Automatic and Controlled Processes in the Analytisis of Hierarchical Structure

Targets are identified faster if they appear at the same level (global vs. local) as the target on the previous trial. This effect has been attributed to a controlled attentional process wherein participants attend to the level containing the target on trial n − 1, thus facilitating performance if target level repeats on trial n. An alternative explanation (Lamb & Yund, 1966) is that automatic activation of level-specific neural mechanisms is responsible. The controlled-process hypothesis predicts better performance whenever target level is predictable, because participants can anticipate, and thus attend to, the appropriate level. The automatic-process hypothesis predicts better performance when target level repeats, regardless of target-level predictability. In the present studies, level repetitions facilitated performance regardless of target-level predictability. The data support the automatic-process explanation of level repetition and other attentional effects. The data illustrate how an automatic process can give rise to performance that seems to reflect more cognitive or strategic mechanisms.     

Approximate entropy and point correlation dimension of heart rate variability in healthy subjects

The contribution of nonlinear dynamics to heart rate variability in healthy humans was examined using surrogate data analysis. Several measures of heart rate variability were used and compared. Heart rates were recorded for three hours and original data sets of 8192 R-R intervals created. For each original data set (n=34), three surrogate data sets were made by shuffling the order of the R-R intervals while retaining their linear correlations. The difference in heart rate variability between the original and surrogate data sets reflects the amount of nonlinear structure in the original data set. Heart rate variability was analyzed by two different nonlinear methods, point correlation dimension and approximate entropy. Nonlinearity, though under 10 percent, could be detected with both types of heart rate variability measures. More importantly, not only were the correlations between these measures and the standard deviation of the R-R intervals weak, the correlation among the nonlinear measures themselves was also weak (generally less than 0.6). This suggests that in addition to standard linear measures of heart rate variability, the use of multiple nonlinear measures of heart rate variability might be useful in monitoring heart rate dynamics.     

Ratio requirement and reinforcer effects in concurrent fixed-interval fixed-ratio schedules

The fixed-ratio requirement was varied in concurrent fixed-interval fixed-ratio schedules. Fixed-interval responding was reinforced by food. In different phases, fixed-ratio responding was reinforced by food or water. There was a direct relation between the ratio requirement and interval response rates when both responses were reinforced with food, but essentially no relation when the reinforcers were different. The role of reinforcers in concurrent schedules merits detailed study.     

Coding strategies,perceptual grouping,and the “variability effect” in free recall

Three experiments examined the effects of constant vs. varied input of letter strings on recall, and then examined the effects of such training in the learning of new lists of letter strings. Letter strings were constructed from pairs of trigrams spatially grouped, and were presented either consistently or with different spatial groupings on successive presentations. In Experiments I and II, varied input produced substantially greater recall than constant input. When transferred to a new list of letter strings, containing either the same general structure or a new scrambled structure, recall of the second list was determined primarily by conditions of first-list input, and unaffected by second-list structure. Although the "variability effect" did not appear in the training phase of Experiment III, Varied input led subjects to regroup or integrate the letter sequences more frequently and produced similar transfer effects as in Experiments I and II.     

On-line brain stimulation: Measurement of threshold of reinforcement

This program and interface for a small computer (PDP8/e) performs the following operations: generates and delivers constant current stimulation to the brain of an animal, monitors electrical resistance at the stimulating electrode, and calculates the threshold of reinforcement based upon the frequency of characteristic pauses in the animal’s responding.     

An objective test of goodness of fit of the continuous strength model in STM

The continuous strength model of recognition memory was evaluated in a task where Ss were tested for recognition of 10-number lists using a rating procedure. Maximum likelihood estimates of the parameters of the model were obtained by an iterative method on a high-speed computer, and a chi-square goodness-of-fit test was performed for individual Ss. For 15 of 20 Ss, the chi-square values were nonsignificant, p < .05, indicating that the model provided a good fit to the data. Although the model gave a good fit to the data, the Δm measure of sensitivity was highly correlated with a true recognition score computed by subtracting false alarmsfrom correct recognitions.