The old switcheroo: when target environmental sounds elicit a novelty P3

The Pause-then-Cancel model of human action-stopping: Theoretical considerations and empirical evidence

The ability to stop already-initiated actions is a key cognitive control ability. Recent work on human action-stopping has been dominated by two controversial debates. First, the contributions (and neural signatures) of attentional orienting and motor inhibition after stop-signals are near-impossible to disentangle. Second, the timing of purportedly inhibitory (neuro)physiological activity after stop-signals has called into question which neural signatures reflect processes that actually contribute to action-stopping. Here, we propose that a two-stage model of action-stopping - proposed by Schmidt and Berke (2017) based on subcortical rodent recordings - may resolve these controversies. Translating this model to humans, we first argue that attentional orienting and motor inhibition are inseparable because orienting to salient events like stop-signals automatically invokes broad motor inhibition, reflecting a fast-acting, ubiquitous Pause process. We then argue that inhibitory signatures after stop-signals differ in latency because they map onto two sequential stages: the salience-related Pause and a slower, stop-specific Cancel process. We formulate the model, discuss recent supporting evidence in humans, and interpret existing data within its context.

Methodological Considerations about the Use of Bimodal Oddball P300 in Psychiatry: Topography and Reference Effect

Event-related potentials (ERPs) bimodal oddball task has disclosed increased sensitivity to show P300 modulations to subclinical symptoms. Even if the utility of such a procedure has still to be confirmed at a clinical level, gathering normative values of this new oddball variant may be of the greatest interest. We specifically addressed the challenge of defining the best location for the recording of P3a and P3b components and selecting the best reference to use by investigating the effect of an offline re-reference procedure on recorded bimodal P3a and P3b. Forty young and healthy subjects were submitted to a bimodal (synchronized and always congruent visual and auditory stimuli) three-stimulus oddball task in which 140 frequent bimodal stimuli, 30 deviant “target” stimuli and 30 distractors were presented. Task consisted in clicking as soon as possible on the targets, and not paying attention to frequent stimuli and distractors. This procedure allowed us to record, for each individual, the P3a component, referring to the novelty process related to distractors processing, and the P3b component, linked to the processing of the target stimuli. Results showed that both P3a and P3b showed maximal amplitude in Pz. However, P3a displayed a more central distribution. Nose reference was also shown to give maximal amplitudes compared with average and linked mastoids references. These data were discussed in light of the necessity to develop multi-site recording guidelines to furnish sets of ERPs data comparable across laboratories.

ERP and pupil responses to deviance in an oddball paradigm

We investigated the relationship between, and functional significance of, P300, novelty P3, and the pupil dilation response (PDR). Subjects categorized stimuli including (a) words of a frequent category, (b) words of an infrequent category (14%), and (c) pictures of the frequent category ("novels"; 14%). The P300 and novelty P3 were uncorrelated with the PDR and differed in their response to experimental manipulation. Therefore, although the three physiological responses often co-occur, they appear to each manifest a distinct function: The PDR may be more closely linked to aspects of behavioral responding than the event-related potentials. Within participants, P300 and PDR latencies accounted for unique portions of the reaction time variance, and amplitudes of all three responses were larger for stimuli recalled on a subsequent test, compared to not recalled. We discuss the possibility that all three responses reflect norepinephric input from the locus coeruleus.

The component structure of event-related potentials in the p300 speller paradigm

We investigated the componential structure of event-related potentials elicited while participants use the P300 BCI. Six healthy participants "typed" all characters in a 6 × 6 matrix twice in a random sequence. A principal component analysis indicated that in addition to the P300, target flashes elicited an earlier frontal positivity, possibly a Novelty P3. The amplitudes of both P300 and the Novelty P3 varied with the matrix row in which the target character was located. However, the P300 elicited by row flashes was largest for targets in the lower part of the matrix, whereas the Novelty P3 elicited by column flashes was largest in the top part. Classification accuracy using stepwise linear discriminant analysis mirrored the pattern in the Novelty P3 (an accuracy difference of 0.1 between rows 1 and 6). When separate classifiers were generated to rely solely on the P300 or solely on the Novelty P3, the latter function led to higher accuracy (a mean accuracy difference of about 0.2 between classifiers). A possible explanation is that some nontarget flashes elicit a P300, leading to lower selection accuracy of the respective classifier. In an additional set of data from six different participants we replicated the ERP structure of the initial analyses and characterized the spatial distributions more closely by using a dense electrode array. Overall, our findings provide new insights in the componential structure of ERPs elicited in the P300 speller paradigm and have important implications for optimizing the speller's selection accuracy.

