Endogenous modulation of delta phase by expectation-A replication of Stefanics et al., 2010.

The human brain efficiently extracts the temporal statistics of sensory environments and automatically generates expectations about future events. An influential Hypothesis holds that these expectations can find their implementation in neural oscillations, notably in the delta band (.5-3 Hz). Rhythmic fluctuations of cortical excitement are thought to align and match up in phase to the temporal structure of the sensory environment. This alignment is thought to result in the more excitable phase range of neural oscillations to overlap with the predicted onset of sensory events which in turn results in more efficient processing of sensory input, especially so in audition. An unresolved issue concerns whether such phase-aligned rhythmic brain activity is driven exclusively by the exogenous temporal structure of the input, or whether it also reflects phase re-alignment due to endogenous expectations based on stimulus probability and task relevance. In a seminal study, Stefanics et al. (2010) presented stimuli in a rhythmic stream and observed that delta phase consistency across trials was modulated by endogenous target onset expectations: delta phase consistency was higher prior to more probable (strongly expected) compared to less probable (weakly expected) target onsets. The present study replicates Experiment II of the original study, most importantly the modulation of delta phase consistency by endogenous expectations, and underlines a direct relationship between phase locking and behaviour. Our additional analyses locate the sources of the delta phase-alignment to motor, pre-motor, parietal, and temporal areas, and provide evidence for an ongoing delta oscillation, in line with the interpretation of oscillatory phase alignment rather than a transient evoked response. Importantly, this work shows that the phase of delta oscillations can be modulated by top-down control, and hence qualifies as a potential mechanism for the neural implementation of (rhythmic) temporal predictions.

Modality-specific tracking of attention and sensory statistics in the human electrophysiological spectral exponent.

A hallmark of electrophysiological brain activity is its 1/f-like spectrum - power decreases with increasing frequency. The steepness of this 'roll-off' is approximated by the spectral exponent, which in invasively recorded neural populations reflects the balance of excitatory to inhibitory neural activity (E:I balance). Here, we first establish that the spectral exponent of non-invasive electroencephalography (EEG) recordings is highly sensitive to general (i.e., anaesthesia-driven) changes in E:I balance. Building on the EEG spectral exponent as a viable marker of E:I, we then demonstrate its sensitivity to the focus of selective attention in an EEG experiment during which participants detected targets in simultaneous audio-visual noise. In addition to these endogenous changes in E:I balance, EEG spectral exponents over auditory and visual sensory cortices also tracked auditory and visual stimulus spectral exponents, respectively. Individuals' degree of this selective stimulus-brain coupling in spectral exponents predicted behavioural performance. Our results highlight the rich information contained in 1/f-like neural activity, providing a window into diverse neural processes previously thought to be inaccessible in non-invasive human recordings.

Neural attentional-filter mechanisms of listening success in middle-aged and older individuals.

Successful listening crucially depends on intact attentional filters that separate relevant from irrelevant information. Research into their neurobiological implementation has focused on two potential auditory filter strategies: the lateralization of alpha power and selective neural speech tracking. However, the functional interplay of the two neural filter strategies and their potency to index listening success in an ageing population remains unclear. Using electroencephalography and a dual-talker task in a representative sample of listeners (N = 155; age=39-80 years), we here demonstrate an often-missed link from single-trial behavioural outcomes back to trial-by-trial changes in neural attentional filtering. First, we observe preserved attentional-cue-driven modulation of both neural filters across chronological age and hearing levels. Second, neural filter states vary independently of one another, demonstrating complementary neurobiological solutions of spatial selective attention. Stronger neural speech tracking but not alpha lateralization boosts trial-to-trial behavioural performance. Our results highlight the translational potential of neural speech tracking as an individualized neural marker of adaptive listening behaviour.

Spatial Attention and Temporal Expectation Exert Differential Effects on Visual and Auditory Discrimination.

