Evidence For Extinction Research Articles

Ibotenate lesions of the hippocampus enhance latent inhibition in conditioned taste aversion and increase resistance to extinction in conditioned taste preference.

In 2 experiments, the effects of axon-sparing lesions of the hippocampus on performance in aversive and appetitive taste conditioning tasks were investigated. In Experiment 1, hippocampally lesioned rats showed no impairment of conditioned taste aversion learning relative to control subjects, but they did display an increased sensitivity to latent inhibition (LI). In Experiment 2, the same hippocampectomized rats acquired a conditioned taste preference but failed to show any evidence of extinction. The influence of the neurotoxic lesion on LI is in the opposite direction to the effect typically found following hippocampal damage induced by traditional methods. Accordingly, the data present challenges for most current theories of hippocampal function.

The near-IR and milliarcsec radio structure of PKS 1345 + 125

We present near-IR (2.2 μm) photometry at high spatial resolution (0.62 arcsec |$\text {pixel}^{-1}$|⁠) and 6-cm radio observations (beamwidth ∼ 10 mas) of the central regions of the Seyfert galaxy PKS 1345 + 125, which is a radio-loud and an ultraluminous IRAS system. The near-IR data confirm the presence of two nuclei within an asymmetric outer envelope. We find little evidence for extinction within the central regions, thus supporting a previous hypothesis in which the interstellar medium of the Seyfert galaxy has been stripped during a recent merger. The radio structure is resolved into a linear feature misaligned by |$\sim 49^\circ$| with respect to the position angle defining the two near-IR nuclei. This suggests that the previously observed optical line emission within the western (Seyfert) nucleus is not due to any narrow-line region or extended narrow-line region associated with the radio elliptical, thus distinguishing PKS 1345 + 125 from archetypal double-nucleus Seyferts such as Mkn 78 and NGC 5929. PKS 1345 + 125 is therefore likely to be the result of the recent merger of radio elliptical and Seyfert spiral galaxies. In spite of the asymmetric nature of the isophotes, the averaged near-IR luminosity distribution can be well described by an |$r^{1/4}$| law for radii |$\lt 10$| arcsec, with evidence for a diffuse envelope of low surface brightness beyond this point. The stellar component within this complex is hence developing the appearance of a cD galaxy.

Recognition of visual letter strings following injury to the posterior visual spatial attention system

Abstract Unilateral posterior lesions often produce a deficit in visual spatial attention. One result of this deficit is a loss of information from a word contralateral to the lesion when presented simultaneously with an ipsilateral word (interword extinction). However, when a single word presented at fixation covers the same visual angle there is frequently no extinction (Sieroff & Michel, 1987). Why are centred words not extinguished? Our studies attempt to discover the reason by comparing centred word and nonword letter strings. Nonwords do show extinction. Words are processed more accurately and show little evidence of extinction. Compound words appear to act like normal words, but segmenting letters into separate strings increases extinction. These results suggest that spatial attention is unnecessary for access to the lexical network that produces a visual word form.

Interstellar extinction in the direction of the Merope dark cloud in pleiades

The dependence of interstellar extinction on distance in the direction of the dark cloud south of Merope is determined using photoelectric photometry of 93 stars in the Vilnius photometric system. The cloud front edge is detected at 120–130 pc from the Sun and the distance of the Pleiades cluster is found to be 127 pc. Mean extinctionAV in the Merope cloud is of the order of 1.0 mag. There is no evidence of extinction at distances exceeding the Merope cloud distance. Variable extinction method yieldsR=AV/EB-V=3.6, while the maximum polarization wavelength method gives the value 3.4. Some Pleiades stars are suspected to be unresolved binaries.

A contribution to the structural chemistry of A-type rare earth sesquioxides

La 2O 3 and Nd 2O 3 have been annealed at temperatures between 1000 and 1600°C for decontamination. Only products annealed at least at these temperatures appeared to be monophasic. Both X-ray powder and electron single-crystal diffraction revealed the A-type sesquioxide structure. No difference could be found in samples either quenched or slowly cooled to room temperature. Two space groups, P 3m1 and P6 3 mmc , are reported for the A-type structure. X-Ray powder studies seemed to support the latter on the evidence of extinctions. Electron diffraction from single crystals, however, indicated the space group P 3m1 , confirming the so-called Pauling structure, while P6 3 mmc can now be excluded unequivocally.

Positive interanimal transfer with a control for arousal.

Three experiments used rats and a non-shock passive avoidance task to differentiate between learning and non-specific arousal hypotheses of the interanimal transfer phenomenon. In the first experiment with 57 rats, a multi-trial training procedure was used and positive transfer was obtained from rats receiving “trained-brain” extract injections but not from rats receiving injections of extracts from aroused controls. The second experiment used a one-trial training procedure with 49 rats and reproduced the results of Exp. 1. The third experiment with 56 rats showed some evidence of extinction and spontaneous recovery while this was not found with rats receiving injections from aroused controls. A fourth experiment indicated that the brain-extract solutions of Exps. 1 to 3 contained relatively high concentrations of protein. No detectable concentrations of RNA were discerned. The behavioral results were consistent with the notion that the interanimal transfer resulted from a learning transfer rather than a nonspecific arousal transfer.

Reinforcing properties of nonnutritive sweeteners in dry compound.

Previous research on the reinforcing properties of saccharin used saccharin in solution with water, a primary reinforcer. In the present study rats were given extensive runway training with dry pellets containing sodium saccharin combined with purified kaolin. Even after 250 trials, neither the runway response nor the consummatory response showed any evidence of extinction.

Paleoclimatologic and Paleobiologic Implications of Louann Salt Deposition: ABSTRACT

On the assumption that the Louann Salt mass extends below the Gulf of Mexico basin, its volume is calculated at about 4 million km3. If such an amount of salt is added to the volume of present ocean water, together with other post-Paleozoic salts in Africa and the Middle East, the ocean water at the close of the Paleozoic is found to be at least 20 percent saltier than that of the present. The evidence of extinction of many forms of marine life at the close of the Paleozoic probably reflects the inability of marine animals to survive in such salty waters, but it also suggests that such saltiness was not typical of Paleozoic seas and was a consequence of Permian climatic and weathering conditions. The extraction and accumulation of the Louann Salt mass required prolonged continuance of evaporating conditions. The extensive presence of eolian sandstone in the Triassic System of North America, South America, Africa, Antarctica, Australia, and Europe indicates that desert and semiarid regions probably were far more extensive then than now, and that highly evaporative winds were the agencies affecting the return to normal oceanic salinity as the Louann Salt was deposited. In turn, surviving animal stocks were able to proliferate and fill the Jurassic seas. It is probable that these conditions also exercised significant control in accumulation of such nonmetallic deposits as phosphates, uranium, potash, sulfur, and bauxite. End_of_Article - Last_Page 1833------------