Conditional deviant repetition in the oddball paradigm modulates processing at the level of P3a but not MMN.

The auditory system has an amazing ability to rapidly encode auditory regularities. Evidence comes from the popular oddball paradigm, in which frequent (standard) sounds are occasionally exchanged for rare deviant sounds, which then elicit signs of prediction error based on their unexpectedness (e.g., MMN and P3a). Here, we examine the widely neglected characteristics of deviants being bearers of predictive information themselves; naive participants listened to sound sequences constructed according to a new, modified version of the oddball paradigm including two types of deviants that followed diametrically opposed rules: one deviant sound occurred mostly in pairs (repetition rule), the other deviant sound occurred mostly in isolation (non-repetition rule). Due to this manipulation, the sound following a first deviant (either the same deviant or a standard) was either predictable or unpredictable based on its conditional probability associated with the preceding deviant sound. Our behavioral results from an active deviant detection task replicate previous findings that deviant repetition rules (based on conditional probability) can be extracted when behaviorally relevant. Our electrophysiological findings obtained in a passive listening setting indicate that conditional probability also translates into differential processing at the P3a level. However, MMN was confined to global deviants and was not sensitive to conditional probability. This suggests that higher-level processing concerned with stimulus selection and/or evaluation (reflected in P3a) but not lower-level sensory processing (reflected in MMN) considers rarely encountered rules.

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.

That sounds awful! Does sound unpleasantness modulate the mismatch negativity and its habituation?

There are sounds that most people perceive as highly unpleasant, for instance, the sound of rubbing pieces of polystyrene together. Previous research showed larger physiological and neural responses for such aversive compared to neutral sounds. Hitherto, it remains unclear whether habituation, i.e., diminished responses to repeated stimulus presentation, which is typically reported for neutral sounds, occurs to the same extent for aversive stimuli. We measured the mismatch negativity (MMN) in response to rare occurrences of aversive or neutral deviant sounds within an auditory oddball sequence in 24 healthy participants, while they performed a demanding visual distractor task. Deviants occurred as single events (i.e., between two standards) or as double deviants (i.e., repeating the identical deviant sound in two consecutive trials). All deviants elicited a clear MMN, and amplitudes were larger for aversive than for neutral deviants (irrespective of their position within a deviant pair). This supports the claim of preattentive emotion evaluation during early auditory processing. In contrast to our expectations, MMN amplitudes did not show habituation, but increased in response to deviant repetition-similarly for aversive and neutral deviants. A more fine-grained analysis of individual MMN amplitudes in relation to individual arousal and valence ratings of each sound item revealed that stimulus-specific MMN amplitudes were best predicted by the interaction of deviant position and perceived arousal, but not by valence. Deviants with perceived higher arousal elicited larger MMN amplitudes only at the first deviant position, indicating that the MMN reflects preattentive processing of the emotional content of sounds.

Markov chains as a proxy for the predictive memory representations underlying mismatch negativity.

Events not conforming to a regularity inherent to a sequence of events elicit prediction error signals of the brain such as the Mismatch Negativity (MMN) and impair behavioral task performance. Events conforming to a regularity lead to attenuation of brain activity such as stimulus-specific adaptation (SSA) and behavioral benefits. Such findings are usually explained by theories stating that the information processing system predicts the forthcoming event of the sequence via detected sequential regularities. A mathematical model that is widely used to describe, to analyze and to generate event sequences are Markov chains: They contain a set of possible events and a set of probabilities for transitions between these events (transition matrix) that allow to predict the next event on the basis of the current event and the transition probabilities. The accuracy of such a prediction depends on the distribution of the transition probabilities. We argue that Markov chains also have useful applications when studying cognitive brain functions. The transition matrix can be regarded as a proxy for generative memory representations that the brain uses to predict the next event. We assume that detected regularities in a sequence of events correspond to (a subset of) the entries in the transition matrix. We apply this idea to the Mismatch Negativity (MMN) research and examine three types of MMN paradigms: classical oddball paradigms emphasizing sound probabilities, between-sound regularity paradigms manipulating transition probabilities between adjacent sounds, and action-sound coupling paradigms in which sounds are associated with actions and their intended effects. We show that the Markovian view on MMN yields theoretically relevant insights into the brain processes underlying MMN and stimulates experimental designs to study the brain's processing of event sequences.

