Showing papers by "University of Maryland, Baltimore County published in 1977"

Sources of peer group homogeneity.

Abstract: Conformity pressures, disproportionate group-leaving by deviates, and homophilic membership selection are identified as three sources of homogeneity in student friendship groups. Fortynine high school friendship groups are tested to determine which of these three mechanisms contributes most to their homogeneity. Homophilic selection accountedfor much of the groups' homogeneity, conformity pressures made a small contribution, and group-leaving contributed nothing to homogeneity. It is suggested that the magnitude of peer influence on aspirations has been overestimated in the status-attainment literature.

Uninstructed human responding: sensitivity to ratio and interval contingencies.

Abstract: College students' presses on a telegraph key were occasionally reinforced by light onsets in the presence of which button presses (consummatory responses) produced points later exchangeable for money. One student's key presses were reinforced according to a variable-ratio schedule; key presses of another student in a separate room were reinforced according to a variable-interval schedule yoked to the interreinforcement intervals produced by the first student. Instructions described the operation of the reinforcement button, but did not mention the telegraph key; instead, key pressing was established by shaping. Performances were comparable to those of infrahuman organisms: variable-ratio key-pressing rates were higher than yoked variable-interval rates. With some yoked pairs, schedule effects occurred so rapidly that rate reversals produced by schedule reversals were demonstrable within one session. But sensitivity to these contingencies was not reliably obtained with other pairs for whom an experimenter demonstrated key pressing or for whom the reinforcer included automatic point deliveries instead of points produced by button presses. A second experiment with uninstructed responding demonstrated sensitivity to fixed-interval contingencies. These findings clarify prior failures to demonstrate human sensitivity to schedule contingencies: human responding is maximally sensitive to these contingencies when instructions are minimized and the reinforcer requires a consummatory response.

Lateral diffusion in phospholipid multibilayers measured by fluorescence recovery after photobleaching

Abstract: The method of fluorescence recovery after photobleaching has been used to measure the temperature dependence of the lateral diffusion coefficients (D) of two fluorescent lipid analogues in phospholipid multibilayers of various compositions. The probes employed were 3,3-dioctadecyloxocarbocyanine (diO-C18(3) and N-4-nitrobenz-2-oxa-1,3-diazole phosphatidylethanolamine (NBD-PE). In fluid egg phosphatidylcholine multibilayers at 25 degrees C, D was about 4 X 10(-8) cm2/s for NBD-PE and 1.5 X 10(-7) cm2/s for diO-C18(3) and was moderately temperature dependent (2-fold change over 10 degrees C). Equimolar cholesterol reduced D for NBD-PE in these multibilayers by a factor of 2. A greater than 100-fold decrease in D was detected in dimyristoylphosphatidylcholine multibilayers at approximately 23 degree C, which coincides with the gel-to-liquid-crystalline transition temperature, Tm (D 5 X 10(-8) cm2/s at T greater than Tm to D less than 5 X 10(-10) cm2/s at T less than Tm). Equimolar cholesterol abolished this transition behavior, raising D below Tm and decreasing D above Tm. These results confirm and extend previous studies of lateral diffusion employing magnetic resonance and other optical techniques and give additional confidence in the fluorescence methods.

Population pressure and agricultural intensity

Abstract: A positive relationship between population pressure and agricultural intensity is fundamental to Boserup's thesis of agricultural growth and to several of its modifications Correlation analysis reveals a strong positive association between the population densities and agricultural intensities of a sample of tropical subsistence agriculturalists; the variation in population densities accounts for fifty-eight percent of the variation in the logarithm of agricultural intensities The addition of subsistence and environmental factors to the model increases the explained variation and suggests several modifications of Boserup's thesis

Attention training: the use of overcorrection avoidance to increase the eye contact of autistic and retarded children

Abstract: A crucial first step in teaching and training the retarded and autistic is to develop and maintain eye contact with the therapist. Functional movement training (an overcorrection procedure) plus edibles and praise were compared with edibles and praise alone as a method of developing eye contact in three such children. In both conditions, the child was given food and praise when eye contact occurred within 5 sec of the therapist's verbal prompt: "Look at me." Functional movement training avoidance plus edibles and praise produced about 90% attention for the three children, while edibles and praise alone were less effective (eye contact never exceeded 55%). Functional movement training avoidance combined with edibles and praise appears to be an effective method of teaching eye contact and possibly other forms of instruction-following to behaviorally disordered children who are not always responsive to positive consequences.

