Electrophysiological evidence for notation independence in numerical processing

BACKGROUND: A dominant view in numerical cognition is that numerical comparisons operate on a notation independent representation (Dehaene, 1992). Although previous human neurophysiological studies using scalp-recorded event-related potentials (ERPs) on the numerical distance effect have been interpreted as supporting this idea, differences in the electrophysiological correlates of the numerical distance effect in symbolic notations (e.g. Arabic numerals) and non-symbolic notations (e.g. a set of visually presented dots of a certain number) are not entirely consistent with this view. METHODS AND RESULTS: Two experiments were conducted to resolve these discrepancies. In Experiment 1, participants performed a symbolic and a non-symbolic numerical comparison task ("smaller or larger than 5?") with numerical values 1–4 and 6–9 while ERPs were recorded. Consistent with a previous report (Temple & Posner, 1998), in the symbolic condition the amplitude of the P2p ERP component (210–250 ms post-stimulus) was larger for values near to the standard than for values far from the standard whereas this pattern was reversed in the non-symbolic condition. However, closer analysis indicated that the reversal in polarity was likely due to the presence of a confounding stimulus effect on the early sensory ERP components for small versus larger numerical values in the non-symbolic condition. In Experiment 2 exclusively large numerosities (8–30) were used, thereby rendering sensory differences negligible, and with this control in place the numerical distance effect in the non-symbolic condition mirrored the symbolic condition of Experiment 1. CONCLUSION: Collectively, the results support the claim of an abstract semantic processing stage for numerical comparisons that is independent of input notation

Caffeine Boosts Preparatory Attention for Reward-related Stimulus Information

The intake of caffeine and the prospect of reward have both been associated with increased arousal, enhanced attention, and improved behavioral performance on cognitive tasks, but how they interact to exert these effects is not well understood. To investigate this question, we had participants engage in a two-session cued-reward cognitive task while we recorded their electrical brain activity using scalp electroencephalography. The cue indicated whether monetary reward could be received for fast and accurate responses to a color-word Stroop stimulus that followed. Before each session, participants ingested decaffeinated coffee with either caffeine (3-mg/kg bodyweight) or placebo (3-mg/kg bodyweight lactose). The behavioral results showed that both caffeine and reward-prospect improved response accuracy and speed. In the brain, reward-prospect resulted in an enlarged frontocentral slow wave (contingent negative variation, or CNV) and reduced posterior alpha power (indicating increased cortical activity) before stimulus presentation, both neural markers for preparatory attention. Moreover, the CNV enhancement for reward-prospect trials was considerably more pronounced in the caffeine condition as compared to the placebo condition. These interactive neural enhancements due to caffeine and reward-prospect were mainly visible in preparatory attention activity triggered by the cue (CNV). In addition, some interactive neural enhancements in the processing of the Stroop target stimulus that followed were also observed. The results suggest that caffeine facilitates the neural processes underlying attentional preparation and stimulus processing, especially for task-relevant information

Cognitive control in social situations: A role for the dorsolateral prefrontal cortex

Using functional magnetic resonance imaging (fMRI), we investigated brain activity elicited by a computer-animated child's actions that appeared consistent and inconsistent with a computer-animated adult's instructions. Participants observed a computer-animated adult verbally instructing a computer-animated child to touch one of two objects. The child performed correctly in half of the trials and incorrectly in the other half. We observed significantly greater activity when the child performed incorrectly compared to correctly in regions of the dorsolateral prefrontal cortex (DLPFC) that have been implicated in maintaining our intentions in working memory and implementing cognitive control. However, no such effects were found in regions of the posterior superior temporal sulcus (posterior STS) that have been posited to interpret other people's behavior. These findings extend the role of the DLPFC in cognitive control to evaluating the social outcomes of other people's behavior and provide important new constraints for theories of how the posterior STS contributes to social cognition

Prestimulus oscillatory brain activity interacts with evoked recurrent processing to facilitate conscious visual perception.

We investigated whether prestimulus alpha-band oscillatory activity and stimulus-elicited recurrent processing interact to facilitate conscious visual perception. Participants tried to perceive a visual stimulus that was perceptually masked through object substitution masking (OSM). We showed that attenuated prestimulus alpha power was associated with greater negative-polarity stimulus-evoked ERP activity that resembled the visual awareness negativity (VAN), previously argued to reflect recurrent processing related to conscious perception. This effect, however, was not associated with better perception. Instead, when prestimulus alpha power was elevated, a preferred prestimulus alpha phase was associated with a greater VAN-like negativity, which was then associated with better cue perception. Cue perception was worse when prestimulus alpha power was elevated but the stimulus occurred at a nonoptimal prestimulus alpha phase and the VAN-like negativity was low. Our findings suggest that prestimulus alpha activity at a specific phase enables temporally selective recurrent processing that facilitates conscious perception in OSM

High-Field fMRI Reveals Brain Activation Patterns Underlying Saccade Execution in the Human Superior Colliculus

