In this model, words are regarded as points in a multidimensional space and word recognition is a probabilistic inference process. When the dimensionality of the feature space is low, the Bayesian model predicts inverse effectiveness; when the dimensionality is high, the enhancement is maximal at intermediate auditory noise levels. When the auditory and visual stimuli differ slightly in high noise, the model makes a counterintuitive prediction: as sound quality increases, the proportion of reported words corresponding to the visual stimulus should first increase and then decrease. We confirm this prediction in a behavioral experiment. We conclude that auditory-visual speech perception obeys the same notion of optimality previously observed only for simple multisensory stimuli. [ABSTRACT FROM AUTHOR]

Segregation of auditory inputs into meaningful acoustic groups is a key element of auditory scene analysis. Previously, we showed that two interwoven sets of tones differing widely along multiple feature dimensions (duration, pitch and location) were pre-attentively separated into different groups, and that tones separated in this manner did not elicit the mismatch negativity component with respect to each other. Grouping was studied with human subjects using a stimulus rate too slow to induce streaming. Here, we varied the separation of tone sequences along a single feature dimension, i.e. frequency. Frequency differences were either 24 Hz (small) or 1054 Hz (large). Two relatively slow stimulus rates were used (2.7 or 1 tone/s) to explicitly investigate grouping outside the so-called ‘streaming effect’, which requires rates of about 4 tones/s or faster. Two tones were presented in a quasi-random manner with embedded trains of one to four identical tones in a row. Deviants were defined as frequency switches after trains of four identical tones. Mismatch negativity was only elicited for small frequency switches at the slower stimulation rate. The data indicate that pre-attentive grouping of tones occurred when the frequency difference that separated them was large, regardless of stimulation rate. For small frequency differences, inputs were only grouped separately when the stimulation rate was relatively fast. [ABSTRACT FROM AUTHOR]

Background: Viewing a speaker's articulatory movements substantially improves a listener's ability to understand spoken words, especially under noisy environmental conditions. In this study we investigated the ability of patients with schizophrenia to integrate visual and auditory speech. Our objective was to determine to what extent they experience benefit from visual articulation and to detail under what listening conditions they might show the greatest impairments.Methods: We assessed the ability to recognize auditory and audiovisual speech in different levels of noise in 18 patients with schizophrenia and compared their performance with that of 18 healthy volunteers. We used a large set of monosyllabic words as our stimuli in order to more closely approximate performance in everyday situations.Results: Patients with schizophrenia showed deficits in their ability to derive benefit from visual articulatory motion. This impairment was most pronounced at signal-to-noise levels where multisensory gain is known to be maximal in healthy control subjects. A surprising finding was that despite known early auditory sensory processing deficits and reports of impairments in speech processing in schizophrenia, patients' performance in unisensory auditory speech perception remained fully intact.Conclusions: Thus, the results showed a specific deficit in multisensory speech processing in the absence of any measurable deficit in unisensory speech processing and suggest that sensory integration dysfunction may be an important and, to date, rather overlooked aspect of schizophrenia. [ABSTRACT FROM AUTHOR]

