The effects of initial movement dynamics on human responses to postural perturbations

Falls are a major cause of injury, and often occur while turning, reaching, or bending. Yet, we have little understanding of how an ongoing feet-in place activity at the onset of imbalance, and its associated cognitive and biomechanical demands, influence our ability to recover balance. In the current study, we used an ankle-rocking paradigm to determine how the nature of the baseline task influences the balance recovery response to a backward support surface translation. Fourteen participants were instructed to “recover balance without stepping” and were perturbed at vertical while standing quietly (“S”), while ankle rocking and moving forward (“A_f”), or while ankle rocking and moving backward (“A_b”). The results showed that changes in rocking velocity at the time of the perturbation elicited changes in the incidence of stepping, magnitude of trunk angular displacements (p < .01), and the onset latencies of distal muscles (gastrocnemius and soleus, both p < .01) used to recover balance. In addition, plots of onset latencies across all muscles showed that onset latencies appeared to occur earlier in many muscles when participants held a static position compared to when they performed a dynamic task at the onset of the perturbation. The results suggest that muscle activities used to recover balance are tailored to the nature of the perturbation and the ongoing task, and that onset latencies are later when participants are performing a dynamic as opposed to static task at the time of a perturbation. These findings support previous research suggesting that automatic postural responses are highly adaptable to environmental, situational, and task demands.     

Conditioning of counter-empathetic emotional responses

The present research tested the hypothesis that the quality of an observer's vicarious emotional response, as measured by autonomic, expressive, and self-report indexes, is a function of the observer's conditioning history with particular facial expressive displays of emotion. It was predicted that conditions of congruence (Symmetry) between the affective expression of a model and the outcome (shock or reward) presented to an observer would enhance initial empathetic responses, but that conditions of incongruence (Asymmetry) between the model's displays and observer's outcomes would lead to counter-empathetic responses. These changes in the quality of observers' vicarious emotional responses should generalize to a test phase when no rewards or punishments are presented to observers. The results for all measures were consistent and indicate that asymmetric conditioning modified the initial empathetic responses of observers to either counter-empathetic responses or indifference. On the other hand, symmetric conditioning enhanced observers' initial empathetic responses. These effects were evident in the test phase when no reinforcements were administered to the subject. The results are consistent with the theoretical assumption that facial expressions of emotion can acquire meaning and hedonic valence because of their predictive significance and thus can function as conditioned stimuli capable of evoking empathetic and counter-empathetic emotional responses.     

Conditioning of stimuli with nonzero initial value

In five experiments, rats received conditioning of either moderately attractive or moderately aversive flavors using either a strongly negative lithium chloride (LiCl) or a strongly positive Polycose as the reinforcer. In each case, testing was done with a compound of the two moderately valued stimuli to determine the amount of associative change produced by the pairing. In both within-subject and between-subjects designs, the amount of associative change was greater for a signal whose moderate value was opposite in valence from that of the reinforcer. This suggests that, like learned stimulus value, inherent stimulus value can modulate further associative learning.     

Divided attention, order of report and responses to immediately successive signals

Two effects, “divided-attention” and “order of report”, are operationally denned. Their relative contributions to the reduction in efficiency which accompanies the recognition of difficult nonverbal signals, presented simultaneously, is considered. Experiment I evaluated the two effects in the absence of a fixed order of report and emphasis instructions, confounding features of previous studies. The results showed: an overall impairment of performance with simultaneous signals; a contribution of both effects to the decrement, with a suggestion of the primacy of the “order of report” effect; and a significant interaction between the latter effect and modality, such that visual signals showed the greater effect. Experiment II using similar signals tested the assumption that simultaneity of presentation is a necessary condition for obtaining reduced efficiency with multiple signals. The assumption was only partially confirmed, a significant decrement in performance occurring only for the second of two successively presented signals. Similarities between the two sets of results are noted, as well as between these and modality differences obtained with verbal materials. Two possible accounts of the data are proposed, one based on “input”, the other on “storage” models of divided-attention. The hypothesis that subjects report the most clearly perceived signal first is rejected as an independent explanation.     

Biased reasoning: adaptive responses to health risk feedback

The present study examined reactions toward repeated self-relevant feedback. Participants in a community health screening received feedback about their cholesterol level on two separate occasions. Reactions to the first feedback were examined with regard to feedback valence and expectedness. The findings showed that negative feedback was devalued, but only when it was unexpected. Feedback consistency was incorporated into analyses of the second feedback. Again, results showed that negative feedback was not always devalued-only when it was inconsistent with the first feedback. Furthermore, positive feedback was not unconditionally accepted. When receiving unexpected positive feedback of low consistency, recipients were doubtful about its accuracy. Conversely, expected positive feedback was accepted regardless of its consistency. These results suggest that negative or unexpected positive feedbacks evoke greater sensitivity to feedback consistency, indicating elaborate cognitive processing. Theoretical accounts of these findings are discussed.     

Conditioning of electrodermal responses through vicarious instigation and through perceived threat to a performer

Abstract.— In order to demonstrate vicarious classical conditioning, and to investigate the necessity of vicarious instigation for vicarious conditioning of skin conductance responses, two groups of 32 students each observed a performer ( P ) allegedly trying to solve easy and difficult number series displayed for both the P and the observers ( Os ). Difficult problems served as CS+ and easy ones as CS-for os in both groups; indicated shock to the P as unconditioned stimulus (UCS) for one group, and perceived threat of shock to P as UCS for the other. Within the two groups half of the os were instructed to empathize with the P , whereas the other half was instructed just to watch her movements. The results demonstrated vicarious instigation and conditioning for the group having indicated shock as UCS, and conditioning without instigation for the group having perceived threat of shock as UCS. Since results for the conditioned response and the vicariously instigated response go beyond earlier interpretations, a theoretical elaboration in the cognitive direction is argued for.     

