Phasic alertness and temporal expectations

Responses to visual stimuli are faster when the stimuli occur simultaneously with auditory accessory stimuli. This is despite the fact that accessory stimuli offer no information regarding the required response. Performance is also improved when auditory stimuli precede rather than accompany the visual targets. This effect is assumed to arise from phasic alertness, a short-lived increase in the brain‘s readiness for information processing. Here, we ask how phasic alertness and accessory stimulation work in concert. Specifically, we investigated how auditory alerting modulates the effects of subsequent accessory stimuli on a visual choice reaction task. Accessory stimuli supported performance in the absence of alerting cues, but impaired performance when alerting cues had been presented before (Experiment 1). This reversed accessory stimulus effect did not stem from expectations regarding stimulus combinations (Experiment 2). In sum, our findings reveal that phasic alerting changes the accessory stimulus effect from beneficial to detrimental for performance.

Phasic alerting cues temporarily increase the brain's arousal state. In younger and older participants, visual processing speed in a whole report task, estimated based on the theory of visual attention, is increased in cue compared to no-cue conditions. In younger participants, phasic alerting effects on visual processing speed have been linked to intrinsic functional connectivity (iFC) within the cingulo-opercular network. Robertson (2014) suggested that the connectivity of the right fronto-parietal network is essential for maintaining alertness capabilities in aging. The present study assessed whether older participants' ability to profit from warning cues is related to iFC in the cingulo-opercular or right fronto-parietal network. We obtained resting-state functional magnetic resonance imaging data from 31 older participants. By combining an independent component analysis and dual regression, we investigated iFC in both networks. A voxel-wise multiple regression in older participants revealed that higher phasic alerting effects on visual processing speed were significantly associated with lower right fronto-parietal network iFC. We then compared healthy older participants to a previously reported sample of younger participants to assess whether behaviour-iFC relationships are age group specific. The comparison revealed that the association between phasic alerting and cingulo-opercular network iFC is significantly lower in older than in younger adults. Additionally, it yielded a stronger association between phasic alerting and right fronto-parietal network iFC in older versus younger participants. The results support a particular role of the right fronto-parietal network in maintaining phasic alerting capabilities in aging.

We investigated adult age differences in phasic alerting effects on visual attention. Parameters of visual attention capacity and selectivity, based on the Theory of Visual Attention, were measured together with electroencephalograpy (EEG) in a partial letter report task, in which half of the visual stimulus displays were preceded by an auditory warning cue. Younger adults showed an alertness-related increase in the parameter visual processing capacity. The behavioral alerting effect co-occured with reduced latencies of stimulus-related visual event-related lateralizations (ERLs), indicating faster stimulus processing in the visual stream. By contrast, older adults, on average, did not benefit from the alerting cue, neither on the behavioral nor electrophysiological level. Assuming that the age differences may result from ineffective processing of the warning signal, we analysed EEG power and phase-locking time-locked to the cue. We found a cue-related increase in both power and phase-locking with a maximum in the alpha band across age groups. Importantly, this cue-related response was stronger in older than younger adults. Furthermore, the cue-related increase in power and phase-locking was negatively correlated with the behavioral alerting effect in the older group. These findings indicate age-related changes in the brain network underlying alertness and attention. More specifically, older adults' may benefit less from alerting cues than younger adults, if their neural response is strongly driven by the cue and, thus, hinders the effective use of the warning signal to foster processing of the following stimulus.

To perform continuous tasks requiring sustained attention over extended periods of time, it is necessary to maintain an adequate level of arousal. Arousal – the energetic state of the cognitive system – influences the capacity to engage with task-relevant events. Although a strong connection between sustained attention and arousal is widely recognised, little is known about whether or how arousal levels are adjusted to support performance. Visual performance is known to benefit from the temporal anticipation of task-relevant events. However, it is not clear whether anticipation also alters the ongoing state of arousal. In the current study, we addressed this question by using a continuous task design to measure the ongoing state of arousal while attending occasional targets. Throughout the experiment, participants reported visual targets which appeared briefly at the centre of the screen. Crucially, the targets either appeared at fixed intervals, rendering them temporally predictable, or at random times. We estimated arousal using pupil dilation and used psychophysics and computational modelling (TVA) to measure how temporal predictability influences perceptual parameters. We demonstrate that temporal regularity embedded within a continuous-performance task improves performance and shifts the levels of arousal to anticipate predictable targets. Predictable targets led to phasic increases in arousal before their onsets in a background of otherwise low tonic arousal. In contrast, temporally unpredictable targets led to an increase in tonic arousal overall. Accordingly, we argue that arousal is sensitive to varying levels of temporal predictability, and dynamically adapts to task demands.

Temporal expectations can be induced experimentally by creating temporal-regularities, for instance by presenting cues which are associated with specific time-intervals preceding targets (cue-based expectations). Even without these, expectations for an upcoming event increase with time according to the hazard-rate function – the conditional probability of an event to occur, given it has not occurred yet. Previous studies showed that cue-based temporal expectations depend on spatial attention: to benefit from information regarding stimulus onset, observers need to attend to its location. Here we examined whether hazard-rate expectations effects also depend on spatial attention. In two experiments, we used two variations of a spatial-cueing task, with cue-target interval length varying in order to create an increasing hazard-rate. A spatial-cue appeared at the beginning of each trial in order to manipulate spatial attention (valid/invalid/neutral). After a random interval (500-2100ms) sampled from a uniform distribution, a target (asterisk) appeared briefly (33ms) and participants were instructed to indicate its location side as fast as possible (Exp. 1) or perform a single-button speeded-response (Exp. 2). Using mixed-effects modelling, we show in both experiments a validity effect on reaction-time (valid < invalid), along an overall effect of hazard-rate, such that reaction-time decreased with increasing intervals. These findings indicate that unlike cue-based temporal expectations, hazard-rate predictions affect performance both within and outside spatial locus of attention.