Individual differences in everyday multitasking behavior and its relation to cognition and personality.

Our ability to multitask-focus on multiple tasks simultaneously-is one of the most critical functions of our cognitive system. This capability has shown to have relations to cognition and personality in empirical studies, which have received much attention recently. This review article integrates the available findings to examine how individual differences in multitasking behavior are linked with different cognitive constructs and personality traits to conceptualize what multitasking behavior represents. In this review, we highlight the methodological differences and theoretical conceptions. Cognitive constructs including executive functions (i.e., shifting, updating, and inhibition), working memory, relational integration, divided attention, reasoning, and prospective memory were investigated. Concerning personality, the traits of polychronicity, impulsivity, and the five-factor model were considered. A total of 43 studies met the inclusion criteria and entered the review. The research synthesis directs us to propose two new conceptual models to explain multitasking behavior as a psychometric construct. The first model demonstrates that individual differences in multitasking behavior can be explained by cognitive abilities. The second model proposes that personality traits constitute a moderating effect on the relation between multitasking behavior and cognition. Finally, we provide possible future directions for the line of research.

Transfer of Tactile Learning from Trained to Untrained Body Parts Supported by Cortical Coactivation in Primary Somatosensory Cortex.

A pioneering study by Volkmann (1858) revealed that training on a tactile discrimination task improved task performance, indicative of tactile learning, and that such tactile learning transferred from trained to untrained body parts. However, the neural mechanisms underlying tactile learning and transfer of tactile learning have remained unclear. We trained groups of human subjects (female and male) in daily sessions on a tactile discrimination task either by stimulating the palm of the right hand or the sole of the right foot. Task performance before training was similar between the palm and sole. Posttraining transfer of tactile learning was greater from the trained right sole to the untrained right palm than from the trained right palm to the untrained right sole. Functional magnetic resonance imaging (fMRI) and multivariate pattern classification analysis revealed that the somatotopic representation of the right palm in contralateral primary somatosensory cortex (SI) was coactivated during tactile stimulation of the right sole. More pronounced coactivation in the cortical representation of the right palm was associated with lower tactile performance for tactile stimulation of the right sole and more pronounced subsequent transfer of tactile learning from the trained right sole to the untrained right palm. In contrast, coactivation of the cortical sole representation during tactile stimulation of the palm was less pronounced and no association with tactile performance and subsequent transfer of tactile learning was found. These results indicate that tactile learning may transfer to untrained body parts that are coactivated to support tactile learning with the trained body part.SIGNIFICANCE STATEMENT Perceptual skills such as the discrimination of tactile cues can improve by means of training, indicative of perceptual learning and sensory plasticity. However, it has remained unclear whether and if so, how such perceptual learning can occur if the training task is very difficult. Here, we show for tactile perceptual learning that the representation of the palm of the hand in primary somatosensory cortex (SI) is coactivated to support learning of a difficult tactile discrimination task with tactile stimulation of the sole of the foot. Such cortical coactivation of an untrained body part to support tactile learning with a trained body part might be critically involved in the subsequent transfer of tactile learning between the trained and untrained body parts.

Heading for Personalized rTMS in Tinnitus: Reliability of Individualized Stimulation Protocols in Behavioral and Electrophysiological Responses.

BACKGROUND: Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation tool potentially modulating pathological brain activity. Its clinical effectiveness is hampered by varying results and characterized by inter-individual variability in treatment responses. RTMS individualization might constitute a useful strategy to overcome this variability. A precondition for this approach would be that repeatedly applied protocols result in reliable effects. The condition tinnitus provides the advantage of immediate behavioral consequences (tinnitus loudness changes) after interventions and thus offers an excellent model to exemplify TMS personalization. OBJECTIVE: The aim was to investigate the test-retest reliability of short rTMS stimulations in modifying tinnitus loudness and oscillatory brain activity as well as to examine the feasibility of rTMS individualization in tinnitus. METHODS: Three short verum (1, 10, 20 Hz; 200 pulses) and one sham (0.1 Hz; 20 pulses) rTMS protocol were administered on two different days in 22 tinnitus patients. Before and after each protocol, oscillatory brain activity was recorded with electroencephalography (EEG), together with behavioral tinnitus loudness ratings. RTMS individualization was executed on the basis of behavioral and electrophysiological responses. Stimulation responders were identified via consistent sham-superior increases in tinnitus loudness (behavioral responders) and alpha power increases or gamma power decreases (alpha responders/gamma responders) in accordance with the prevalent neurophysiological models for tinnitus. RESULTS: It was feasible to identify individualized rTMS protocols featuring reliable tinnitus loudness changes (55% behavioral responder), alpha increases (91% alpha responder) and gamma decreases (100% gamma responder), respectively. Alpha responses primary occurred over parieto-occipital areas, whereas gamma responses mainly appeared over frontal regions. On the contrary, test-retest correlation analyses per protocol at a group level were not significant neither for behavioral nor for electrophysiological effects. No associations between behavioral and EEG responses were found. CONCLUSION: RTMS individualization via behavioral and electrophysiological data in tinnitus can be considered as a feasible approach to overcome low reliability at the group level. The present results open the discussion favoring personalization utilizing neurophysiological markers rather than behavioral responses. These insights are not only useful for the rTMS treatment of tinnitus but also for neuromodulation interventions in other pathologies, as our results suggest that the individualization of stimulation protocols is feasible despite absent group-level reliability.