Deviants violating higher-order auditory regularities can become predictive and facilitate behaviour.

The human auditory system is believed to represent regularities inherent in auditory information in internal models. Sounds not matching the standard regularity (deviants) elicit prediction error, alerting the system to information not explainable within currently active models. Here, we examine the widely neglected characteristic of deviants bearing predictive information themselves. In a modified version of the oddball paradigm, using higher-order regularities, we set up different expectations regarding the sound following a deviant. Higher-order regularities were defined by the relation of pitch within tone pairs (rather than absolute pitch of individual tones). In a deviant detection task participants listened to oddball sequences including two deviant types following diametrically opposed rules: one occurred mostly in succession (high repetition probability) and the other mostly in isolation (low repetition probability). Participants in Experiment 1 were not informed (naïve), whereas in Experiment 2 they were made aware of the repetition rules. Response times significantly decreased from first to second deviant when repetition probability was high-albeit more in the presence of explicit rule knowledge. There was no evidence of a facilitation effect when repetition probability was low. Significantly more false alarms occurred in response to standards following high compared with low repetition probability deviants, but only in participants aware of the repetition rules. These findings provide evidence that not only deviants violating lower- but also higher-order regularities can inform predictions about auditory events. More generally, they confirm the utility of this new paradigm to gather further insights into the predictive properties of the human brain.

Neural processing of orientation differences between the eyes' images.

The aim of this study was to explore the neural mechanisms underlying visual processing of brief stimuli that were either the same in the two eyes or differed in orientation between the two eyes. To examine the neural mechanisms, I measured event-related potentials (ERPs) to 200-ms sine-wave gratings differing in orientation between the eyes from 0° to 90°. The gratings were either both of high contrast or both of low contrast. They elicited typical ERPs at occipital electrodes, with a first major component (P100) 100 ms after stimulus onset and a second major component (N170) 170 ms after stimulus onset. Global electrical field strength and focal amplitudes of both components were affected by grating contrast: High-contrast gratings elicited larger amplitudes than low-contrast gratings, confirming that neural responses depend on stimulus salience. P100 amplitude followed a U-shaped function: It was larger when the orientations were the same in the two eyes (yielding binocular fusion), intermediate when the orientations were maximally different between the eyes (leading to binocular rivalry), and smallest for in-between orientation differences. N170 amplitude followed a linear function: It was smallest when the orientations were the same and increased with orientation difference between the eyes. These results suggest that the P100 reflects processes in which the binocular input are offset against each other, and that the N170 reflects binocular rivalry. I argue that the N170 shows the effects of reciprocal inhibition and adaptation--both critical factors in theories of binocular rivalry.

Encoding of deterministic and stochastic auditory rules in the human brain: The mismatch negativity mechanism does not reflect basic probability.

Regularities in a sequence of sounds can be automatically encoded in a predictive model by the auditory system. When a sound deviates from the one predicted by the model, a mismatch negativity (MMN) is elicited, which is taken to reflect a prediction error at a particular level of the model hierarchy. Although there are many studies on deterministic regularities, only a few have investigated the brain's ability to encode non-deterministic regularities. We studied a simple stochastic regularity: two tone pitches (standards, each occurring on 45% of trials); this regularity was occasionally violated by another tone pitch (deviant, occurring on 10% of trials). We found MMN when the deviant's pitch was outside those of the standards, but not when it was between them. Importantly, when we alternated the occurrence of the same two standards, making them deterministic, the deviant elicited MMN, even when its pitch was between those of the standards. Thus, although the MMN system is extremely powerful in establishing even quite complex deterministic regularities, it fails with a simple stochastic regularity. We argue that the MMN system does not know basic probability.

