(Eckerman, Lanson, and Cumming, 1968), and schedules of reinforcement (Ferster, 1960), but also with the use of this procedure as a baseline from which effects of drugs , hypnosis (Ferster, Levitt, Zimmerman, and Brady, 1961), and brain lesions (Spaet and Harlow, 1943) Procedure Preliminary training. After magazine training, the response requirement was increased to a fixed ratio of five responses (FR 5) on the center key, which was alternately illuminated with three hues (amber, red, and green). Responses on the illuminated key were reinforced with 3-sec grain magazine presentation.

In a study by Corman, Meyer & Meyer (1967), open-field activity was investigated with normal rats, as well as with rats having septal or amygdaloid lesions. A stimulus change was introduced into the open-field and changes in activity and amount of time spent in the center of the field were observed. Although the study was not directly concerned with exploratory behavior, the basic technique appears to provide an adequate setting for observing exploratory behavior in its relation to stimulus properties of the environment.It is well known (and demonstrated by this experiment) that rats exhibit a "wall-hugging" tendency in apparati. Using an open-field, this tendency can be utilized to demonstrate the effects of stimulus introduction. In the homogeneous open-field the rat spends relatively little time in the area toward the center of the field. An area may be defined as the center of the field, and stimuli can be introduced into this area. If the stimulus elicits approach, it is over-riding the "wall-hugging" tendency and a reliable difference between time-in-center scores with and without specific stimuli in the center of the field should be observed.The purpose of the present study is to introduce a relatively simple stimulus change into the open-field environment and to observe whether the change is sufficient to alter the behavior of the S. EXPERIMENT 1 METHOD Subjects and ApparatusThe Ss were 27 male hooded rats. The rats ranged from 81 to 84 days of age at the beginning of the experiment. The Ss had continual access to food and water except during test trials.The apparatus was an open field 45-in. sq, enclosed by walls 24-in. in height. The walls of the apparatus were dark grey, and the floor consisted of 9-in. sq of black linoleum tile. A removable start box, 9-in. by 9-in. by 12-in., was used. The start box had two sides and was placed in one corner of the open field so that the walls of the field completed the box. A hinged .top permitted insertion of the animal into the start box and a long handle permitted the box to be lifted from the field at the beginning of the trial. The field was illuminated by a 15-W florescent light suspended 20-in. above the center of the field. The experimenter sat adjacent to the field in the otherwise darkened room. Two hand switches connected to a graphic recorder permitted recording of locomotion and the amount of time spent in the center of the field. PROCEDURE Prior to the beginning of the experiment, the animals were gentled. At the beginning of a test period the animal was Psychon. Sci., 1968. Vol. 13 (I) placed in the start box. One min later the start box was gently lifted from the open-field apparatus. The animal was then observed for three min. Three·behavioral measures were taken: latency in leaving the starting square, a locomotion score (number of squares entered during the test period), and time-in-center (total time, in seconds, in contact with squares other than those adjacent to the walls of the apparatus). A square was counted as entered if the animal placed...

In a 3 by 3 factorial design, 27 rats were given 50 trials of avoidance conditioning in a shuttlebox. The main effects of shock (.2, .4

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