Novel sounds as a psychophysiological measure of listening effort in older listeners with and without hearing loss

OBJECTIVE

To investigate whether task-irrelevant novel sounds presented during an auditory task can provide information about the level of listening effort.

METHODS

Event-related potentials (ERPs) were recorded for novel sounds presented during two Experiments, a frequency discrimination task and a speech-perception-in-noise (SPIN) test, each with varying degrees of task difficulty (easy, medium, hard). Difficulty was adjusted to the individual frequency discrimination threshold and 50% speech recognition signal-to-noise ratio (SNR), respectively. Older listeners (age range 60-86 years) with either normal hearing for their age or a mild-to-moderate hearing loss participated.

RESULTS

Amplitudes of Novelty P3 and late positive potential (LPP) increased with increasing task difficulty, whereas amplitudes of N1 and N2 decreased. Participants with hearing loss had significantly larger LPP amplitudes in the easy condition of the SPIN test than did normal-hearing listeners. Most correlations between ERP amplitudes and behavioral data were not significant suggesting that listening effort is not a simple equivalent of behavioral performance.

CONCLUSIONS

LPP amplitude appeared to be the most sensitive component for capturing listening effort reflecting the arousal level of the listener.

SIGNIFICANCE

ERPs to novel sounds could be easily recorded during hearing tests and provide an objective physiological measure of listening effort, thus supplementing behavioral performance data.

The component structure of ERP subsequent memory effects in the Von Restorff paradigm and the word frequency effect in recall

We examined the degree to which ERP components elicited by items that are isolated from their context, either by their font size ("size isolates") or by their frequency of usage, are correlated with subsequent immediate recall. Study lists contained (a) 15 words including a size isolate, (b) 14 high frequency (HF) words with one low frequency word ("LF isolate"), or (c) 14 LF words with one HF word. We used spatiotemporal PCA to quantify ERP components. We replicated previously reported P300 subsequent memory effects for size isolates and found additional correlations with recall in the novelty P3, a right lateralized positivity, and a left lateralized slow wave that was distinct from the slow wave correlated with recall for nonisolates. LF isolates also showed evidence of a P300 subsequent memory effect and also elicited the left lateralized subsequent memory effect, supporting a role of distinctiveness in word frequency effects in recall.

Abnormal distracter processing in adults with attention-deficit-hyperactivity disorder

BACKGROUND

Subjects with Attention-Deficit Hyperactivity Disorder (ADHD) are overdistractible by stimuli out of the intended focus of attention. This control deficit could be due to primarily reduced attentional capacities or, e. g., to overshooting orienting to unexpected events. Here, we aimed at identifying disease-related abnormalities of novelty processing and, therefore, studied event-related potentials (ERP) to respective stimuli in adult ADHD patients compared to healthy subjects.

METHODS

Fifteen unmedicated subjects with ADHD and fifteen matched controls engaged in a visual oddball task (OT) under simultaneous EEG recordings. A target stimulus, upon which a motor response was required, and non-target stimuli, which did not demand a specific reaction, were presented in random order. Target and most non-target stimuli were presented repeatedly, but some non-target stimuli occurred only once ('novels'). These unique stimuli were either 'relative novels' with which a meaning could be associated, or 'complete novels', if no association was available.

RESULTS

In frontal recordings, a positive component with a peak latency of some 400 ms became maximal after novels. In healthy subjects, this novelty-P3 (or 'orienting response') was of higher magnitude after complete than after relative novels, in contrast to the patients with an undifferentially high frontal responsivity. Instead, ADHD patients tended to smaller centro-parietal P3 responses after target signals and, on a behavioural level, responded slower than controls.

CONCLUSION

The results demonstrate abnormal novelty processing in adult subjects with ADHD. In controls, the ERP pattern indicates that allocation of meaning modulates the processing of new stimuli. However, in ADHD such a modulation was not prevalent. Instead, also familiar, only context-wise new stimuli were treated as complete novels. We propose that disturbed semantic processing of new stimuli resembles a mechanism for excessive orienting to commonly negligible stimuli in ADHD.

