David A. Strobel

Protein preference in protein-malnourished monkeys

10 protein-malnourished monkeys and 8 dietary controls were run in a preference experiment designed to look at the differences in the way the 2 groups accepted foods containing various amounts of protein. Each monkey was given choices among diets containing 2%, 3.5%, or 25% protein, and non-food objects. The protein-malnourished monkeys showed a marked preference for the high-protein food; the adequately nourished monkeys chose all foods at the same ratio. The results indicated that a rapid learning process was involved in the formation of a preference for high-protein foods. The colors of the 2% and the 25% diets were then reversed, and the protein-malnourished monkeys showed a temporary disruption in their preference behavior, but they soon established a stable preference for the high-protein food. The experimental results are consistent with the hypothesis that protein-malnourished rhesus monkeys have a specific hunger for protein.

Manipulatory responsiveness in protein-malnourished monkeys

Two groups of rhesus monkeys were placed on diets containing either 3% or 25% protein at 210 days of age and tested consecutively on two puzzle manipulation tasks varying in difficulty. Malnourished Ss were able to learn to solve the puzzles in the absence of food rewards but showed significantly lower final performance levels on the easier puzzles than did controls. The more complex puzzles were learned with equal difficulty by the high- and low-protein groups. Manipulatory responsiveness in this study was interpreted to be partially influenced by secondary diseases associated with protein-calorie malnutrition.

Cue-locus—A factor in the behavioral deficiency of the developing protein-malnourished monkey (Macaca mulatta)

Four groups of infant rhesus monkeys were separated from their mothers at 90 days of age, housed individually, and placed on purified diets which contained either 25 or 3.5% protein at 120 or 210 days of age. At approximately 1,375 days of age, brightness discrimination problems were presented in which the locus of the cues was either central or peripheral and the area of the different cues was varied. No significant differences were found for diet, cue area, or diet × area interaction for peripherally located cues on original learning, shift 1, or reversal conditions. A significant decline in performance levels was detected for all groups as the area of the cues decreased in the central locus condition. Subjects maintained on diets deficient in protein, which were reversed to central cues, exhibited a marked decrement in performance when compared to the high protein controls. Further, malnourished subjects were considerably inferior to high protein animals on the smallest cue areas in shift 1 and shift 2 leading to a significant diet × cue area interaction. Under reversal conditions for centrally located cues, low protein subjects were found to perform at significantly lower levels than the high protein controls. These results are consistent with both a visual sampling model of attention and a number of two-stage models of attention.

Behavioral Deficiencies in Protein-Deprived Monkeys

It is a well documented fact that large numbers of people in the world, predominantly children in underdeveloped countries, suffer from protein-calorie malnutrition (Behar, L968; Coursin, 1965). Some of the major investigations conducted with human beings suggest that malnutrition experienced early in life may produce a permanent alteration of the phenotypic expression of the normal intellectual and social development of the child (Cravioto and Robles, 1963, 1965; Stoch and Smythe, 1963). Studies concerning severe protein-calorie malnutrition reveal profound behavioral deficiencies in children who suffer such a nutritional deficit before they are six months of age (Brockman and Ricciuti, 1971; Pollitt, 1972). Cravioto and Robles (1965) have reported deficiencies in adaptive behavior, interpersonal social abilities, language acquisition, and motor skills. It is apparent, then, that children with a history of protein-calorie malnutrition exhibit deficits in a variety of developmental tasks when compared to adequately nourished children.

Visual discrimination in the protein-malnourished rhesus ☆

Abstract Chronically protein-deprived rhesus monkeys and their normal controls were exposed to three successive visual discrimination problems which were designed to investigate the role of attentional processes and the separation of stimulus and response loci in the mastery of such discriminations. The pattern of results was inconsistent with attentional or motivational explanations and seemed to point, rather, to a deficit in the basic learning processes underlying visual discrimination.

Blocking Effects in Two-Choice Discrimination Tasks in Rhesus Monkeys Macaca Mulatta

The present experiments investigated blocking effects in rhesus monkeys (Macaca mulatta) in a discrimination learning paradigm using a single stimulus modality. Two experimental chambers were used. In one the monkeys were required to operate a joystick in order to manipulate a Pacman figure to consume one of two stimuli (S+ and S-) appearing on a video screen. In the other the monkeys were required to press Plexiglas panels mounted in front of the screens to indicate their choice of the stimuli. Correct responses resulted in the delivery of marshmallows. Results indicated (a) consistent occurrence of blocking, (b) no unblocking due to increased magnitude of reward, and (c) no differences due to task requirements in the two different chambers. These studies extend our knowledge of blocking effects to monkeys and provide novel procedures for using monkeys in basic learning research.

Malnutrition and social isolation: Learning in the developing rhesus monkey

Abstract Early diet and environment were manipulated in a factorial experiment in which the mastery of a spatial delayed alternation task was investigated. Protein-calorie malnutrition resulted in a retarded rate of acquisition while partial social isolation appeared to enhance performance relative to socially reared groups. No interaction was found between treatments.

Reactions to intrinsic and extrinsic rewards in protein-malnourished monkeys.

10 rhesus monkeys were tested on a 12-part puzzle manipulation apparatus. 6 of 10 Ss were maintained on a protein-deficient diet containing 3.5% casein by weight, while the remaining 4 Ss received a high-protein diet containing 25% casein by weight. The high-protein animals had an elevated manipulation rate as compared with low-protein fed Ss when the only source of reinforcement was the manipulation of the puzzles (intrinsic reward). However, when food (extrinsic reward) was introduced the low-protein fed Ss manipulated at a level equal to or greater than the high-protein fed animals. Introduction of 100% and partial reinforcement conditions showed manipulation rates to be relatively consistent between the two groups. Extinction conditions, however, showed a significant difference between the high- and low-protein fed animals after partial reinforcement. With the removal of the food reward the low-protein fed animals exhibited a much more rapid reduction of manipulatory activity than the high-protein fed Ss. The more rapid extinction of the manipulation response by low-protein fed monkeys suggests that extrinsic reward is a much more salient variable for these Ss than intrinsic reward.

Dominance measurements of low and high protein reared rhesus macaques

Dominance behavior of rhesus macaques on either low or high protein diets was measured by: (a) dominant/aggressive interactions and (b) food competition. The results demonstrated that high protein raised rhesus scored significantly higher on dominant/aggressive interactions when compared to low protein raised rhesus. However, when food was introduced as an incentive for competition, the high protein reared rhesus did not outcompete the low protein reared rhesus in two age groups and for the third age group the low protein rhesus macaques significantly outcompeted the high protein animals. The differences of the value of food incentive between the low and high protein rhesus was suggested as the factor influencing the change in behavior of the low protein animals in a social situation.

DEVICE FOR STUDY OF COMMUNICATION OF DOMINANCE WITHOUT PHYSICAL CONTACT

Dominance competition between paired rhesus monkeys (ns = 4) was compared using a standard apparatus, the Wisconsin General Test Apparatus, and a new device called the Parallel Competition Box. The Parallel Competition Box does not allow physical contact between individual Ss during testing as does the Wisconsin General Test Apparatus. Results comparing the Parallel Competition Box and the Wisconsin General Test Apparatus on food incentive competition indicate that physical contact is not necessary for assertion and maintenance of dominance between socialized rhesus monkeys.