The place of man in the development of Darwin's theory of transmutation.

Abstract: This argument has emphasized the professional character of Darwin's early activities, largely in order to balance the usual portrayal of the amateurishness of his early training and field of study. Arguing this way has revealed the interplay between Darwin's personal interests and his professional obligations, the latter being particularly important for the period from October 1836 to July 1837. In several instances, notably the treatment of his collections, the progress of his thought followed the professional lead directly. In the absence of such a lead Darwin did not pursue certain issues, if only for lack of time. Thus the subject of man did not figure in his initial formulation of a transmutationist position. Only after the commitment to the new point of view had been made did the issues emerge which will be treated in Part II of this article. However, we may close by noting Darwin's inherited disposition on the subject: in the summer of 1837 Darwin responded to Lyell's claim that the change from irrational animal to rational man represented “a phenomenon of a distinct kind from the passage from the more simple to the more perfect forms of animal organization and instinct” with a fanciful doodle in the margin.121 The thoughts behind the bemused scribbling were to occupy a good portion of Darwin's time for the next two years.

Yoked variable-ratio and variable-interval responding in pigeons.

Abstract: Pigeons' key pecks were maintained by variable-ratio or variable-interval schedules of food reinforcement. For pairs of pigeons in one group, variable-ratio reinforcement was arranged for one pigeon's pecks; for the second pigeon, reinforcement was arranged according to a variable-interval schedule yoked to the interreinforcement times produced by the first pigeon. For pairs of pigeons in another group, variable-interval reinforcement was arranged for one pigeon's pecks; for the second pigeon, reinforcement was arranged according to a variable-ratio schedule yoked to the interreinforcement responses produced by the first pigeon. For each pair, the yoking procedure was maintained for four or five consecutive sessions of 50 reinforcements each. In more than three-quarters of the pairs, variable-ratio response rates were higher than variable-interval rates within two sessions; in all cases, the rate difference developed within four sessions.

Gasoline conservation: a procedure for measuring and reducing the driving of college students.

Abstract: The study sought to motivate college students to reduce the number of miles they drove each day and thus save gasoline. Students in two psychology classes were divided by class into two groups. The experimental group was offered various combinations of prizes such as cash, a tour of a mental-health facility, car servicing, and a university parking sticker for reducing driving. The value of the prize received was scaled in terms of per cent reduction in driving. The contrast group received no inducements. The condition in which the experimental group's mileage reduction was reinforced was counterbalanced by two baseline conditions. Several special recording procedures were used to reduce and detect the possibility of subjects altering their odometers, the source of the driving data. Experimental subjects reduced their average daily mileage by 20% relative to the initial baseline; the contrast group did not change. During the one-month reinforcement condition, the 12 experimental subjects saved some 170 gallons (worth $102) of gasoline.

Changes of mechanisms and product distributions in the hydrolysis of benzo[a]pyrene-7,8-diol 9,10-epoxide metabolites induced by changes in pH.

Abstract: Fur die Hydrolyse der Titelverbindungen (I) und (II) in Wasser und wasrigem Dioxan werden die pH-Geschwindigkeitsprofile bestimmt.

Development of spinal cord bioelectric activity in spinal chick embryos and its behavioral implications.

Abstract: Embryonic behavior of the chick is the product of spontaneous multiunit burst discharges within the ventral spinal cord. The present study describes the ontogeny of spinal cord burst discharges in embryos which were deprived of brain input by removing several neural tube segments of 2-day embryos at cervical or mid-thoracic levels. Characteristics of bioelectric activity present in both intact and chronically transected cords are: (a) the appearance of spike discharges; (b) the organization of unit discharges into synchronized multiunit bursts; (c) the establishment of intracord synchronization of burst discharges over wide expanses of cord tissue; (d) an increase in burst duration and complexity at 7 days due to the appearance of the burst afterdischarge; (e) an increase in the amount of burst activity from 6 to 13 days followed by a decline until hatching at 21 days; (f) a shift from periodic to irregular patterns of burst activity at 13 days; and (g) the existence of the cord burst discharge as a correlate of embryonic movement. Several differences were found between burst activity from chronic spinal and intact embryos: (a) cervical spinal embryos were significantly less active than controls from 15 through 19 days; and (b) long sequences of unusual repetitive burst afterdischarges appeared in chronic spinal embryos by 13 days. The results indicate that the transected embryonic spinal cord is remarkably autogenous in function, although patterns of activity unique to the transected cord appear and increase in prominence during later stages of incubation.

