Kwun Kei Ng

Contingent negative variation and its relation to time estimation: a theoretical evaluation

The relation between the contingent negative variation (CNV) and time estimation is evaluated in terms of temporal accumulation and preparation processes. The conclusion is that the CNV as measured from the electroencephalogram (EEG) recorded at fronto-central and parietal-central areas is not a direct reflection of the underlying interval timing mechanism(s), but more likely represents a time-based response preparation/decision-making process.

Temporal Accumulation and Decision Processes in the Duration Bisection Task Revealed by Contingent Negative Variation

The duration bisection paradigm is a classic task used to examine how humans and other animals perceive time. Typically, participants first learn short and long anchor durations and are subsequently asked to classify probe durations as closer to the short or long anchor duration. However, the specific representations of time and the decision rules applied in this task remain the subject of debate. For example, researchers have questioned whether participants actually use representations of the short and long anchor durations in the decision process rather than merely a response threshold that is derived from those anchor durations. Electroencephalographic (EEG) measures, like the contingent negative variation (CNV), can provide information about the perceptual and cognitive processes that occur between the onset of the timing stimulus and the motor response. The CNV has been implicated as an electrophysiological marker of interval timing processes such as temporal accumulation, representation of the target duration, and the decision that the target duration has been attained. We used the CNV to investigate which durations are involved in the bisection categorization decision. The CNV increased in amplitude up to the value of the short anchor, remained at a constant level until about the geometric mean (GM) of the short and long anchors, and then began to resolve. These results suggest that the short anchor and the GM of the short and long anchors are critical target durations used in the bisection categorization decision process. In addition, larger mean N1P2 amplitude differences were associated with larger amplitude CNVs, which may reflect the participant’s precision in initiating timing on each trial across a test session. Overall, the results demonstrate the value of using scalp-recorded EEG to address basic questions about interval timing.

Reduced functional segregation between the default mode network and the executive control network in healthy older adults: A longitudinal study

The effects of age on functional connectivity (FC) of intrinsic connectivity networks (ICNs) have largely been derived from cross-sectional studies. Far less is known about longitudinal changes in FC and how they relate to ageing-related cognitive decline. We evaluated intra- and inter-network FC in 78 healthy older adults two or three times over a period of 4years. Using linear mixed modeling we found progressive loss of functional specialization with ageing, evidenced by a decline in intra-network FC within the executive control (ECN) and default mode networks (DMN). In contrast, longitudinal inter-network FC between ECN and DMN showed a u-shaped trajectory whereby functional segregation between these two networks initially increased over time and later decreased as participants aged. The rate of loss in functional segregation between ECN and DMN was associated with ageing-related decline in processing speed. The observed longitudinal FC changes and their associations with processing speed remained after correcting for longitudinal reduction in gray matter volume. These findings help connect ageing-related changes in FC with ageing-related decline in cognitive performance and underscore the value of collecting concurrent longitudinal imaging and behavioral data.

Differential age-dependent associations of gray matter volume and white matter integrity with processing speed in healthy older adults

Slower processing speed (PS), a highly robust feature of cognitive aging, is associated with white matter (WM) deterioration and gray matter volume (GMV) loss. Traditional linear regression models assume a constant relationship between brain structure and cognition over time. To probe for variation in the association between WM and GMV and PS over time, we used a novel sparse varying coefficient model on data collected from 126 relatively healthy older adults (67 females, aged 58-85years) evaluated with MRI and a standardized neuropsychological test-battery. We found that WM microstructural differences indexed by fractional anisotropy values in the fronto-striatal tracts (internal and external capsule) showed a stronger association with PS before the age of 70years. Contrastingly, GMV values of the left putamen and middle occipital gyrus were more strongly correlated with PS after 70years. Additionally, within GM and WM compartments, there was heterogeneity in the temporal sequence in which different cortical and subcortical elements were most strongly associated with PS. Together, these observations provide a more nuanced account of the relationships between different structural components of the aging brain and processing speed, a key cognitive domain affected in relatively healthy older adults.

The functional role of the frontal cortex in pre-attentive auditory change detection

Accounts of the functional role of the frontal cortex in pre-attentive auditory change detection include attention switching, response inhibition, contrast enhancement, and activation of a predictive model. These accounts assume different sequential activation patterns between the temporal and frontal cortices: Change detection in the auditory areas of the superior temporal cortex (STC) followed by inferior frontal cortex (IFC) activation for attention switching and response inhibition; STC preceded by IFC activation for contrast enhancement; and an IFC-STC-IFC activation sequence for the predictive model. We used the event-related optical signal (EROS), which provides a temporal resolution of milliseconds and a spatial resolution of 5 to 10mm, combined with lagged correlation path modeling to examine the response of the right frontal and temporal cortices to auditory duration deviants of varying magnitude. Event-related potentials (ERPs) were also recorded, as was the slow optical (hemodynamic) brain response. The data analyses revealed temporal-frontal, frontal-temporal-frontal, and temporal-frontal activation patterns when the deviants represented relatively large, medium, and small changes from the standard stimulus, respectively. These results indicate that the degree of deviance modulates spatio-temporal dynamics within the STC-IFC auditory change detection network.

The regulation of positive and negative social feedback: A psychophysiological study

Everyday social evaluations are psychologically potent and trigger self-reflective thoughts and feelings. The present study sought to examine the psychophysiological impact of such evaluations using eye tracking, pupillometry, and heart-rate variability. Fifty-nine healthy adult volunteers received rigged social feedback (criticism and praise) based on their photograph. Gaze data were collected to investigate processes of attentional deployment/allocation toward the self or the evaluator expressing criticism or praise. Whereas voluntary attention was directed to evaluators who expressed praise, attention was drawn to one’s own picture after criticism. Pupil dilation and heart-rate variability were larger in response to criticism as compared to praise, suggesting a flexible and adaptive emotion regulatory effort in response to social information that triggers an affective response. Altogether, healthy individuals recruited more regulatory resources to cope with negative (as compared to positive) social feedback, and this processing of social feedback was associated with adjustments in self-focused attention.

