Stimulus Onset Research Articles

Specifying Precision in Visual-orthographic Prediction Error Representations for a Better Understanding of Efficient Reading.

Efficient visual word recognition presumably relies on orthographic prediction error (oPE) representations. On the basis of a transparent neurocognitive computational model rooted in the principles of the predictive coding framework, we postulated that readers optimize their percept by removing redundant visual signals, allowing them to focus on the informative aspects of the sensory input (i.e., the oPE). Here, we explore alternative oPE implementations, testing whether increased precision by assuming all-or-nothing signaling and more realistic word lexicons results in adequate representations underlying efficient word recognition. We used behavioral and electrophysiological data (i.e., EEG) for model evaluation. More precise oPE representations (i.e., implementing a binary signaling and a frequency-sorted lexicon with the 500 most common five-letter words) explained variance in behavioral responses and electrophysiological data 300 msec after stimulus onset best. The original less-precise oPE representation still best explains early brain activation. This pattern suggests a dynamic adaption of represented visual-orthographic information, where initial graded prediction errors convert into binary representations, allowing accurate retrieval of word meaning. These results offer a neuro-cognitive plausible account of efficient word recognition, emphasizing visual-orthographic information in the form of prediction error representations central to the transition from perceptual processing to the access of word meaning.

EXPRESS: Activation of the Motor System Following Gaze Cues is Determined by Hand Access, Not Hand Proximity.

The influence of gaze cues on target prioritization (reaction times (RTs)) and movement execution (movement trajectories) differs based on the ability of the human gaze cue model to manually interact with the targets. Whereas gaze cues consistently impacted RTs, movement trajectories may only be affected when the hands of the human model had the potential to interact with the target. However, the perceived ability to interact with the targets was confounded by the proximity between the model's hands and the targets. The current study explored if the influence of gaze cues on movement trajectories is shaped by the model's potential to access and interact with the targets using their hands or simply the proximity of the hands. A centrally presented human model randomly gazed towards one of two peripheral target locations. Participants executed aiming movements to targets that non-predictively appeared at one location at a stimulus onset asynchrony of 100, 350, or 850 ms. In Experiment 1, the model's hands could not directly access the targets as each was holding a tray. In Experiment 2, the hands had direct access to the targets, but their palms-downwards orientation and wrist-flexed posture rendered efficiently interacting with the targets unlikely. Although RTs showed a facilitation effect of the gaze cue in both experiments, changes in movement trajectories were only observed when the model had direct access to the target (Experiment 2). The results of the current study suggest that the gaze model's direct hand access is necessary for the social gaze cues to influence movement execution.

The strength of confidence is involved in controlling the intensity of attentional allocation

Subjective confidence and uncertainty are closely related to cognition and behavior. However, direct evidence that subjective confidence controls attention allocation is lacking. This study aimed to clarify whether subjective confidence could be involved in controlling attention allocation and intensity. We created a model for predicting the participants’ subjective confidence and verified its validity. Then, an electroencephalogram was recorded while the participants engaged in a behavioral task aimed to allocate their attention based on their confidence level. We observed a negative correlation where trials with higher confidence were associated with shorter reaction times to the target. Regarding event-related potentials (ERPs), we observed higher P1 potentials (early component of the ERP waveform after stimulus onset) in the ipsilateral occipital area during target presentation. Additionally, we observed lower frontoparietal P3a potentials (component of the ERP waveform associated with attention) in the high-confidence condition. We observed a higher alpha (8–12 Hz) power in the ipsilateral occipitoparietal area of the target presentation in the low-confidence condition. Subjective confidence might influence attentional allocation and intensity, possibly achieved by suppressing processing in the target-absent space. Our findings provided important insights into the role of subjective confidence in cognitive and behavioral control.

Under pressure in the Eriksen flanker task.

