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Kathy A. Low
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Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2015) 27 (8): 1513–1527.
Published: 01 August 2015
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When analyzing visual scenes, it is sometimes important to determine the relevant “grain” size. Attention control mechanisms may help direct our processing to the intended grain size. Here we used the event-related optical signal, a method possessing high temporal and spatial resolution, to examine the involvement of brain structures within the dorsal attention network (DAN) and the visual processing network (VPN) in preparation for the appropriate level of analysis. Behavioral data indicate that the small features of a hierarchical stimulus (local condition) are more difficult to process than the large features (global condition). Consistent with this finding, cues predicting a local trial were associated with greater DAN activation. This activity was bilateral but more pronounced in the left hemisphere, where it showed a frontal-to-parietal progression over time. Furthermore, the amount of DAN activation, especially in the left hemisphere and in parietal regions, was predictive of subsequent performance. Although local cues elicited left-lateralized DAN activity, no preponderantly right activity was observed for global cues; however, the data indicated an interaction between level of analysis (local vs. global) and hemisphere in VPN. They further showed that local processing involves structures in the ventral VPN, whereas global processing involves structures in the dorsal VPN. These results indicate that in our study preparation for analyzing different size features is an asymmetric process, in which greater preparation is required to focus on small rather than large features, perhaps because of their lesser salience. This preparation involves the same DAN used for other attention control operations.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2014) 26 (10): 2400–2415.
Published: 01 October 2014
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We investigated the dynamics of brain processes facilitating conscious experience of external stimuli. Previously, we proposed that alpha (8–12 Hz) oscillations, which fluctuate with both sustained and directed attention, represent a pulsed inhibition of ongoing sensory brain activity. Here we tested the prediction that inhibitory alpha oscillations in visual cortex are modulated by top–down signals from frontoparietal attention networks. We measured modulations in phase-coherent alpha oscillations from superficial frontal, parietal, and occipital cortices using the event-related optical signal (EROS), a measure of neuronal activity affording high spatiotemporal resolution, along with concurrently recorded EEG, while participants performed a visual target detection task. The pretarget alpha oscillations measured with EEG and EROS from posterior areas were larger for subsequently undetected targets, supporting alpha's inhibitory role. Using EROS, we localized brain correlates of these awareness-related alpha oscillations measured at the scalp to the cuneus and precuneus. Crucially, EROS alpha suppression correlated with posterior EEG alpha power across participants. Sorting the EROS data based on EEG alpha power quartiles to investigate alpha modulators revealed that suppression of posterior alpha was preceded by increased activity in regions of the dorsal attention network and decreased activity in regions of the cingulo-opercular network. Cross-correlations revealed the temporal dynamics of activity within these preparatory networks before posterior alpha modulation. The novel combination of EEG and EROS afforded localization of the sources and correlates of alpha oscillations and their temporal relationships, supporting our proposal that top–down control from attention networks modulates both posterior alpha and awareness of visual stimuli.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2013) 25 (6): 887–902.
Published: 01 June 2013
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Coordination between networks of brain regions is important for optimal cognitive performance, especially in attention demanding tasks. With the event-related optical signal (a measure of changes in optical scattering because of neuronal activity) we can characterize rapidly evolving network processes by examining the millisecond-scale temporal correlation of activity in distinct regions during the preparatory period of a response mode switching task. Participants received a precue indicating whether to respond vocally or manually. They then saw or heard the letter “L” or “R,” indicating a “left” or “right” response to be implemented with the appropriate response modality. We employed lagged cross-correlations to characterize the dynamic connectivity of preparatory processes. Our results confirmed coupling of frontal and parietal cortices and the trial-dependent relationship of the right frontal cortex with response preparation areas. The frontal-to-modality-specific cortex cross-correlations revealed a pattern in which first irrelevant regions were deactivated, and then relevant regions were activated. These results provide a window into the subsecond scale network interactions that flexibly tune to task demands.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2012) 24 (9): 1941–1959.
Published: 01 September 2012
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The significance of stimuli is linked not only to their nature but also to the sequential structure in which they are embedded, which gives rise to contingency rules. Humans have an extraordinary ability to extract and exploit these rules, as exemplified by the role of grammar and syntax in language. To study the brain representations of contingency rules, we recorded ERPs and event-related optical signal (EROS; which uses near-infrared light to measure the optical changes associated with neuronal responses). We used sequences of high- and low-frequency tones varying according to three contingency rules, which were orthogonally manipulated and differed in processing requirements: A Single Repetition rule required only template matching, a Local Probability rule required relating a stimulus to its context, and a Global Probability rule could be derived through template matching or with reference to the global sequence context. ERP activity at 200–300 msec was related to the Single Repetition and Global Probability rules (reflecting access to representations based on template matching), whereas longer-latency activity (300-450 msec) was related to the Local Probability and Global Probability rules (reflecting access to representations incorporating contextual information). EROS responses with corresponding latencies indicated that the earlier activity involved the superior temporal gyrus, whereas later responses involved a fronto-parietal network. This suggests that the brain can simultaneously hold different models of stimulus contingencies at different levels of the information processing system according to their processing requirements, as indicated by the latency and location of the corresponding brain activity.
Journal Articles
Publisher: Journals Gateway
Journal of Cognitive Neuroscience (2006) 18 (4): 637–650.
Published: 01 April 2006
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Cognitive aging theories emphasize the decrease in efficiency of inhibitory processes and attention control in normal aging, which, in turn, may result in reduction of working memory function. Accordingly, some of these age-related changes may be due to faster sensory memory decay or to inefficient filtering of irrelevant sensory information (sensory gating). Here, event-related brain potentials and the event-related optical signal were recorded in younger and older adults passively listening to tone trains. To determine whether age differentially affects decay of sensory memory templates over short intervals, trains were separated by delays of either 1 or 5 sec. To determine whether age affects the suppression of responses to unattended repeated stimuli, we evaluated the brain activity elicited by successive train stimuli. Some trains started with a shorter-duration stimulus (deviant trains). Results showed that both electrical and optical responses to tones were more persistent with repeated stimulation in older adults than in younger adults, whereas the effects of delay were similar in the two groups. A mismatch negativity (MMN) was elicited by the first stimulus in deviant trains. This MMN was larger for 1- than 5-sec delay, but did not differ across groups. These data suggest that age-related changes in sensory processing are likely due to inefficient filtering of repeated information, rather than to faster sensory memory decay. This inefficient filtering may be due to, or interact with, reduced attention control. Furthermore, it may increase the noise levels in the information processing system and thus contribute to problems with working memory and speed of processing.