Second-order conditioning of the rabbit's nictitating membrane response. Interstimulus interval and frequency of CS-CS pairings.

Second-order conditioning of the rabbit's nictitating membrane response (NMR) was investigated when second-order trials (CS1-CS2) were intermixed with first-order trials (CS2-US) from the outset of training. Experiment 1 showed that CR acquisition to CS1 was inversely related to the CS1-CS2 interval but nevertheless extended to an interval of 8,400 ms. Experiment 2 revealed that CR acquisition of CS1 was an inverted-U function of the number of CS1-CS2 trials relative to a fixed number of CS2-US trials. Experiment 3 directly contrasted second-order conditioning with a reinforced serial compound procedure (CS1-CS2-US) and a mixed procedure in which second-order trials were intermixed with the reinforced serial compound. Second-order conditioning was about half the strength of either the reinforced serial compound or the mixed procedure, which were similar. The present results are discussed with respect to the relative strength of excitatory and inhibitory processes in second-order conditioning.     

Improving the retrieval of information from external sources

A major barrier to successful retrieval from external sources (e.g., electronic databases) is the tremendous variability in the words that people use to describe objects of interest. The fact that different authors use different words to describe essentially the same idea means that relevant objects will be missed; conversely, the fact that the same word can be used to refer to many different things means that irrelevant objects will be retrieved. We describe a statistical method called latent semantic indexing, which models the implicit higher order structure in the association of words and objects and improves retrieval performance by up to 30%. Additional large performance improvements of 40% and 67% can be achieved through the use of differential term weighting and iterative retrieval methods.     

Performance of humans in concurrent avoidance/positive-reinforcement schedules

Performance maintained under concurrent schedules consisting of a variable-interval avoidance component and a variable-interval positive-reinforcement component was studied in three human subjects using points exchangeable for money as the reinforcer. The rate of responding in the avoidance component increased, and the rate of responding in the positive-reinforcement component declined, as a function of the frequency of point-losses avoided in the avoidance component. The performance of all three subjects conformed to equations proposed by Herrnstein to describe behavior in concurrent schedules. The logarithms of the ratios of the response rates in the two components, and the logarithms of the ratios of the times spent in the two components, were linearly related to the logarithms of the ratios of the frequency of loss avoidance in the avoidance component to the frequency of reinforcement in the positive-reinforcement component. When a changeover delay of 5.0 sec was imposed, the slopes of the linear functions were close to 1.0 in the case of two subjects, whereas the third subject exhibited significant undermatching. For two subjects the changeover delay was then reduced to 2.0 sec; in both cases the slopes of the linear functions were lower than under the 5.0-sec condition. One subject participated in a third phase, in which no changeover delay was imposed; there was a further reduction in the slopes of the linear functions.     

The acquisition of observing.

Pigeons were exposed to stimuli correlated with the presence or absence of a variable-interval 60-second schedule of reinforcement only while they depressed a crossbar or "perch." In the first experiment, the stimuli were different tilts of a line displayed on the key. When the difference in brightness between the line and the background (salience) was maximal, seven of eight birds acquired the discrimination, but when the difference was reduced by 50%, only one succeeded. In the second experiment, wavelength of chamber illumination served as the relevant dimension. Neither experiment showed a large effect attributable to the magnitude of the difference (disparity) between the positive and the negative stimulus. Individual differences in time spent observing were positively correlated with level of discrimination in the presence of the stimuli. All birds produced the positive stimulus for a greater proportion of the available time than they did the negative stimulus. This may be the mechanism that provides selective reinforcement of observing. Finally, the formation of a discrimination was analyzed in terms of changes in the proportion of time spent in contact with the discriminative stimuli.     

JOB ATTRIBUTES PREFERRED BY FEMALE HEALTH PROFESSIONALS, BEFORE AND AFTER ENTERING THE WORK FORCE

A longitudinal study of 125 female health professionals' preferences for 12 job characteristics was carried out at graduation and 20 months later. After employment respondents placed increased importance on skill development and respect received, and less emphasis on security and promotion opportunities. At follow-up the most valued attributes were skill development, chance to accomplish something worthwhile and friendliness of co-workers, while physical surroundings, pay and promotion were ranked as least important. Self concept measures derived from Bern's Sex Role Inventory (1974) had not changed since graduation. In both surveys, a significant association was found between masculinity and the importance attached to taking part in decisions. The results contribute to the debate concerning the intrinsic-extrinsic dichotomy in work motivation.     

Associative facilitation of word recognition as measured from a neutral prime

It is shown that lexical decision times to strong associates with an associative strength of approximately 40% are facilitated relative to targets following a neutral prime, “blank,” whereas very weak associates with an associative strength of less then 3% are neither facilitated nor inhibited. It is also shown that relative to the “blank” baseline time, a row of crosses inhibits processing of the following target. The latter finding has implications for earlier studies that have used crosses as a neutral prime. In these studies, facilitation effects have been overestimated and inhibition effects have been underestimated. Neely 1976 has proposed a predict-and-match strategy according to which subjects are assumed to predict one or more targets from the prime and to match the actual target onto the predicted targets. A part of this theory is not supported by the present data. The results are discussed in terms of the two-process theory of expectancy (Posner & Snyder, 1975). They are also considered in the light of a recent theory by Becker (1980). As an alternative interpretation of part of the reported data, a coherence assumption by the subjects about all reading materials is introduced.     

Premenstrual syndrom

Premenstrual syndrome is a condition with cyclical mood changes occurring in 30 % of the female population of fertile ages. The symptom development is very closely related to the luteal phase indicating the existence of one or more factors during the luteal phase that provoke mental symptoms in sensitive patients. This is further supported by the fact that hysterectomized women with no menstrual bleedings but with the ovarian hormone cycle continue to show cyclical mood changes without having the cycle phase. The nature of the symptom provocating factor is still unknown but the ovarian hormones progesterone and/or estradiol are suspected. This as certain women taking oral contraceptives and sequential postmenopausal estrogen-progestagen treatment achieve mood changes. Psychological and personality factors are probably also involved, at least in the degree of the mood change and the type of mood experienced.     

The role of noradrenaline in learned behaviors: studies using DSP4

DSP4 (N-2-chloroethyl-N-ethyl-2-bromobenzylamine) is a novel noradrenaline (NA) neurotoxin sufficiently selective, following systemic administration, to be a pharmacological tool of much potential; this possibility has warranted the extensive use of DSP4 to study the role of noradrenaline in learned behaviors. Thus, after DSP4 treatment (50 mg/kg) a very robust two-way active avoidance impairment is incurred and this deficit remained over a wide range of stimulus conditions and parameters. On the other hand, the acquisition of relatively simple tasks such as one-way active avoidance, fear conditioning, step-down passive avoidance and taste-aversion conditioning, was only slightly affected or not affected at all. DSP4 administration caused a retardation of the rate of acquisition of a "right-turn" running response for food reward in a modified T-maze, and an attenuation of the exteroceptive context effect in taste-aversion conditioning and extinction. In spite of a few similar results, NA-depletions following DSP4 generally do not produce the same behavioral effects as the 6-Hydroxydopamine lesions but are more akin to the locus coeruleus lesion. An hypothesis of the role of central NA, based mainly upon the shuttle box procedure, incorporates a function in establishing the Signal-Response association, in adapting to situations that require a correct response to stress and in maintaining an adequate span of attention to the range of environmental events presented in any given learning situation.