Anticipation of an impending stimulus shapes the state of the sensory systems, optimizing neural and behavioral responses. Here, we studied the role of brain oscillations in mediating spatial and temporal anticipations. Because spatial attention and temporal expectation are often associated with visual and auditory processing, respectively, we directly contrasted the visual and auditory modalities and asked whether these anticipatory mechanisms are similar in both domains. We recorded the magnetoencephalogram in healthy human participants performing an auditory and visual target discrimination task, in which cross-modal cues provided both temporal and spatial information with regard to upcoming stimulus presentation. Motivated by prior findings, we were specifically interested in delta (1-3 Hz) and alpha (8-13 Hz) band oscillatory state in anticipation of target presentation and their impact on task performance. Our findings support the view that spatial attention has a stronger effect in the visual domain, whereas temporal expectation effects are more prominent in the auditory domain. For the spatial attention manipulation, we found a typical pattern of alpha lateralization in the visual system, which correlated with response speed. Providing a rhythmic temporal cue led to increased postcue synchronization of low-frequency rhythms, although this effect was more broadband in nature, suggesting a general phase reset rather than frequency-specific neural entrainment. In addition, we observed delta-band synchronization with a frontal topography, which correlated with performance, especially in the auditory task. Combined, these findings suggest that spatial and temporal anticipations operate via a top-down modulation of the power and phase of low-frequency oscillations, respectively.

Local cortical desynchronization and pupil-linked arousal differentially shape brain states for optimal sensory performance.

Instantaneous brain states have consequences for our sensation, perception, and behaviour. Fluctuations in arousal and neural desynchronization likely pose perceptually relevant states. However, their relationship and their relative impact on perception is unclear. We here show that, at the single-trial level in humans, local desynchronization in sensory cortex (expressed as time-series entropy) versus pupil-linked arousal differentially impact perceptual processing. While we recorded electroencephalography (EEG) and pupillometry data, stimuli of a demanding auditory discrimination task were presented into states of high or low desynchronization of auditory cortex via a real-time closed-loop setup. Desynchronization and arousal distinctly influenced stimulus-evoked activity and shaped behaviour displaying an inverted u-shaped relationship: States of intermediate desynchronization elicited minimal response bias and fastest responses, while states of intermediate arousal gave rise to highest response sensitivity. Our results speak to a model in which independent states of local desynchronization and global arousal jointly optimise sensory processing and performance.

Alpha Oscillations in the Human Brain Implement Distractor Suppression Independent of Target Selection.

In principle, selective attention is the net result of target selection and distractor suppression. The way in which both mechanisms are implemented neurally has remained contested. Neural oscillatory power in the alpha frequency band (∼10 Hz) has been implicated in the selection of to-be-attended targets, but there is lack of empirical evidence for its involvement in the suppression of to-be-ignored distractors. Here, we use electroencephalography recordings of N = 33 human participants (males and females) to test the preregistered hypothesis that alpha power directly relates to distractor suppression and thus operates independently from target selection. In an auditory spatial pitch discrimination task, we modulated the location (left vs right) of either a target or a distractor tone sequence, while fixing the other in the front. When the distractor was fixed in the front, alpha power relatively decreased contralaterally to the target and increased ipsilaterally. Most importantly, when the target was fixed in the front, alpha lateralization reversed in direction for the suppression of distractors on the left versus right. These data show that target-selection-independent alpha power modulation is involved in distractor suppression. Although both lateralized alpha responses for selection and for suppression proved reliable, they were uncorrelated and distractor-related alpha power emerged from more anterior, frontal cortical regions. Lending functional significance to suppression-related alpha oscillations, alpha lateralization at the individual, single-trial level was predictive of behavioral accuracy. These results fuel a renewed look at neurobiological accounts of selection-independent suppressive filtering in attention.SIGNIFICANCE STATEMENT Although well established models of attention rest on the assumption that irrelevant sensory information is filtered out, the neural implementation of such a filter mechanism is unclear. Using an auditory attention task that decouples target selection from distractor suppression, we demonstrate that two sign-reversed lateralized alpha responses reflect target selection versus distractor suppression. Critically, these alpha responses are reliable, independent of each other, and generated in more anterior, frontal regions for suppression versus selection. Prediction of single-trial task performance from alpha modulation after stimulus onset agrees with the view that alpha modulation bears direct functional relevance as a neural implementation of attention. Results demonstrate that the neurobiological foundation of attention implies a selection-independent alpha oscillatory mechanism to suppress distraction.

Implicit temporal predictability enhances pitch discrimination sensitivity and biases the phase of delta oscillations in auditory cortex.

