Structural Stability within the Lateral Cerebellar Nucleus of the Rat Following Complex Motor Learning

Complex motor learning, but not mere motor activity, has been previously shown to induce structural modifications within the cerebellar cortex. The present experiment examined whether similar changes occur within one of the primary output targets of the region of the cerebellar cortex in which these structural changes were described, the lateral cerebellar nucleus (LCN; dentate nucleus). Adult female rats were randomly allocated to one of three training conditions. Acrobatic condition (AC) rats were trained to complete a complex motor learning task consisting of a series of elevated obstacles while motor control (MC) condition animals were forced to traverse a flat obstacle-free runway equal in length to the AC task. Inactive condition (IC) animals received no motor training. Unbiased stereological techniques and electron microscopy were used to obtain estimates of synapse number and postsynaptic density (PSD) length within the LCN. Results showed that neither synapse number nor PSD length was significantly altered as a function of training condition. These results indicate that complex motor skill learning is associated with structural plasticity within the cerebellar cortex and with structural stability within the lateral cerebellar nucleus.     

Forced serial processing of words and letter strings: A reexamination

Words and nonword strings, three and seven letters long, were displayed serially (i.e., one letter at a time) or simultaneously, with or without a backward mask following display of each letter or string. Recognition of words, and of individual letters within words, was markedly impaired in the masked serial condition relative to the unmasked serial, unmasked simultaneous, and masked simultaneous conditions. Analogous differences were smaller or nonexistent for seven-letter nonwords; however, three-letter nonwords produced relatively “wordlike” data. Implications for the issue of spatially serial vs. parallel processing in word recognition are discussed.     

A problem-solving model for teaching remedial arithmetic to handicapped young children

An operant problem-solving model was used to assist two handicapped young boys to learn the concept of number. During the initial baseline condition, with intermittent teacher-attention contingencies in a classroom setting, both boys were performing number concept tasks at about the 50% level of accuracy. The situation was changed to a one-to-one, tutor-pupil arrangement, with continuous reinforcement for correct responses. This alteration failed to increase the subjects' accuracy rates. Training was initiated in which the covert part of the response chain was made overt (e.g., attending and counting out loud) so that mediating responses could be monitored and reinforced. Once the subjects were performing at a high degree of accuracy, the reinforcers for the mediating responses were systematically eliminated and only final solution responses were reinforced. Accuracy of problem solutions remained high after training.This research was supported by the U.S. Office of Education, Division of Research, Bureau of Education for the Handicapped, Project No. 23–2030, Grant No. OEG-0-9-232030-0762(032). Linda S. Berner contributed to the execution of the study. Her assistance is greatly appreciated.     

The effects of forced serial processing on identification of words and random letter strings

Skilled readers identified words and random letter strings displayed one letter at a time on the screen of a computer-controlled oscilloscope. Letters were either displayed in a single position, or painted left-to-right in adjacent positions. Adjacent displays were either unmasked, masked by a letter-like pattern following each letter (backward masking) or masked by a pattern preceding each letter (forward masking). Unmasked words were identified with a high degree of accuracy, and accuracy was independent of the exposure duration of the letters over the range 50–200 msec. Masked adjacent word displays and one-position word displays were identified much less accurately, and accuracy was highly dependent on letter exposure duration. In contrast to these results, identification of random strings, or of letters within random strings, was almost unaffected by the presence of the mask and was dependent on letter exposure duration under all display conditions. The results are interpreted as evidence that (a) masking forces subjects to process serial displays one letter at a time, and (b) words, or large segments of words, are habitually processed in parallel, while random strings are processed as a series of individual letters or small chunks.     

Aggressor's response to the victim's facial expression of emotion

Male college students (N = 96) were met by an experimental confederate who either agreed or disagreed with their opinion. The subjects were then given an opportunity to deliver electric shock to the confederate (victim), who responded to the shock with a facial expression of anger, fear, joy, or neutrality. The opinion condition had no effect, but the victim's facial expressions were clearly perceived by the subjects and two of them significantly influenced the amount of shock delivered to the victim by the subjects. The expression of enjoyment (smile) increased aggression while that of anger decreased aggression. The effects of the fear and neutral expressions did not differ from each other, and neither had a consistent significant effect on the amount of shock administered by the subjects.     

Situation-specific variables as determinants of perceived environmental aesthetic quality and perceived crowdedness

It was hypothesized that relevant situation-specific variables may act along with objective physical conditions to determine environmental perception, and that the exclusive use of the physical level of an environmental stimulus to predict behavior may, therefore, be inadequate. A 2 × 4 between-subjects design was employed in which an attitudinally similar or dissimilar confederate interacted with a subject at one of four distances. As hypothesized, subjects who interacted with a similar confederate judged the environment to be of higher aesthetic quality, perceived themselves to be less crowded, and felt affectively more positive than subjects who interacted with a dissimilar other. The results were also interpreted as supporting the utility of the Byrne-Clore (1970) reinforcementaffect model of evaluative responses as a means of predicting environmental perception and the behavioral response to environmental stimuli.     

Indefinite Divisibility

Some hold that the lesson of Russell’s paradox and its relatives is that mathematical reality does not form a ‘definite totality’ but rather is ‘indefinitely extensible’. There can always be more sets than there ever are. I argue that certain contact puzzles are analogous to Russell’s paradox this way: they similarly motivate a vision of physical reality as iteratively generated. In this picture, the divisions of the continuum into smaller parts are ‘potential’ rather than ‘actual’. Besides the intrinsic interest of this metaphysical picture, it has important consequences for the debate over absolute generality. It is often thought that ‘indefinite extensibility’ arguments at best make trouble for mathematical platonists; but the contact arguments show that nominalists face the same kind of difficulty, if they recognize even the metaphysical possibility of the picture I sketch.