Involuntary shifts of spatial attention contribute to distraction-Evidence from oscillatory alpha power and reaction time data.

Imagine you are focusing on the traffic on a busy street to ride your bike safely when suddenly you hear the siren of an ambulance. This unexpected sound involuntarily captures your attention and interferes with ongoing performance. We tested whether this type of distraction involves a spatial shift of attention. We measured behavioral data and magnetoencephalographic alpha power during a cross-modal paradigm that combined an exogenous cueing task and a distraction task. In each trial, a task-irrelevant sound preceded a visual target (left or right). The sound was usually the same animal sound (i.e., standard sound). Rarely, it was replaced by an unexpected environmental sound (i.e., deviant sound). Fifty percent of the deviants occurred on the same side as the target, and 50% occurred on the opposite side. Participants responded to the location of the target. As expected, responses were slower to targets that followed a deviant compared to a standard. Crucially, this distraction effect was mitigated by the spatial relationship between the targets and the deviants: responses were faster when targets followed deviants on the same versus different side, indexing a spatial shift of attention. This was further corroborated by a posterior alpha power modulation that was higher in the hemisphere ipsilateral (vs. contralateral) to the location of the attention-capturing deviant. We suggest that this alpha power lateralization reflects a spatial attention bias. Overall, our data support the contention that spatial shifts of attention contribute to deviant distraction.

Auditory representations for long lasting sounds: Insights from event-related brain potentials and neural oscillations.

The basic features of short sounds, such as frequency and intensity including their temporal dynamics, are integrated in a unitary representation. Knowledge on how our brain processes long lasting sounds is scarce. We review research utilizing the Mismatch Negativity event-related potential and neural oscillatory activity for studying representations for long lasting simple versus complex sounds such as sinusoidal tones versus speech. There is evidence for a temporal constraint in the formation of auditory representations: Auditory edges like sound onsets within long lasting sounds open a temporal window of about 350 ms in which the sounds' dynamics are integrated into a representation, while information beyond that window contributes less to that representation. This integration window segments the auditory input into short chunks. We argue that the representations established in adjacent integration windows can be concatenated into an auditory representation of a long sound, thus, overcoming the temporal constraint.

The detection of higher-order acoustic transitions is reflected in the N1 ERP.

The auditory system features various types of dedicated change detectors enabling the rapid parsing of auditory stimulation into distinct events. The activity of such detectors is reflected by the N1 ERP. Interestingly, certain acoustic transitions show an asymmetric N1 elicitation pattern: whereas first-order transitions (e.g., a change from a segment of constant frequency to a frequency glide [c-to-g change]) elicit N1, higher-order transitions (e.g., glide-to-constant [g-to-c] changes) do not. Consensus attributes this asymmetry to the absence of any available sensory mechanism that is able to rapidly detect higher-order changes. In contrast, our study provides compelling evidence for such a mechanism. We collected electrophysiological and behavioral data in a transient-detection paradigm. In each condition, a random (50%-50%) sequence of two types of tones occurred, which did or did not contain a transition (e.g., c-to-g and constant stimuli or g-to-c and glide tones). Additionally, the rate of pitch change of the glide varied (i.e., 10 vs. 40 semitones per second) in order to increase the number of responding neural assemblies. The rate manipulation modulated transient ERPs and behavioral detection performance for g-to-c transitions much stronger than for c-to-g transitions. The topographic and tomographic analyses suggest that the N1 response to c-to-g and also to g-to-c transitions emerged from the superior temporal gyrus. This strongly supports a sensory mechanism that allows the fast detection of higher-order changes.

Cross-modal distractors modulate oscillatory alpha power: the neural basis of impaired task performance.

Unexpected novel sounds capture one's attention, even when irrelevant to the task pursued (e.g., playing video game). This often comes at a cost to the task (e.g., slower responding). The neural basis for this behavioral distraction effect is not well understood and is subject of this study. Our approach was motivated by findings from cuing paradigms suggesting a link between modulations in oscillatory activity and voluntary attention shifts. The current study tested whether oscillatory activity is also modulated by a task-irrelevant auditory distractor, reflecting a neural signature of an involuntary shift of attention and accounting for the impaired task performance. We reanalyzed magnetoencephalographic data collected via an auditory-visual distraction paradigm in which a task-relevant visual stimulus was preceded by a task-irrelevant sound on each trial. In 87.5% this was a regular sound (Standard); in 12.5% this was a novel sound (Distractor). We compared nonphase locked oscillatory activity in a time window prior to the visual target as a function of the experimental manipulation (Distractor, Standard). We found low power in the pretarget time window for Distractors compared to Standards in the alpha and beta frequency bands. Importantly, individual alpha power correlated with response speed on a trial-by-trial basis for the Distractor only. Sources were localized to the occipital cortex, and also to the parietal and supratemporal cortices. These findings support our hypothesis that the distractor-related alpha power modulation indexes an involuntary shift of attention which accounts for the impaired task performance.

