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An operant conditioning history can produce highly uniform kinematic performances by cats on a motor-driven treadmill, but in the present work there was additional stimulus control such that the animals moved smoothly backward or forward on the belt, "startled," or reached for a food tray at the front of the chamber. The resulting responses were filmed and EMG records were taken from VL (vastus lateralis, a knee extensor) or IP (iliopsoas, a hip flexor) or both muscles. Both ipsilateral and bilateral responses were observed, and sometimes the change was restricted to just one portion of the VL or IP activity, showing precise moment-to-moment control. Forelimb reaching caused an early VL burst prior to touchdown, which may help understanding of extensor bursts that "anticipate" the contact of a limb. In other cases, an absence of control of hindlimb events was the major finding. No evidence was gained for vestibular or neck reflexes, since there was no response to large isolated head or neck excursions. Also, an animal might complete a full hindlimb step without any VL activity. It was concluded that acquired stimulus control could bring about marked separations of functional subdivisions of the step cycle. |
