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Biomedical subjects

W Hirst

Publications and source records attributed to W Hirst.

16 recordsLinked to original sources
PubMed1989

On the representation of events: a study of orientation, recall, and recognition.

Examined the representation of real-world events in memory as a function of orientation toward a videotaped sequence in which 2 people play a board game. In 4 experiments, analyzed subjects' segmentation of the videotaped sequence into events, using a technique developed by Newtson (1973). A comparison of segmentation patterns with performance on recognition, recall, and cued-recall tasks indicated that recall of events changed as a function of subjects' orientation toward the videotape, whereas recognition of events did not. The authors conclude that orientation toward an episodic sequence affects how rather than what events are represented in memory. An account of how orientation might affect the encoding and the representation of events is offered.

Adult↗
PubMed1988

Amnesia and second language learning.

The ability of an anterograde amnesic C.S. to learn a second language is assessed. First, her claim that she learned Italian while amnesic was examined in a series of formal tests of Italian. Second, C.S. and her husband were tutored in French and her acquisition was compared to that of her husband's. Third, C.S.'s ability to learn other kinds of verbal material with practice was investigated. The implications of C.S.'s apparent ability to learn a second language in the presence of a severe deficit for memory for other kinds of verbal material is discussed.

Amnesia↗
PubMed1988

Memory strategies with brain damage.

The ability of anterograde amnesics with and without a history of alcoholism and patients with frontal lobe damage to think about memory, memorizing, and remembering was assessed. Alcoholic Korsakoffs' and frontal lobe patients' knowledge and use of memory strategies was deficient when compared with controls whereas nonalcoholic amnesics' was not. The use of the categorization mnemonic was assessed in a verbal learning experiment. Frontal lobe patients failed to spontaneously categorize a categorizable word list when trying to memorize it. Nevertheless, when forced to categorize the list, they benefited from the imposed structure. Nonalcoholic amnesics spontaneously categorized the list and benefited from the resulting organization.

Alcohol Amnestic Disorder↗
PubMed1988

Frequency encoding of token and type information.

Two experiments examined how attention to stimulus attributes affects knowledge of frequency of occurrence. In Experiment 1, orienting tasks were used to direct subjects' attention to either the category membership or the initial letters of words. In Experiment 2, subjects' attention to words, category membership, and initial letters was directed with explicit instructions. The results of these two experiments suggest that attention to specific stimulus attributes may be necessary to initiate the encoding of frequency information. We discuss the implications of these results for claims that the encoding of frequency of occurrence is automatic.

Attention↗
PubMed1988

More on recognition and recall in amnesics.

Hirst et al. (1986) reported that amnesic forced-choice recognition was relatively preserved when compared with amnesic recall. They equated normal recognition and amnesic recognition by extending exposure time for the amnesics and then comparing amnesic recall and normal recall. Amnesic recall was worse than normal recall, despite equated recognition. We conducted two experiments to extend that result. Experiment 1 established that the findings of Hirst et al. are not paradigm specific and hold when amnesic recognition and normal recognition are equated by increasing the retention interval for normals. In Experiment 2 we further established the generality of the result by examining yes-no recognition. Findings further specify the selective nature of the direct memory deficit in amnesics.

Amnesia↗
PubMed1987

Characterizing attentional resources.

Other studies have found that it is easier to divide attention when messages can be discriminated on the basis of stimulus and response features. The present study extended these results and explored whether dual-task performance is a function of similarity of central processing and, more specifically, the semantic similarity of the competing messages. In a dichotic listening task, subjects detected targets in concurrent messages that either differed semantically and required different central processing (the mixed condition) or were semantically similar and required similar central processing (the same condition). Three criteria are developed to determine whether the tasks in the mixed condition call upon distinct resources. The results are discussed in terms of three metaphors for resources: fuel, structure, and skills.

Attention↗
PubMed1986

Semantic classification in aphasia: a study of basic, superordinate, and function relations.

Nonfluent and fluent aphasics were given classification tasks that required the aphasics to identify three kinds of relations: same basic level category, same superordinate level category, and same function. The subjects received the items in word and picture form. In addition the aphasics were required to name the items they were asked to classify. The results showed that the ability to classify is more disrupted in fluent aphasia than in nonfluent aphasia. Within fluent aphasia, the degree to which classification is disrupted is dependent upon the type of relation being tested. While the overall performance of the fluent aphasics was depressed in comparison to nonfluent aphasics, it was significantly more depressed on function relations. The ability to name an item had a significant effect on the ability to classify only for basic level items.

Adolescent↗
PubMed1986

Further characterization of patients with amnesia after cardiac arrest: preserved recognition memory.

