Memory

Author(s):  
Max Deutscher

Memory is central to every way in which we deal with things. One might subsume memory under the category of intellect, since it is our capacity to retain what we sense, enjoy and suffer, and thus to become knowing in our perception and other activities. As intelligent retention, memory cannot be distinguished from our acquisition of skills, habits and customs – our capabilities both for prudence and for deliberate risk. As retention, memory is a vital condition of the formation of language. Amnesia illustrates dramatically the difference between memory as retention of language and skills, and memory as the power to recollect and to recognize specific things. In amnesia we lose, not our general power of retention, but recall of facts – the prior events of our life, and our power to recognize people and places. Amnesiacs recognize kinds of things. They know it is a wristwatch they are wearing, while unable to recognize it as their own. This recall of events and facts which enables us to recognize things as our own, is more than just the ability to give correctly an account of them. One might accurately describe some part of one’s past inadvertently, or after hypnosis, or by relying on incidental information. Thus, present research on memory both as retention and as recall of specific episodes, attempts to characterize the connection which persists between experience and recall. Neurological or computer models of connectivity owe something to traditional notions of a memory trace, but emphasize also the re-tracing of original memories by later experience and by intervening episodes of recall.

Author(s):  
Maxwell Deutscher

Memory is central to every way in which we deal with things. One might subsume memory under the category of intellect, since it is our capacity to retain what we sense, enjoy and suffer, and thus to become knowing in our perception and other activities. As intelligent retention, memory cannot be distinguished from our acquisition of skills, habits and customs – our capabilities both for prudence and for deliberate risk. As retention, memory is a vital condition of the formation of language. Amnesia illustrates dramatically the difference between memory as retention of language and skills, and memory as the power to recollect and to recognize specific events and situations. In amnesia we lose, not our general power of retention, but rather our recall of facts – the prior events of our life, and our power to recognize people and places. Amnesiacs recognize kinds of things. They may know it is a wristwatch they are wearing, while unable to recognize it as their own. This recall of events and facts that enables us to recognize things as our own, is more than just the ability to give correctly an account of them. One might accurately describe some part of one’s past inadvertently, or after hypnosis, or by relying on incidental information. Thus, present research on memory both as retention and as recall of specific episodes, attempts to describe the connection which persists between experience and recall. Neurological or computer models of such a connection owe something to traditional notions of a memory trace, but emphasize also the re-tracing of original memories by later experience and episodes of recall. Historically, recollection has often been thought of as a mode of perceiving the past. Such an idea lends an exaggerated status to the role of imagery, which is but one member of a family of recollective activities that includes reliving, remembering, reminiscing and mulling over what has happened. It may be not in having imagery but in miming someone’s behaviour that one relives an event. Also, like imagery, what we feel about the past may seem integral to recollection. A sense of being brought close to the past arises particularly when events that involve our feelings are concerned. Yet we may also recollect an event, vividly and accurately, while feeling clinically detached from it, devoid of imagery. How a past event or situation remains connected with subsequent recollection has become a principal theoretical question about memory. It is argued that it is because of what we did or experienced that we recollect it. Otherwise, we are only imagining it or relying upon ancillary information. Neurological or computer models of such a connection owe something to traditional notions of a memory trace, but emphasize also the re-tracing of original memories by later experience and episodes of recall. Some argue that our very idea of memory is that of the retention of a structural analogue of what we do recall of them. Such an idea is not of some perfect harmony between what we remember and our recollection of it. Rather, it is suggested, only to the extent that we retain a structural analogue of some aspect of an event or situation do we remember, rather than imagine or infer it.


