Perceptual and Motor Skills, 1977,45, 1059-1067. @ Perceptual and Motor Skills 1977
EFFECTS OF AGE, SEX, AND BRIGHTNESS OF FIELD O N OPEN-FIELD BEHAVIORS OF RATS1 DEBORAH LEVY SELIGER
Rutgers-The
State University, Camden, New Jersey
Summary.--48 male and 48 female Holtzman rats, ages 50, 100, and 150 days, were tested in s black or white open field to determine the effect of varying brightness of the field upon ambulation and defecation scores. There were significant negative correlations between all ambulation and defecation scores, except for the 50-day-old animals. Ambulation scores decreased over trials for all animals; defecation scores remained the same. Trials did not interact with age, sex, or brightness on either measure. In both fields females crossed more squares than males at ages 100 and 150 days, but there were no sex differences in ambulation at age 50 days. Most notable was a sex difference as a function of brightness of field; whereas male scores did not differ, females ambulated significantly more and tended to defecate less in the white field. Results are described in terms of the need for standardization of the open field.
Since Calvin Hall introduced the open field in 1934, it has become one of the most widely used tests in animal psychology. Primarily because it is simple to construct, easy to use, and applicable to a wide variety of experimental manipulations, there has developed an enormous body of published reports involving the test. However, the open-field literature abounds with contradictions and failures of replication; similar treatments often report increased behaviors, decreased behaviors, or no change at all. As Denenberg ( 1969) and Walsh and Cummins ( 1976) point out in their critical reviews, much of the problem is due to lack of standardization of the apparatus. Research results are reported from investigations of open fields of varying shapes, sizes, colors, etc., and generalizations are then freely made in attempts to explain basic constructs. The most frequently reported constructs in open-field studies are those of emotionality or fearfulness, defined most typically as number of boli excreted in the field in a given period of time, and ambulation or activity, defined most typically as number of squares crossed in the field in a given period of time. Some frequently reported results are: ambulation and defecation are negatively correlated (Hall, 1936; Walsh & Cummins, 1976) ; females ambulate more than males (Furchtgott, Wechkin, & Dees, 1961; Archer, 1975) ; males defecate more than females (Broadhurst, 1958; Archer, 1975) ; ambulation decreases with age (Broadhurst, 1958; Furchtgott, et dl., 1961; Valle, 1971); ambulation decreases over trials (Whimby & Denenberg, 1967; Denenberg, 1969; Archer, 'Send requests for reprints to Dr. Deborah Levy Seliger, Department of Psychology, Rutgers-The State University, Camden, New Jersey 08102.
1060
D. L. SELIGER
1973) ; defecation decreases over trials (Broadhurst, 1969; Walsh & Cummins, 1976). These results are not reported consistently, and for each of the above findings, there are enough contradictory reports to warrant reexamination using standardized equipment and procedures. As Walsh and Cummins ( 1976) point out, among the many characteristics of the apparatus yet to be standardized is the brightness or color of the field; some investigators have used a black field with white lines while others have used a white field with black lines. While results from studies using different fields have often been in disagreement, the effect of varying the brightness of the field while holding other variables constant has not yet been reported. The purpose of the present experiment was to elaborate further the factors affecting open-field behaviors. An attempt was made to determine the effects of varying brightness of the open field on the ambulation and defecation behaviors of rats of different sexes and ages.
METHOD Subjects The subjects were 48 male and 48 female Holtzman rats, purchased from West Jersey Biological Supply, Inc., Wenonah, N. J. Upon arrival from the supplier, one-third of the animals were 45-days-old, one-third 95-days-old, and one-third 145-days-old. All subjects were housed individually in standard Wahmann laboratory cages, and had ad lib. access to food and water. Laboratory temperature was maintained at approximately 72" F. Appdrdtas The test apparatus consisted of a wood field, 48 in. square, with walls 12 in. high. The floor of the field was divided by thin stripes 12 in. apart, yielding 16 1-ft. squares. The floors and walls of the field were reversible, with one side painted flat black with white stripes on the floor, and the other side painted flat white with black stripes on the floor. A mesh screen, hinged to the field, was available to place on top of the field during testing, if this became necessary. Illumination was from two 40-w clear white fluorescent bulbs suspended 78 in. above the floor of the field. These were covered by a rectangular translucent plastic shield, 46 X 22 in., providing steady, diffuse illumination over the entire field. Pro cedare Upon arrival at the laboratory, the subjects were randomly placed into two brightness-of-field groups, the groups being equated for sex and age. The animals were allowed five days to adapt to the laboratory. At 50, 100, or 150 days of age, each subject was transferred, in the home cage, to the field and was placed in a square in the corner of the field. All subjects were placed in the same square, facing the same direction. The number of squares entered, with
FACTORS IN OPEN-FIELD BEHAVIOR
loGl
entrance defined as placing both forepaws in a square, and the number of boli deposited by each animal during a 2-min. trial were recorded. Each subject received one trial a day for five consecutive days. The field was washed after each trial. For each sex and age, one-half of the animals were tested in the black field, and the other half in the white field. After the first test trial only, each subject was weighed before being returned to the home cage.
