The effect of encoding training on perceptual recall

The effect of encoding training on tachistoscopic performance was measured by training groups of Ss in either an octal or a standardized English encoding of nine place binary numbers. A control group of Ss was allowed to encode ad lib during an equivalent training period. Performance was measured before, during and after the encoding training. It was found that imposing a code on S impaired tachistoscopic performance both during and for some time after the encoding training. Possible reasons for this effect are discussed.     

Vocalization-at-presentation and immediate recall, with varying presentation-rates

An experiment is reported in which the subject read visually presented lists with four different degrees of vocalization; immediately after reading each list he was required to reproduce it either aloud or in writing. Each list consisted of eight consonants and presentation rates were varied between I and 4 letters per sec. For any given series of lists, the subject was asked either to read the letters silently, or to mouth them silently, or to whisper them, or to say them aloud while reading.

At the fastest presentation-rate immediate recall improved monotonically with the degree of vocalization during reading of the lists; at slower rates this generalization held less well, especially for the lower degrees of vocalization. Vocalization was most helpful at the highest presentation-rate.

The overall amount correctly recalled was better for more slowly presented lists and for written as opposed to spoken recall. Analysis of the errors suggested that acoustic confusions were affected by the conditions of presentation; and that serial order intrusions were independent of presentation-or recall-conditions. An apparent variation of transpositions with voicing-and-recall-method failed to reach statistical significance. Theoretical implications of the experiment are discussed, including reference to Broadbent's theory of short-term memory (1958).     

Intermittency in human manual tracking tasks

We confirm Craik's (1947) observation that the human manual1y tracking a visual target behaves like an intermittent servo-control1er. Such tracking responses are indicative of "sampled" negative-feedback control but could be the result of other, continuous, mechanisms. Tracking performance therefore was recorded in a task in which visual feedback of the position of the hand-held joystick could be eliminated. Depriving the subjects of visual feedback led to smoother tracking and greatly reduced the signal power of their responses between 0.5-1.8 Hz. Their responses remained intermittent when they used feedback of their own position but not of the target to track a remembered (virtual) target. Hence, intermittency in tracking behavior is not exclusively a signature of visual feedback control but also may be a sign of feedback to memorized waveforms. Craik's (1947) suggestion that the intermittency is due to a refractory period following each movement was also tested. The errors measured at the start of each intermittent response, during tracking of slow waveforms, showed evidence of a small error deadzone (measuring 0.7 cm on the VDU screen or 0.80 degrees at the eye). At higher target speeds, however, the mean size of starting errors increased, and the upper boundary of the distribution of starting error was close to that expected of a refractory delay of approximately 170 ms between responses. We consider a model of the control system that can fit these results by incorporating an error deadzone within a feedback control loop. We therefore propose that the initiation of intermittent tracking responses may be limited by a positional error deadzone and that evidence for a refractory period between successive corrective movements can be satisfied without evoking an explicit timing or sampling mechanism.     

Is the cerebellum a smith predictor?

The motor system may use internal predictive models of the motor apparatus to achieve better control than would be possible by negative feedback. Several theories have proposed that the cerebellum may form these predictive representations. In this article, we review these theories and try to unify them by reference to an engineering control model known as a Smith Predictor. We suggest that the cerebellum forms two types of internal model. One model is a forward predictive model of the motor apparatus (e.g., limb and muscle), providing a rapid prediction of the sensory consequences of each movement. The second model is of the time delays in the control loop (due to receptor and effector delays, axonal conductances, and cognitive processing delays). This model delays a copy of the rapid prediction so that it can be compared in temporal register with actual sensory feedback from the movement. The result of this comparison is used both to correct for errors in performance and as a training signal to learn the first model. We discuss evidence that the cerebellum could form both of these models and suggest that the cerebellum may hold at least two separate Smith Predictors. One, in the lateral cerebellum, would predict the movement outcome in visual, egocentric, or peripersonal coordinates. Another, in the intermediate cerebellum, would predict the consequences in motor coordinates. Generalization of the Smith Predictor theory is discussed in light of cerebellar involvement in nonmotor control systems, including autonomic functions and cognition.     

Orientation-invariant transfer of training in the identification of rotated natural objects

The effects of stimulus orientation on naming were examined in two experiments in which subjects identified line drawings of natural objects following practice with the objects at the same or different orientations. Half the rotated objects were viewed in the orientation that matched the earlier presentations, and half were viewed at an orientation that mismatched the earlier presentations. Systematic effects of orientation on naming time were found during the early presentations. These effects were reduced during later presentations, and the size of this reduction did not depend on the orientation in which the object had been seen originally. The results are consistent with a dual-systems model of object identification in which initially large effects of disorientation are the result of a normalization process such as mental rotation, and in which attenuation of the effects is due to a shift from the normalization system to a feature/part-based     

The "REST" program: a new treatment system for the oppositional defiant adolescent

This study compared the REST (Real Economy System for Teens) program with traditional talk therapy in the treatment of oppositional defiant adolescents. The REST program uses rules for five target behaviors: room care, personal hygiene, completion of chores, abusiveness, and safety violations. Objective measures and subjective parental ratings were taken. Twenty-five adolescents were assigned to each therapy group. In the REST program the adolescent was provided with only food and shelter. The adolescent had to earn money through the REST allowance program to pay for everything else. Earning the allowance was made contingent upon compliance with all rules for the five target behaviors. The results showed significantly greater improvement on all target behaviors for the REST program than for traditional therapy. In addition, parents of adolescents in the REST group reported that their adolescents seemed happier, more relaxed, and closer to them.