The interplay between the anticipation and subsequent online processing of emotional stimuli as measured by pupillary dilatation: the role of cognitive reappraisal

Emotions can occur during an emotion-eliciting event, but they can also arise when anticipating the event. We used pupillary responses, as a measure of effortful cognitive processing, to test whether the anticipation of an emotional stimulus (positive and negative) influences the subsequent online processing of that emotional stimulus. Moreover, we tested whether individual differences in the habitual use of emotion regulation strategies are associated with pupillary responses during the anticipation and/or online processing of this emotional stimulus. Our results show that, both for positive and negative stimuli, pupillary diameter during the anticipation of emotion-eliciting events is inversely and strongly correlated to pupillary responses during the emotional image presentation. The variance in this temporal interplay between anticipation and online processing was related to individual differences in emotion regulation. Specifically, the results show that high reappraisal scores are related to larger pupil diameter during the anticipation which is related to smaller pupillary responses during the online processing of emotion-eliciting events. The habitual use of expressive suppression was not associated to pupillary responses in the anticipation and subsequent online processing of emotional stimuli. Taken together, the current data suggest (most strongly for individuals scoring high on the habitual use of reappraisal) that larger pupillary responses during the anticipation of an emotional stimulus are indicative of a sustained attentional set activation to prepare for an upcoming emotional stimulus, which subsequently directs a reduced need to cognitively process that emotional event. Hence, because the habitual use of reappraisal is known to have a positive influence on emotional well-being, the interplay between anticipation and online processing of emotional stimuli might be a significant marker of this well-being.

Probing Interval Timing with Scalp-Recorded Electroencephalography (EEG)

Humans, and other animals, are able to easily learn the durations of events and the temporal relationships among them in spite of the absence of a dedicated sensory organ for time. This chapter summarizes the investigation of timing and time perception using scalp-recorded electroencephalography (EEG), a non-invasive technique that measures brain electrical potentials on a millisecond time scale. Over the past several decades, much has been learned about interval timing through the examination of the characteristic features of averaged EEG signals (i.e., event-related potentials, ERPs) elicited in timing paradigms. For example, the mismatch negativity (MMN) and omission potential (OP) have been used to study implicit and explicit timing, respectively, the P300 has been used to investigate temporal memory updating, and the contingent negative variation (CNV) has been used as an index of temporal decision making. In sum, EEG measures provide biomarkers of temporal processing that allow researchers to probe the cognitive and neural substrates underlying time perception.

Distractor Expectancy Effects on Interval Timing

The influence of non-temporal distractor stimuli on interval timing under conditions expected to elicit covert shifts of attention was examined using seconds range stimuli and the duration bisection task. Distractor stimuli appeared in positions peripheral to the timing signal on half of the trials, but participants were instructed to maintain fixation on the timing stimulus while their eye positions were monitored using an eye-tracker. In Experiment 1, participants ignored the distractors, whereas in Experiment 2 participants counted the distractors. In both experiments, trials with distractors were judged as longer than equivalent duration trials without distractors. Presenting a cue that indicated whether or not the subsequent trial would include distractors (Experiment 3) eliminated this lengthening effect. Taken together, these results suggest that when the presence of distractor stimuli during a trial is uncertain, distractor expectation captures attention that would otherwise be allocated to timing, with the result that perceived duration is shorter on trials in which distractors are absent.

Carrying the past to the future: Distinct brain networks underlie individual differences in human spatial working memory capacity.

ABSTRACT Spatial working memory (SWM) relies on the interplay of anatomically separated and interconnected large‐scale brain networks. EEG studies often observe load‐associated sustained negative activity during SWM retention. Yet, whether and how such sustained negative activity in retention relates to network‐specific functional activation/deactivation and relates to individual differences in SWM capacity remain to be elucidated. To cover these gaps, we recorded concurrent EEG‐fMRI data in 70 healthy young adults during the Sternberg delayed‐match‐to‐sample SWM task with three memory load levels. To a subset of participants (N=28) that performed the task properly and had artefact‐free fMRI and EEG data, we employed a novel temporo‐spatial principal component analysis to derive load‐dependent negative slow wave (NSW) from retention‐related event‐related potentials. The associations between NSW responses with SWM capacity were divergent in the higher (N=14) and lower (N=14) SWM capacity groups. Specifically, larger load‐related increase in NSW amplitude was associated with greater SWM capacity for the higher capacity group but lower SWM capacity for the lower capacity group. Furthermore, for the higher capacity group, larger NSW amplitude was related to greater activation in bilateral parietal areas of the fronto‐parietal network (FPN) and greater deactivation in medial frontal gyrus and posterior mid‐cingulate cortex of the default mode network (DMN) during retention. In contrast, the lower capacity group did not show similar pattern. Instead, greater NSW was linked to higher deactivation in right posterior middle temporal gyrus. Our findings shed light on the possible differential EEG‐informed neural network mechanism during memory maintenance underlying individual differences in SWM capacity. HIGHLIGHTSNegative slow wave (NSW) is related to spatial working memory (SWM) load during retentionNSW in the high and low capacity groups showed divergent associations with SWM capacity and network activitiesNSW was related to higher FPN activation and DMN deactivation in the high capacity groupNSW was related to greater temporal deactivation in the low capacity groupDistinct NSW‐related brain networks are related to individual differences in SWM capacities