Does maternal responding imply reduced infant crying? A critique of the 1972 Bell and Ainsworth report.

Abstract: GEWIRTZ, JACOB L., and BOYD, ELIZABETH F. Does Maternal Responding Imply Reduced Infant Crying? A Critique of the 1972 Bell and Ainsworth Report. CHILD DEVELOPMENT, 1977, 48, 1200-1207. An examination was made of the published rank correlations (p's) from which Bell and Ainsworth concluded that mothers who responded more consistently and promptly to their infants' crying in earlier quarters of the first year had infants who cried less often and long in later quarters of that year. Technical limitations critically restrict interpretations of those p's: (a) intercorrelations were of intrinsically contingent measures; (b) the overlapping, dependent intercorrelations were correlated within and between matrices, with unknown Type I error levels; and (c) there were no statistical controls for likely antecedent and concurrent determinants of the 2 outcome-variable sets. Apart from these technical concerns, Bell and Ainsworth's assumption that maternal responding to crying is the inverse of maternal ignoring of crying and their main conclusions from the between-quarter correlations that depended on it were questioned on the bases of (a) the defined independence between the maternal responding and ignoring variables, (b) the positive within-quarter pattern of correlation between them, and (c) the failure to present between-quarter correlations between maternal responding and infant crying. At the same time, Bell and Ainsworth's data were remote from the level of detail required by an operant-learning account (to which, nevertheless, many have referred them). Under such a learning account, various outcomes would be plausible, including the outcome Bell and Ainsworth emphasized. It was concluded that Bell and Ainsworth's main conclusion, that maternal responding implied a reduction in infant crying, was not supported by their data.

Floral Induction of Vegetative Plants Supplied a Purified Fraction of Deoxyribonucleic Acid from Stems of Flowering Plants

Abstract: It has been found that floral induced stems of flowering tobacco ( Nicotiana tabacum cv. Wis. 38) plants contain large amounts of rapidly renaturing DNA, whereas noninduced stems of vegetative plants contain only small amounts. In addition, it has been shown that the striking qualitative difference in DNA between stems of flowering and vegetative plants mimics the over-all quantitative difference in DNA content (on a fresh weight basis). Therefore, the extra DNA in stems of flowering plants seems, at least in part, to represent preferential synthesis of rapidly renaturing DNA. Rapidly renatured DNA (flowering plants) has been purified (cesium chloride gradients) from heated-cooled DNA solution and under noninductive conditions has been tested for floral activity. It has been found that when rapidly renatured DNA in buffer solution is supplied to axillary vegetative buds of vegetative plants and then the axillary buds are defoliated every 4th day for 12 days, the treated buds change into flower buds. On the other hand, control axillary buds supplied buffer solution alone remain vegetative. In stem segments from flowering plants, the concept, discussed in previous reports, that indole-3-acetic acid may modify in vitro bud expression by directly affecting DNA synthesis has been reviewed. On the basis of this report, the concept is elaborated by proposing here that indole-3-acetic acid may act partially in bud expression by directly suppressing synthesis of rapidly renaturing DNA.

Finite procedures for sofic systems

Abstract: A sofic system is a symbolic flow defined by a finite semigroup. We exhibit finite procedures, involving only the defining semigroup, for answering cetain questions about a sofic system and for constructing certain subshifts of finite type associated with a sofic system.

Initial Characterization of Hexose and Hexitol Phosphoenolpyruvate-Dependent Phosphotransferases of Staphylococcus aureus

Abstract: The phosphoenolpyruvate sugar phosphotransferases of Staphylococcus aureus were surveyed biochemically to determine substrate range, inducibility and constitutivity, and requirements for soluble sugar-specific proteins. The substrate range is similar to that of the phosphotransferases of enteric bacteria, but the staphylococcal mannose and sorbitol systems are very inefficient. In addition, S. qureus has phosphotransferase activities for lactose and sucrose. The systems tested fell into two broad classes. Sugars for which there was substantial constitutive activity (fructose, mannose, sucrose, and glucose and its nonmetabolized analogues) did not require sugar-specific soluble factors for phosphorylation. Only in the case of fructose did growth in the presence of these constitutive sugars induce the corresponding phosphotransferase activity to higher levels. Kinetic experiments with each of these constitutive sugars yielded biphasic Hofstee plots; i.e., the kinetics were not characteristic of single enzymes. Preliminary experiments suggest that sucrose phosphorylation may involve the glucose and/or fructose systems. Truly inducible sugar phosphotransferase systems represent a second class; those for lactose and mannitol are the only members thus far identified. These systems are absent from uninduced cells, require soluble sugar-specific factors, and exhibit linear Hofstee plots. Sorbitol is apparently transported very poorly by intact cells but is an inducer of the mannitol system; it is phosphorylated efficiently in vitro by extracts of cells grown on either hexitol, but is taken up by intact cells at 0.1% of the mannitol rate.

