2003

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Distributed neural activity during object, spatial and integrated processing in humans

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Authors:

  • Emiliana R. Simon-Thomas

  • Kim Brodsky

  • Cammy Willing

  • Rashmi Sinha

  • Robert T. Knight

Date: 2003

PubMed: 12706225

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Abstract:

Information about the form and the spatial location of objects is seamlessly integrated during visual perception. We used event-related potentials (ERPs) to explore neural activity related to processing form, location or the combination of both kinds of features. Healthy subjects performed three versions of a 'match-to-sample' task: a two-object task, a two-location task and an integrated object-location task. Responses were quickest and most accurate during the integrated task, slower and less accurate in the two-location task and slowest and least accurate in the two-object task. ERPs locked to the 'sample' stimulus at encoding, and to the 'target' stimulus during feature comparison differentiated between tasks. 'Sample' stimulus ERPs exhibited task-specific posterior cortical involvement in processing distinct visual features. 'Target' stimulus ERPs revealed task-related differences in features associated with frontal lobe mediated attentional processes: an early latency P300 showed increased amplitude during the integrated task. Results from this experiment support the view that distinct neural circuits mediate form vs. location processing and that form-location integration engages both pathways and upregulates frontal-parietal association networks.

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The regulatory function of self-conscious emotion: insights from patients with orbitofrontal damage

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Authors:

  • Jennifer S. Beer

  • Erin A. Heerey

  • Dacher Keltner

  • Robert T. Knight

Date: 2003

PubMed: 14561114

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Abstract:

Although once considered disruptive, self-conscious emotions are now theorized to be fundamentally involved in the regulation of social behavior. The present study examined the social regulation function of self-conscious emotions by comparing healthy participants with a neuropsychological population--patients with orbitofrontal lesions--characterized by selective regulatory deficits. Orbitofrontal patients and healthy controls participated in a series of tasks designed to assess their social regulation and self-conscious emotions. Another task assessed the ability to infer others' emotional states, an appraisal process involved in self-conscious emotion. Consistent with the theory that self-conscious emotions are important for regulating social behavior, the findings show that deficient behavioral regulation is associated with inappropriate self-conscious emotions that reinforce maladaptive behavior. Additionally, deficient behavioral regulation is associated with impairments in interpreting the self-conscious emotions of others.

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The neural substrates of visual implicit memory: do the two hemispheres play different roles?

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Authors:

  • Neal E. A. Kroll

  • Andrew P. Yonelinas

  • Mark M. Kishiyama

  • Kathleen Baynes

  • Robert T. Knight

  • Michael S. Gazzaniga

Date: 2003

PubMed: 14511536

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Abstract:

Identification of visually presented words is facilitated by implicit memory, or visual priming, for past visual experiences with those words. There is disagreement over the neuro-anatomical substrates of this form of implicit memory. Several studies have suggested that this form of priming relies on a visual word-form system localized in the right occipital lobe, whereas other studies have indicated that both hemispheres are equally involved. The discrepancies may be related to the types of priming tasks that have been used because the former studies have relied primarily on word-stem completion tasks and the latter on tasks like word-fragment completion. The present experiments compared word-fragment and word-stem measurements of visual implicit memory in patients with right occipital lobe lesions and patients with complete callosotomies. The patients showed normal visual implicit memory on fragment completion tests, but essentially no visual priming on standard stem completion tests. However, when we used a set of word stems that had only one correct solution for each test item, as was true of the items in the fragment completion tests, the patients showed normal priming effects. The results indicate that visual implicit memory for words is not solely dependent upon the right hemisphere, rather it reflects changes in processing efficiency in bilateral visual regions involved in the initial processing of the items. However, under conditions of high lexical competition (i.e., multiple completion word stems), the lexical processes, which are dominant in the left hemisphere, overshadow the visual priming supported by the left hemisphere.

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Prefrontal cortex and episodic memory: integrating findings from neuropsychology and event-related neuroimaging.

