Bradley N. Jack

Self-initiated actions result in suppressed auditory but amplified visual evoked components in healthy participants

Self-suppression refers to the phenomenon that sensations initiated by our own movements are typically less salient, and elicit an attenuated neural response, compared to sensations resulting from changes in the external world. Evidence for self-suppression is provided by previous ERP studies in the auditory modality, which have found that healthy participants typically exhibit a reduced auditory N1 component when auditory stimuli are self-initiated as opposed to externally initiated. However, the literature investigating self-suppression in the visual modality is sparse, with mixed findings and experimental protocols. An EEG study was conducted to expand our understanding of self-suppression across different sensory modalities. Healthy participants experienced either an auditory (tone) or visual (pattern-reversal) stimulus following a willed button press (self-initiated), a random interval (externally initiated, unpredictable onset), or a visual countdown (externally initiated, predictable onset-to match the intrinsic predictability of self-initiated stimuli), while EEG was continuously recorded. Reduced N1 amplitudes for self- versus externally initiated tones indicated that self-suppression occurred in the auditory domain. In contrast, the visual N145 component was amplified for self- versus externally initiated pattern reversals. Externally initiated conditions did not differ as a function of their predictability. These findings highlight a difference in sensory processing of self-initiated stimuli across modalities, and may have implications for clinical disorders that are ostensibly associated with abnormal self-suppression.

Goal-Directed and Habit-Like Modulations of Stimulus Processing during Reinforcement Learning

Recent research has shown that perceptual processing of stimuli previously associated with high-value rewards is automatically prioritized even when rewards are no longer available. It has been hypothesized that such reward-related modulation of stimulus salience is conceptually similar to an “attentional habit.” Recording event-related potentials in humans during a reinforcement learning task, we show strong evidence in favor of this hypothesis. Resistance to outcome devaluation (the defining feature of a habit) was shown by the stimulus-locked P1 component, reflecting activity in the extrastriate visual cortex. Analysis at longer latencies revealed a positive component (corresponding to the P3b, from 550–700 ms) sensitive to outcome devaluation. Therefore, distinct spatiotemporal patterns of brain activity were observed corresponding to habitual and goal-directed processes. These results demonstrate that reinforcement learning engages both attentional habits and goal-directed processes in parallel. Consequences for brain and computational models of reinforcement learning are discussed. SIGNIFICANCE STATEMENT The human attentional network adapts to detect stimuli that predict important rewards. A recent hypothesis suggests that the visual cortex automatically prioritizes reward-related stimuli, driven by cached representations of reward value; that is, stimulus–response habits. Alternatively, the neural system may track the current value of the predicted outcome. Our results demonstrate for the first time that visual cortex activity is increased for reward-related stimuli even when the rewarding event is temporarily devalued. In contrast, longer-latency brain activity was specifically sensitive to transient changes in reward value. Therefore, we show that both habit-like attention and goal-directed processes occur in the same learning episode at different latencies. This result has important consequences for computational models of reinforcement learning.

We make predictions about eye of origin of visual input: Visual mismatch negativity from binocular rivalry.

The visual mismatch negativity (vMMN) is a negative component of event-related potentials (ERPs). It occurs when an infrequent visual stimulus, a deviant, is randomly and unpredictably presented in a sequence of frequent visual stimuli, the standards, and is thought to reflect prediction and prediction error of visual input. We investigated the sensitivity of vMMN to eye of origin (utrocular) information as well as to orientation information. We presented 80% of binocular rivalry standards (one grating to one eye and an identical, orthogonally oriented grating to the other eye), and 20% of deviants, either by swapping the gratings between the eyes to change the eye of origin of the gratings (an eye-swap deviant) or by rotating the gratings by 45° to change the orientation of the gratings (an orientation deviant). We found an orientation vMMN that was maximal at about 250 ms and an eye-swap vMMN that was maximal at about 380 ms. We also found deviance-related activity to both sorts of stimuli earlier than is traditionally defined as a vMMN. We used standardized low-resolution brain electromagnetic tomography (sLORETA) to localize each vMMN component and found similar sources for both vMMNs in occipital and frontal areas of the brain but differences in parietal and temporal areas. We conclude that eye of origin information can be used to elicit vMMN, that eye-swap vMMN is different to orientation vMMN, and that vMMN can be generated from information of which observers are unaware.

