Continuous Repertoire: Multiple-Response Control by a Continuous Stimulus Dimension

1978 ◽  
Vol 43 (1) ◽  
pp. 63-68 ◽  
Author(s):  
Donald G. Wildemann
Keyword(s):  
Human Subjects ◽  
Stimulus Dimension ◽  
Positive Transfer ◽  
Multiple Response ◽  
Response Control ◽  
Continuous Response ◽  
Fine Grain ◽  
Stimulus Continuum ◽  
Response Dimension

Three points of correspondence were trained between a continuous stimulus dimension and a quasi-continuous response dimension. Human subjects were then tested with novel test stimuli from the stimulus continuum to determine whether appropriate new mapping responses would be emitted. A procedure was developed to allow a fine-grain analysis of the mapping responses. Data indicated that use of continuous stimulus and response dimensions results in significant positive transfer to untrained values.

Sensory Feedback Does Not Cause Selective Adaptation of Human “Command Neurons”

1977 ◽  
Vol 44 (2) ◽  
pp. 447-451 ◽  
Author(s):  
David A. Rosenbaum ◽  
Michael Radford
Keyword(s):  
Present Experiment ◽  
Motor System ◽  
Sensory Feedback ◽  
Negative Transfer ◽  
Human Subjects ◽  
Selective Adaptation ◽  
Positive Transfer ◽  
Command Neurons ◽  
Body Movements ◽  
Human Motor

It has been proposed that body movements are partly controlled by a neural hierarchy, with cells at successively higher levels controlling increasing numbers of muscles engaged in functionally equivalent responses. In addition to physiological support for the hypothesis, obtained from infrahuman species, evidence from human subjects has been obtained in the form of negative transfer between successive similar responses. This negative transfer has been attributed to selective adaptation of “command neurons” in the human motor system. The present experiment found no evidence for negative (or positive) transfer between passive and active movements, suggesting that selective adaptation of human command neurons is caused by efference rather than afference.

Components of Attentional Set-switching

2005 ◽  
Vol 52 (2) ◽  
pp. 83-98 ◽  
Author(s):  
M. F. S. Rushworth ◽  
R. E. Passingham ◽  
A. C. Nobre
Keyword(s):  
Task Switching ◽  
Human Subjects ◽  
Event Related Potentials ◽  
Neural Correlates ◽  
Stimulus Dimension ◽  
Task Switch ◽  
Attentional Set ◽  
Set Switching ◽  
Related Potentials ◽  
The Way

Abstract. A series of distinct event-related potentials (ERPs) have been recorded from the scalp of human subjects as they switch from one task to another. It is possible that task switching may depend on different mechanisms depending on whether the switch requires a change in attentional set, in other words the redirecting of attention to different aspects of a sensory stimulus, or whether it requires a change in intentional set, in others words a change in the way that responses are selected. To address this issue, the current study recorded ERPs while subjects switched between attentional sets and the results were compared with those of a previous investigation in which subjects switched between intentional sets. Subjects selected stimuli according to two conflicting attentional sets, each emphasizing one visual stimulus dimension (colour, shape). Pairs of stimuli, only one of which was to be attended, were presented for between eight and seventeen trials then either a switch or a stay cue was shown. The switch cue instructed subjects to switch from the current attentional set to the other set, while the stay cue instructed subjects to maintain the current set. Comparing ERPs time-locked to the switch and stay cues revealed neural correlates of the initiation of a task switch. Comparing the ERPs time locked to the first stimuli after either stay or switch cues identified neural correlates of the implementation of a task switch. A similar modulation over parietal electrodes was seen when subjects were switching between either attentional or intentional sets. While an intentional set switch began with a medial frontal modulation, attentional set switching began with a lateral frontal modulation. Implementing a new attentional set was associated with modulation of relatively early visual potentials, while implementing a new intentional set was associated with modulation of later response-related potentials. The results confirm that task switching consists of a number of constituent processes which may be taxed to different degrees depending on whether a task-switch paradigm requires subjects to change the way in which they select stimuli or responses.