Visual object representations can be formed outside the focus of voluntary attention: evidence from event-related brain potentials.

There is an ongoing debate whether visual object representations can be formed outside the focus of voluntary attention. Recently, implicit behavioral measures suggested that grouping processes can occur for task-irrelevant visual stimuli, thus supporting theories of preattentive object formation (e.g., Lamy, D., Segal, H., & Ruderman, L. Grouping does not require attention. Perception and Psychophysics, 68, 17-31, 2006; Russell, C., & Driver, J. New indirect measures of "inattentive" visual grouping in a change-detection task. Perception and Psychophysics, 67, 606-623, 2005). We developed an ERP paradigm that allows testing for visual grouping when neither the objects nor its constituents are related to the participant's task. Our paradigm is based on the visual mismatch negativity ERP component, which is elicited by stimuli deviating from a regular stimulus sequence even when the stimuli are ignored. Our stimuli consisted of four pairs of colored discs that served as objects. These objects were presented isochronously while participants were engaged in a task related to the continuously presented fixation cross. Occasionally, two color deviances occurred simultaneously either within the same object or across two different objects. We found significant ERP differences for same- versus different-object deviances, supporting the notion that forming visual object representations by grouping can occur outside the focus of voluntary attention. Also our behavioral experiment, in which participants responded to color deviances--thus, this time the discs but, again, not the objects were task relevant--showed that the object status matters. Our results stress the importance of early grouping processes for structuring the perceptual world.

Lengthy suppression from similar stimuli during rapid serial visual presentation.

The stimulus at any point in the visual field is rarely static during normal viewing: observer and object movement conspire to produce a continually changing series of stimuli. Our aim was to study both the short- and long-term interactions between responses to a series of stimuli presented at a single visual location. We used rapid serial visual presentation (RSVP) in which the stimuli were randomly oriented gratings delivered at the rate of 30 per second. Human subjects pressed a key whenever they saw a target orientation, for example horizontal. The results were analyzed by finding two orientations before each key-press. The first preceded the key-press by the reaction time, and the second preceded the first by an interval of variable duration. There were two main findings. First, the subject was more likely to press the key when the target was immediately preceded by a grating of similar orientation. This facilitation presumably results from the summation of sub-threshold inputs. Second, a key-press was reduced in probability when a target orientation was preceded by a similar orientation with an interstimulus interval of 100-400 ms. The time course of this suppression is similar to that seen in attentional blink experiments.

The quest for the genuine visual mismatch negativity (vMMN): Event-related potential indications of deviance detection for low-level visual features.

Research shows that the visual system monitors the environment for changes. For example, a left-tilted bar, a deviant, that appears after several presentations of a right-tilted bar, standards, elicits a classic visual mismatch negativity (vMMN): greater negativity for deviants than standards in event-related potentials (ERPs) between 100 and 300 ms after onset of the deviant. The classic vMMN is contributed to by adaptation; it can be distinguished from the genuine vMMN that, through use of control conditions, compares standards and deviants that are equally adapted and physically identical. To determine whether the vMMN follows similar principles to the auditory mismatch negativity (MMN), in two experiments we searched for a genuine vMMN from simple, physiologically plausible stimuli that change in fundamental dimensions: orientation, contrast, phase, and spatial frequency. We carefully controlled for attention and eye movements. We found no evidence for the genuine vMMN, despite adequate statistical power. We conclude that either the genuine vMMN is a rather unstable phenomenon that depends on still-to-be-identified experimental parameters, or it is confined to visual stimuli for which monitoring across time is more natural than monitoring over space, such as for high-level features. We also observed an early deviant-related positivity that we propose might reflect earlier predictive processing.