Transfer and non-transfer successive incentive contrast effects in the rat

Recent evidence concerning successive incentive contrast suggests the occurrence of both positive and negative contrast effects under both non-transfer and transfer conditions. There are three types of explanation for these contrast effects, based on frustration theory, sequential theory and adaptation level theory (perceptual accounts). One of the critical experiments favouring perceptual accounts, Collier and Marx (1959), is subject to a number of methodological criticisms. This experiment was repeated, with modifications to take account of these criticisms, and extended to include transfer, as well as non-transfer, conditions. There was no evidence of contrast. In a further experiment using Collier and Marx's procedure with lever pressing and panel pushing, positive and negative, transfer and non-transfer effects were found using Noyes pellets rather than sucrose as reward. It is suggested that these results contribute some support to perceptual accounts of incentive contrast, although no present theory is entirely satisfactory.     

Using response times to detect aberrant responses in computerized adaptive testing

A lognormal model for response times is used to check response times for aberrances in examinee behavior on computerized adaptive tests. Both classical procedures and Bayesian posterior predictive checks are presented. For a fixed examinee, responses and response times are independent; checks based on response times offer thus information independent of the results of checks on response patterns. Empirical examples of the use of classical and Bayesian checks for detecting two different types of aberrances in response times are presented. The detection rates for the Bayesian checks outperformed those for the classical checks, but at the cost of higher false-alarm rates. A guideline for the choice between the two types of checks is offered.This study received funding from the Law School Admission Council (LSAC). The opinions and conclusions contained in this paper are those of the authors and do not necessarily reflect the policy and position of LSAC. The authors are most indebted to Wim M. M. Tielen for his computational assistance and to the US Defense Manpower Data Center for the permission to use the ASVAB data set in the empirical examples.     

Some effects of discriminable goal-box conditions on the learning of a successive discrimination

In an attempt to confirm and extend a previous reslt, rats were trained on two tasks where a signal delivered at the start of each trial indicated which of two paths through a maze would be rewarded. In Experiment I both paths led to the same goal-box, and it was found that performance was better when the state of the goal-box was different on trials with each of the two signals. In Experiment II the two paths led to spatially separated goal-boxes. It was found that when the states of the two goal-boxes were discriminably different but the state of each of them remained the same from trial to trial, performance was better than when their states varied irregularly. It is suggested that these results have interesting implications for theories of behaviour.     

A choice procedure to assess the aversive effects of drugs in rodents

The goal of this series of experiments was to develop an operant choice procedure to examine rapidly the punishing effects of intravenous drugs in rats. First, the cardiovascular effects of experimenter‐administered intravenous histamine, a known aversive drug, were assessed to determine a biologically active dose range. Next, rats responded on each of two levers with concurrently available fixed‐ratio 1 schedules of food reinforcement. Intravenous histamine was delivered along with food when responses were made on one of the options, and the lever on which both food and histamine were contingent was switched on a regular basis. A dose of 1.0 mg/kg/inj of histamine was effective in moving responding to the alternate lever, whereas saline, 0.1, or 0.3 mg/kg/inj of histamine were not. Histamine injections produced reliable selection of the alternate lever when they were presented on the same lever for three consecutive sessions, but not when they were switched between levers on each session. In addition, histamine produced greater selection of the alternate lever when it was presented with shorter intertrial interval durations. These findings indicate that, with appropriate parameters, the aversive effects of histamine and perhaps other drugs can be established rapidly using a concurrent choice procedure.     

Interaction effects in successive visual displays: An extension of the Eriksen-Collins paradigm

The paradigm of Eriksen and Collins, in which one-haft of the elements of a display is assigned randomly to each of two successively presented fields, was applied to the visual discrimination of one- and two-dimensional Markov constraints. In contrast with the two-flash masking paradigm, performance in the Eriksen-Collins paradigmimproves as the interval between the successively presented fields is shortened. Constraint thresholds may increase with interfield intervals as short as 20 msec. In contrast with the results of most visual information-processing tasks, increasing the duration of each field may result in sharplyelevated thresholds. The elevation of thresholds can be reduced through repeated presentation. Sharp asymmetries are also obtained with differential brightness of the two fields.     

Experimenter effects on responses to explicitly sexual stimuli

Experimenter effects on responses to explicitly sexual stimuli were investigated in 63 single undergraduate males and 89 single undergraduate females. A completely factorial design with sex of subject, sex of experimenter, and experimenter's style of interacting (informal vs formal) as the independent factors was employed. While the variables under investigation did not have an overriding effect on the outcome measures, at least one experimenter attribute was discovered to significantly influence a large percentage of the variables assessed: The data suggest that informal experimenters permit less socially desirable responses and more generalized arousal than formal experimenters. In addition to replicating earlier work on experimenter effects, the present study serves to delineate a possible set of cues by which experimenters may influence their subjects' arousal to explicitly sexual stimuli.     

Conditioning and post-hospital generalization of nondelusional responses in a chronic psychotic patient

An operant conditioning approach was successful in getting a chronic psychotic patient to give factual answers to direct questions that had previously elicited only delusional responses. Multiple baseline and reversal controls established that the changes were due to the experimental procedure. The subject was a female patient classified as paranoid schizophrenic who had persisted in giving bizarre responses to direct questions regarding her identity, age, and personal history during 26 yr of hospitalization. She was discharged after factual answers to these questions had been obtained, but operant conditioning trials were continued in the community to promote generalization. Two follow-up interviews were conducted 36 and 52 days after discharge to evaluate generalization. No generalization was found in the first interview, but the second gave evidence of some generalization.