Adapting to one novel condition of a motor task has been shown to generalize to other naïve conditions (i.e., motor generalization). In contrast, learning one task affects the proficiency of another task that is altogether different (i.e. motor transfer). Much more is known about motor generalization than about motor transfer, despite of decades of behavioral evidence. Moreover, motor generalization is studied as a probe to understanding how movements in any novel situations are affected by previous experiences. Thus, one could assume that mechanisms underlying transfer from trained to untrained tasks may be same as the ones known to be underlying motor generalization. However, the direct relationship between transfer and generalization has not yet been shown, thereby limiting the assumption that transfer and generalization rely on the same mechanisms. The purpose of this study was to test whether there is a relationship between motor generalization and motor transfer. To date, ten healthy young adult subjects were scored on their motor generalization ability and motor transfer ability on various upper extremity tasks. Although our current sample size is too small to clearly identify whether there is a relationship between generalization and transfer, Pearson product-moment correlation results and a priori power analysis suggest that a significant relationship will be observed with an increased sample size by 30%. If so, this would suggest that the mechanisms of transfer may be similar to those of motor generalization.

The objective of this study was to analyze the auditory feedback system and the pitch-shift reflex in relation to vibrato. 11 subjects (female n = 8, male n = 3) without speech, hearing, or neurological disorders were used. Compensation magnitude, adaptation magnitude, relative response phase, and passive and active perception were recorded when the subjects were subjected to auditory feedback perturbed by phasic amplitude and F0 modulation, or “vibrato”. “Tremolo,” or phasic amplitude modulation, was used as a control. Significant correlation was found between the ability to perceive vibrato and tremolo in active trials and the ability to perceive in passive trials (p=0.01). Passive perceptions were lower (more sensitive) than active perceptions (p< 0.01). Adaptation vibrato trials showed significant modulation magnitude (p=0.031), while tremolo did not. The two conditions were significantly different (p<0.01). There was significant phase change for both tremolo and vibrato, but vibrato phase change was greater, nearly 180° (p<0.01). In the compensation trials, the modulation change from control to vibrato trials was significantly greater than the change from control to tremolo (p=0.01). Vibrato and tremolo also had significantly different average phase change (p<0.01). It can be concluded that the auditory feedback system tries to cancel out dynamic pitch perturbations by cancelling them out out-of-phase. Similar systems must be used to adapt and to compensate to vibrato. Despite the auditory feedback system’s online monitoring, the passive perception was still better than active perception, possibly because it required only one task (perceiving) rather than two (perceiving and producing). The pitch-shift reflex compensates to the sensitivity of the auditory feedback system, as shown by the increased perception of vibrato over tremolo.

Previous studies have shown that experimentally implemented formant perturbations result in production of compensatory responses in the opposite direction of the perturbations. In this study, we investigated how participants adapt to a) auditory perturbations that shift formants to a specific point in the vowel space and hence remove variability of formants (focused perturbations), and b) auditory perturbations that preserve the natural variability of formants (uniform perturbations). We examined whether the degree of adaptation to focused perturbations was different from adaptation to uniform adaptations. We found that adaptation magnitude of the first formant (F1) was smaller in response to focused perturbations. However, F1 adaptation was initially moved in the same direction as the perturbation, and after several trials the F1 adaptation changed its course toward the opposite direction of the perturbation. We also found that adaptation of the second formant (F2) was smaller in response to focused perturbations than F2 responses to uniform perturbations. Overall, these results suggest that formant variability is an important component of speech, and that our central nervous system takes into account such variability to produce more accurate speech output.