Carson Pun

Neglected Time: Impaired Temporal Perception of Multisecond Intervals in Unilateral Neglect

Recent neuroimaging and neuropsychological studies have suggested that the right hemisphere, particularly frontal regions, is important for the perception of the passage of time. We examined the ability to estimate durations of up to 60 sec in a group of eight patients with unilateral neglect. When estimating multisecond intervals, neglect patients grossly underestimated all durations. On average, healthy controls (HC) demonstrated reasonably accurate estimates of all durations tested. Although the right hemisphere lesioned control patients without neglect also tended to underestimate durations, these underestimations were significantly better than the performance of the neglect group. These findings suggest a pivotal role for a right hemisphere fronto-parietal network in the accurate perception of multisecond durations. Furthermore, these findings add to a growing body of literature suggesting that neglect cannot be understood simply in terms of a bias in orienting attention to one side of space. Additional deficits of the kind demonstrated here are likely to be crucial in determining the nature and extent of the loss of conscious awareness for contralesional events.

Your Divided Attention, Please! The Maintenance of Multiple Attentional Control Sets over Distinct Regions in Space.

When non-informative peripheral cues precede a target defined by a specific feature, cues that share the critical feature will capture attention while cues that do not will be effectively ignored. We tested whether different attentional control sets can be simultaneously maintained over distinct regions of space. Participants were instructed to respond only to specific colored targets at specific locations. Most trials included non-predictive cues whose location and/or color were either congruent or incongruent with the spatial and/or color properties of the impending target. We observed contingent capture only for cues that were consistent with the attentional control set applied to that region of space. This is the first demonstration that separate attentional control sets can be simultaneously maintained at distinct spatial locations, with implications for the flexibility of endogenous control over automatic attentional orienting.

Multiple attentional control settings influence late attentional selection but do not provide an early attentional filter.

When one is responding to targets containing a specific feature, non-predictive peripheral cues that share this feature lead to faster responses to the target, while cues that do not contain the target feature effectively are ignored, providing evidence for the role of attentional control settings (ACSs) in the contingent capture hypothesis. It is unclear, however, at what stage of processing multiple ACSs are implemented. We took advantage of the excellent temporal resolution of electroencephalography to demonstrate that the maintenance of multiple ACSs influences later stages of attentional selection rather than providing an early attentional filter. N2pc analyses for cues and targets revealed a similar degree of spatial capture for any peripheral cue, regardless of control settings, with target P3s reflecting the application of the ACS color contingencies.

Neural correlates of cognitive decline in older adults at-risk for developing MCI: Evidence from the CDA and P300

Improving the ability to detect Alzheimer’s disease (AD) at the earliest stages is essential to effectively treat afflicted individuals. Electrophysiological signatures are a promising avenue for earlier diagnosis. In the present study, we investigated an ERP component associated with visual working memory capacity, the contralateral delay activity (CDA). Our participants were undiagnosed and supposedly healthy members of the community, but were defined to be at-risk for Mild Cognitive Impairment (MCI) based on performance from a brief, standardized neuropsychological test. We found that older adults at-risk for MCI had a reduced visual working memory capacity and reduced differentiation of the CDA. In a second experiment, we found that the P300, a well-characterized ERP component shown to be useful in determining conversion from MCI to AD, showed reduced amplitude in our at-risk group. Together, these findings suggest that electrophysiological signatures may be especially sensitive markers of the very earliest stages of AD.

In and out of consciousness: Sustained electrophysiological activity reflects individual differences in perceptual awareness

Although significant advances in our understanding of the cognitive and neural processes involved in conscious awareness have occurred in recent years, the precise mechanisms that support consciousness remain elusive. Examining the neural correlates associated with the moment a stimulus enters or exits conscious awareness is one way to potentially identify the neural mechanisms that give rise to consciousness. In the present study, we recorded neural activity using electroencephalography (EEG) while participants observed a bilateral shape-from-motion (SFM) display. While the display is in motion, the observer perceives an object that is immediately segregated from a noisy background. After the motion stops, the observer’s experience of the object remains momentarily in awareness, before it eventually fades out of consciousness back into the noisy background. Consistent with subjective reports of perceptual experience, we observed a prominent sustained posterior contralateral negativity known as the contralateral delay activity (CDA). This activity was sustained only in conditions associated with sustained awareness. Interestingly, the amplitude of the CDA was correlated with individual differences in visual awareness, suggesting that this activity plays a significant role in the maintenance of objects in consciousness. The CDA is typically associated with visual short-term memory (VSTM), suggesting that conscious visual awareness may be mediated by the same neural and cognitive mechanisms that support VSTM. Our results demonstrate that the CDA may reflect the contents of conscious awareness, and therefore can provide a measure to track when information moves in and out of consciousness.

The right time and the left time: Spatial associations of temporal cues affect target detection in right brain-damaged patients

Humans map timewords such as “yesterday” or “future” onto a mental timeline that holds temporally earlier events on the left side of space and temporally later events on the right side. The perception of time and spatial mapping both are partially subserved by right temporo-parietal brain regions. We tested stroke patients with right-hemisphere lesions on a spatio-temporal cueing task to see whether spatial associations of noninformative temporal cues would elicit the same cognitive deficits as do typical stimulus-driven exogenous cues. While our right brain-damaged patients were able to maintain a mental timeline with words referring to the past sitting to the left and words referring to the future sitting to the right, we also observed that the typical deficit in disengaging from incongruently cued locations persists for noninformative cues that are mapped onto a mental spatial continuum.