Naloxone and Pavlovian fear conditioning

Previous research has shown that pretreating rats with the opiate antagonist naloxone increases the freezing that follows painful electric shock. Three experiments, using freezing behavior as a dependent variable, were carried out to determine whether the drug might cause this effect by enhancing fear conditioning. Two of the studies employed a differential context fear-conditioning paradigm. Naloxone did not affect freezing behavior during the preshock adaptation period. In Experiment 1, naloxone was found to increase resistance to extinction in the S+ context. In Experiment 2, naloxone was found to increase freezing in the S+ context. This effect was dependent upon administering naloxone during training but not dependent on administering it during testing. The third study employed a generalization paradigm. It was found that naloxone's effect on postshock freezing was dependent on the place of testing; as the contextual cues of the test chamber were changed from those of the conditioning chamber, the effect of naloxone on freezing was reduced. The results of these experiments lend strong support to the hypothesis that naloxone increases freezing by enhancing the conditioning of fear to contextual stimuli associated with shock.     

Spontaneous configuring to a tone-light compound using appetitive training

Rats were trained to bar-press for water in the presence of a simultaneous compound tone-light stimulus using a discrete-trial procedure. Different groups were given between 300 and 3900 trials. When subsequently tested in extinction, all rats showed consistent levels of responding to the compound stimulus but responding to the tone and light components declined as a function of number of training trials. This is a demonstration of spontaneous configuring. Two other experiments showed that with similar procedures generalization from a component of the training stimulus to other values on the same continuum decreases with increased training with the compound stimulus. It was concluded that configuring and generalization from a single stimulus involve the same processes.     

Some theory and results for metrics for bounded response scales

In an earlier note, a new metric for bounded response scales (MBR) was introduced which resembles the city-block metric but is bounded above. It was suggested the MBR may be more appropriate than minkowski metrics for data obtained with bounded response scales. In this article, some formal properties of the MBR are investigated and it is shown that it is indeed a metric. Empirical predictions are then derived from the MBR and contrasted with those of a “monotonicity hypothesis,” which holds that dissimilarity judgements tend to be biased towards overestimation of larger distances, and with the predictions of the minkowski metrics, which imply additivity of collinear segments. Some empirical results are presented which contradict the monotonicity hypothesis and the minkowski metrics, and favor the MBR. Finally, the logic used to motivate the MBR is invoked to define a subadditive concatenation for bounded norms in the one-dimensional case, which may be useful in psychophysical work where the upper bounds are often real, rather than due to the response scale. This concatenation predicts understimation for doubling and overestimation for halving and middling tasks.     

A characterization of stochastic independence by association,with an application to random utility theory

A characterization of stochastic independence in terms of association of random variables is given. The result is applied to yield a simple proof of the Sattath-Tversky inequality without continuity assumptions.     

A procedural theory of eye movements in doing arithmetic

A procedural theory of eye movement that accounts for main features of the stochastic behavior of eye-fixation durations and direction of movement of saccades in the process of solving arithmetic exercises of addition and subtraction is presented. The best-fitting distribution of fixation durations with a relatively simple theoretical justification consists of a mixture of an exponential distribution and the convolution of two exponential distributions. The eye movements themselves were found to approximate a random walk that fits rather closely in both adult and juvenile subjects the motion postulated by the normative algorithm ordinarily taught in schools. Certain structural features of addition and subtraction exercises, such as the number of columns, the presence or absence of a carry or a borrow, are well known to affect their difficulty. In this study, regressions on such structural variables were found to account for only a relatively small part of the variation in eye-fixation durations.     

A biased random walk model for two choice reaction times

This paper generalizes Stone's (1960, Psychometrika 25, 251–260) random walk model of two choice response times (RTs) that is based on the sequential probability ratio test (SPRT) and that predicts equal correct and incorrect RTs to the same response. The generalized version allows a bias of the type found in signal detection theory to enter directly into the accumulation process so that ambivalent evidence may be seen as slightly favoring one alternative. The resulting biased SPRT model can predict any relation between correct and incorrect mean RTs. In particular, unlike the special symmetric case of Link and Heath's (1975, Psychometrika 40, 77–105) relative judgment theory (RJT), the biased SPRT model can predict that correct mean RTs are faster for one response but slower for the other. The biased SPRT model, the classical SPRT model, and the symmetric RJT model are all fit to the data of an RT deadline experiment reported by Green and Luce (1973, Attention and performance, New York: Academic Press) and it is shown that, of the three, the biased SPRT model provides the best account. Finally, a method for incorporating the same sort of bias into RJT models is sketched out.     

Behavioral thresholds for tones during infancy

An adaptive up-down tracking procedure was used in combination with a visually reinforced head turn response to examine auditory sensitivity for 500, 2000, and 8000-Hz tone bursts in infants 6 to 18 months of age. Six- and 10-month-old infants were tested with headphone presentation of stimuli, while 10-, 14, and 18-month-olds were tested in sound field. Infant threshold estimates for both headphone and sound field were within 15 dB of adult comparisons for all frequencies and age groups. Six-month-olds were significantly less sensitive to the 8000-Hz tone than to either of the lower frequency stimuli, but older infants demonstrated approximately equal sensitivity for all three frequencies tested.     

Speaker bias in children's evaluation of the external consistency of statements

The hypothesis of this study is that an assumption of speaker credibility affects children's judgments of the external consistency of statements. In two experiments, first and third grade children (6 and 8 years of age, respectively) and college adults were read short paragraphs containing contradictory information from a contextual source and a speaker. The contextual source was described as either authoritative or nonauthoritative and discredited. The speaker was either an adult or child. Thus the contextual source was either more or less reliable than the speaker. Subjects were asked to affirm or contradict the speaker's statement, and to choose either the source or the speaker as most believable. The results showed that adult responses varied with the contextual source alone, while the responses of the first graders varied primarily with the speaker's age. The responses of the third graders varied with both factors. The results suggest young children can assess the external consistency of statements but frequently do not because of their assumptions about speakers and other performance factors.     

Stimulus control of responding by response-reinforcer temporal contiguity

The stimulus properties of brief disruptions in response-reinforcer temporal contiguity were investigated using a discrete trial conditional discrimination procedure. Key pecking (nondelay) or key pecking followed by a brief interval of nonpecking (delay) in the sample component produced a stimulus change (choice component). Pecks in the choice component to one of two alternatives resulted in food or blackout, conditional upon which response requirement was met in producing the choice component. A baseline condition, in which key pecking always produced the choice component and correct choices were arranged randomly, alternated with experimental conditions that included nondelay and delay values of either 0.2, 0.5, or 1.0 sec between the last key peck and the initiation of the choice component. All subjects accurately discriminated brief temporal delays between a response and stimulus change, with choice accuracy increasing for three of four subjects as the temporal disruption in contiguity increase. Implications of the research for the study of delayed reinforcement, response-independent reinforcement, and the discrimination of causality are discussed.