RESULTS In order to determine the over-all relationship between ambulation and defecation, total squares crossed and total boli excreted over the five test trials for all subjects were correlated. The significant negative Pearson correlation of .001) indicated that animals which were highly arnbula-0.40 (df = 94, p tory defecated less than animals with lower ambulation. Total squares and total boli were correlated as a function of age, sex, brightness of field, and trials. These results are presented in Table 1, which shows that all correlations between squares and boli were negative and significant for all levels of all factors, except for the
EFFECTS OF AGE, SEX, AND BRIGHTNESS OF FIELD O N OPEN-FIELD BEHAVIORS OF RATS1 DEBORAH LEVY SELIGER
Rutgers-The
State University, Camden, New Jersey
Summary.--48 male and 48 female Holtzman rats, ages 50, 100, and 150 days, were tested in s black or white open field to determine the effect of varying brightness of the field upon ambulation and defecation scores. There were significant negative correlations between all ambulation and defecation scores, except for the 50-day-old animals. Ambulation scores decreased over trials for all animals; defecation scores remained the same. Trials did not interact with age, sex, or brightness on either measure. In both fields females crossed more squares than males at ages 100 and 150 days, but there were no sex differences in ambulation at age 50 days. Most notable was a sex difference as a function of brightness of field; whereas male scores did not differ, females ambulated significantly more and tended to defecate less in the white field. Results are described in terms of the need for standardization of the open field.
Since Calvin Hall introduced the open field in 1934, it has become one of the most widely used tests in animal psychology. Primarily because it is simple to construct, easy to use, and applicable to a wide variety of experimental manipulations, there has developed an enormous body of published reports involving the test. However, the open-field literature abounds with contradictions and failures of replication; similar treatments often report increased behaviors, decreased behaviors, or no change at all. As Denenberg ( 1969) and Walsh and Cummins ( 1976) point out in their critical reviews, much of the problem is due to lack of standardization of the apparatus. Research results are reported from investigations of open fields of varying shapes, sizes, colors, etc., and generalizations are then freely made in attempts to explain basic constructs. The most frequently reported constructs in open-field studies are those of emotionality or fearfulness, defined most typically as number of boli excreted in the field in a given period of time, and ambulation or activity, defined most typically as number of squares crossed in the field in a given period of time. Some frequently reported results are: ambulation and defecation are negatively correlated (Hall, 1936; Walsh & Cummins, 1976) ; females ambulate more than males (Furchtgott, Wechkin, & Dees, 1961; Archer, 1975) ; males defecate more than females (Broadhurst, 1958; Archer, 1975) ; ambulation decreases with age (Broadhurst, 1958; Furchtgott, et dl., 1961; Valle, 1971); ambulation decreases over trials (Whimby & Denenberg, 1967; Denenberg, 1969; Archer, 'Send requests for reprints to Dr. Deborah Levy Seliger, Department of Psychology, Rutgers-The State University, Camden, New Jersey 08102.
1060
D. L. SELIGER
1973) ; defecation decreases over trials (Broadhurst, 1969; Walsh & Cummins, 1976). These results are not reported consistently, and for each of the above findings, there are enough contradictory reports to warrant reexamination using standardized equipment and procedures. As Walsh and Cummins ( 1976) point out, among the many characteristics of the apparatus yet to be standardized is the brightness or color of the field; some investigators have used a black field with white lines while others have used a white field with black lines. While results from studies using different fields have often been in disagreement, the effect of varying the brightness of the field while holding other variables constant has not yet been reported. The purpose of the present experiment was to elaborate further the factors affecting open-field behaviors. An attempt was made to determine the effects of varying brightness of the open field on the ambulation and defecation behaviors of rats of different sexes and ages.
METHOD Subjects The subjects were 48 male and 48 female Holtzman rats, purchased from West Jersey Biological Supply, Inc., Wenonah, N. J. Upon arrival from the supplier, one-third of the animals were 45-days-old, one-third 95-days-old, and one-third 145-days-old. All subjects were housed individually in standard Wahmann laboratory cages, and had ad lib. access to food and water. Laboratory temperature was maintained at approximately 72" F. Appdrdtas The test apparatus consisted of a wood field, 48 in. square, with walls 12 in. high. The floor of the field was divided by thin stripes 12 in. apart, yielding 16 1-ft. squares. The floors and walls of the field were reversible, with one side painted flat black with white stripes on the floor, and the other side painted flat white with black stripes on the floor. A mesh screen, hinged to the field, was available to place on top of the field during testing, if this became necessary. Illumination was from two 40-w clear white fluorescent bulbs suspended 78 in. above the floor of the field. These were covered by a rectangular translucent plastic shield, 46 X 22 in., providing steady, diffuse illumination over the entire field. Pro cedare Upon arrival at the laboratory, the subjects were randomly placed into two brightness-of-field groups, the groups being equated for sex and age. The animals were allowed five days to adapt to the laboratory. At 50, 100, or 150 days of age, each subject was transferred, in the home cage, to the field and was placed in a square in the corner of the field. All subjects were placed in the same square, facing the same direction. The number of squares entered, with
FACTORS IN OPEN-FIELD BEHAVIOR
loGl
entrance defined as placing both forepaws in a square, and the number of boli deposited by each animal during a 2-min. trial were recorded. Each subject received one trial a day for five consecutive days. The field was washed after each trial. For each sex and age, one-half of the animals were tested in the black field, and the other half in the white field. After the first test trial only, each subject was weighed before being returned to the home cage.
RESULTS In order to determine the over-all relationship between ambulation and defecation, total squares crossed and total boli excreted over the five test trials for all subjects were correlated. The significant negative Pearson correlation of .001) indicated that animals which were highly arnbula-0.40 (df = 94, p tory defecated less than animals with lower ambulation. Total squares and total boli were correlated as a function of age, sex, brightness of field, and trials. These results are presented in Table 1, which shows that all correlations between squares and boli were negative and significant for all levels of all factors, except for the
