EFFECTS OF ENVIRONMENTAL STIMULATION ON THE LIGHT-REINFORCING OPERANT IN MICE

Kish (1955) reported that mice will press a lever at a low rate to turn on a dim light. He has indicated that this behavior may reflect the operation of an exploratory or curiosity drive and suggested that a test of this hypothesis would be to determine the efficiency of light as a reinforcer following stimulus deprivation. This implies that an explorarory drive is a general nonspecific need for stimulation. Animals raised in a stimulating environment should display a lower rate of light-reinforced operant response than animals raised in a less stimulating environment. Furthermore, if a need for stimulation is general, sensory input to one modality should affect the reinforcing properties of stimuli in another modality. Accordingly, an attempt was made to examine the effects of rearing in an enriched auditory environment on responding for visual stimulation in mice. Twenty-two C57B1/10 male and female mice between 25 and 32 days of age were divided into two groups matched for age, sex, and litter. One group was subjected to 12 days of discontinuous (.I sec. on, .2 sec. off) auditory stimulation (2000 cps, 45 db). The control group remained in the normal laboratory environment. Both groups were kept in darkness throughout the 12-day period. Testing was carried out in a preference box with internal dimensions of 4 in. X 10 in. X 6% in., which contained two milk glass panels in two adjacent corners. A depression of a panel activated a circuit to illuminate the milk glass with light of 80 to 90 ft-c. (maximum intensity) for .I sec. On test Day 1, operant levels and side preferences were taken for each S for 20 min. with both panels disconnected from the lights. During Day 2, each animal received light for each press on the right (or left) side; while on Day 3, he received the light for presses on the opposite side in 20-min, sessions. The side presentation order was balanced within both the experimental and control groups. A repeated measures analysis of variance was performed on the data for Days 2 and 3 combined, and the treatment (sound-no sound environment) X test condition (lightno light) interaction was significant (p < .05). Ms for light-sound = 45.6; light-no sound = 51.2; dark-sound = 34.4; dark-no sound = 22.7).' Regardless of the location of the light, Ss receiving early sound treatment responded equally often to light and dark panels. Control animals pressed the light-producing panel as often as the experimental group but pressed the dark panel less. A preference for the right panel on Day 1 remained significant on Days 2 and 3 (p < .01). There was no difference between the two groups in operant level. Thus, these results show that environmental stimulation in one modality can modify later preference for stimulus change in another modality. The failure of the experimental group to show a preference for light after auditory enrichment supports the assumption that a need for stimulation is general. These findings are consistent with those of Tapp and Simpson (1966) who found that food deprivation increased the reinforcing value of the onset of light for rats.