News and Events

Attractors and noise: twin drivers of decisions and multistability.

Publication Type:

Journal Article

Source:

NeuroImage, Volume 52, Number 3, p.740–51 (2010)

URL:

http://www.sciencedirect.com/science/article/pii/S1053811910000637

Keywords:

Animals, Brain, Brain: physiology, Decision Making, Decision Making: physiology, Humans, Models, Neurological, Neurons, Neurons: physiology, perception, Perception: physiology

Abstract:

Perceptual decisions are made not only during goal-directed behavior such as choice tasks, but also occur spontaneously while multistable stimuli are being viewed. In both contexts, the formation of a perceptual decision is best captured by noisy attractor dynamics. Noise-driven attractor transitions can accommodate a wide range of timescales and a hierarchical arrangement with "nested attractors" harbors even more dynamical possibilities. The attractor framework seems particularly promising for understanding higher-level mental states that combine heterogeneous information from a distributed set of brain areas.

Texture-based tasks are little affected by second tasks requiring peripheral or central attentive fixation.

Publication Type:

Journal Article

Source:

Perception, Volume 20, Number 4, p.483–500 (1991)

Keywords:

Attention, Discrimination (Psychology), Fixation, Humans, Ocular, Pattern Recognition, Task Performance and Analysis, Visual, Visual Fields

Abstract:

Experiments are described in which observers attempted to perform concurrently two separate visual tasks. Two types of tasks were used: the identification of a T-shaped or L-shaped letter target, and the detection or localization of a texture element of unique orientation (texture target) within a dense texture. Combining these tasks to form various task pairs, performance as a function of stimulus onset asynchrony (SOA) was established separately for each task in a pair. In addition, performance was measured when each task was carried out by itself. When paired, two identification tasks (T or L) on (two) letter targets required a significantly larger SOA than either identification task by itself. This outcome suggests the involvement of serial performance and competition for a limited resource, confirming that letter identification requires attentive fixation. However, when the identification of a central letter target was paired with the localization (upper or lower hemifield) of an eccentric texture target, performance in the pair was comparable to performance of each task by itself. This suggests parallel performance and a lack of conflict over resources. The outcome was similar when the identification of an eccentric letter target was paired with the detection (present or absent) of an eccentric texture target. These results are consistent with the possibility that localization and detection of a textural singularity do not require attentive fixation.

Vision outside the focus of attention.

Publication Type:

Journal Article

Source:

Perception & psychophysics, Volume 48, Number 1, p.45–58 (1990)

ISBN:

0031-5117 (Print)

URL:

http://www.springerlink.com/content/86843130788w2x06/

Keywords:

Attention, Discrimination Learning, Fixation, Form Perception, Humans, Ocular, Orientation, Pattern Recognition, Perceptual Masking, Psychophysics, Visual, Visual Fields

Abstract:

We investigated the relationship between focal attention and a feature-gradient detection that is performed in a parallel manner. We found that a feature gradient can be detected without measurable impairment of performance even while a concurrent form-recognition task is carried out. In spite of the fact that the form-recognition task engages focal attention and thus removes attentive resources from the vicinity of the feature gradient. This outcome suggests strongly that certain perceptions concerning salient boundaries and singularities in a visual scene can be accomplished without the aid of resource-limited processes, such as focal attention, and, by implication, that there may exist two distinct perceptual faculties (one attentive, the other not) that are able to bring complementary kinds of visual information simultaneously to our awareness.

Vision: attention makes the cup flow over.

Publication Type:

Journal Article

Source:

Current biology : CB, Volume 18, Number 16, p.R713–5 (2008)

URL:

http://www.cell.com/current-biology/abstract/S0960-9822(08)00820-8

Keywords:

Attention, Evoked Potentials, Humans, Visual, Visual Perception

Abstract:

Scalp potentials are surprisingly informative about visual attention: a recent study that used them to record neural responses to up to four superimposed visual patterns simultaneously has now revealed the flow of attentional signals back to visual cortex.

Axon outgrowth along segmental nerves in the leech. I. Identification of candidate guidance cells.

Publication Type:

Journal Article

Source:

Developmental biology, Volume 132, Number 2, p.471–85 (1989)

URL:

http://www.sciencedirect.com/science/article/pii/0012160689902431

Keywords:

Animals, Axons, Axons: physiology, Axons: ultrastructure, Blastomeres, Blastomeres: cytology, Cell Movement, Epidermis, Epidermis: cytology, Fluorescent Antibody Technique, Leeches, Leeches: embryology, Morphogenesis, Muscles, Muscles: embryology, Nervous System, Nervous System: embryology, Nervous System: ultrastructure, Neurons, Neurons: ultrastructure, Time Factors

Abstract:

We studied the development of the major extraganglionic components of the germinal plate in embryos of the glossiphoniid leech Helobdella triserialis to improve our understanding of the mechanism of segmental nerve formation. We examined the outgrowth of groups of axons from ganglionic neurons into the segmental nerves, the migration of peripheral neurons and epidermal specializations to their definitive sites, and the development of circular and longitudinal muscle fibers. We visualized axons, as well as neurons and epidermal specializations, by means of fluorescent cell lineage tracers injected earlier into blastomeres and muscle fibers by means of immunofluorescence. The development of cells in all groups was found to follow a stereotyped pattern. Axons of ganglionic neurons approach some identified peripheral neurons located along the segmental nerve paths but not, in general, epidermal specializations and muscle fibers. Near the somata of a subset of peripheral neurons they approach, axons cease or interrupt their growth. These findings identify a set of candidate guidance cells for axonal outgrowth in the leech, similar to those previously described in the developing nervous system of insects.

Axon outgrowth along segmental nerves in the leech. II. Identification of actual guidance cells.

Publication Type:

Journal Article

Source:

Developmental biology, Volume 132, Number 2, p.486–501 (1989)

URL:

http://www.sciencedirect.com/science/article/pii/0012160689902443

Keywords:

Animals, Axons, Axons: physiology, Axons: ultrastructure, Bisbenzimidazole, Dextrans, Fluoresceins, Fluorescence, Fluorescent Dyes, Histocytochemistry, Lasers, Leeches, Leeches: embryology, Lysine, Lysine: analogs & derivatives, Microscopy, Nervous System, Nervous System: embryology, Nervous System: ultrastructure, Neurons, Neurons: physiology, Neurons: radiation effects, Neurons: ultrastructure, Rhodamines, Staining and Labeling

Abstract:

Some peripheral neurons, previously identified as candidate guidance cells for axonal outgrowth along the segmental nerves in embryos of the glossiphoniid leech Helobdella triserialis, were photoablated by laser illumination to ascertain whether their presence is necessary for generation of the normal axonal growth pattern. These experiments showed that focal photoablation of peripheral neurons nz3 or pz8 prevents normal axonal outgrowth along the ultraposterior nerve path or along the distal sector of the medial-anterior nerve path, respectively, in conformance with the inference that these two neurons do function as guidance cells. However, ablation of these neurons affects axon outgrowth only if the neurons are illuminated prior to the end of a sensitive period in segmental development. By contrast, photoablation of previously identified candidate guidance cells situated on the anterior-anterior and posterior-posterior nerve paths, among them peripheral neurons nz1, nz2, oz1, oz2, pz6, and LD1, does not prevent normal axonal outgrowth. It is possible that the guidance role, if any, of these neurons is facultative rather than necessary, since each of the several neurons that lies on either of these nerve paths may provide an alternative axon guidance cue.

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