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After training with a variable-interval schedule of positive reinforcement, pigeons were tested for stimulus generalization along the hue dimension. For one group, the stimulus was located on the response key. For a second group, the stimulus was located on a surface adjacent to the response key. The stimulus-on-key group produced the typical steep gradients normally found with hue stimuli; the stimulus-off-key group produced flat gradients. After discrimination training between the presence and absence of the hue stimulus, both groups produced decremental gradients. In a second experiment, naive pigeons were trained to peck a transparent key with the stimulus surface located approximately 3.8 cm behind the key. When tested for generalization, the hue gradients were decremental. The results suggest that location of the stimulus in the line of sight with pecking is a necessary condition for stimulus control by hue after nondifferential training.

Indirect systolic time indices were used to evaluate serial changes in left ventricular function during pregnancy in 13 normal patients and five patients with compensated cardiac conditions. Changes in both groups tended to parallel each other. In both groups, serial LVET index decreased, PEP index increased, and PEP/LVET ratio increased. Q-S2 index decreased in the normal group in midpregnancy and was inconsistent in the cardiac group. In the immediate postpartum period, LVET index returned to baseline values but PEP and PEP/LVET remained increased in both groups. Results of multiple comparison tests demonstrated that the largest (or smallest) value of each systolic time interval during pregnancy was observed in either the periods of the weeks 28 to 34 or 34 to 38. No significant differences were noted in intergroup comparison between the normal and cardiac groups. These data suggest that consistent changes in cardiac function may be determined during pregnancy by the noninvasive technique of indirect systolic time interval evaluation. These changes may reflect a change in left ventricular contractility, preload or afterload. The differences may persist even in the immediate postpartum period when cardiac output and heart rate have decreased to normal, suggesting residual changes in intrinsic left ventricular function. In patients with compensated heart disease, indirect tests of left ventricular function generally reflect the changes in normal pregnant women.