We observed that patients with amnesia after cardiac arrest had preserved recognition memory despite profound loss of recall memory. In the present study, rate of forgetting was measured in six amnesic subjects for both recall and recognition memory of verbal material. The data show that recall decayed significantly faster for the amnesic subjects than for controls, whereas the rate of forgetting for recognition memory was comparable in both groups. Dissociation between recall and recognition performance is a feature of the amnesic syndrome after cardiac arrest.

Adult↗
PubMed1986

Recognition and recall in amnesics.

Although there is considerable agreement that performance in direct memory tasks (e.g., recall, recognition) is more disrupted by amnesia than performance in indirect memory tasks (e.g., mirror reading, word completion), one may be able to further circumscribe the deficit within the domain of direct memory tasks. The present article explores whether recall is disproportionately disrupted by amnesia compared to recognition. If amnesia affects memory uniformly across different direct memory measures, recall of normal controls should not differ from the recall of amnesics when recognition scores of these two groups are equated. On the other hand, if recall is disproportionately disrupted, normal recall should be superior to amnesic recall even when recognition is equated. The present study equated amnesic recognition with that of controls by providing amnesics with 8 s of study time and normal subjects with 0.5 s. Amnesics with Korsakoff's syndrome, amnesics with other etiologies, and appropriate controls were examined. Normal recall was superior to amnesic recall even when no differences were found in recognition. The results further specify the selective nature of amnesia.

Alcohol Amnestic Disorder↗
PubMed1976

A study of the influence of magnesium ions on the conformation of ribosomal ribonucleic acid and on the stability of the larger subribosomal particle of rabbit reticulocytes.

Mg2+ was shown to affect the conformation of rRNA over the range of 0.03-1.2M-KCl. The species studies were Escherichia coli S-rRNA and L-rRNA (the RNA moieties of the smaller and larger subribosomal particles respectively) and rabbits S-rRNA and L-rRNA. 2. The addition of Mg2+ to rRNA in reconstitution buffer (0.35M-KCl0.01M-Tris/HCl, pH7.2) at 20 degrees C let to an increase in bihelical secondary structure through the formation of additional (mainly A-U) base-pairs (e.g. an additional approx. 58 A-U base-pairs per molecule of E. coli S-rRNA as judged by u.v. difference spectrophotometry...

Ammonium Chloride↗
PubMed1976

Re-activation of the peptidyltransferase centre of rabbit reticulocyte ribosomes after inactivation by exposure to low concentrations of magnesium ion.

1. The larger subrivosomal particles of rabbit reticulocytes retained full activity in the puromycin reaction and in poly(U)-directed polyphenylalanine synthesis after 4h at 0 degrees C when buffered 0.5M-NH4Cl/10-30mM-MgCl2 was the solvent. 2. Activity in the puromycin reaction was diminished to approx 10% after 15-30 min at 0 degrees C when the concentration of MgCl2 was lowered to 2mM. 3. Activity was not restored when the concentration of MgCl2 was raised from 2mM to 10-30 mM at 0 degrees C. However, activity was recovered as measured by both assay systems when the ribosome fraction was heated to 37 degrees C at the higher concentrations of MgCl2. 4. Recovery of activity was noted during the course of the polyphenylalanine synthesis in 50 mM-KCl/5mM-MgCl2/25mM-Tris/HCl, pH 7.6, at 37 degrees C. Re-activation was slow at 20 degrees C and below. 5. No more than about 5% of the protein moiety of the subparticle was lost in 0.5M-NH4Cl on decreasing MgCl2 concentration from 10mM to 2mM. No proteins were detected in the supernatant fractions by gel electrophoresis after ribosomes were separated by differential centrifugation. The supernatant fraction was not essential for the recovery of activity. However, at higher (e.g. 1M) concentrations of NH4Cl, proteins were split from the subparticle. 6. The loss and regain of activity found on lowering and restoring the concentration of MgCl2 at 0.5M-NH4Cl appears to arise from a conformational change that does not seem to be associated with a loss and regain of particular proteins. 7. A 2% decrease in E260 was noticed when the concentration of Mg2+ was restored, and the change in the spectrum indicated a net increase of approx. 100A-U base-pairs per subribosomal particle. 8. When the concentration of Mg2+ was restored, S20,W of the subparticle remained at 52+/- 1S until the sample was incubated at 37 degrees C when S20,W increased to 56 +/- 1S compared with the value of 58 +/- 1S for the subparticle as originally isolated.

Acyltransferases↗
PubMed1976

The circular dichroism of ribosomal ribonucleic acids.