Does compensatory neural activity survive old-old age?

One mechanism that may allow older adults to continue to successfully perform certain cognitive tasks is to allocate more resources than their younger counterparts. Most prior studies have not included individuals beyond their 70s. Here, we investigated whether compensatory increases in neural activity previously observed in cognitively high-performing young-old adults would continue into old-old age. Event-related potentials were recorded from 72 cognitively high performing subjects, aged 18 to 96 years old, while they participated in a subject-controlled novelty oddball paradigm in which they determined viewing duration of standard, target, and novel visual stimuli. Compared to young and middle-aged subjects, both young-old and old-old subjects exhibited an impairment of preliminary mismatch/match detection operations, indexed by an attenuated anterior N2 component. This may have placed a greater burden on the subsequent controlled decision-making process, indexed by the P3, necessitating the allocation of more resources. The relationship between age and resource allocation, as measured by P3 amplitude, from midlife to very old age (45-96 years old) followed an inverted u-shaped curve (quadratic function). It peaked between the late 60s and early 70s. Thereafter, there was an inverse relationship between age and resource appropriation. This relationship remained significant after controlling for differences in task performance and MMSE. Examining the size of the P3 component across different age groups suggests that although cognitively high performing adults in their early 80s exhibit a reduction in P3 amplitude, they have a relatively well-preserved capacity to appropriate resources. However, by the late 80s, there is a robust decline (relative to young-old adults) in the size of the P3. Our results indicate that when carrying out controlled processing linked to directing attention to salient events, cognitively high performers reach the boundary of their capacity, albeit relatively late in life. This limits their ability to appropriate additional resources as compensatory activity for age-related impairments in earlier visual processing, and suggests that such a mechanism does not tend to "survive" old-old age.

To Ignore or Explore: Top–Down Modulation of Novelty Processing

Attending to novelty is a critical element of human behavior and learning. Novel events can serve as task-irrelevant distracters or as potential sources of engagement by interesting or important aspects of one's environment. An optimally functioning brain should have the capacity to respond differentially to novel events depending on the circumstances in which they occur. In the present study, a subject-controlled variant of the visual novelty oddball paradigm was employed under two different conditions in which novel stimuli were characterized either as distracters from a main task or as potentially meaningful “invitations” to explore the environment. Differences in context, derived from varying the emphasis of task instructions, strongly modulated both the behavioral and electrophysiological response to novelty. This modulation was not observed for processing earlier than the P3 component. Subjects who encountered novel events that served as distracters limited the amount of attention and processing resources they appropriated. Remarkably, under this condition, there were no differences in overall P3 amplitude, late positive slow-wave activity, or viewing duration between rare novel and frequent standard events. In contrast, subjects who encountered novel events as potential opportunities to explore augmented the attention and processing resources directed toward these events (as reflected by a larger P3 amplitude, late positive slow-wave activity, and longer viewing durations). Our results suggest that the processing of novelty within the visual modality involves several stages, including: (1) the relatively automatic detection of unfamiliar, novel stimuli (indexed by the N2); (2) the voluntary allocation of resources determined by the broader context in which a novel event occurs (indexed by the P3); and (3) the sustained processing of novelty (indexed by late positive slow-wave activity). This study provides evidence of the brain's ability to generate differential responses to novel events according to the circumstances under which they are encountered. It also points to a greater degree of top–down modulation of the processing of novelty than has been previously emphasized. We suggest that less commonly studied variables, such as subject control, may provide additional insight into the different ways in which novelty is processed.

The use of evoked potentials in sleep research

Averaged event-related potentials (ERPs) represent sensory and cognitive processing of stimuli during wakefulness independent of behavioral responses, and reflect the underlying state of the CNS (central nervous system) during sleep. Components measured during wakefulness which are reflective of arousal state or the automatic switching of attention are sensitive to prior sleep disruption. Components reflecting active attentional influences during the waking state appear to be preserved in a rudimentary form during REM sleep, but in a way that highlights the differences in the neurochemical environment between wakefulness and REM sleep. Certain ERP components only appear within sleep. These begin to emerge at NREM sleep onset and may reflect inhibition of information processing and thus have utility as markers of the functional status of sleep preparatory mechanisms. These large amplitude NREM components represent synchronized burst firing of large number of cortical cells and are a reflection of the nervous system's capacity to generate delta frequency EEG activity. As such they are useful in assessing the overall integrity of the nervous system in populations not showing substantial amounts of SWS as measured using traditional criteria. While requiring care in their interpretation, ERPs nonetheless provide a rich tool to investigators interested in probing the nervous system to evaluate daytime functioning in the face of sleep disruption, the ability of the sleeping nervous system to monitor the external environment, and the ability of the nervous system to respond to stimuli in a manner consistent with the initiation or maintenance of sleep.