Gray Bananas and a Red Letter A - From Synesthetic Sensation to Memory Colors.

Grapheme-color synesthesia is a condition in which objectively achromatic graphemes induce concurrent color experiences. While it was long thought that the colors emerge during perception, there is growing support for the view that colors are integral to synesthetes' cognitive representations of graphemes. In this work, we review evidence for two opposing theories positing either a perceptual or cognitive origin of concurrent colors: the cross-activation theory and the conceptual-mediation model. The review covers results on inducer and concurrent color processing as well as findings concerning the brain structure and grapheme-color mappings in synesthetes and trained mappings in nonsynesthetes. The results support different aspects of both theories. Finally, we discuss how research on memory colors could provide a new perspective in the debate about the level of processing at which the synesthetic colors occur.

Neural dynamics of breaking continuous flash suppression.

Sensory input to the human visual system often becomes accessible to cognition and overt report during processing. We investigated neural precursors of conscious vision using EEG recordings and the popular breaking continuous flash suppression (bCFS) paradigm. In this technique, a mask consisting of high-contrast dynamic patterns is presented to one eye, predominating over a target stimulus presented to the other eye. The time needed for the target stimulus to overcome the suppression is thought to reflect the transition from unconscious to conscious perception. In bCFS trials with slow responses, indicative of potent suppression, a time-frequency analysis showed reduced occipital gamma power (33-38 Hz) contralaterally to the visual hemifield where the target was presented 0.27 to 0.21 s prior to the behavioral response. This neural activity was concurrent with a local phase reset and enhanced long-range phase synchronization in the theta band (7 Hz). Such a pattern did not arise in a control condition in which suppression was not induced. Thus, the theta phase reset and synchronization in bCFS trials precede a break from suppression, likely initiating a re-routing of information such that the neural representation of the target is updated more efficiently than that of the competing mask. Overall, these findings mark the emergence of a binocularly integrated percept that can be consciously selected for a behavioral response.

Time-based expectations entail preparatory motor activity.

Human behavior is guided by expectations that facilitate perception of upcoming events or reaction to them. In natural settings expectations are often implicitly based on time, e.g., when making a phone call one would expect to hear either a person answering (earlier) or a voicemail greeting (later). We investigated how time-based expectations can improve performance in the absence of explicit prior information on the pending stimulus or the associated response. Visual stimuli were presented after a characteristic short or long foreperiod, and a forced-choice categorization using either the left or the right hand was required. The electroencephalogram (EEG) revealed a decrease in central 9-12 Hz power over the course of the trial. Moreover, lateralized pre-motor potentials were observed which changed polarity after the short foreperiod. At stimulus onset, amplitudes of pre-motor potentials co-varied with performance, so that higher (more negative) amplitudes were associated with slower responses to unexpected targets. Altogether, the results suggest that implicit time-based expectations entail effector-specific preparatory brain activity, which is inhibited until the expected onset time of the event. Thus, time-based expectations prepare for action.

Combined EMD-sLORETA Analysis of EEG Data Collected during a Contour Integration Task.

Lately, Ensemble Empirical Mode Decomposition (EEMD) techniques receive growing interest in biomedical data analysis. Event-Related Modes (ERMs) represent features extracted by an EEMD from electroencephalographic (EEG) recordings. We present a new approach for source localization of EEG data based on combining ERMs with inverse models. As the first step, 64 channel EEG recordings are pooled according to six brain areas and decomposed, by applying an EEMD, into their underlying ERMs. Then, based upon the problem at hand, the most closely related ERM, in terms of frequency and amplitude, is combined with inverse modeling techniques for source localization. More specifically, the standardized low resolution brain electromagnetic tomography (sLORETA) procedure is employed in this work. Accuracy and robustness of the results indicate that this approach deems highly promising in source localization techniques for EEG data.