BACKGROUND: The superior colliculus (SC) has been shown to play a crucial role in the initiation and coordination of eye- and head-movements. The knowledge about the function of this structure is mainly based on single-unit recordings in animals with relatively few neuroimaging studies investigating eye-movement related brain activity in humans. METHODOLOGY/PRINCIPAL FINDINGS: The present study employed high-field (7 Tesla) functional magnetic resonance imaging (fMRI) to investigate SC responses during endogenously cued saccades in humans. In response to centrally presented instructional cues, subjects either performed saccades away from (centrifugal) or towards (centripetal) the center of straight gaze or maintained fixation at the center position. Compared to central fixation, the execution of saccades elicited hemodynamic activity within a network of cortical and subcortical areas that included the SC, lateral geniculate nucleus (LGN), occipital cortex, striatum, and the pulvinar. CONCLUSIONS/SIGNIFICANCE: Activity in the SC was enhanced contralateral to the direction of the saccade (i.e., greater activity in the right as compared to left SC during leftward saccades and vice versa) during both centrifugal and centripetal saccades, thereby demonstrating that the contralateral predominance for saccade execution that has been shown to exist in animals is also present in the human SC. In addition, centrifugal saccades elicited greater activity in the SC than did centripetal saccades, while also being accompanied by an enhanced deactivation within the prefrontal default-mode network. This pattern of brain activity might reflect the reduced processing effort required to move the eyes toward as compared to away from the center of straight gaze, a position that might serve as a spatial baseline in which the retinotopic and craniotopic reference frames are aligned

Electrophysiological Evidence for Spatiotemporal Flexibility in the Ventrolateral Attention Network

Successful completion of many everyday tasks depends on interactions between voluntary attention, which acts to maintain current goals, and reflexive attention, which enables responding to unexpected events by interrupting the current focus of attention. Past studies, which have mostly examined each attentional mechanism in isolation, indicate that volitional and reflexive orienting depend on two functionally specialized cortical networks in the human brain. Here we investigated how the interplay between these two cortical networks affects sensory processing and the resulting overt behavior. By combining measurements of human performance and electrocortical recordings with a novel analytical technique for estimating spatiotemporal activity in the human cortex, we found that the subregions that comprise the reflexive ventrolateral attention network dissociate both spatially and temporally as a function of the nature of the sensory information and current task demands. Moreover, we found that together with the magnitude of the early sensory gain, the spatiotemporal neural dynamics accounted for the high amount of the variance in the behavioral data. Collectively these data support the conclusion that the ventrolateral attention network is recruited flexibly to support complex behaviors

Neural correlates of audiovisual motion capture

Visual motion can affect the perceived direction of auditory motion (i.e., audiovisual motion capture). It is debated, though, whether this effect occurs at perceptual or decisional stages. Here, we examined the neural consequences of audiovisual motion capture using the mismatch negativity (MMN), an event-related brain potential reflecting pre-attentive auditory deviance detection. In an auditory-only condition occasional changes in the direction of a moving sound (deviant) elicited an MMN starting around 150 ms. In an audiovisual condition, auditory standards and deviants were synchronized with a visual stimulus that moved in the same direction as the auditory standards. These audiovisual deviants did not evoke an MMN, indicating that visual motion reduced the perceptual difference between sound motion of standards and deviants. The inhibition of the MMN by visual motion provides evidence that auditory and visual motion signals are integrated at early sensory processing stages

Intermodal attention affects the processing of the temporal alignment of audiovisual stimuli

The temporal asynchrony between inputs to different sensory modalities has been shown to be a critical factor influencing the interaction between such inputs. We used scalp-recorded event-related potentials (ERPs) to investigate the effects of attention on the processing of audiovisual multisensory stimuli as the temporal asynchrony between the auditory and visual inputs varied across the audiovisual integration window (i.e., up to 125 ms). Randomized streams of unisensory auditory stimuli, unisensory visual stimuli, and audiovisual stimuli (consisting of the temporally proximal presentation of the visual and auditory stimulus components) were presented centrally while participants attended to either the auditory or the visual modality to detect occasional target stimuli in that modality. ERPs elicited by each of the contributing sensory modalities were extracted by signal processing techniques from the combined ERP waveforms elicited by the multisensory stimuli. This was done for each of the five different 50-ms subranges of stimulus onset asynchrony (SOA: e.g., V precedes A by 125–75 ms, by 75–25 ms, etc.). The extracted ERPs for the visual inputs of the multisensory stimuli were compared among each other and with the ERPs to the unisensory visual control stimuli, separately when attention was directed to the visual or to the auditory modality. The results showed that the attention effects on the right-hemisphere visual P1 was largest when auditory and visual stimuli were temporally aligned. In contrast, the N1 attention effect was smallest at this latency, suggesting that attention may play a role in the processing of the relative temporal alignment of the constituent parts of multisensory stimuli. At longer latencies an occipital selection negativity for the attended versus unattended visual stimuli was also observed, but this effect did not vary as a function of SOA, suggesting that by that latency a stable representation of the auditory and visual stimulus components has been established