Can human listeners use implicit temporal contingencies in auditory input to form temporal predictions, and if so, how are these predictions represented endogenously? To assess this question, we implicitly manipulated temporal predictability in an auditory pitch discrimination task: unbeknownst to participants, the pitch of the standard tone could either be deterministically predictive of the temporal onset of the target tone, or convey no predictive information. Predictive and non-predictive conditions were presented interleaved in one stream, and separated by variable inter-stimulus intervals such that there was no dominant stimulus rhythm throughout. Even though participants were unaware of the implicit temporal contingencies, pitch discrimination sensitivity (the slope of the psychometric function) increased when the onset of the target tone was predictable in time (N = 49, 28 female, 21 male). Concurrently recorded EEG data (N = 24) revealed that standard tones that conveyed temporal predictions evoked a more negative N1 component than non-predictive standards. We observed no significant differences in oscillatory power or phase coherence between conditions during the foreperiod. Importantly, the phase angle of delta oscillations (1-3 Hz) in auditory areas in the post-standard and pre-target time windows predicted behavioral pitch discrimination sensitivity. This suggests that temporal predictions are encoded in delta oscillatory phase during the foreperiod interval. In sum, we show that auditory perception benefits from implicit temporal contingencies, and provide evidence for a role of slow neural oscillations in the endogenous representation of temporal predictions, in absence of exogenously driven entrainment to rhythmic input.

Prestimulus neural alpha power predicts confidence in discriminating identical auditory stimuli.

When deciding upon a sensory stimulus, the power of prestimulus neural alpha oscillations (~10 Hz) has been shown to hold information on a perceiver's bias, or confidence, as opposed to perceptual sensitivity per se. Here, we test whether this link between prestimulus alpha power and decision confidence, previously established in vision and somatosensation, also holds in the auditory modality. Moreover, confidence usually depends on the physical evidence available in the stimulus as well as on decision accuracy. It is unclear in how far the link between prestimulus alpha power and confidence holds when physical stimulus evidence is entirely absent, and thus accuracy does not vary. We here analysed electroencephalography data from a paradigm where human listeners (N = 17) rated their confidence in the discrimination of the pitch of two tones that were, unbeknownst to the listeners, identical. Lower prestimulus alpha power as recorded at central channel sites was predictive of higher confidence ratings. Furthermore, this link was not mediated by auditory evoked activity. Our results support a direct link between prestimulus alpha power and decision confidence. This effect, first, shows up in the auditory modality similar to vision and somatosensation, and second, is present also in the complete absence of physical evidence in the stimulus and in the absence of varying accuracy. These findings speak to a model wherein low prestimulus alpha power increases neural baseline excitability, which is reflected in enhanced stimulus-evoked neural responses and higher confidence.

Temporal Expectation Modulates the Cortical Dynamics of Short-Term Memory.

Increased memory load is often signified by enhanced neural oscillatory power in the alpha range (8-13 Hz), which is taken to reflect inhibition of task-irrelevant brain regions. The corresponding neural correlates of memory decay, however, are not yet well understood. In the current study, we investigated auditory short-term memory decay in humans using a delayed matching-to-sample task with pure-tone sequences. First, in a behavioral experiment, we modeled memory performance over six different delay-phase durations. Second, in a MEG experiment, we assessed alpha-power modulations over three different delay-phase durations. In both experiments, the temporal expectation for the to-be-remembered sound was manipulated so that it was either temporally expected or not. In both studies, memory performance declined over time, but this decline was weaker when the onset time of the to-be-remembered sound was expected. Similarly, patterns of alpha power in and alpha-tuned connectivity between sensory cortices changed parametrically with delay duration (i.e., decrease in occipitoparietal regions, increase in temporal regions). Temporal expectation not only counteracted alpha-power decline in heteromodal brain areas (i.e., supramarginal gyrus), but also had a beneficial effect on memory decay, counteracting memory performance decline. Correspondingly, temporal expectation also boosted alpha connectivity within attention networks known to play an active role during memory maintenance. The present data show how patterns of alpha power orchestrate short-term memory decay and encourage a more nuanced perspective on alpha power across brain space and time beyond its inhibitory role.SIGNIFICANCE STATEMENT Our sensory memories of the physical world fade quickly. We show here that this decay of short-term memory can be counteracted by so-called temporal expectation; that is, knowledge of when to expect a sensory event that an individual must remember. We also show that neural oscillations in the "alpha" (8-13 Hz) range index both the degree of memory decay (for brief sound patterns) and the respective memory benefit from temporal expectation. Spatially distributed cortical patterns of alpha power show opposing effects in auditory versus visual sensory cortices. Moreover, alpha-tuned connectivity changes within supramodal attention networks reflect the allocation of neural resources as short-term memory representations fade.