Probing the causal role of prestimulus interregional synchrony for perceptual integration via tACS.

The phase of prestimulus oscillations at 7-10 Hz has been shown to modulate perception of briefly presented visual stimuli. Specifically, a recent combined EEG-fMRI study suggested that a prestimulus oscillation at around 7 Hz represents open and closed windows for perceptual integration by modulating connectivity between lower order occipital and higher order parietal brain regions. We here utilized brief event-related transcranial alternating current stimulation (tACS) to specifically modulate this prestimulus 7 Hz oscillation, and the synchrony between parietal and occipital brain regions. To this end we tested for a causal role of this particular prestimulus oscillation for perceptual integration. The EEG was acquired at the same time allowing us to investigate frequency specific after effects phase-locked to stimulation offset. On a behavioural level our results suggest that tACS did modulate perceptual integration, however, in an unexpected manner. On an electrophysiological level our results suggest that brief tACS does induce oscillatory entrainment, as visible in frequency specific activity phase-locked to stimulation offset. Together, our results do not strongly support a causal role of prestimulus 7 Hz oscillations for perceptual integration. However, our results suggest that brief tACS is capable of modulating oscillatory activity in a temporally sensitive manner.

Spatial Mnemonic Encoding: Theta Power Decreases and Medial Temporal Lobe BOLD Increases Co-Occur during the Usage of the Method of Loci.

The method of loci is one, if not the most, efficient mnemonic encoding strategy. This spatial mnemonic combines the core cognitive processes commonly linked to medial temporal lobe (MTL) activity: spatial and associative memory processes. During such processes, fMRI studies consistently demonstrate MTL activity, while electrophysiological studies have emphasized the important role of theta oscillations (3-8 Hz) in the MTL. However, it is still unknown whether increases or decreases in theta power co-occur with increased BOLD signal in the MTL during memory encoding. To investigate this question, we recorded EEG and fMRI separately, while human participants used the spatial method of loci or the pegword method, a similarly associative but nonspatial mnemonic. The more effective spatial mnemonic induced a pronounced theta power decrease source localized to the left MTL compared with the nonspatial associative mnemonic strategy. This effect was mirrored by BOLD signal increases in the MTL. Successful encoding, irrespective of the strategy used, elicited decreases in left temporal theta power and increases in MTL BOLD activity. This pattern of results suggests a negative relationship between theta power and BOLD signal changes in the MTL during memory encoding and spatial processing. The findings extend the well known negative relation of alpha/beta oscillations and BOLD signals in the cortex to theta oscillations in the MTL.

Ensemble Empirical Mode Decomposition Analysis of EEG Data Collected during a Contour Integration Task.

We discuss a data-driven analysis of EEG data recorded during a combined EEG/fMRI study of visual processing during a contour integration task. The analysis is based on an ensemble empirical mode decomposition (EEMD) and discusses characteristic features of event related modes (ERMs) resulting from the decomposition. We identify clear differences in certain ERMs in response to contour vs noncontour Gabor stimuli mainly for response amplitudes peaking around 100 [ms] (called P100) and 200 [ms] (called N200) after stimulus onset, respectively. We observe early P100 and N200 responses at electrodes located in the occipital area of the brain, while late P100 and N200 responses appear at electrodes located in frontal brain areas. Signals at electrodes in central brain areas show bimodal early/late response signatures in certain ERMs. Head topographies clearly localize statistically significant response differences to both stimulus conditions. Our findings provide an independent proof of recent models which suggest that contour integration depends on distributed network activity within the brain.

Electrophysiological correlates of voice learning and recognition.