Teaching Note -Taking Skills to Underachieving College Students

Abstract: The present study attempted to develop a note-taking program that would teach college students to recognize and record the most important information from lectures. In addition, a method was developed for reliably evaluating the accuracy of students" notes. A non-graded university course was created in which the subject matter was sexual behavior. Three groups of students, two experimental and one control group, attended the course lectures. The two experimental groups received a note-taking program, the key features of which were: modeling, discrimination training, practice, prompting, shaping, fading, and positive feedback. The results showed that the two experimental groups increased the percent of critical lecture points in their notes from baseline to posttraining by 23 and 18 percent, whereas the control group’s percent of critical lecture points decreased by 9 percent. During a one-lecture generalization probe (a different instructor gave the lecture) the experimental groups averaged 60 and...

Evolutionary conservation of chloroplast genes coding for the large subunits of fraction 1 protein.

Abstract: Crystalline fraction 1 protein, obtained from four species of Nicotiana, have identical polypeptide compositions and isoelectric points. However, the tryptic peptide map of the large subunit of this protein from N. knightiana and N. paniculata differs from that of N. tomentosa and N. tomentosiformis. Since the large subunits of fraction 1 protein are coded by chloroplast DNA, the difference in their primary structure reflects the structural changes of the chloroplast genes containing the coding information. This indicates that the rate of mutation of chloroplast DNA seems to be higher than predicated from the analysis of isoelectric points of this protein.

Magnitudes of score differences produced within sessions in a cooperative exchange procedure1

Abstract: Interest centered on maximal score differences produced within sessions during two-party exchange. Subjects chose between earning money independently or through potentially higher-paying exchange. In the exchange option, only one person could produce points for the other on a trial. Because each exchange response (“give”) required the giver to forego earning points independently, the larger the score difference produced (i.e., the further ahead in earnings the other person was put), the greater the reduction in the giver's earnings if the other person did not reciprocate. Results showed that scores were usually equal at the end of each session, and that subjects maintained close equality of scores throughout each session. When a response-cost contingency that punished the alternation of giving was introduced, however, large within-session score differences developed. These large differences continued to be produced after the response-cost contingency was removed. Finally, when subjects were told that the session could end at any moment, score differences were sharply reduced, indicating that production of score differences remained under the control of discriminative stimuli associated with the likelihood of reciprocation. The study suggests that with appropriate procedures, an experimental analysis of behavioral phenomena associated with the concept of “trust” may be possible.

Power laws in compartmental analysis— II. numerical evaluation of semi-Markov models

Abstract: A semi-Markov model for tracer kinetics is formulated for certain two-and three-compartment systems for which the residence time in compartment 2 may have a stable or exponentially modified stable distribution. The method requires numerical inversion of complex Fourier transforms. The model is used to predict the proportion of a single dose of lead retained by blood, bone, and soft tissue, where the lead residence time in bone has a distribution of power-law type. The power-law models reproduced the sometimes observed increase of blood lead level due to slow release of lead from bone, whereas the usual linear compartment model with matched parameters did not show this effect.

Autoshaping: Relation of feeder color to choice of key color

Abstract: In a two-key autoshaping procedure with pigeons, sessions consisted of 60 trials in which the simultaneous presentation of a red key and a green key was followed by operation of the feeder. In some sessions the feeder light was red; in others it was green. On the first session of exposure to this procedure, pigeons’ autoshaped pecks occurred first and predominantly on the key whose color matched the feeder color, and this preference was resistant to change when, for each pigeon, the other feeder color was used in a second session. With other pigeons, the first autoshaping session with a given feeder color was preceded by a session of feeder presentations alone (no keys) with the other feeder color. For these pigeons, key-color preferences were inconsistent. A formal model is used to assess the contributions of generalization and overshadowing to these data.

Socioeconomic factors influencing the rate of non‐promotion in elementary schools

Abstract: (1977). Socioeconomic factors influencing the rate of non‐promotion in elementary schools. Peabody Journal of Education: Vol. 54, No. 4, pp. 275-281.