Neurophysiological evidence of efference copies to inner speech

Efference copies refer to internal duplicates of movement-producing neural signals. Their primary function is to predict, and often suppress, the sensory consequences of willed movements. Efference copies have been almost exclusively investigated in the context of overt movements. The current electrophysiological study employed a novel design to show that inner speech – the silent production of words in one’s mind – is also associated with an efference copy. Participants produced an inner phoneme at a precisely specified time, at which an audible phoneme was concurrently presented. The production of the inner phoneme resulted in electrophysiological suppression, but only if the content of the inner phoneme matched the content of the audible phoneme. These results demonstrate that inner speech – a purely mental action – is associated with an efference copy with detailed auditory properties. These findings suggest that inner speech may ultimately reflect a special type of overt speech.

Brain activity from stimuli that are not perceived: Visual mismatch negativity during binocular rivalry suppression

Predictive coding explains visual perception as the result of an interaction between bottom-up sensory input and top-down generative models at each level of the visual hierarchy. Evidence for this comes from the visual mismatch negativity (vMMN): a more negative ERP for rare, unpredictable visual stimuli-deviants, than for frequent, predictable visual stimuli-standards. Here, we show that the vMMN does not require conscious experience. We measured the vMMN from monocular luminance-decrement deviants that were either perceived or not during binocular rivalry dominance or suppression, respectively. We found that both sorts of deviants elicited the vMMN at about 250 ms after stimulus onset, with perceived deviants eliciting a bigger vMMN than not-perceived deviants. These results show that vMMN occurs in the absence of consciousness, and that consciousness enhances the processing underlying vMMN. We conclude that generative models of visual perception are tested, even when sensory input for those models is not perceived.

Impaired mismatch negativity to frequency deviants in individuals at ultra-high risk for psychosis, and preliminary evidence for further impairment with transition to psychosis

BACKGROUND There is evidence to suggest that people with established psychotic disorders show impairments in the mismatch negativity induced by a frequency-deviant sound (fMMN), and that these impairments worsen with the deterioration of psychotic symptoms. This study aimed to test whether individuals at ultra-high risk (UHR) for psychosis show pre-morbid impairments in fMMN, and if so, whether fMMN continues to deteriorate with transition to psychosis. METHOD fMMN was recorded in a cohort of UHR individuals (n=42) and compared to healthy controls (n=29). Of the 27 UHR participants who returned for a second EEG session, six participants had transitioned to psychosis by 12-month follow-up (UHR-T) and were compared to the 21 participants who did not transition (UHR-NT). RESULTS fMMN amplitude was significantly reduced, relative to healthy controls, in the UHR cohort. Furthermore, UHR-T individuals showed a significant decrease in fMMN amplitude over the period from baseline to post-transition; this reduction was not observed in UHR-NT. CONCLUSIONS These results suggest that fMMN is abnormal in UHR individuals, as has repeatedly been found previously in people with established psychotic disorders. The finding that fMMN impairment worsens with transition to psychosis is consistent with the staging model of psychosis; however, caution must be taken in interpreting these findings, given the extremely small sample size of the UHR-T group.

Does the ventriloquist illusion assist selective listening

Driver (1996) reported that the ventriloquist illusion can enhance selective listening of speech. Participants in his study listened to target and distractor words from a single loudspeaker while watching lip movements of the target words on a video monitor either above the loudspeaker or displaced to the left or right. He found that participants were more accurate in repeating the target words when the video was displaced from the loudspeaker than when the video was directly above the loudspeaker. Driver proposed that the ventriloquist illusion dragged the target sounds toward the location of the lip movements, freeing them from interference from the distractor words. However, successful attempts at replicating this finding are rare (we know of only three successful replications from 19 attempts). In five experiments, we found a weak advantage for selective listening from displaced lip movements only when there was a convincing ventriloquist illusion. We conclude that the ventriloquist illusion is necessary to confer the advantage for selective listening from displaced lip movements but that the phenomenon is a fleeting one at best.

Cross‐modal symbolic processing can elicit either an N2 or a protracted N2/N400 response

A cross-modal symbolic paradigm was used to elicit EEG activity related to semantic incongruence. Twenty-five undergraduate students viewed pairings of visual lexical cues (e.g., DOG) with congruent (50% of trials) or incongruent (50%) auditory nonlexical stimuli (animal vocalizations; e.g., sound of a dog woofing or a cat meowing). In one condition, many different pairs of congruent/incongruent stimuli were shown, whereas in a second condition only two pairs of stimuli were repeatedly shown. A typical N400-like pattern of incongruence-related activity (including activity in the N2 time window) was evident in the condition using many stimuli, whereas the incongruence-related activity in the two-stimuli condition was confined to differential N2-like activity. A supplementary analysis excluded stimulus characteristics as the source of this differential activity between conditions. We found that a single individual performing a fixed task can demonstrate either a protracted N400-like pattern of activity or a more temporally focused N2-like pattern of activity in response to the same stimulus, which suggests that the N2 may be a precursor to the protracted N400 response.