Listeners can recognize familiar human voices from variable utterances, suggesting the acquisition of speech-invariant voice representations during familiarization. However, the neurocognitive mechanisms mediating learning and recognition of voices from natural speech are currently unknown. Using electrophysiology, we investigated how representations are formed during intentional learning of initially unfamiliar voices that were later recognized among novel voices. To probe the acquisition of speech-invariant voice representations, we compared a "same sentence" condition, in which speakers repeated the study utterances at test, and a "different sentence" condition. Although recognition performance was higher for same compared with different sentences, substantial voice learning also occurred for different sentences, with recognition performance increasing across consecutive study-test-cycles. During study, event-related potentials elicited by voices subsequently remembered elicited a larger sustained parietal positivity (∼250-1400 ms) compared with subsequently forgotten voices. This difference due to memory was unaffected by test sentence condition and may thus reflect the acquisition of speech-invariant voice representations. At test, voices correctly classified as "old" elicited a larger late positive component (300-700 ms) at Pz than voices correctly classified as "new." This event-related potential OLD/NEW effect was limited to the same sentence condition and may thus reflect speech-dependent retrieval of voices from episodic memory. Importantly, a speech-independent effect for learned compared with novel voices was found in beta band oscillations (16-17 Hz) between 290 and 370 ms at central and right temporal sites. Our results are a first step toward elucidating the electrophysiological correlates of voice learning and recognition.

Brain networks supporting perceptual grouping and contour selection.

The human visual system groups local elements into global objects seemingly without effort. Using a contour integration task and EEG source level analyses, we tested the hypothesis that perceptual grouping requires a top-down selection, rather than a passive pooling, of neural information that codes local elements in the visual image. The participants were presented visual displays with or without a hidden contour. Two tasks were performed: a central luminance-change detection task and a peripheral contour detection task. Only in the contour-detection task could we find differential brain activity between contour and non-contour conditions, within a distributed brain network including parietal, lateral occipital and primary visual areas. Contour processing was associated with an inflow of information from lateral occipital into primary visual regions, as revealed from the slope of phase differences between source level oscillations within these areas. The findings suggest that contour integration results from a selection of neural information from lower visual areas, and that this selection is driven by the lateral occipital cortex.

Right-hemisphere specialization for contour grouping.

Previous studies often revealed a right-hemisphere specialization for processing the global level of compound visual stimuli. Here we explore whether a similar specialization exists for the detection of intersected contours defined by a chain of local elements. Subjects were presented with arrays of randomly oriented Gabor patches that could contain a global path of collinearly arranged elements in the left or in the right visual hemifield. As expected, the detection accuracy was higher for contours presented to the left visual field/right hemisphere. This difference was absent in two control conditions where the smoothness of the contour was decreased. The results demonstrate that the contour detection, often considered to be driven by lateral coactivation in primary visual cortex, relies on higher-level visual representations that differ between the hemispheres. Furthermore, because contour and non-contour stimuli had the same spatial frequency spectra, the results challenge the view that the right-hemisphere advantage in global processing depends on a specialization for processing low spatial frequencies.

Prestimulus oscillatory phase at 7 Hz gates cortical information flow and visual perception.

Although we have the impression that visual information flows continuously from our sensory channels, recent studies indicate that this is likely not the case. Rather, we sample visual stimuli rhythmically, oscillating at 5-10 Hz. Electroencephalography (EEG) studies have demonstrated that this rhythmicity is reflected by the phase of ongoing brain oscillations in the same frequency. Theoretically, brain oscillations could underlie the rhythmic nature of perception by providing transient time windows for information exchange, but this question has not yet been systematically addressed. We recorded simultaneous EEG-fMRI while human participants performed a contour integration task and show that ongoing brain oscillations prior to stimulus onset predict functional connectivity between higher and lower level visual processing regions. Specifically, our results demonstrate that the phase of a 7 Hz oscillation prior to stimulus onset predicts perceptual performance and the bidirectional information flow between the left lateral occipital cortex and right intraparietal sulcus, as indicated by psychophysiological interaction and dynamic causal modeling. These findings suggest that human brain oscillations periodically gate visual perception at around 7 Hz by providing transient time windows for long-distance cortical information transfer. Such gating might be a general mechanism underlying the rhythmic nature of human perception.

Electrophysiological correlates of visual adaptation and sensory competition.

The face-sensitive evoked N170 component of the event related potential (ERP) is reduced if another face is presented before when compared to the previous presentation of a low-level control stimulus (phase-scrambled face). This effect is thought to reflect category-specific adaptation processes. Similarly, presenting two faces concurrently also reduces the N170, suggesting that stimuli compete for neural representations in the occipito-temporal cortex as early as 170 ms. Here we compared the ERPs obtained for two faces or for a face and a phase-scrambled face in three different conditions: (1) a first stimulus (S1) followed by a second one (S2), similarly to previous adaptation paradigms; (2) S1 remaining on screen when S2 appeared, as previously used in studies of competition; (3) or S1 and S2 having simultaneous onset and offset as well. We found a significant and stimulus specific reduction of the N170 in both conditions where the onset of S1 preceded the onset of S2. In contrast, simultaneous presentation of the two stimuli had no specific effect on the ERPs at least until 200 ms post-stimulus onset. This suggests either that competition does not lead to early repetition suppression or that the absence of a larger N170 response to two simultaneously presented face stimuli compared to a single stimulus reflects competition between overlapping representations. Overall, our results show that the asynchronous presentation of S1 and S2 is critical to observe stimulus specific reduction of the N170, presumably reflecting adaptation-related processes.