Difficulty of discrimination modulates attentional capture for deviant information

It has been reported that an increased difficulty of discrimination between standard and target enhances P3a for typical nontarget. To elucidate the mechanism of this effect on deviant processing, the P300 event-related brain potential (ERP) was elicited using a visual three-stimulus oddball paradigm (standard circle, .70, target circle, .15, and nontarget/target square, .15). Four task conditions were defined by a combination of two category types of rare square (nontarget or target) and two levels of discrimination difficulty between standard and target circles (easy or difficult). In the difficult conditions, P3a was elicited by both nontarget and target square. Our findings suggest that the difficulty of discrimination between standard and target enhances attentional capture, rather than inhibition, for deviant information. This study has implications for understanding the attentional mechanisms of deviant processing.

Human experience seeking correlates with hippocampus volume: convergent evidence from manual tracing and voxel-based morphometry

Experience seekers continuously pursue novel environmental stimuli, a tendency linked to genetic variation in mesolimbic dopamine transmission. However, the neuroanatomical basis accompanying these genetic and neurochemical associations is unknown. Animal and human experimental results suggest a central role for the hippocampus in processing novel stimuli. Here, we explored whether differences in human experience seeking are related to variations in hippocampal volume. High-resolution anatomic MR images were analyzed in 40 individuals who ranged from low through high on a validated experience seeking personality scale. Manual tracing analysis demonstrated positive correlation between right hippocampal volumes and scores on the experience seeking scale. A separate voxel-based morphometric analysis confirmed these results and localized the significant increase to the anterior portion of right hippocampal grey matter. We tested and were able to reject the possibility that results were mediated by a personality trait related to, but distinct from, experience seeking. The present data provide the first direct evidence for a relationship between human experience seeking and brain structure. In addition, these results provide new ecologically relevant evidence for a link between right anterior hippocampus and novelty processing.

Visual novel stimuli in an ERP novelty oddball paradigm: effects of familiarity on repetition and recognition memory

The orienting response, the brain's reaction to novel and/or out of context familiar events, is reflected by the novelty P3 of the ERP. Contextually novel events also engender high rates of recognition memory. We examined, under incidental and intentional conditions, the effects of visual symbol familiarity on the novelty P3 recorded during an oddball task and on the parietal episodic memory (EM) effect, an index of recollection. Repetition of familiar, but not unfamiliar, symbols elicited a reduction in the novelty P3. Better recognition performance for the familiar symbols was associated with a robust parietal EM effect, which was absent for the unfamiliar symbols in the incidental task. These data demonstrate that processing of novel events depends on expectation and whether stimuli have preexisting representations in long-term semantic memory.

Increased responsiveness to novelty is associated with successful cognitive aging

The animal literature suggests that exposure to more complex, novel environments promotes neurogenesis and cognitive performance in older animals. Studies in humans indicate that participation in intellectually stimulating activities may serve as a buffer against mental decline and help to sustain cognitive abilities. Here, we show that across old adults, increased responsiveness to novel events (as measured by viewing duration and the size of the P3 event-related potential) is strongly linked to better performance on neuropsychological tests, especially those involving attention/executive functions. Cognitively high performing old adults generate a larger P3 response to visual stimuli than cognitively average performing adults. These results suggest that cognitively high performing adults successfully manage the task by appropriating more resources and that the increased size of their P3 component represents a beneficial compensatory mechanism rather than less efficient processing.