1. The c.d. (circular dichroism) of Drosophila melanogaster rRNA (42% G+C) and of G+C-rich fragments (78% G+C) obtained by partial hydrolysis of rabbit L-rRNA (the largest RNA species isolated from the large subribosomal particle) were measured and found to differ substantially. 2. To interpret these spectra a relation between c.d. of bihelical RNA and % G+C was derived, namely delta epsilonfG = AFG2+bfG+c, where deltaepsilonfG is the c.d. of RNA characterized by a mole fraction, fG, of guanine nucleotides and a, b and c are constants. 3. A frame of reference was established by studying the c.d. of a range of rRNA species, including S-rRNA (the RNA species isolated from the smaller subribosomal particle) and L-rRNA of Escherichia coli. 4. It was found for the rRNA species studied that 0.60+/-0.05 of residues appear to form bihelical secondary structure. 5. A higher helical content, 0.66+/-0.05, was found for the G+C-rich fragment of L-rRNA. The difference in the c.d. of rabbit L-rRNA and of D. melanogaster rRNA is attributable to the dependence of c.d. of the bihelical parts on %G+C. 6. The minimum in c.d. at 295 nm increases with increasing %G+C. The c.d. of rRNA was compared with that of the parent subparticle in this region of the spectrum, where high precision may be attained.

Animals↗
PubMed1976

The construction and analysis of sucrose gradients for use with zonal rotors.

The rate of sedimentation of a particle in a sucrose solution depends on the viscosity and density of the medium. These two variables are related to the sucrose concentration and the temperature of the medium by new simple equations. These equations were used in a rapid iterative procedure that relates the distance moved by a zone in a continuous sucrose gradient to its sedimentation coefficient. It is shown by comparison with experiment that this iterative method allows the distance moved by a zone to be calculated rapidly. The method may therefore be used to optimize the separation of particles in a sucrose-gradient-centrifugation experiment. The method also allows the unknown sedimentation coefficients of several zones to be measured from a single sucrose-gradient-centrifugation experiment.

Animals↗
PubMed1973

A study of the thermal stability of ribosomes and biologically active subribosomal particles.

1. The ability of Escherichia coli ribosomes to function in poly(U)-directed protein synthesis was measured at elevated temperatures by using thermostable supernatant factors from Bacillus stearothermophilus. The amount of polyphenylalanine synthesized at 55 degrees C was about the same as at 37 degrees C, but the rate of synthesis was increased approximately fivefold. At 60 degrees C the activity of the ribosomes was halved. 2. E. coli ribosomes can sustain the loss of approx. 10% of the double-helical secondary structure of RNA without losing activity. 3. Within the active ribosome the double-helical secondary structure of the rRNA moiety is stabilized compared with isolated rRNA, as judged by enzymic hydrolysis and by measurements of E(260). 4. The main products, over the range 0-55 degrees C, of ribonuclease T(1) digestion of the smaller subribosomal particle of E. coli were two fragments (s(0) (20,w) 15S and 25.3S) of approximately one-quarter and three-quarters of the size of the intact molecule, revealing the presence of a ;weak spot' where intramolecular bonds appear insufficient to hold the fragments together. 5. Subribosomal particles of B. stearothermophilus were more stable to heating, by approx. 10 degrees C, than those of E. coli, and the stabilization of double-helical secondary structure of the RNA moiety was more striking. 6. Rabbit reticulocyte ribosomes were active in poly(U)-directed protein synthesis at 45 degrees C, and half the activity was lost after heating to 53 degrees C. Active subribosomal particles of rabbit reticulocytes and of oocytes of Xenopus laevis, like the bacterial subribosomal particles, underwent a conformational change to a slower-sedimenting form on heating. The temperature range of the transition depended on the species. 7. Slower-sedimenting particles, whether produced by EDTA treatment or by heating, had different ;melting' profiles compared with active subribosomal particles, providing another indication of conformational differences. 8. Comparison of the properties of the various subribosomal particles revealed greater variation in the secondary structure of the protein moieties (judged by measurement of circular dichroism) than in the secondary structure of the RNA moieties, which appeared to have features in common.

Animals↗
PubMedDate not supplied

Deficits in recall following partial and complete commissurotomy.

There have been reports in the literature of both impaired (Zaidel and Sperry, 1974) and intact (LeDoux et al., 1977) memory performance following callosotomy. In the present article, memory is examined in patients who received either partial or complete callosotomy in an effort to determine (1) if there is a memory deficit following callosotomy, (2) if certain types of callosotomy are more likely to lead to a deficit (i.e., anterior vs posterior), and (3) if there is a global memory deficit or if some mnemonic functions are affected more than others. Patients receiving either partial or complete section of the corpus callosum were examined pre- and postoperatively on standardized memory tests and tests of recall and recognition. In addition, two patients with complete callosotomy and matched control subjects were given tests of verbal recall and recognition. A deficit in both visual and verbal recall was found in patients with posterior section, but not those receiving anterior section. No impairment was found on tests of verbal recognition for any patients. Posterior callosal section generally includes the hippocampal commissure and other hippocampal connections, while anterior sectioning does not. Given the known importance of the hippocampus (Milner, 1970) and the differences between recall and recognition memory (Bransford and Johnson, 1972) in normal memory functioning, several hypotheses are proposed as to why these results might be expected.

Adult↗