Short- and long-range neural synchrony in grapheme-color synesthesia.

Grapheme-color synesthesia is a perceptual phenomenon where single graphemes (e.g., the letter "E") induce simultaneous sensations of colors (e.g., the color green) that were not objectively shown. Current models disagree as to whether the color sensations arise from increased short-range connectivity between anatomically adjacent grapheme- and color-processing brain structures or from decreased effectiveness of inhibitory long-range connections feeding back into visual cortex. We addressed this issue by examining neural synchrony obtained from EEG activity, in a sample of grapheme-color synesthetes that were presented with color-inducing versus non-color-inducing graphemes. For color-inducing graphemes, the results showed a decrease in the number of long-range couplings in the theta frequency band (4-7 Hz, 280-540 msec) and a concurrent increase of short-range phase-locking within lower beta band (13-20 Hz, 380-420 msec at occipital electrodes). Because the effects were both found in long-range synchrony and later within the visual processing stream, the results support the idea that reduced inhibition is an important factor for the emergence of synesthetic colors.

Top-down control in contour grouping.

Human observers tend to group oriented line segments into full contours if they follow the Gestalt rule of 'good continuation'. It is commonly assumed that contour grouping emerges automatically in early visual cortex. In contrast, recent work in animal models suggests that contour grouping requires learning and thus involves top-down control from higher brain structures. Here we explore mechanisms of top-down control in perceptual grouping by investigating synchronicity within EEG oscillations. Human participants saw two micro-Gabor arrays in a random order, with the task to indicate whether the first (S1) or the second stimulus (S2) contained a contour of collinearly aligned elements. Contour compared to non-contour S1 produced a larger posterior post-stimulus beta power (15-21 Hz). Contour S2 was associated with a pre-stimulus decrease in posterior alpha power (11-12 Hz) and in fronto-posterior theta (4-5 Hz) phase couplings, but not with a post-stimulus increase in beta power. The results indicate that subjects used prior knowledge from S1 processing for S2 contour grouping. Expanding previous work on theta oscillations, we propose that long-range theta synchrony shapes neural responses to perceptual groupings regulating lateral inhibition in early visual cortex.

Neural mechanisms of selective exposure: an EEG study on the processing of decision-consistent and inconsistent information.

Decision makers tend to prefer decision-consistent information and/or neglect decision-inconsistent information (selective exposure). In the present EEG study the neural mechanisms of the classic selective exposure effect were examined by investigating oscillatory brain responses to consistent vs. inconsistent information. Twenty participants made an economic decision and subsequently were exposed to 45 consistent and 45 inconsistent images concerning their decision. EEG was recorded from 31 electrodes and differences between oscillatory brain responses towards consistent and inconsistent information were examined. The main result was an increase of induced theta power (5-8Hz, 0-0.7s) in the consistent compared to the inconsistent condition at right temporo-parietal electrodes, as well as a corresponding increase of evoked theta power at frontal electrodes. Since theta oscillations are often observed during memory formation, we conclude that decision-consistent information triggers memory formation, whereas decision-inconsistent information seems not to do so. This finding supports the classic motivational perspective of Leon Festinger on the selective exposure effect.

Prefrontally driven downregulation of neural synchrony mediates goal-directed forgetting.

Neural synchronization between distant cell assemblies is crucial for the formation of new memories. To date, however, it remains unclear whether higher-order brain regions can adaptively regulate neural synchrony to control memory processing in humans. We explored this question in two experiments using a voluntary forgetting task. In the first experiment, we simultaneously recorded electroencephalography along with fMRI. The results show that a reduction in neural synchrony goes hand-in-hand with a BOLD signal increase in the left dorsolateral prefrontal cortex (dlPFC) when participants are cued to forget previously studied information. In the second experiment, we directly stimulated the left dlPFC with repetitive transcranial magnetic stimulation during the same task, and show that such stimulation specifically boosts the behavioral forgetting effect and induces a reduction in neural synchrony. These results suggest that prefrontally driven downregulation of long-range neural synchronization mediates goal-directed forgetting of long-term memories.