117,570 research outputs found
Neural mechanisms for stimulus selection in cortical areas of the macaque subserving object vision
No full textThe present article reviews some recent work on the neuronal mechanisms underlying space-based and feature-based stimulus selection in the primate occipito-temporal pathway of cortical visual processing. Clear evidence demonstrates that activity in areas V4 and IT is high for a stimulus which is selected either for its position in space or for its features, while it is considerably suppressed for other, irrelevant stimuli. Data are discussed within a conceptual framework whereby objects in the visual field always compete for focal resources. According to task demands, any kind of input (objects of a certain category, objects with a certain form, color or motion, objects at a certain location) can be behaviorally relevant. A short-term description (working memory) of the currently relevant object properties controls competitive bias in the visual system, such that inputs matching that description are favored to the disadvantage of task-irrelevant inputs. This framework emphasizes a tight, causal link between memory signals and mechanisms for stimulus selection in visual cortex. In all cases gating of neural activity was constrained by spatial factors. In area V4, responses to an ignored stimulus in the receptive field of the recorded neuron were maximally suppressed when the monkey attended to a second stimulus located within the boundary of the same receptive field, while suppression was virtually absent when attention was directed to a second stimulus well outside the receptive field border. In IT cortex, suppressed responses depended on both the selected and ignored stimuli being within the hemifield contralateral to the recorded hemisphere, while suppression was much reduced when the stimuli were presented across the vertical midline. These spatial constraints on the occurrence of modulation of visual responses may reflect limitations imposed by the local pattern of reciprocal inhibitory connections, which are supposed to underlie competitive interactions among objects in the field, that is among object representations in cortex
Serial attention mechanisms in visual search: a critical look at the evidence
No full textUntil a few years ago, visual search tasks were of exclusive pertinence to psychophysicists and cognitive psychologists trying to understand the operating principles and computational constraints of visual perception and visual selective attention. In recent years, cognitive neuroscience, with its powerful tools, has started to explore more directly the neuronal mechanisms underlying search performance in humans and macaques, aiming at the same general goals. New observations from a number of cognitive neuroscience approaches are promising a near future of great excitement in this field of research. This article offers a critical review of some of these recent contributions and highlights some of the interpretational problems that they pose
Does the macaque monkey provide a good model for studying human executive control? A comparative behavioral study of task switching.
No full textThe ability to swiftly and smoothly switch from one task set to another is central to intelligent behavior, because it allows an organism to flexibly adapt to ever changing environmental conditions and internal needs. For this reason, researchers interested in executive control processes have often relied on task-switching paradigms as powerful tools to uncover the underlying cognitive and brain architecture. In order to gather fundamental information at the single-cell level, it would be greatly helpful to demonstrate that non-human primates, especially the macaque monkey, share with us similar behavioral manifestations of task-switching and therefore, in all likelihood, similar underlying brain mechanisms. Unfortunately, prior attempts have provided negative results (e.g., Stoet & Snyder, 2003b), in that it was reported that macaques do not show the typical signature of task-switching operations at the behavioral level, represented by switch costs. If confirmed, this would indicate that the macaque cannot be used as a model approach to explore human executive control mechanisms by means of task-switching paradigms. We have therefore decided to re-explore this issue, by conducting a comparative experiment on a group of human participants and two macaque monkeys, whereby we measured and compared performance costs linked to task switching and resistance to interference across the two species. Contrary to what previously reported, we found that both species display robust task switching costs, thus supporting the claim that macaque monkeys provide an exquisitely suitable model to study the brain mechanisms responsible for maintaining and switching task sets
Visual selective attention and the effects of monetary rewards
No full textOutcomes of actions, in the form of rewards and punishments, are known to shape behavior. For example, an action followed by reward will be more readily elicited on subsequent encounters with the same stimuli and context -- a phenomenon known as the law of effect. These consequences of rewards (and punishments) are important because they reinforce adaptive behaviors at the expense of competing ones, thus increasing fitness of the organism in its environment. However, it is unknown whether similar influences regulate covert mental processes, such as visual selective attention. Visual selective attention allows privileged processing of task-relevant information, while inhibiting distracting contextual elements. Using variable monetary rewards as arbitrary feedback on performance, we tested whether acts of attentional selection, and in particular the resulting aftereffects, can be modulated by their consequences. Results show that the efficacy of visual selective attention can be sensibly adjusted by external feedback. Specifically, although lingering inhibition of distractors is robust after highly rewarded selections, it is eliminated after poorly rewarded selections. This powerful feature of visual selective attention provides attentive processes with both flexibility and self-regulation properties