2002 ◽  
Vol 357 (1424) ◽  
pp. 1039-1051 ◽  
Author(s):  
Ranulfo Romo ◽  
Adrián Hernández ◽  
Antonio Zainos ◽  
Carlos Brody ◽  
Emilio Salinas

Humans and monkeys have similar abilities to discriminate the difference in frequency between two consecutive mechanical vibrations applied to their fingertips. This task can be conceived as a chain of neural operations: encoding the two consecutive stimuli, maintaining the first stimulus in working memory, comparing the second stimulus with the memory trace left by the first stimulus and communicating the result of the comparison to the motor apparatus. We studied this chain of neural operations by recording and manipulating neurons from different areas of the cerebral cortex while monkeys performed the task. The results indicate that neurons of the primary somatosensory cortex (S1) generate a neural representation of vibrotactile stimuli which correlates closely with psychophysical performance. Discrimination based on microstimulation patterns injected into clusters of S1 neurons is indistinguishable from that produced by natural stimuli. Neurons from the secondary somatosensory cortex (S2), prefrontal cortex and medial premotor cortex (MPC) display at different times the trace of the first stimulus during the working–memory component of the task. Neurons from S2 and MPC appear to show the comparison between the two stimuli and correlate with the behavioural decisions. These neural operations may contribute to the sensory–discrimination process studied here.


1965 ◽  
Vol 17 (4) ◽  
pp. 323-328 ◽  
Author(s):  
N. O'connor ◽  
Beate Hermelin

Twelve imbeciles and 12 normals, matched for their digit memory span, were presented with three digit numbers successively and simultaneously. Seven speeds of presentation were used. Each simultaneous speed of presentation had a corresponding successive speed. Subjects were required to recall digits on the conclusion of presentation of each number. Each performance was scored as the number of errors for each digit. With simultaneous presentations the difference between the groups was significant only at fast presentation speed, where the normals were significantly better than the imbeciles. Imbeciles improved at slow speeds and became as good as normals. In the case of successive presentations differences between groups occur only in relation to the second digit, which the normals remember better than the subnormals. Both groups remember the first digit worst as rates of presentation become progressively slower. Results are explained in terms of input restriction and of memory trace decay.


1962 ◽  
Vol 14 ◽  
pp. 149-155 ◽  
Author(s):  
E. L. Ruskol

The difference between average densities of the Moon and Earth was interpreted in the preceding report by Professor H. Urey as indicating a difference in their chemical composition. Therefore, Urey assumes the Moon's formation to have taken place far away from the Earth, under conditions differing substantially from the conditions of Earth's formation. In such a case, the Earth should have captured the Moon. As is admitted by Professor Urey himself, such a capture is a very improbable event. In addition, an assumption that the “lunar” dimensions were representative of protoplanetary bodies in the entire solar system encounters great difficulties.


1997 ◽  
Vol 161 ◽  
pp. 491-504 ◽  
Author(s):  
Frances Westall

AbstractThe oldest cell-like structures on Earth are preserved in silicified lagoonal, shallow sea or hydrothermal sediments, such as some Archean formations in Western Australia and South Africa. Previous studies concentrated on the search for organic fossils in Archean rocks. Observations of silicified bacteria (as silica minerals) are scarce for both the Precambrian and the Phanerozoic, but reports of mineral bacteria finds, in general, are increasing. The problems associated with the identification of authentic fossil bacteria and, if possible, closer identification of bacteria type can, in part, be overcome by experimental fossilisation studies. These have shown that not all bacteria fossilise in the same way and, indeed, some seem to be very resistent to fossilisation. This paper deals with a transmission electron microscope investigation of the silicification of four species of bacteria commonly found in the environment. The Gram positiveBacillus laterosporusand its spore produced a robust, durable crust upon silicification, whereas the Gram negativePseudomonas fluorescens, Ps. vesicularis, andPs. acidovoranspresented delicately preserved walls. The greater amount of peptidoglycan, containing abundant metal cation binding sites, in the cell wall of the Gram positive bacterium, probably accounts for the difference in the mode of fossilisation. The Gram positive bacteria are, therefore, probably most likely to be preserved in the terrestrial and extraterrestrial rock record.


1994 ◽  
Vol 144 ◽  
pp. 421-426
Author(s):  
N. F. Tyagun

AbstractThe interrelationship of half-widths and intensities for the red, green and yellow lines is considered. This is a direct relationship for the green and yellow line and an inverse one for the red line. The difference in the relationships of half-widths and intensities for different lines appears to be due to substantially dissimilar structuring and to a set of line-of-sight motions in ”hot“ and ”cold“ corona regions.When diagnosing the coronal plasma, one cannot neglect the filling factor - each line has such a factor of its own.


