Self-control in male and female rats

Eight male and 8 female Wistar rats were exposed to a discrete-trial procedure in which they chose between the presentation of a small (one pellet) or a large (three pellets) reinforcer. The delay to the small and large reinforcer was 6.0 s in the first condition of Experiment 1. Subjects consistently chose the large reinforcer. When the delay to the small reinforcer was decreased to 0.1 s in the next experimental condition, all subjects continued to choose the large 6.0-s delayed reinforcer. When the contingencies correlated with the two levers were reversed in the next experimental condition, the majority of subjects (5 males and 6 females) still chose the large delayed reinforcer over the small immediately presented reinforcer. The delay to the small reinforcer was maintained at 6.0 s, but the delay to the large reinforcer was varied among 9.0, 15.0, 24.0, and 36.0 s in Experiment 2, in which 4 males and 4 females participated. Most subjects consistently chose the large increasingly delayed reinforcer, although choice for the small 6.0-s delayed reinforcer developed in some females when the large reinforcer was delayed for 24.0 or 36.0 s. These choice patterns were not predicted from a literal application of a model that says choice should favor the alternative correlated with the higher (amount/delay) ratio.     

The effects of component duration on multiple-schedule performance in closed and open economies.

Pigeons responded on multiple variable-interval variable-interval schedules of reinforcement in an open and a closed economy. Equal duration components were increased in duration while the component rates of reinforcement were held constant, the component schedules were reversed, and component duration was decreased. In the open economy, daily sessions were limited to 1 hr, and subjects were maintained at 80% of their free-feeding weights through supplemental feeding when necessary in their home cages. In the closed economy, subjects were housed in their experimental chambers and no deprivation regimen was enforced. Relative response rate decreased as components were lengthened in the open economy, whereas in the closed economy relative rate increased as components were lengthened. Response proportions overmatched reinforcer proportions to a greater extent at long component durations in the closed economy, but there was no systematic effect of component duration on responding in the open economy.     

Effect of mouth opening on bite-force discrimination

The purpose of this study was to determine whether different extents of mouth opening affect normal subjects' (N = 24; 12 women, 12 men) ability to discriminate differences in their interincisor bite force. Three mouth openings were selected including 50, 70, and 90 percent of maximum opening for each subject. Bite force was measured using a specially designed strain gauge scale which permitted subjects to monitor visually when their biting force equalled a preset resistance. Resistance forces of 500 and 1000 gm. were selected as standards. The procedure involved the use of a modified method of constant stimuli in which each subject was presented with a series of paired resistance settings, one at a time--the first resistance setting being the standard and the second resistance was the comparator. This paired-comparisons procedure was continued until the subjects' difference limen (DL) value (the threshold of discrimination between two forces) could be established. An analysis of variance yielded no significant differences in subjects' ability to discriminate bite force as a function of mouth opening.     

Imagery limitations in totally congenitally blind subjects

Research on totally blind subjects performing tasks that involve visual imagery has often shown that they do not behave differently from matched sighted subjects, even when their blindness is congenital. If visual imagery is based on visual perception, such tasks may not required visual imagery. In the present article visual images are considered as representations maintaining some properties of visible objects and constructed on the basis of information from various sources. Owing to the absence of visual experience, the limitations of such representations are explored in a series of experiments requiring memorization of single nouns, pairs of nouns, or triplets of nouns associated with a cue noun. Recall by blind subjects was impaired when multiple interactive images (with noun pairs and triplets) are formed. The poorer recall of blind subjects reflected also loss of order information. Recall was better for both groups with locative noun cues and high-imagery targets.     

Mecamylamine prevents the enhancement of retention induced by lysine vasopressin in mice

Lysine vasopressin (0.03 microgram/kg, sc) enhanced retention of a one-trial, step-through inhibitory avoidance task when injected into male Swiss mice immediately post-training, as indicated by retention performance 48 h later. A low dose of the vasopressin antagonist, AAVP (0.01 microgram/kg, sc), did not significantly affect retention, whereas a higher dose (0.03 microgram/kg, sc) impaired retention. Neither lysine vasopressin nor AAVP modified latencies to step-through of mice that had not received a footshock during training. The simultaneous injection of AAVP (0.01 microgram/kg, sc) prevented the enhancement of retention induced by lysine vasopressin. The influence of lysine vasopressin on retention was antagonized by the simultaneous administration of mecamylamine (5 mg/kg, sc) but not by hexamethonium (5 mg/kg, sc), atropine (0.5 mg/kg, sc), or methylatropine (0.5 mg/kg, sc). A modulatory role of vasopressin on the activity of central cholinergic nicotinic mechanisms which participate in memory formation is suggested.