Sensorimotor synchronization: Motor responses to pseudoregular auditory patterns

Musically trained and untrained subjects (N=30) were asked to synchronize their finger tapping with stimuli in auditory patterns. Each pattern comprised six successive tonal stimuli of the same duration, the first of which was accented by a different frequency. The duration of interstimulus onset intervals (ISIs) gradually increased or decreased in constant steps toward the end of the patterns. Four values of such steps were used in different trials: 20, 30, 45, and 60 msec. Various time-control mechanisms are hypothesized as being simultaneously responsible for subjects’ incorrect reproduction of the internal temporal ratios of the stimulus patterns. The mechanism of assimilation (of a central tendency) led subjects to enforce a regular (isochronous) structure on the patterns. The influence of other time-control mechanisms (distinction, subjective expression of an accent, sequential transfer) was expressed mainly in differences between intertap onset intervals (ITIs) and the corresponding ISIs at the beginning of the patterns. The duration of the first two ITIs was in the majority of the trials in an inverse ratio to the ratio of the respective ISIs. The distortions resulting from the timing mechanisms concerned were more pronounced in the performance of nonmusicians than in that of musicians.     

Human sensitivity to temporal proximity: The role of spatial and temporal speed gradients

Estimates of temporal proximity (sometimes called time-to-collision) from random-dot flow patterns are shown to be based upon retinal speed, rather than upon changes in dot density. Neither the spatial nor the temporal gradient of motion is essential to the task, but estimates can be made from either alone. Performance is unaffected by the addition of rotational motion, suggesting that observers axe capable of extracting the radial component of motion, which contains all the relevant information, from complex stimuli.     

Communicative behavior of mothers of stuttering and nonstuttering high-risk children prior to the onset of stuttering

This portion of a multiyear prospective study was designed to investigate the communicative style, speaking rate, and language complexity of 93 mothers of preschool children with a parental history of stuttering. At the initial session none of the children sampled was regarded as being a stutterer. One year later, 26 of the children were classified as stutterers. Statistical analyses revealed that prior to the onset of stuttering the mothers of these children did not differ from the mothers of the children who continued to be seen as nonstutterers with respect to either communicative style or speaking rate. The only significant difference between the two groups of mothers was the complexity of their language. The pre-onset mean lengths of utterance (MLUs) of the mothers of children who later came to be regarded as stutterers were significantly shorter than those of the mothers whose children continued to be viewed as being fluent. These findings suggest that the communicative behavior of mothers of normally fluent children do not contribute to the development of stuttering.     

Sparing and recovery of function in spinal larval frogs (Rana catesbeiana): effect of level of transection.

Bullfrog tadpoles with cervical or midthoracic transection of the spinal cord were allowed to recover for 5 weeks, at which time axonal growth across the transection site was assessed by transport of horseradish peroxidase. Weekly behavioral tests included those for posture, spontaneous locomotion, cutaneously elicited swimming, and intersegmental coordination. Behavioral and electrophysiological assessments suggest that behavioral recovery depends, at least in part, on the growth of fibers across the transection site. Anatomical and behavioral recovery does not appear to differ with the level of spinal transection, but there was greater sparing of posture, spontaneous locomotion, and stimulus-induced locomotion in tadpoles with thoracic transection of the spinal cords.