Author(s):  
Jules S. Jaffe ◽  
Robert M. Glaeser

Although difference Fourier techniques are standard in X-ray crystallography it has only been very recently that electron crystallographers have been able to take advantage of this method. We have combined a high resolution data set for frozen glucose embedded Purple Membrane (PM) with a data set collected from PM prepared in the frozen hydrated state in order to visualize any differences in structure due to the different methods of preparation. The increased contrast between protein-ice versus protein-glucose may prove to be an advantage of the frozen hydrated technique for visualizing those parts of bacteriorhodopsin that are embedded in glucose. In addition, surface groups of the protein may be disordered in glucose and ordered in the frozen state. The sensitivity of the difference Fourier technique to small changes in structure provides an ideal method for testing this hypothesis.


Author(s):  
P. Maupin-Szamier ◽  
T. D. Pollard

We have studied the destruction of rabbit muscle actin filaments by osmium tetroxide (OSO4) to develop methods which will preserve the structure of actin filaments during preparation for transmission electron microscopy.Negatively stained F-actin, which appears as smooth, gently curved filaments in control samples (Fig. 1a), acquire an angular, distorted profile and break into progressively shorter pieces after exposure to OSO4 (Fig. 1b,c). We followed the time course of the reaction with viscometry since it is a simple, quantitative method to assess filament integrity. The difference in rates of decay in viscosity of polymerized actin solutions after the addition of four concentrations of OSO4 is illustrated in Fig. 2. Viscometry indicated that the rate of actin filament destruction is also dependent upon temperature, buffer type, buffer concentration, and pH, and requires the continued presence of OSO4. The conditions most favorable to filament preservation are fixation in a low concentration of OSO4 for a short time at 0°C in 100mM sodium phosphate buffer, pH 6.0.


Author(s):  
Y. H. Liu

Ordered Ni3Fe crystals possess a LI2 type superlattice similar to the Cu3Au structure. The difference in slip behavior of the superlattice as compared with that of a disordered phase has been well established. Cottrell first postulated that the increase in resistance for slip in the superlattice structure is attributed to the presence of antiphase domain boundaries. Following Cottrell's domain hardening mechanism, numerous workers have proposed other refined models also involving the presence of domain boundaries. Using the anomalous X-ray diffraction technique, Davies and Stoloff have shown that the hardness of the Ni3Fe superlattice varies with the domain size. So far, no direct observation of antiphase domain boundaries in Ni3Fe has been reported. Because the atomic scattering factors of the elements in NijFe are so close, the superlattice reflections are not easily detected. Furthermore, the domain configurations in NioFe are thought to be independent of the crystallographic orientations.


Author(s):  
E.M. Waddell ◽  
J.N. Chapman ◽  
R.P. Ferrier

Dekkers and de Lang (1977) have discussed a practical method of realising differential phase contrast in a STEM. The method involves taking the difference signal from two semi-circular detectors placed symmetrically about the optic axis and subtending the same angle (2α) at the specimen as that of the cone of illumination. Such a system, or an obvious generalisation of it, namely a quadrant detector, has the characteristic of responding to the gradient of the phase of the specimen transmittance. In this paper we shall compare the performance of this type of system with that of a first moment detector (Waddell et al.1977).For a first moment detector the response function R(k) is of the form R(k) = ck where c is a constant, k is a position vector in the detector plane and the vector nature of R(k)indicates that two signals are produced. This type of system would produce an image signal given bywhere the specimen transmittance is given by a (r) exp (iϕ (r), r is a position vector in object space, ro the position of the probe, ⊛ represents a convolution integral and it has been assumed that we have a coherent probe, with a complex disturbance of the form b(r-ro) exp (iζ (r-ro)). Thus the image signal for a pure phase object imaged in a STEM using a first moment detector is b2 ⊛ ▽ø. Note that this puts no restrictions on the magnitude of the variation of the phase function, but does assume an infinite detector.


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