A classical observation in experimental psychology is a reduction in reaction time and response accuracy under time pressure (TP). This speed-accuracy tradeoff may be understood from the combined perspectives of affordance competition and urgency gating. This view implies that action programs compete with each other from stimulus onset until the final response. Furthermore, responses are thought to be determined not just by the outcome of this competition but also by the urgency to respond. The latter aspect may play an important role in the case of speed stress. An experiment was conducted employing the Eriksen flanker task with different levels of TP. Behavioral, electromyographic (EMG), and electroencephalographic (EEG) data were registered. In the EEG analysis, source-level time-frequency activity was isolated for three sources (occipito-temporal, motor, and medial-frontal cortex). Inter-source phase coherence was computed to assess the neural dynamics underlying the effects of TP and flanker congruency. The EEG and EMG data revealed that TP affects visuo-motor links and motoric processes, while the flanker congruency effect was present from a very early level up to the final response. The present findings fit well within the combined perspectives of affordance competition and urgency gating.

Top-down and emotional attention in blind and sighted individuals.

There is evidence that congenitally blind individuals possess superior auditory perceptual skills compared to sighted people. However, relatively little is known about the auditory-specific cortical correlates of spatial attention in the blind and how task-irrelevant emotional stimulus features could further modulate such neural processes. This study tested blind and sighted participants in a challenging auditory discrimination task. All participants were blindfolded and seated between loudspeakers at 45-degree angles, while pseudowords were randomly presented. The task was to identify target sounds from either the left or the right speaker while ignoring nontarget stimuli, the irrelevant loudspeaker, and irrelevant speaker identity. Emotional valence-neutral, happy, fearful, threatening-of pseudowords was task-irrelevant, focusing solely on syllable detection. Our focus was on measuring the moment-to-moment deployment of auditory-selective attention. This was achieved using the lateralized N2ac event-related potential component characterised by greater negativity at anterior electrodes on the side contralateral to an attended auditory stimulus and observed 75 to 250 ms after stimulus onset. We observed that blind individuals showed better behavioural performance and reduced N2ac amplitudes than sighted individuals. Furthermore, for both groups, N2ac amplitudes were increased for the target compared to nontarget stimuli and stimuli appearing at spatially relevant versus irrelevant locations. Our study highlights the superiority of auditory processing capabilities in blind individuals. The results also highlight the N2ac component's sensitivity to top-down attentional engagement and emotional attention, offering new insights into how blind and sighted individuals process auditory information.

The acute effect of bitemporal electroconvulsive therapy on synchronous changes in heart rate variability and heart rate in patients with depression.


The transient autonomic nervous system responses induced by electroconvulsive therapy (ECT) may serve as critical indicators of treatment efficacy and potential side effects; however, their precise characteristics remains unclear. Considering that the intense stimulation of ECT may disrupt the typical antagonistic relationship between the sympathetic and parasympathetic branches, this study aims to conduct a meticulous analysis of the rapid changes in heart rate variability and heart rate during ECT, with a particular focus on their synchronized interplay.
Methods:
Pulse interval sequences were collected from fifty sessions of bitemporal ECT administered to twenty-seven patients diagnosed with major depressive disorder. The average heart rate (HR) and ultra-short term (UST) heart rate variability (HRV) indices RMSSD and SDNN, as well as the Poincaré indices SD1, SD2 and SD2/SD1, were calculated using a 10-second sliding window with a step size of 1 second. In particular, the synchronous changes between SD1, SD2, SD2/SD1 and HR were analyzed.
Results:
The synchronous changes of the indices showed different characteristics over time. In particular, SD1, SD2 and HR increased significantly by 41.50±11.45 ms, 33.97±10.98 ms and 9.68±2.00 bpm respectively between 8 and 20 seconds, whereas they decreased significantly by 19.89±9.07 ms, 17.54±8.54 ms and 3.80±1.33 bpm respectively between 45 and 53 seconds after ECT stimulus onset. SD1, SD2 and SD2/SD1 all had highly significant positive correlations with HR in the above phases.
Conclusion:
 The results suggest that bitemporal ECT induces the sympathetic and parasympathetic co-activation during the early ictal period and brief co-inhibition approximately 45 seconds after stimulus. Our findings may provide new insights comprehending the mechanisms of ECT and its associated cardiovascular risks.&#xD.

