Absolute and relative sensitivity of the scotopic system of rat: Electroretinography and behavior

The goal of the present study was to relate the dark and light-adapted flash sensitivity of the scotopic threshold response (STR) and rod b-wave of the electroretinogram (ERG) to behaviorally measured rod increment threshold responses. Small amplitudes of the dark-adapted STR and b-wave, the latter after application of NMDA, were found to increase in proportion to flash intensity. The value obtained for the sensitivity of the b-wave would be expected if signals from rods were summed linearly by the rod bipolar cell. The sensitivity of the STR could not be accounted for in terms of rod signal convergence as the source of this ERG component is still unknown. Increment threshold responses of rats were measured behaviorally in an operant conditioning chamber. At absolute threshold, on average 1 in 2400 rods were activated by the test flash. Comparison of the adaptive effects of background lights on behaviorally measured scotopic sensitivity and rod ERG sensitivity suggest that the increment threshold sensitivity of rat is regulated at three different sites in the retina.

Positive Incentive Contrast as a Function of Age and Length of Training in Rats

Exp. I demonstrated that positive incentive contrast effects in an operant conditioning chamber produced by an increase in the concentration of a saccharine solution in 30 180-day-old rats (older animals) are not found in 30 25-day-old rats (younger rats). Exp. II indicated that the probability of obtaining positive contrast with 60 male albino rats is a positive function of the length of the preshift period.

Response Patterning in the Operant-Conditioning Situation with Twenty-Four-Hour Intertrial Interval

16 female, albino rats served as Ss in an investigation of performance on single and double-alternation sequences of reward-nonreward. Ss were run in an operant conditioning chamber with a 24-hr. intenrial interval. The results indicated that Ss receiving the single-alternation reward-nonreward sequence learned to respond appropriately, i.e., fast on reward days, slow on nonreward days, while Ss run under the double-alternation sequence did not exhibit appropriate responding. The results are seen as being supportive of Capaldi's sequential hypothesis.