Stimulus preference and its effect on visual habituation and dishabituation in four-month-old infants.

The rate of habituation and rehabituation and the magnitude of dishabituation were investigated in four-month-old infants (24 boys, 24 girls) as a function of stimulus preference. Infants were habituated to either a preferred or nonpreferred stimulus and rehabituated with the opposite stimulus. Infants initially viewing a preferred stimulus required more trials to habituate and fewer trials to rehabituate than those in the nonpreferred group. In addition, the magnitude of dishabituation was greater for infants in the latter group. The data were discussed in terms of the importance of stimulus preference in studies of infant habituation.

Effect of varying sucrose concentration on macrobehavioral aspects of licking in the rat.

Rats (eight male, eight female) were trained to lick 32% and 4% sucrose solutions for three minutes per day on four consecutive days. Measures of the number of licks revealed robust positive and negative contrast effects. Analysis of the burst-pause pattern of licking revealed that the decrease in licking characteristic of the negative contrast effect resulted from a decrease in the number of bursts, while the increase in licking characteristic of the positive contrast effect was the result of a shortening of the interburst interval.

Contrast effects in the rat: a developmental study.

Two experiments investigated and development of positive and negative contrast effects in the consummatory behavior of juvenile and adult rats. Over a 4-day session, animals were given alternating 30-sec presentations of 2 bottles containing either 32 or 4% sucrose solutions. In Experiment I, different groups of rats were tested both cross-sectionally and longitudinally using a cohort-sequential design. Cross-sectionally, animals at all ages exhibited both types of contrast and demonstrated increasing positive contrast effects with greater age. Discrepancies between the longitudinal and cross-sectional samples were found to be due to the repeated testing procedure of the former design. Experiment II replicated the positive and negative contrast effects in the juvenile animals, indicating that the processes responsible for contrast effects are operating in the rat at a very early age.