Which kind of transition is important for sound representation? An event-related potential study.

Auditory transients (such as sound onset or a frequency transition within a continuous sound) are assumed to parse the auditory input into smaller units enabling the formation of unitary sound representations separately for each segment. This was discovered by using the mismatch negativity (MMN) component of the event-related potential (ERP) that taps into auditory sensory memory representations. For unstructured sounds, MMN amplitude decreased or even vanished with increasing the temporal distance of an irregular feature (deviance, e.g. duration decrement) relative to the onset of an otherwise regularly occurring sound, whereas for sounds that were segmented by a transient, MMN persisted. It has been speculated that the P1-N1-P2 complex, indexing the sensory encoding of the transient, determines the temporal units of the acoustic input that are represented by the information processing system. To test this hypothesis, we utilized a previously reported asymmetry in the sensory encoding of physically identical but time-reversed transitions between segments of constant and gliding frequency. In separate blocks, we regularly presented 1400-ms sounds with a centered constant-to-glide or glide-to-constant transition. Occasionally and unpredictably, one of the regularly occurring sounds was shortened in duration to 910 ms. We found larger transition-related P1-N1-P2 potentials accompanied by larger deviance-related MMN amplitudes for sounds with constant-to-glide transition than for sounds with glide-to-constant transition. This provides evidence that it is the precise sensory encoding of the transition which is crucial for automatically parsing the auditory input into smaller units, thus enabling the formation of unitary sound representations even for late segments.

The representation of unattended, segmented sounds: a mismatch negativity (MMN) study.

The detection of an irregular, potentially relevant change (deviance) in the regular, unattended acoustic environment is ensured by the automatic deviance detection mechanism. It underlies the formation of a regularity representation and a comparison of an incoming sound with this representation. A mismatch outcome of this comparison evokes the mismatch negativity (MMN) of the event-related potential. For unattended pure tones the automatic deviance detection mechanism operates most efficiently for initial sound parts, which is why these are suggested to contribute more to sound representation than later parts. A transient that physically segments the sound can overcome this temporal constraint in sound representation. Whether the resulting individual (initial and terminal) sound segments or the joined two-segments give rise to the regularity representation is addressed here. We took advantage that the MMN attenuation to the second of two successive deviances (deviance-repetition effect) is more pronounced when the deviances belong to the same unit of representation. We measured MMN for two deviances (frequency modulations) within segmented sounds that either occurred within the initial or the terminal segment, or that were split across both segments. Unexpectedly, we did not obtain a deviance-repetition effect. Instead, we obtained a temporal distance effect: With increasing temporal distance from deviance-onset relative to segment-onset the MMN amplitude decreased. Furthermore, this effect did not depend on whether the deviance occurred in the initial or in the terminal segment. Thus, (for the current approach) we suggest that the regularity representation is based on the individual rather than joined segments.

Differential processing of terminal tone parts within structured and non-structured tones.

Recent studies utilizing the mismatch negativity (MMN) event-related potential (ERP) revealed that when a repetitive sequence of sinusoidal tones is presented, the occasional insertion of a short deviation into some of the tones leads to the elicitation of an MMN only if it occurs during the initial 300 ms, but not beyond. In contrast, deviations occurring in speech sounds elicit MMN even beyond 300 ms. We conducted two experiments to resolve this conflict. We hypothesised that an additional transient within an otherwise unstructured tone may overcome this limitation. First, we tested for MMN to a deviance at the terminal part of a 650 ms tone which did or did not contain a gap. Only when the tone included the gap, MMN was obtained. Second, we compared the gap condition with two noise conditions, in which the gap was replaced by modulated white noise. The noise conditions differed with respect to the saliency of the perceived interruption of the tone. In all three conditions, MMN was elicited. These results demonstrate that structuring a sinusoidal tone by a gap or a noise interval is sufficient to regain MMN. It is suggested that the introduction of an additional transient triggers a new integration window overcoming the temporal constraints of automatic tone representation. This resolves the seeming contradiction between MMN studies using tonal and speech sounds.