A Time Course Analysis of the Conceptual and Affective Meanings of Words.

Words are the basic units of language and vital for comprehending the language system. Lexical processing research has always focused on either conceptual or affective word meaning. Previous studies have indirectly compared the conceptual and affective meanings of words. This study used emotion-laden words, a special type of dual-meaning word, to directly compare the time course of processing conceptual and affective word meanings. Free association was applied in Experiment 1 to investigate the time course of conceptual and affective meanings in dual-meaning words. The results showed that conceptual-meaning processing was superior to affective-meaning processing. In Experiment 2, the semantic/affective priming paradigm was used to directly compare the time courses of processing conceptual and affective word meanings by manipulating stimulus onset asynchrony (SOA) in different ways. The results showed that semantic and affective priming effects could be obtained under short SOA conditions, with no differences between them. Consistent with Experiment 1, only the semantic priming effect was observed in the long SOA condition. These findings suggest that the conceptual and affective meanings of words have different time courses. The conceptual meaning of words includes automatic and controlled processing, whereas the affective meaning mainly involves automatic processing.

Cortical encoding of spatial structure and semantic content in 3D natural scenes.

Our visual system enables us to effortlessly navigate and recognize real-world visual environments. Functional magnetic resonance imaging (fMRI) studies suggest a network of scene-responsive cortical visual areas, but much less is known about the temporal order in which different scene properties are analysed by the human visual system. In this study, we selected a set of 36 full-colour natural scenes that varied in spatial structure and semantic content that our male and female human participants viewed both in 2D and 3D while we recorded magnetoencephalography (MEG) data. MEG enables tracking of cortical activity in humans at millisecond timescale. We compared the representational geometry in the MEG responses with predictions based on the scene stimuli using the representational similarity analysis framework. The representational structure first reflected the spatial structure in the scenes in time-window 90-125 ms, followed by the semantic content in time-window 140-175 ms after stimulus onset. The 3D stereoscopic viewing of the scenes affected the responses relatively late, from around 140 ms from stimulus onset. Taken together, our results indicate that the human visual system rapidly encodes a scene's spatial structure and suggest that this information is based on monocular instead of binocular depth cues.Significance statement Our visual system enables us to recognize and navigate our visual surroundings seemingly effortlessly, but what exactly happens in our brains remains poorly understood. With the help of time-resolved brain imaging (magnetoencephalography, MEG), we found that the brain first encodes the spatial structure of a scene (e.g., cluttered or navigable) before its semantic content (e.g., a car park or farm). Brain imaging studies typically use 2D pictures as stimuli. Here we asked whether binocular disparity, a depth cue which arises from our two eyes seeing the scene from slightly different angles, aids the coding of the spatial structure. Our results suggest that this 3D depth cue plays little role in the rapid, initial sensing of our spatial surroundings.

Temporal Unfolding of Spelling-to-sound Mappings in Visual (Non)word Recognition.

Behavioral research has shown that inconsistency in spelling-to-sound mappings slows visual word recognition and word naming. However, the time course of this effect remains underexplored. To address this, we asked skilled adult readers to perform a 1-back repetition detection task that did not explicitly involve phonological coding, in which we manipulated lexicality (high-frequency words vs. pseudowords) and sublexical spelling-to-sound consistency (treated as a dichotomous-consistent vs. inconsistent-and continuous dimension), while recording their brain electrical activity. The ERP results showed that the adult brain distinguishes between real and nonexistent words within 119-172 msec after stimulus onset (early N170), likely reflecting initial, rapid access to a primitive visuo-orthographic representation. The consistency of spelling-to-sound mappings exerted an effect shortly after the lexicality effect (172-270 msec; late N170), which percolated to the 353- to 475-msec range but only for real words. This suggests that, in expert readers, orthographic and phonological codes become available automatically and nearly simultaneously within the first 200 msec of the recognition process. We conclude that the early coupling of orthographic and phonological information plays a core role in visual word recognition by mature readers. Our findings support "quasiparallel" processing rather than strict cognitive seriality in early visual word recognition.