Probing the limits of alpha power lateralisation as a neural marker of selective attention in middle-aged and older listeners.

In recent years, hemispheric lateralisation of alpha power has emerged as a neural mechanism thought to underpin spatial attention across sensory modalities. Yet, how healthy ageing, beginning in middle adulthood, impacts the modulation of lateralised alpha power supporting auditory attention remains poorly understood. In the current electroencephalography study, middle-aged and older adults (N = 29; ~40-70 years) performed a dichotic listening task that simulates a challenging, multitalker scenario. We examined the extent to which the modulation of 8-12 Hz alpha power would serve as neural marker of listening success across age. With respect to the increase in interindividual variability with age, we examined an extensive battery of behavioural, perceptual and neural measures. Similar to findings on younger adults, middle-aged and older listeners' auditory spatial attention induced robust lateralisation of alpha power, which synchronised with the speech rate. Notably, the observed relationship between this alpha lateralisation and task performance did not co-vary with age. Instead, task performance was strongly related to an individual's attentional and working memory capacity. Multivariate analyses revealed a separation of neural and behavioural variables independent of age. Our results suggest that in age-varying samples as the present one, the lateralisation of alpha power is neither a sufficient nor necessary neural strategy for an individual's auditory spatial attention, as higher age might come with increased use of alternative, compensatory mechanisms. Our findings emphasise that explaining interindividual variability will be key to understanding the role of alpha oscillations in auditory attention in the ageing listener.

Transcranial alternating current stimulation with speech envelopes modulates speech comprehension.

Cortical entrainment of the auditory cortex to the broadband temporal envelope of a speech signal is crucial for speech comprehension. Entrainment results in phases of high and low neural excitability, which structure and decode the incoming speech signal. Entrainment to speech is strongest in the theta frequency range (4-8 Hz), the average frequency of the speech envelope. If a speech signal is degraded, entrainment to the speech envelope is weaker and speech intelligibility declines. Besides perceptually evoked cortical entrainment, transcranial alternating current stimulation (tACS) entrains neural oscillations by applying an electric signal to the brain. Accordingly, tACS-induced entrainment in auditory cortex has been shown to improve auditory perception. The aim of the current study was to modulate speech intelligibility externally by means of tACS such that the electric current corresponds to the envelope of the presented speech stream (i.e., envelope-tACS). Participants performed the Oldenburg sentence test with sentences presented in noise in combination with envelope-tACS. Critically, tACS was induced at time lags of 0-250 ms in 50-ms steps relative to sentence onset (auditory stimuli were simultaneous to or preceded tACS). We performed single-subject sinusoidal, linear, and quadratic fits to the sentence comprehension performance across the time lags. We could show that the sinusoidal fit described the modulation of sentence comprehension best. Importantly, the average frequency of the sinusoidal fit was 5.12 Hz, corresponding to the peaks of the amplitude spectrum of the stimulated envelopes. This finding was supported by a significant 5-Hz peak in the average power spectrum of individual performance time series. Altogether, envelope-tACS modulates intelligibility of speech in noise, presumably by enhancing and disrupting (time lag with in- or out-of-phase stimulation, respectively) cortical entrainment to the speech envelope in auditory cortex.

Aging affects the balance of neural entrainment and top-down neural modulation in the listening brain.

Healthy aging is accompanied by listening difficulties, including decreased speech comprehension, that stem from an ill-understood combination of sensory and cognitive changes. Here, we use electroencephalography to demonstrate that auditory neural oscillations of older adults entrain less firmly and less flexibly to speech-paced (∼3 Hz) rhythms than younger adults' during attentive listening. These neural entrainment effects are distinct in magnitude and origin from the neural response to sound per se. Non-entrained parieto-occipital alpha (8-12 Hz) oscillations are enhanced in young adults, but suppressed in older participants, during attentive listening. Entrained neural phase and task-induced alpha amplitude exert opposite, complementary effects on listening performance: higher alpha amplitude is associated with reduced entrainment-driven behavioural performance modulation. Thus, alpha amplitude as a task-driven, neuro-modulatory signal can counteract the behavioural corollaries of neural entrainment. Balancing these two neural strategies may present new paths for intervention in age-related listening difficulties.

The Human Neural Alpha Response to Speech is a Proxy of Attentional Control.