The Effect of Overtraining on Transfer between Tasks Involving the Same Stimulus Dimension

1971 ◽  
Vol 23 (2) ◽  
pp. 234-242
Author(s):  
A. H. Winefield ◽  
M. A. Jeeves
Keyword(s):  
Negative Transfer ◽  
Brightness Discrimination ◽  
Stimulus Dimension ◽  
Successive Discrimination ◽  
Positive Transfer ◽  
Transfer Effects

Two experiments are reported in which transfer effects between two discrimination tasks are examined following differing amounts of training on the first task. The two tasks were a conditional (successive) discrimination involving black/white cues, and a simultaneous brightness discrimination involving the same black/white cues. In Experiment I the conditional task was presented first and in Experiment II the simultaneous task was presented first. The results of Experiment I show overall negative transfer which is not directly related to the amount of training. The results of Experiment II, however, reveal positive transfer although again the amount of training produced no significant effect. These seemingly discrepant findings are explained in terms of the difficulty of the conditional task and the development of rigid position stereotypes. It is argued that the concept of frustration-instigated behaviour is necessary to account for the results.

Aspects of microanalysis in a transmission electron microscope

1978 ◽  
Vol 36 (1) ◽  
pp. 510-511
Author(s):  
R. Sinclair ◽  
B.E. Jacobson
Keyword(s):  
Grain Size ◽  
Electron Beam ◽  
Electron Microscope ◽  
Chemical Analysis ◽  
Transmission Electron Microscope ◽  
Vapor Deposition ◽  
Critical Currents ◽  
X Ray ◽  
Fine Grain ◽  
Transmission Electron

INTRODUCTIONThe prospect of performing chemical analysis of thin specimens at any desired level of resolution is particularly appealing to the materials scientist. Commercial TEM-based systems are now available which virtually provide this capability. The purpose of this contribution is to illustrate its application to problems which would have been intractable until recently, pointing out some current limitations.X-RAY ANALYSISIn an attempt to fabricate superconducting materials with high critical currents and temperature, thin Nb3Sn films have been prepared by electron beam vapor deposition [1]. Fine-grain size material is desirable which may be achieved by codeposition with small amounts of Al2O3 . Figure 1 shows the STEM microstructure, with large (∽ 200 Å dia) voids present at the grain boundaries. Higher quality TEM micrographs (e.g. fig. 2) reveal the presence of small voids within the grains which are absent in pure Nb3Sn prepared under identical conditions. The X-ray spectrum from large (∽ lμ dia) or small (∽100 Ǻ dia) areas within the grains indicates only small amounts of A1 (fig.3).

Superior 2X2 Slides

1975 ◽  
Vol 33 ◽  
pp. 158-159
Author(s):  
Harry Schaefer ◽  
Bruce Wetzel
Keyword(s):  
New York ◽  
High Resolution ◽  
Black And White ◽  
Fine Grain ◽  
White Film

High resolution 24mm X 36mm positive transparencies can be made from original black and white negatives produced by SEM, TEM, and photomicrography with ease, convenience, and little expense. The resulting 2in X 2in slides are superior to 3¼in X 4in lantern slides for storage, transport, and sturdiness, and projection equipment is more readily available. By mating a 35mm camera directly to an enlarger lens board (Fig. 1), one combines many advantages of both. The negative is positioned and illuminated with the enlarger and then focussed and photographed with the camera on a fine grain black and white film.Specifically, a Durst Laborator 138 S 5in by 7in enlarger with 240/200 condensers and a 500 watt Opale bulb (Ehrenreich Photo-Optical Industries, Inc., New York, NY) is rotated to the horizontal and adjusted for comfortable eye level viewing.