Cortical responses to conflicting binocular stimuli in mouse primary visual cortex.

Binocular vision requires that the brain integrate information coming from each eye. These images are combined (fused) to generate a meaningful composite image. Differences between images, within a range, provide useful information about depth (stereopsis). Interocular disparities that are not effectively combined result in diplopia and rivalry. The neural mechanisms underlying these binocular interactions remain poorly understood. Using a combination of visually evoked potential (VEP) recordings, unit recordings, and 2-photon calcium imaging in the binocular region of mouse primary visual cortex (bV1), we probed the neural mechanisms underlying the processing of two distinct forms of disparate binocular signals. Using a dichoptic display, introduction of a spatial interocular phase disparity in grating stimuli reduced VEP magnitude through decreased neuronal firing in the early phase of the response (40-80 ms after stimulus onset, corresponding to the VEP negativity). Introduction of an interocular orientation disparity also decreased VEP magnitude, but this difference was driven by an increase in firing in the late portion of the visual response (100-200 ms after stimulus onset, corresponding to the VEP positivity). This increase in activity was observed for both regular-spiking (putative excitatory) and fast-spiking (putative parvalbumin-positive inhibitory) units. By contrast, visually evoked calcium responses of somatostatin-positive interneurons decreased with introduction of the interocular orientation disparity. Based on these results, we propose that interocular phase differences largely suppress bV1 responses via feedforward thalamocortical interactions, whereas interocular orientation differences prolong visually evoked activity in bV1 through somatostatin-positive interneuron-mediated disinhibition.

Putting things into perspective: Which visual cues facilitate automatic extraretinal symmetry representation?

Objects project different images when viewed from varying locations, but the visual system can correct perspective distortions and identify objects across viewpoints. This study investigated the conditions under which the visual system allocates computational resources to construct view-invariant, extraretinal representations, focusing on planar symmetry. When a symmetrical pattern lies on a plane, its symmetry in the retinal image is degraded by perspective. Visual symmetry activates the extrastriate visual cortex and generates an Event Related Potential (ERP) called Sustained Posterior Negativity (SPN). Previous research has shown that the SPN is reduced for perspective symmetry during secondary tasks. We hypothesized that perspective cost would decrease when visual cues support extraretinal representation. To test this, 120 participants viewed symmetrical and asymmetrical stimuli presented in a frontoparallel or perspective view. The task did not explicitly involve symmetry; participants discriminated the luminance of the patterns. Participants completed four experimental blocks: (1) Baseline block: no depth cues; (2) Monocular viewing block: stimuli viewed with one eye; (3) Static frame block: pictorial depth cues from elements within a flat surface with edges; (4) Moving frame block: motion parallax enhanced 3D interpretation before stimulus onset. Perspective cost was calculated as the difference between SPN responses to frontoparallel and perspective views. Contrary to our pre-registered hypotheses, the perspective cost was consistent across all four blocks. We conclude that the tested visual cues do not substantially reduce the computational cost of processing perspective symmetry.

Reward and Efficacy Modulate the Rate of Anticipatory Pupil Dilation.

Pupil size is a well-established marker of cognitive effort, with greater efforts leading to larger pupils. This is particularly true for pupil size during task performance, whereas findings on anticipatory effort triggered by a cue stimulus are less consistent. For example, a recent report by Frömer etal. found that in a cued-Stroop task, behavioral performance and electrophysiological markers of preparatory effort allocation were modulated by cued reward and 'efficacy' (the degree to which rewards depended on good performance), but pupil size did not show a comparable pattern. Here, we conceptually replicated this study, employing an alternative approach to the pupillometry analyses. In line with previous findings, we found no modulation of absolute pupil size in the cue-to-target interval. Instead, we observed a significant difference in the rate of pupil dilation in anticipation of the target: pupils dilated more rapidly for high-reward trials in which rewards depended on good performance. This was followed by a significant difference in absolute pupil size within the first hundreds of milliseconds following Stroop stimulus onset, likely reflecting a lagging effect of anticipatory effort allocation. Finally, the slope of pupil dilation was significantly correlated with behavioral response times, and this association was strongest for the high-reward, high-efficacy trials, further supporting that the rate of anticipatory pupil dilation reflects anticipatory effort. We conclude that pupil size is modulated by anticipatory effort, but in a highly temporally-specific manner, which is best reflected by the rate of dilation in the moments just prior to stimulus onset.