Human alpha (~10 Hz) oscillatory power is a prominent neural marker of cognitive effort. When listeners attempt to process and retain acoustically degraded speech, alpha power enhances. It is unclear whether these alpha modulations reflect the degree of acoustic degradation per se or the degradation-driven demand to a listener's attentional control. Using an irrelevant-speech paradigm and measuring the electroencephalogram (EEG), the current experiment demonstrates that the neural alpha response to speech is a surprisingly clear proxy of top-down control, entirely driven by the listening goals of attending versus ignoring degraded speech. While (n = 23) listeners retained the serial order of 9 to-be-recalled digits, one to-be-ignored sentence was presented. Distractibility of the to-be-ignored sentence parametrically varied in acoustic detail (noise-vocoding), with more acoustic detail of distracting speech increasingly disrupting listeners' serial memory recall. Where previous studies had observed decreases in parietal and auditory alpha power with more acoustic detail (of target speech), alpha power here showed the opposite pattern and increased with more acoustic detail in the speech distractor. In sum, the neural alpha response reflects almost exclusively a listener's goal, which is decisive for whether more acoustic detail facilitates comprehension (of attended speech) or enhances distraction (of ignored speech).

Neural tracking of attended versus ignored speech is differentially affected by hearing loss.

Hearing loss manifests as a reduced ability to understand speech, particularly in multitalker situations. In these situations, younger normal-hearing listeners' brains are known to track attended speech through phase-locking of neural activity to the slow-varying envelope of the speech. This study investigates how hearing loss, compensated by hearing aids, affects the neural tracking of the speech-onset envelope in elderly participants with varying degree of hearing loss (n = 27, 62-86 yr; hearing thresholds 11-73 dB hearing level). In an active listening task, a to-be-attended audiobook (signal) was presented either in quiet or against a competing to-be-ignored audiobook (noise) presented at three individualized signal-to-noise ratios (SNRs). The neural tracking of the to-be-attended and to-be-ignored speech was quantified through the cross-correlation of the electroencephalogram (EEG) and the temporal envelope of speech. We primarily investigated the effects of hearing loss and SNR on the neural envelope tracking. First, we found that elderly hearing-impaired listeners' neural responses reliably track the envelope of to-be-attended speech more than to-be-ignored speech. Second, hearing loss relates to the neural tracking of to-be-ignored speech, resulting in a weaker differential neural tracking of to-be-attended vs. to-be-ignored speech in listeners with worse hearing. Third, neural tracking of to-be-attended speech increased with decreasing background noise. Critically, the beneficial effect of reduced noise on neural speech tracking decreased with stronger hearing loss. In sum, our results show that a common sensorineural processing deficit, i.e., hearing loss, interacts with central attention mechanisms and reduces the differential tracking of attended and ignored speech. NEW & NOTEWORTHY: The present study investigates the effect of hearing loss in older listeners on the neural tracking of competing speech. Interestingly, we observed that whereas internal degradation (hearing loss) relates to the neural tracking of ignored speech, external sound degradation (ratio between attended and ignored speech; signal-to-noise ratio) relates to tracking of attended speech. This provides the first evidence for hearing loss affecting the ability to neurally track speech.

Altered temporal dynamics of neural adaptation in the aging human auditory cortex.

Neural response adaptation plays an important role in perception and cognition. Here, we used electroencephalography to investigate how aging affects the temporal dynamics of neural adaptation in human auditory cortex. Younger (18-31 years) and older (51-70 years) normal hearing adults listened to tone sequences with varying onset-to-onset intervals. Our results show long-lasting neural adaptation such that the response to a particular tone is a nonlinear function of the extended temporal history of sound events. Most important, aging is associated with multiple changes in auditory cortex; older adults exhibit larger and less variable response magnitudes, a larger dynamic response range, and a reduced sensitivity to temporal context. Computational modeling suggests that reduced adaptation recovery times underlie these changes in the aging auditory cortex and that the extended temporal stimulation has less influence on the neural response to the current sound in older compared with younger individuals. Our human electroencephalography results critically narrow the gap to animal electrophysiology work suggesting a compensatory release from cortical inhibition accompanying hearing loss and aging.

Spatiotemporal dynamics of auditory attention synchronize with speech.

