Quantitative Analysis of IRT Variability During the First Training Stages of a Variable-Interval Schedule in Rats

Five rats were reinforced under variable-interval schedules with different average interreinforcement intervals (30 seC., 1 min, 2 min, and 4 min). Each animal was run only two sessions of each schedule. The interresponse times (IRTs) were recorded and analyzed. The autocorrelation function of the IRT series and of the IRT time series (number of responses per time interval) were calculated, and absence of periodicity in the subject’s behavior was demonstrated. Frequency distribution of IRTs showed in all cases a similar shape and could be fitted to a gamma probability density function in 60% of cases with a signification level of .01 (Kolmogorov-Smirnoff test). The frequency distributions of the IRT time series were distributed as a Poisson process with a .05 significance level. These results suggest that during variable-interval schedules the responses of the animal can be modeled as a random process characterized by a gamma distribution, as a first approximation.

     

Individual differences in depression,induced mood,and perception of emotionally toned words

The associative network theory of emotion and memory, outlined by Bower (1981), predicts that depressed mood leads to biases which favour the perception of mood-congruent information. In this study, a lexical decision task was used to assess the effects of degree of depression and induced elation and depression on lexical decision times for positive and negative words. Subsequently, subjects were given a recall test for the words presented during the lexical decision task. The results partially offered support for perceptual bias. The data showed that in non-depressed and elation-induced subjects, decision times were differentially affected by hedonic tone. Words of positive nature were responded to significantly faster than were negative words. In mildly depressed and depression-induced, decision times were similar for both types of words (positive and negative). These findings are discussed in relation to the associative network model and a growing amount of empirical research on human emotion and cognition.     

Instrumental conditioning of diastolic blood pressure in essential hypertensive patients

Eighteen male essential hypertensive patients participated in an experiment designed to compare two strategies for controlling high blood pressure. Each strategy was derived from the instrumental learning literature, and the aim was to treat the blood pressure response as an operant and determine the most effective conditioning procedure for manipulating it. The results demonstrate that patients could be conditioned to lower blood pressure by 20% to 30% over a period as brief as four days by providing an external signal and verbal praise contingent upon each reduction in diastolic pressure that met a pre-set criterion.     

Self-disclosure of HIV infection: preliminary results from a sample of Hispanic men.

We examined self-disclosure of HIV infection among 101 seropositive Hispanic men residing in Los Angeles. Results indicated that disclosure was highly selective and presumably influenced by the social, psychological, and material consequences of informing others about one's medical condition. Subjects tended to inform significant others such as parents, friends, and lovers than less significant others such as employers, landlords, and religious leaders. There was a relatively high rate of disclosure (75%) to doctors/dentists who were not treating subjects for HIV infection. Gay and bisexual subjects (89% of the sample) were more inclined to disclose their HIV serostatus to homosexual or bisexual others than to heterosexuals and to inform those who were aware of their sexual orientation. Disclosure increased with severity of disease independently of length of time since testing seropositive. Self-rated negative changes in appearance correlated with disclosure to less significant others. The role of cultural attitudes and values in self-disclosure of HIV infection is discussed.     

A current approach to anticipation in sport / Un enfoque actual de la anticipación en el deporte

The classical cognitive concept of anticipation and timing (for example, reaction time) somewhat limits the study of sports actions under spatio-temporal pressure. The presence, duration and evolution of the information of the opponents, spatio-temporal pressure, the evolution of the athlete’s response movements or the degree of representativeness are some of the issues facilitating research into an anticipation that is better adjusted to the specific circumstances of interception tasks. This article proposes that temporalization of response actions is based on the balance between the spatio-temporal demands of the task, the athlete’s action capabilities and the evolution of the reliability of the available variables. In order to obtain good performance in these actions under pressure, individual perceptual differences and possible interactions with other information sources must also be considered.     

Poststimulation time interval-dependent effects of motor cortex anodal tDCS on reaction-time task performance

Anodal transcranial direct current stimulation (tDCS) induces long-term potentiation-like plasticity, which is associated with long-lasting effects on different cognitive, emotional, and motor performances. Specifically, tDCS applied over the motor cortex is considered to improve reaction time in simple and complex tasks. The timing of tDCS relative to task performance could determine the efficacy of tDCS to modulate performance. The aim of this study was to compare the effects of a single session of anodal tDCS (1.5 mA, for 15 min) applied over the left primary motor cortex (M1) versus sham stimulation on performance of a go/no-go simple reaction-time task carried out at three different time points after tDCS—namely, 0, 30, or 60 min after stimulation. Performance zero min after anodal tDCS was improved during the whole course of the task. Performance 30 min after anodal tDCS was improved only in the last block of the reaction-time task. Performance 60 min after anodal tDCS was not significantly different throughout the entire task. These findings suggest that the motor cortex excitability changes induced by tDCS can improve motor responses, and these effects critically depend on the time interval between stimulation and task performance.     

Motivational deficits in schizophrenia relate to abnormalities in cortical learning rate signals

Individuals from across the psychosis spectrum display impairments in reinforcement learning. In some individuals, these deficits may result from aberrations in reward prediction error (RPE) signaling, conveyed by dopaminergic projections to the ventral striatum (VS). However, there is mounting evidence that VS RPE signals are relatively intact in medicated people with schizophrenia (PSZ). We hypothesized that, in PSZ, reinforcement learning deficits often are not related to RPE signaling per se but rather their impact on learning and behavior (i.e., learning rate modulation), due to dysfunction in anterior cingulate and dorsomedial prefrontal cortex (dmPFC). Twenty-six PSZ and 23 healthy volunteers completed a probabilistic reinforcement learning paradigm with occasional, sudden, shifts in contingencies. Using computational modeling, we found evidence of an impairment in trial-wise learning rate modulation (α) in PSZ before and after a reinforcement contingency shift, expressed most in PSZ with more severe motivational deficits. In a subsample of 22 PSZ and 22 healthy volunteers, we found little evidence for between-group differences in VS RPE and dmPFC learning rate signals, as measured with fMRI. However, a follow-up psychophysiological interaction analysis revealed decreased dmPFC-VS connectivity concurrent with learning rate modulation, most prominently in individuals with the most severe motivational deficits. These findings point to an impairment in learning rate modulation in PSZ, leading to a reduced ability to adjust task behavior in response to unexpected outcomes. At the level of the brain, learning rate modulation deficits may be associated with decreased involvement of the dmPFC within a greater RL network.