Neural correlates of phonetic categorization under auditory (phoneme) and visual (grapheme) modalities

This study assessed the neural mechanisms and relative saliency of categorization for speech sounds and comparable graphemes (i.e., visual letters) of the same phonetic label. Given that linguistic experience shapes categorical processing, and letter-speech sound matching plays a crucial role during early reading acquisition, we hypothesized sound phoneme and visual grapheme tokens representing the same linguistic identity might recruit common neural substrates, despite originating from different sensory modalities. Behavioral and neuroelectric brain responses (ERPs) were acquired as participants categorized stimuli from sound (phoneme) and homologous letter (grapheme) continua each spanning a /da/−/ga/ gradient. Behaviorally, listeners were faster and showed stronger categorization of phoneme compared to graphemes. At the neural level, multidimensional scaling of the EEG revealed responses self-organized in a categorial fashion such that tokens clustered within their respective modality beginning ∼150–250 ms after stimulus onset. Source-resolved ERPs further revealed modality-specific and overlapping brain regions supporting phonetic categorization. Left inferior frontal gyrus and auditory cortex showed stronger responses for sound category members compared to phonetically ambiguous tokens, whereas early visual cortices paralleled this categorical organization for graphemes. Auditory and visual categorization also recruited common visual association areas in extrastriate cortex but in opposite hemispheres (auditory = left; visual = right). Our findings reveal both auditory and visual sensory cortex supports categorical organization for phonetic labels within their respective modalities. However, a partial overlap in phoneme and grapheme processing among occipital brain areas implies the presence of an isomorphic, domain-general mapping for phonetic categories in dorsal visual system

Cochlear implantation in adults with acquired single-sided deafness improves cortical processing and comprehension of speech presented to the non-implanted ears: a longitudinal EEG study.

Former studies have established that individuals with a cochlear implant (CI) for treating single-sided deafness experience improved speech processing after implantation. However, it is not clear how each ear contributes separately to improve speech perception over time at the behavioural and neural level. In this longitudinal EEG study with four different time points, we measured neural activity in response to various temporally and spectrally degraded spoken words presented monaurally to the CI and non-CI ears (5 left and 5 right ears) in 10 single-sided CI users and 10 age- and sex-matched individuals with normal hearing. Subjective comprehension ratings for each word were also recorded. Data from single-sided CI participants were collected pre-CI implantation, and at 3, 6 and 12 months after implantation. We conducted a time-resolved representational similarity analysis on the EEG data to quantify whether and how neural patterns became more similar to those of normal hearing individuals. At 6 months after implantation, the speech comprehension ratings for the degraded words improved in both ears. Notably, the improvement was more pronounced for the non-CI ears than the CI ears. Furthermore, the enhancement in the non-CI ears was paralleled by increased similarity to neural representational patterns of the normal hearing control group. The maximum of this effect coincided with peak decoding accuracy for spoken-word comprehension (600-1200 ms after stimulus onset). The present data demonstrate that cortical processing gradually normalizes within months after CI implantation for speech presented to the non-CI ear. CI enables the deaf ear to provide afferent input, which, according to our results, complements the input of the non-CI ear, gradually improving its function. These novel findings underscore the feasibility of tracking neural recovery after auditory input restoration using advanced multivariate analysis methods, such as representational similarity analysis.

Unexpected sounds induce a rapid inhibition of eye-movement responses.