Attention plays a fundamental role in selectively processing stimuli in our environment despite distraction. Spatial attention induces increasing and decreasing power of neural alpha oscillations (8-12 Hz) in brain regions ipsilateral and contralateral to the locus of attention, respectively. This study tested whether the hemispheric lateralization of alpha power codes not just the spatial location but also the temporal structure of the stimulus. Participants attended to spoken digits presented to one ear and ignored tightly synchronized distracting digits presented to the other ear. In the magnetoencephalogram, spatial attention induced lateralization of alpha power in parietal, but notably also in auditory cortical regions. This alpha power lateralization was not maintained steadily but fluctuated in synchrony with the speech rate and lagged the time course of low-frequency (1-5 Hz) sensory synchronization. Higher amplitude of alpha power modulation at the speech rate was predictive of a listener's enhanced performance of stream-specific speech comprehension. Our findings demonstrate that alpha power lateralization is modulated in tune with the sensory input and acts as a spatiotemporal filter controlling the read-out of sensory content.

Neural Microstates Govern Perception of Auditory Input without Rhythmic Structure.

Human perception fluctuates with the phase of neural oscillations in the presence of environmental rhythmic structure by which neural oscillations become entrained. However, in the absence of predictability afforded by rhythmic structure, we hypothesize that the neural dynamical states associated with optimal psychophysical performance are more complex than what has been described previously for rhythmic stimuli. The current electroencephalography study characterized the brain dynamics associated with optimal detection of gaps embedded in narrow-band acoustic noise stimuli lacking low-frequency rhythmic structure. Optimal gap detection was associated with three spectrotemporally distinct delta-governed neural microstates. Individual microstates were characterized by unique instantaneous combinations of neural phase in the delta, theta, and alpha frequency bands. Critically, gap detection was not predictable from local fluctuations in stimulus acoustics. The current results suggest that, in the absence of rhythmic structure to entrain neural oscillations, good performance hinges on complex neural states that vary from moment to moment. Significance statement: Our ability to hear faint sounds fluctuates together with slow brain activity that synchronizes with environmental rhythms. However, it is so far not known how brain activity at different time scales might interact to influence perception when there is no rhythm with which brain activity can synchronize. Here, we used electroencephalography to measure brain activity while participants listened for short silences that interrupted ongoing noise. We examined brain activity in three different frequency bands: delta, theta, and alpha. Participants' ability to detect gaps depended on different numbers of frequency bands--sometimes one, sometimes two, and sometimes three--at different times. Changes in the number of frequency bands that predict perception are a hallmark of a complex neural system.

Temporal expectations and neural amplitude fluctuations in auditory cortex interactively influence perception.

Alignment of neural oscillations with temporally regular input allows listeners to generate temporal expectations. However, it remains unclear how behavior is governed in the context of temporal variability: What role do temporal expectations play, and how do they interact with the strength of neural oscillatory activity? Here, human participants detected near-threshold targets in temporally variable acoustic sequences. Temporal expectation strength was estimated using an oscillator model and pre-target neural amplitudes in auditory cortex were extracted from magnetoencephalography signals. Temporal expectations modulated target-detection performance, however, only when neural delta-band amplitudes were large. Thus, slow neural oscillations act to gate influences of temporal expectation on perception. Furthermore, slow amplitude fluctuations governed linear and quadratic influences of auditory alpha-band activity on performance. By fusing a model of temporal expectation with neural oscillatory dynamics, the current findings show that human perception in temporally variable contexts relies on complex interactions between multiple neural frequency bands.

Predictions interact with missing sensory evidence in semantic processing areas.

Human brain function draws on predictive mechanisms that exploit higher-level context during lower-level perception. These mechanisms are particularly relevant for situations in which sensory information is compromised or incomplete, as for example in natural speech where speech segments may be omitted due to sluggish articulation. Here, we investigate which brain areas support the processing of incomplete words that were predictable from semantic context, compared with incomplete words that were unpredictable. During functional magnetic resonance imaging (fMRI), participants heard sentences that orthogonally varied in predictability (semantically predictable vs. unpredictable) and completeness (complete vs. incomplete, i.e. missing their final consonant cluster). The effects of predictability and completeness interacted in heteromodal semantic processing areas, including left angular gyrus and left precuneus, where activity did not differ between complete and incomplete words when they were predictable. The same regions showed stronger activity for incomplete than for complete words when they were unpredictable. The interaction pattern suggests that for highly predictable words, the speech signal does not need to be complete for neural processing in semantic processing areas. Hum Brain Mapp 37:704-716, 2016. © 2015 Wiley Periodicals, Inc.