Age-related differences in attention to novelty among cognitively high performing adults

Age-related differences in attention to novel events were studied in well-matched, cognitively high performing old, middle-aged and young subjects. Event-related potentials were recorded during a visual novelty oddball task in which subjects controlled viewing durations that served as a behavioral measure of attentional allocation. All age groups had a larger P3 amplitude and longer viewing duration to novel than to standard stimuli, with no age-related differences in the magnitude of these effects, indicating old individuals were as engaged by the processing of novelty as younger adults. Old subjects had a larger, more anteriorly distributed P3 component to novels and standards. The increased P3 amplitude differs from prior reports of a diminished P3 response with processes, including aging, that have a potentially deleterious impact on the brain. We hypothesise that cognitively high performing old individuals successfully manage the task by relying on additional neural resources and perhaps more effortful frontal activity than their younger counterparts.

Arousal and valence effects on event-related P3a and P3b during emotional categorization

Due to the adaptive value of emotional situations, categorizing along the valence dimension may be supported by critical brain functions. The present study examined emotion-cognition relationships by focusing on the influence of an emotional categorization task on the cognitive processing induced by an oddball-like paradigm. Event-related potentials (ERPs) were recorded from subjects explicitly asked to categorize along the valence dimension (unpleasant, neutral or pleasant) deviant target pictures embedded in a train of standard stimuli. Late positivities evoked in response to the target pictures were decomposed into a P3a and a P3b and topographical differences were observed according to the valence content of the stimuli. P3a showed enhanced amplitudes at posterior sites in response to unpleasant pictures as compared to both neutral and pleasant pictures. This effect is interpreted as a negativity bias related to attentional processing. The P3b component was sensitive to the arousal value of the stimulation, with higher amplitudes at several posterior sites for both types of emotional pictures. Moreover, unpleasant pictures evoked smaller amplitudes than pleasant ones at fronto-central sites. Thus, the context updating process may be differentially modulated by the affective arousal and valence of the stimulus. The present study supports the assumption that, during an emotional categorization, the emotional content of the stimulus may modulate the reorientation of attention and the subsequent updating process in a specific way.

Event-related P3a and P3b in response to unpredictable emotional stimuli

In natural situations, unpredictable events processing often interacts with the ongoing cognitive activities. In a similar manner, the insertion of deviant unpredictable stimuli into a classical oddball task evokes both the P3a and P3b event-related potentials (ERPs) components that are, respectively, thought to index reallocation of attentional resources or inhibitory process and memory updating mechanism. This study aims at characterising the influence of the emotional arousal and valence of a deviant and unpredictable non-target stimulus on these components. ERPs were recorded from 28 sites during a visual three-stimulus oddball paradigm. Unpleasant, neutral and pleasant pictures served as non-target unpredictable items and subjects were asked to realize a perceptually difficult standard/target discrimination task. A temporal principal component analysis (PCA) allowed us to show that non-target pictures elicited both a P3a and a P3b. Moreover, the P3b component was modulated by the emotional arousal and the valence of the pictures. Thus, the memory updating process may be modulated by the affective arousal and valence of unpredictable disturbing stimuli, even if the task does not require any explicit emotional categorization.

Total sleep deprivation and novelty processing: implications for frontal lobe functioning

OBJECTIVE

Mounting evidence suggests that the frontal lobes are particularly vulnerable to total sleep deprivation (TSD). Detection of novelty involves the frontal lobes. The presentation of rare, novel stimuli elicits an event-related potential (novel P3), which maximizes over anterior regions of the scalp. We hypothesized that TSD would impair novelty detection, resulting in a smaller novel P3 over the frontal region, with a topographic shift toward posterior areas.

METHODS

An auditory novelty oddball task was administered to a TSD group after 36 h of waking and again following recovery sleep, and to a control group after 12 h of waking. EEG was recorded from Fz, Cz and Pz.

RESULTS

A large anterior P3 was elicited in the control group. In the TSD group, this novel P3 was smaller at Fz. A later novel positivity appeared in parietal areas. The novel P3 returned to baseline levels and the late novel P3 was difficult to observe following recovery sleep.

CONCLUSIONS

TSD appears to compromise the usual automatic detection of novelty probably due to frontal deactivation. Participants may compensate by relying on posterior brain mechanisms involving active memory comparison. The late novel P3 component may also reflect a secondary effortful attempt to encode and to categorize novel stimuli.

SIGNIFICANCE

This study suggests that TSD may compromise cognitive functioning in different regions of the brain. The detection of novelty, probably mediated by the frontal lobes, is particularly at risk.