Associative knowledge controls deployment of visual selective attention
No full textAccording to some models of visual selective attention, objects in a scene activate corresponding neural representations, which compete for perceptual awareness and motor behavior. During a visual search for a target object, top-down control exerted by working memory representations of the target's defining properties resolves competition in favor of the target. These models, however, ignore the existence of associative links among object representations. Here we show that such associations can strongly influence deployment of attention in humans. In the context of visual search, objects associated with the target were both recalled more often and recognized more accurately than unrelated distractors. Notably, both target and associated objects competitively weakened recognition of unrelated distractors and slowed responses to a luminance probe. Moreover, in a speeded search protocol, associated objects rendered search both slower and less accurate. Finally, the first saccades after onset of the stimulus array were more often directed toward associated than control items
Incidence, associated clinical factors and outcome of hypertensive crises in critically Ill patients: A prospective survey
No full textBackground: Hypertensive crises (HCs) are common among critically ill patients. However, little is known of their epidemiology, particularly actual rate and outcome of affected patients. Primary end-point of the study was to assess incidence of and clinical factors associated with HCs in a cohort of patients admitted to a general ICU. Secondary end-point was to assess the impact of HC on patients' outcome. Methods: All patients consecutively admitted to a general ICU over a 13 months period were included in the study. Incidence of HCs was assessed and associated clinical factors were determined using univariate and multivariate analysis. Length-of-stay and ICU- and in-hospital mortality were evaluated. Results: Incidence of HCs was 15.4%. Factors independently associated with HCs were: ICU-admission for acute medical conditions, cigarette smoking, cancer, coronary artery disease, chronic atrial fibrillation (p<0.05). ICU length-of-stay and ICU-/ in-hospital mortality rate were higher among patients with HCs (p<0.05). Conclusion: HCs are common in critically Ill patients, even if previously normotensive, and are associated with a worse outcome. Associated clinical factors include acute medical conditions leading to ICU admission, cigarette smoking, cancer, coronary artery disease and chronic atrial fibrillation. © 2011 Chelazzi C, et al
Land use and settlement patterns in the Kourion region: a crossanalysis of the MC-LC topography and pottery evidence
No full textLand use and settlement patterns in the Kourion region: a cross-analysis of the MC-LC topography and pottery evidence
No full textThis study, as a preliminary introduction to the results of the Kouris Valley has been addressed to investigate the development trends within the settlement system of the Kouris valley in the Middle Cypriot (MC) to Late Cypriot (LC) period. A cross-analysis has been outlined, based on two linked research steps: the first one focusing upon the topographical evidence (the localization and inter-relation among the identified sites); the second, upon the technological and typological features related to the pottery production in the area. The summing up of the cross results within a larger framework has been useful to suggest a development in function and use of the sites within the chronological range of interest
Volitional covert orienting to a peripheral cue does not suppress cue-induced inhibition of return
No full textDetection reaction time (RT) at an extrafoveal location can be increased by noninformative precues presented at that location or ipsilaterally to it. This cue-induced inhibition is called inhibition of return or ipsilateral inhibition. We measured detection RT to simple light targets at extrafoveal locations that could be designated for covert orienting by local or distant cues. We found that cue-induced inhibition cooccurred in an additive fashion with the direct effects of covert orienting, i.e., it detracted from facilitation at attended locations and increased the disadvantage for unattended locations. Thus, cue-induced inhibition cannot be suppressed by a volitional covert orienting to the cued location; the co-occurrence of different facilitatory and inhibitory effects confirms the simultaneous operation of multiple independent attentional mechanisms during covert orienting
Competitive mechanisms subserve attention in macaque areas V2 and V4
No full textExamined neural mechanisms involved in the modulation of attention in visual processing in extrastriate cortex. The assumption is made that multiple stimuli activate competing populations of neurons and that attention biases this competition in favor of the attended stimulus. Attention has a more limited effect on the neuronal response to a single stimulus. To test this interpretation, we measured the responses of neurons in macaque areas V2 and V4 using a behavioral paradigm that allowed us to isolate automatic sensory processing mechanisms from attentional effects. First, we measured each cell's response to a single stimulus presented alone inside the receptive field or paired with a second receptive field stimulus, while the monkey attended to a location outside the receptive field. Adding the second stimulus typically caused the neuron's response to move toward the response that was elicited by the second stimulus alone. Then, we directed the monkey's attention to one element of the pair. This drove the neuron's response toward the response elicited when the attended stimulus appeared alone. Findings are consistent with the idea that attention biases competitive interactions among neurons, causing them to respond primarily to the attended stimulus. ((c) 1999 APA/PsycINFO, all rights reserved
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