Introduction: Auditory sensory processing dysfunction is a core component of schizophrenia, with deficits occurring at 50 ms post-stimulus firmly established in the literature. Given that the initial afference of primary auditory cortex occurs at least 35 ms earlier, however, an essential question remains: how early in sensory processing do such deficits arise, and do they occur during initial cortical afference or earlier, which would implicate subcortical auditory dysfunction. Objective: To establish the onset of the earliest deficits in auditory processing, we examined the time window demarcating the transition from subcortical to cortical processing; 10 ms to 50 ms during the so-called middle latency responses (MLRs). These remain to be adequately characterized in patients with schizophrenia. Methods: We recorded auditory evoked potentials (AEPs) to simple tone-pips from 15 control subjects and 21 medicated patients with longer-term schizophrenia or schizoaffective disorder (illness duration 16 yr, standard deviation [SD] 9.4 yr), using high-density electrical scalp recordings. Between-group analyses assessed the integrity of the MLRs across groups. In addition, 2 source-localization models were conducted to address whether a distinction between subcortical and cortical generators of the MLRs can be made and whether evidence for differential dorsal and ventral pathway contributions to auditory processing deficits can be established. Results: Robust auditory processing deficits were found for patients as early as 15 ms. Evidence for subcortical generators of the earliest MLR component (P20) was provided by source analysis. Topographical mapping and source localization also pointed to greater decrements in processing in the dorsal auditory pathway of patients, providing support for a theory of pervasive deficits that are organized along the lines of a dorsal-ventral distinction. Conclusions: Auditory sensory dysfunction in schizophrenia begins extremely early in processing, is evident during initial cortical afference and is also seen at earlier subcortical processing stages in the thalamus. The implication is that well-established sensory processing deficits in schizophrenia may be secondary to earlier subcortical dysfunction. Our findings do not preclude the possibility of even earlier deficits in auditory sensory processing during the auditory brainstem responses. [ABSTRACT FROM AUTHOR]

Within the visual modality, it has been shown that attention to a single visual feature of an object such as speed of motion, results in an automatic transfer of attention to other task-irrelevant features (e.g. colour). An extension of this logic might lead one to predict that such mechanisms also operate across sensory systems. But, connectivity patterns between feature modules across sensory systems are thought to be sparser to those within a given sensory system, where interareal connectivity is extensive. It is not clear that transfer of attention between sensory systems will operate as it does within a sensory system. Using high-density electrical mapping of the event-related potential (ERP) in humans, we tested whether attending to objects in one sensory modality resulted in the preferential processing of that object's features within another task-irrelevant sensory modality. Clear evidence for cross-sensory attention effects was seen, such that for multisensory stimuli responses to ignored task-irrelevant information in the auditory and visual domains were selectively enhanced when they were features of the explicitly attended object presented in the attended sensory modality. We conclude that attending to an object within one sensory modality results in coactivation of that object's representations in ignored sensory modalities. The data further suggest that transfer of attention from visual-to-auditory features operates in a fundamentally different manner than transfer from auditory-to-visual features, and indicate that visual-object representations have a greater influence on their auditory counterparts than vice-versa. These data are discussed in terms of ‘priming’ vs. ‘spreading’ accounts of attentional transfer. [ABSTRACT FROM AUTHOR]

Abstract: Seeing a speaker''s facial articulatory gestures powerfully affects speech perception, helping us overcome noisy acoustical environments. One particularly dramatic illustration of visual influences on speech perception is the “McGurk illusion”, where dubbing an auditory phoneme onto video of an incongruent articulatory movement can often lead to illusory auditory percepts. This illusion is so strong that even in the absence of any real change in auditory stimulation, it activates the automatic auditory change-detection system, as indexed by the mismatch negativity (MMN) component of the auditory event-related potential (ERP). We investigated the putative left hemispheric dominance of McGurk-MMN using high-density ERPs in an oddball paradigm. Topographic mapping of the initial McGurk-MMN response showed a highly lateralized left hemisphere distribution, beginning at 175ms. Subsequently, scalp activity was also observed over bilateral fronto-central scalp with a maximal amplitude at ∼290ms, suggesting later recruitment of right temporal cortices. Strong left hemisphere dominance was again observed during the last phase of the McGurk-MMN waveform (350–400ms). Source analysis indicated bilateral sources in the temporal lobe just posterior to primary auditory cortex. While a single source in the right superior temporal gyrus (STG) accounted for the right hemisphere activity, two separate sources were required, one in the left transverse gyrus and the other in STG, to account for left hemisphere activity. These findings support the notion that visually driven multisensory illusory phonetic percepts produce an auditory-MMN cortical response and that left hemisphere temporal cortex plays a crucial role in this process. [Copyright &y& Elsevier]