Microstructure Development in a High Current Density NbTi Superconducting Composite

1985 ◽  
Vol 43 ◽  
pp. 186-189
Author(s):  
P. J. Lee ◽  
D. C. Larbalestier
Keyword(s):  
Current Density ◽  
High Current Density ◽  
Cold Drawing ◽  
Heat Treatments ◽  
Grain Structure ◽  
Fine Grain ◽  
Boundary Film ◽  
Quantitative Basis ◽  
Cold Worked ◽  
Very High

Several features of the metallurgy of superconducting composites of Nb-Ti in a Cu matrix are of interest. The cold drawing strains are generally of order 8-10, producing a very fine grain structure of diameter 30-50 nm. Heat treatments of as little as 3 hours at 300 C (∼ 0.27 TM) produce a thin (1-3 nm) Ti-rich grain boundary film, the precipitate later growing out at triple points to 50-100 nm dia. Further plastic deformation of these larger a-Ti precipitates by strains of 3-4 produces an elongated ribbon morphology (of order 3 x 50 nm in transverse section) and it is the thickness and separation of these precipitates which are believed to control the superconducting properties. The present paper describes initial attempts to put our understanding of the metallurgy of these heavily cold-worked composites on a quantitative basis. The composite studied was fabricated in our own laboratory, using six intermediate heat treatments. This process enabled very high critical current density (Jc) values to be obtained. Samples were cut from the composite at many processing stages and a report of the structure of a number of these samples is made here.

High-resolution observation of sintered alumina (Al2O3) using the specimen-heated and electron-beam-induced conductivity method in a UHR-SEM

1994 ◽  
Vol 52 ◽  
pp. 1046-1047
Author(s):  
K. Ogura ◽  
T. Suzuki ◽  
C. Nielsen
Keyword(s):  
Electron Beam ◽  
High Resolution ◽  
Specimen Preparation ◽  
Conductivity Method ◽  
Fine Grain ◽  
Grain Structures ◽  
Resolution Observation ◽  
Electron Microscopes ◽  
Scanning Electron Microscopes ◽  
Charging Effect

In spite of the complicated specimen preparation, Transmission Electron Microscopes (TEM) have traditionally been used for the investigation of the fine grain structures of sintered ceramics. Scanning Electron Microscopes (SEM) have not been used much for the same purpose as TEM because of poor results caused by the specimen charging effect, and also the lack of sufficient resolution. Here, we are presenting a successful result of high resolution imaging of sintered alumina (pure Al2O3) using the Specimen Heated and Electron Beam Induced Conductivity (SHEBIC) method, which we recently reported, in an ultrahigh resolution SEM (UHR-SEM). The JSM-6000F, equipped with a Field Emission Gun (FEG) and an in-lens specimen position, was used for this application.After sintered Al2O3 was sliced into a piece approximately 0.5 mm in thickness, one side was mechanically polished to get a shiny plane for the observation. When the observation was started at 20 kV, an enormous charging effect occured, and it was impossible to obtain a clear Secondary Electron (SE) image (Fig.1).

High-resolution SEM and STEM of adrenocortical endothelium: Molecular resolution of membrane complexes

1993 ◽  
Vol 51 ◽  
pp. 610-611
Author(s):  
Robert P. Apkarian
Keyword(s):  
Fine Structure ◽  
Low Voltage ◽  
Uranyl Acetate ◽  
Correlative Microscopy ◽  
Coated Pits ◽  
Fine Grain ◽  
Structural Identity ◽  
Cellular Pathways ◽  
Steroidogenic Cells ◽  
Cr Film

A multitude of complex ultrastructural features are involved in endothelial cell (EC) gating and sorting of lipid through capillaries and into steroidogenic cells of the adrenal cortex. Correlative microscopy is necessary to distinguish the structural identity of features involved in specific cellular pathways. In addition to diaphragmed fenestrae that frequently appear in clusters, other 60-80 nm openings; plasmalemma vesicles (PV), channels and pockets fitted with diaphragms of the same dimension, coexist on the thin EC surface. Non-diaphragmed coated pits (CP) (100-120 nm) involved in receptor mediated endocytosis were also present on the EC membrane. The present study employed HRSEM of cryofractured and chromium coated specimens and low voltage HRSTEM of 80 nm thick LX-112 embedded sections stained with 2.0% uranyl acetate. Both preparations were imaged at 25 kV with a Topcon DS-130 FESEM equipped with in-lens stage and STEM detector.HRSEM images of the capillary lumen coated with a lnm continuous fine grain Cr film, provided the ability to scan many openings and resolve (SE-I contrast) the fine structure of diaphragm spokes and central densities (Fig. 1).

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