Unexpected sounds have been shown to trigger a global and transient inhibition of motor responses. Recent evidence suggests that eye movements may also be inhibited in a similar way, but it is not clear how quickly unexpected sounds can affect eye-movement responses. Additionally, little is known about whether they affect only voluntary saccades or also reflexive saccades. In this study, participants performed a pro-saccade and an anti-saccade task while the timing of sounds relative to stimulus onset was manipulated. Pro-saccades are generally reflexive and stimulus-driven, whereas anti-saccades require the generation of a voluntary saccade in the opposite direction of a peripheral stimulus. Unexpected novel sounds inhibited the execution of both pro- and anti-saccades compared to standard sounds, but the inhibition was stronger for anti-saccades. Novel sounds affected response latencies as early as 150 ms before the peripheral cue to make a saccade, all the way to 25 ms after the cue to make a saccade. Interestingly, unexpected sounds also reduced anti-saccade task errors, indicating that they aided inhibitory control. Overall, these results suggest that unexpected sounds yield a global and rapid inhibition of eye-movement responses. This inhibition also helps suppress reflexive eye-movement responses in favor of more voluntarily generated ones.

Working memory updating in the macaque lateral prefrontal cortex.

Working memory updating is an important executive process. Here, we study the single-neuron mechanisms involved in updating versus protecting memory from distractors in the macaque prefrontal cortex. We recorded single-neuron activity from the lateral prefrontal cortex (LPFC) and prearcuate cortex (PAC) while male monkeys performed a task that required them to update their memory of target locations while ignoring distractors. Our findings revealed that neurons in the PAC signaled updated memory locations approximately ∼100 ms after stimulus onset, significantly faster than the ∼400 ms observed in the LPFC. Additionally, PAC neurons exhibited longer encoding of distractor information. Population decoding analyses further indicated that distractor information was maintained in orthogonal subspaces from target information in both regions, minimizing interference. These results demonstrate the distinct temporal dynamics in memory updating processes between the PAC and LPFC and highlight the interplay between robust memory maintenance and updating, suggesting that local neural mechanisms may contribute to these processes.Significance Statement Working memory is a fundamental cognitive function. It stored information in the short term, and this information can be manipulated to allow intelligent behaviors. The lateral prefrontal cortex is involved in this process, but the mechanisms of working memory manipulation remain unclear. Here, we studied one type of manipulation; working memory updating, which refers to the exchange of one memory for another. We found that two adjacent regions in the lateral prefrontal cortex show different updating times: while a posterior region updates memory content very fast, the more anterior region takes significantly longer. These results show that working memory updating may involve multiple operations, such as updating of memory or attention versus updating of motor plans.

The forced-response method: A new chronometric approach to measure conflict processing.

Despite long-standing concerns about the use of free reaction times (RTs) in cognitive psychology, they remain a prevalent measure of conflict resolution. This report presents the forced-response method as a fresh approach to examine speed-accuracy trade-off functions (SATs) in conflict tasks. The method involves fixing the overall response time, varying the onset of stimuli, and observing response expression. We applied this method to an arrow flanker task. By systematically varying the time between stimulus onset and response, we reveal a comprehensive time course of the flanker interference effect that is rarely observed in previous literature. We further show that influential manipulations observed in free-RT paradigms similarly affect accuracy within the forced-response technique, suggesting that the forced-response method retains the core cognitive processing characteristics of traditional free-RT conflict tasks. As a behavioral method that examines the time course of cognitive processing, the forced-response method provides a novel and more nuanced look into the dynamics of conflict resolution.

Delayed accumulation of inhibitory input explains gamma frequency variation with changing contrast in an Inhibition Stabilized Network.