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ABSTRACT

Although it has been speculated for many years that the prefrontal cortex plays a role in long-term memory for events, or episodic memory, only recently have researchers made a concerted attempt to define this role. Most theories of prefrontal function suggest that this region implements “topdown” or “executive” processes that influence a variety of domains, including memory. For example, Luria (1966) postulated a role for the frontal lobes in the regulation of voluntary attention and the organisation of goal-directed behavior. Building on the work of Luria, Shallice (1982) argued that the frontal lobes are required for the attentional selection of schemes of action in novel situations. A complementary role suggested for the prefrontal cortex is the suppression of irrelevant or interfering stimuli (Brutkowski, 1965; Fuster, 1997; Knight, Staines, Swick, & Chao, 1999; Pribram, Ahumada, Hartog, & Roos, 1964; Shimamura, 1995). Teuber (1964) additionally proposed that the frontal lobes prepare sensory areas for environmental changes that will be induced by motor actions. This concept was later extended to include the generation of anticipatory behavioural sets (Fuster, 1997; Nauta, 1971). Several researchers have also postulated a central role for the prefrontal cortex in active, or working memory (Fuster, 1997; Goldman-Rakic, 1987).





AUTHORS

  • Charan Ranganath

  • Robert T. Knight

Date: 2003

ISBN-13: 978-1841692463

ISBN-10: 9781841692463


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A new ERP paradigm for studying individual differences in the executive control of attention

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Authors:

  • Francisco Barceló

  • Jose A. Perianìez

  • Robert T. Knight

Date: 2003

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Abstract:

Event-related potentials (ERPs) provide valuable information about the fast brain dynamics subserving cognitive functions such as atten- tion and working memory. Most ERP studies employ cognitive para- digms with a fixed task-set (i.e., press a button to named targets), but few have measured ERPs time-locked to shifts in set using a task- switching paradigm. The Madrid Card Sorting Test (MCST) is a dual task protocol in which feedback cues signal unpredictable shifts in set (i.e., from “sort cards by colour” to “sort cards by shape”). This pro- tocol offers an integrated analysis of ERPs to both feedback cues and target card events, providing separate ERP indexes for the shifting, updating and rehearsal of attention sets in working memory. Two of these ERP indices are the frontal and posterior aspects of the P300 response. Feedback cues that direct a shift in set also elicit both a frontally distributed P3a potential (300 to 400 ms) and a posteriorly distributed P3b potential (350 to 600 ms). In turn, target card events evoke posterior P3b responses whose amplitude increases as the new task set is gradually rehearsed. In line with current models about the role of prefrontal cortex in the executive control of attention, this P3a/P3b response system appears to reflect the coordinated action of prefrontal and posterior association cortices during the switching and updating of task sets in working memory.

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Spatial asymmetries of auditory event-synthesis in humans

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Authors:

  • Leon Y. Deouell

  • Christina M. Karns

  • Tamara B. Harrison

  • Robert T. Knight

Date: 2003

PubMed: 12531460

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Abstract:

We used the mismatch negativity event-related potential to examine how spatial location and feature variation affect the capacity of the auditory system to automatically respond to pairs of rapid (180 ms apart) acoustic changes within a single tone. When a tone first deviated from a standard tone in source location and then in its duration, we found independent responses to both deviations for right but not left field stimuli. In contrast, when the first deviation was in pitch and the second in duration, only the first deviation elicited a response, regardless of presentation side. These results suggest that information from either side of space is asymmetrically processed even in a free-field, and that the extent of the temporal window of integration is not a fixed property of the auditory system.

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Grouping Influences in Unilateral Visual Neglect

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Authors:

  • Lynn C. Robertson

  • Mirjam Eglin

  • Robert T. Knight

Date: 2003

PubMed: 12916644

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Abstract:

Effects of grouping on unilateral neglect were investigated in 8 neurological patients with right hemisphere damage. It is well documented that arranging items to form a group spanning the midline decreases the magnitude of neglect. In the present study we examined how clusters of groups within the left or right visual field affect neglect and whether isolated groups within the neglected field deflect attention from right-sided displays. We orthogonally varied the strength of grouping on the right and left sides of a display and measured the time to find a predesignated target in one of those groups. Groups on the neglected left side did not affect right-sided target detection any more than an empty left page. However, strength of grouping did affect left sided target detection. These findings are discussed as they relate to attention and preattention in unilateral visual neglect.