Matthew S. Tata

Right frontal cortex generates reward-related theta-band oscillatory activity

When participants in a gambling game are given feedback as to whether they won or lost the previous bet, a series of stereotypical brain electrical responses can be observed in the electroencephalogram (EEG) and the stimulus-locked Event-Related Potential (ERP). These include the Feedback-Related Mediofrontal Negativity (FRN), a posterior P300, and a feedback-induced increase in power at the theta (4 to 8 Hz) band over frontal scalp. Although the generators of the FRN and P300 have been studied previously, little is known about the generator of feedback-induced theta. We employed a gambling game in which participants chose either high-risk/high-reward or low-risk/low-reward bets to investigate these feedback-related responses. The FRN was not modulated by the riskiness of the bet, but both P300 and feedback-induced theta were of greater amplitude following high- relative to low-risk bets. Using a bilateral multi-source Beamformer approach, we localized the induced theta-band responses following wins and losses to partially overlapping regions in the right medial frontal cortex, possibly including the Anterior Cingulate. Using a dipole-fitting approach, we found that the generators of feedback-induced theta are anatomically distinct from those of the FRN and P300.

Attend to it now or lose it forever: Selective attention, metacontrast masking, and object substitution

Metacontrast masking occurs when the visibility of a brief target stimulus is decreased by the subsequent appearance of another nearby visual stimulus. Early explanations of the phenomenon involved low-level mechanisms, but subsequent studies have suggested a role for selective attention. The results of three experiments presented here extend previous findings to the metacontrast paradigm. It is shown that the strength of metacontrast masking increases with the number of distractor items in a display, decreases when the target location is validly but not invalidly precued, and is eliminated when search for the target is efficient (pop-out search) but not when search is inefficient (serial search). A connection between metacontrast masking and object substitution masking is considered.

Early phase of spatial mismatch negativity is localized to a posterior "where" auditory pathway.

The auditory mismatch negativity (MMN) is an event-related potential that reflects early processing of changes in acoustic stimulus features. Although the MMN has been well characterized by previous work, the number, roles, and anatomical locations of its cortical generators remain unresolved. Here, we report that the MMN elicited by occasional deviations in sound location is comprised of two temporally and anatomically distinct phases: an early phase with a generator posterior to auditory cortex and contralateral to the deviant stimulus, and a later phase with generators that are more frontal and bilaterally symmetric. The posterior location of the early-phase generator suggests the engagement of neurons within a putative “where” pathway for processing spatial auditory information.

Warning: Attending to a mask may be hazardous to your perception

Object substitution is a type of backward masking that occurs when a mask appears during visual search for a target. We tested the hypothesis that object substitution is an overwriting process triggered by attentional selection of the mask. Impeding attentional selection of a mask by embedding it in an array of distractors eliminated object substitution. Similarly, object substitution did not occur when the mask appeared in advance of the target and, therefore, could not capture attention during search for the target. However, masking was reinstated when the mask was revealed from background contours at the moment of target onset and could therefore capture attention during search. These observations demonstrate that attentional selection of the mask is a necessary step in this type of masking and suggest that object substitution is active overwriting of unattended information triggered by selection of other visual information at a nearby location.

Neural correlates of auditory distraction revealed in θ-band EEG.

Selective attention involves the exclusion of irrelevant information in order to optimize perception of a single source of sensory input; failure to do so often results in the familiar phenomenon of distraction. The term ‘distraction’ broadly refers to a perceptual phenomenon. In the present study we attempted to find the electrophysiological correlates of distraction using an auditory discrimination task. EEG and event-related potential responses to identical stimuli were compared under two levels of distraction (continuous broad-band noise or continuous speech). Relative to broad-band noise, the presence of a continuous speech signal in the unattended ear impaired task performance and also attenuated the N1 peak evoked by nontarget stimuli in the attended ear. As the magnitude of a peak in the event-related potential waveform can be modulated by differences in intertrial power but also by differences in the stability of EEG phase across trials, we sought to characterize the effect of distraction on intertrial power and intertrial phase locking around the latency of the N1. The presence of continuous speech resulted in a prominent reduction of theta EEG band intertrial phase locking around the latency of the N1. This suggests that distraction may act not only to disrupt a sensory gain mechanism but also to disrupt the temporal fidelity with which the brain responds to stimulus events.