Gamma rhythm (30-70 Hz), thought to represent the interactions between excitatory and inhibitory populations, can be induced by presenting achromatic gratings in the primary visual cortex (V1) and is sensitive to stimulus properties such as size and contrast. In addition, gamma occurs in short bursts, and shows a "frequency-falloff" effect where its peak frequency is high after stimulus onset and slowly decreases to a steady state. Recently, these size-contrast properties and temporal characteristics were replicated in a self-oscillating Wilson-Cowan (WC) model operating as an Inhibition stabilized network (ISN), stimulated by Ornstein-Uhlenbeck (OU)-type inputs. In particular, frequency-falloff was explained by delayed and slowly accumulated inputs arriving at local inhibitory populations. We hypothesized that if the stimulus is preceded by another higher contrast stimulus, frequency-falloff could be abolished or reversed, since the excessive inhibition will now take more time to dissipate. We presented gratings at different contrasts consecutively to two female monkeys while recording gamma using microelectrode arrays in V1 and confirmed this prediction. Further, this model also replicated a characteristic pattern of gamma frequency modulation to counter-phasing stimuli as reported previously. These phenomena were also replicated by an ISN model subject to slow adaptation in feedforward excitatory input. Thus, ISN model with delayed surround input or adapted feedforward input replicates gamma frequency responses to time-varying contrasts.Significance statement Gamma rhythms represent interactions between excitatory and inhibitory populations during visual stimulation. Gamma power and centre frequency varies depending on stimulus features, and onset of stimulus produces a "frequency-fall" trend where onset frequency is higher and subsequently plateaus to a lower value. In an earlier work, we argued, using a noisy rate-model of V1, that a delayed onset of inhibition-drive from the surround populations produced the gamma 'frequency-falloff'. We tested a key prediction of this hypothesis that the frequency-falloff can be abolished or reversed if the stimulus is preceded by a higher contrast stimulus, and confirmed the same by recording from primate primary visual cortex while presenting multiple stimuli consecutively at varying contrasts.

Attenuated processing of vowels in the left temporal cortex predicts speech-in-noise perception deficit in children with autism

BackgroundDifficulties with speech-in-noise perception in autism spectrum disorders (ASD) may be associated with impaired analysis of speech sounds, such as vowels, which represent the fundamental phoneme constituents of human speech. Vowels elicit early (< 100 ms) sustained processing negativity (SPN) in the auditory cortex that reflects the detection of an acoustic pattern based on the presence of formant structure and/or periodic envelope information (f0) and its transformation into an auditory “object”.MethodsWe used magnetoencephalography (MEG) and individual brain models to investigate whether SPN is altered in children with ASD and whether this deficit is associated with impairment in their ability to perceive speech in the background of noise. MEG was recorded while boys with ASD and typically developing boys passively listened to sounds that differed in the presence/absence of f0 periodicity and formant structure. Word-in-noise perception was assessed in the separate psychoacoustic experiment using stationary and amplitude modulated noise with varying signal-to-noise ratio.ResultsSPN was present in both groups with similarly early onset. In children with ASD, SPN associated with processing formant structure was reduced predominantly in the cortical areas lateral to and medial to the primary auditory cortex, starting at ~ 150—200 ms after the stimulus onset. In the left hemisphere, this deficit correlated with impaired ability of children with ASD to recognize words in amplitude-modulated noise, but not in stationary noise.ConclusionsThese results suggest that perceptual grouping of vowel formants into phonemes is impaired in children with ASD and that, in the left hemisphere, this deficit contributes to their difficulties with speech perception in fluctuating background noise.

Rapid, systematic updating of movement by accumulated decision evidence

Acting in the natural world requires not only deciding among multiple options but also converting decisions into motor commands. How the dynamics of decision formation influence the fine kinematics of response movement remains, however, poorly understood. Here we investigate how the accumulation of decision evidence shapes the response orienting trajectories in a task where freely-moving rats combine prior expectations and auditory information to select between two possible options. Response trajectories and their motor vigor are initially determined by the prior. Rats movements then incorporate sensory information in less than 100 ms after stimulus onset by accelerating or slowing depending on how much the stimulus supports their initial choice. When the stimulus evidence is in strong contradiction, rats change their mind and reverse their initial trajectory. Human subjects performing an equivalent task display a remarkably similar behavior. We encapsulate these results in a computational model that maps the decision variable onto the movement kinematics at discrete time points, capturing subjects’ choices, trajectories and changes of mind. Our results show that motor responses are not ballistic. Instead, they are systematically and rapidly updated, as they smoothly unfold over time, by the parallel dynamics of the underlying decision process.