Transient spatial attention modulates distinct components of the auditory ERP

We recorded ERPs to pairs of externally presented tones, T1 and T2, in the absence of attentional cues to determine whether attention is momentarily sustained at the location of a behaviourally relevant sound, and what effect this focusing of attention might have on the neural response to target stimuli. ERPs to T2 were more negative when the preceding T1 was presented on the same side of fixation than when T1 was presented on the opposite side of fixation. This negative difference consisted of an early, parietal phase and a later, frontocentral phase. These results confirm and extend previously reported effects of transient spatial attention on auditory ERPs, and they demonstrate that transient spatial attention has a distinct and robust effect on the early stages of stimulus processing in the auditory system.

Mental Rotational Ability Is Correlated with Spatial but Not Verbal Working Memory Performance and P300 Amplitude in Males

This study investigated how both sex and individual differences in a mental rotation test (MRT) influence performance on working memory (WM). To identify the neural substrate supporting these differences, brain electrical activity was measured using the event-related potential technique. No significant sex differences were observed in a test of verbal WM, however males were significantly faster than females to respond to probe stimuli in a test of spatial WM. This difference was no longer significant after controlling for differences in MRT score, suggesting that rotational ability mediates performance in the spatial memory task for both sexes. A posterior P300 was observed in both tasks as participants encoded information into memory, however the amplitude of the P300 correlated with RT in the spatial task but not in the verbal task. Individual differences in the MRT also correlated with RT and with the amplitude of the P300, but again only in the spatial task. After splitting the analysis by sex, partial correlations controlling for MRT revealed that for males, individual differences in rotational ability completely mediated the correlation between the P300 and RT in the spatial task. This mediating effect was not observed for the female participants. The results therefore suggest a relatively stronger association in males between innate mental rotational ability, spatial memory performance, and brain electrophysiological processes supporting spatial memory.

Dynamics of Distraction: Competition among Auditory Streams Modulates Gain and Disrupts Inter-Trial Phase Coherence in the Human Electroencephalogram

Auditory distraction is a failure to maintain focus on a stream of sounds. We investigated the neural correlates of distraction in a selective-listening pitch-discrimination task with high (competing speech) or low (white noise) distraction. High-distraction impaired performance and reduced the N1 peak of the auditory Event-Related Potential evoked by probe tones. In a series of simulations, we explored two theories to account for this effect: disruption of sensory gain or a disruption of inter-trial phase consistency. When compared to these simulations, our data were consistent with both effects of distraction. Distraction reduced the gain of the auditory evoked potential and disrupted the inter-trial phase consistency with which the brain responds to stimulus events. Tones at a non-target, unattended frequency were more susceptible to the effects of distraction than tones within an attended frequency band.

A lateralized auditory evoked potential elicited when auditory objects are defined by spatial motion.

Scene analysis involves the process of segmenting a field of overlapping objects from each other and from the background. It is a fundamental stage of perception in both vision and hearing. The auditory system encodes complex cues that allow listeners to find boundaries between sequential objects, even when no gap of silence exists between them. In this sense, object perception in hearing is similar to perceiving visual objects defined by isoluminant color, motion or binocular disparity. Motion is one such cue: when a moving sound abruptly disappears from one location and instantly reappears somewhere else, the listener perceives two sequential auditory objects. Smooth reversals of motion direction do not produce this segmentation. We investigated the brain electrical responses evoked by this spatial segmentation cue and compared them to the familiar auditory evoked potential elicited by sound onsets. Segmentation events evoke a pattern of negative and positive deflections that are unlike those evoked by onsets. We identified a negative component in the waveform - the Lateralized Object-Related Negativity - generated by the hemisphere contralateral to the side on which the new sound appears. The relationship between this component and similar components found in related paradigms is considered.

Theta-band phase tracking in the two-talker problem

It is usually easy to understand speech, but when several people are talking at once it becomes difficult. The brain must select one speech stream and ignore distracting streams. We tested a theory about the neural and computational mechanisms of attentional selection. The theory is that oscillating signals in brain networks phase-lock with amplitude fluctuations in speech. By doing this, brain-wide networks acquire information from the selected speech, but ignore other speech signals on the basis of their non-preferred dynamics. Two predictions were supported: first, attentional selection boosted the power of neuroelectric signals that were phase-locked with attended speech, but not ignored speech. Second, this phase selectivity was associated with better recall of the attended speech.