However, none of the monkeys had been trained in any operant tasks previously, and none
had used touchscreens before. In a compartment of the monkeys’ home cages, a touchscreen monitor (Elo TouchSystems, Menlo Park, CA) was mounted at eye level with a stainless steel juice delivery tube positioned so the monkey could comfortably reach the screen and drink at the same time. Pairs of stimuli were presented simultaneously, one on the left and one on the right side of the monitor. Each stimulus value was randomly chosen from KPT-330 order a set of values from 0 to a maximum that could go as high as 25; the two stimuli were never the same value. Dots varied randomly in color, size, and position, and were constrained
so that whenever two dots in an array overlapped, the smaller dot was drawn in front and differed in color from the other dot. For each dot pair presentation, the dot patterns were freshly generated with a random number generator off-screen BMS-907351 cell line before presentation and presented instantaneously on the screen. Animals chose one of the two stimuli by touching it. Monkeys were rewarded with the same number of drops as the assigned value of the chosen stimulus. Solenoid openings were longer (200–300 ms) early in training, when both options were small, but as the average reward value increased solenoid openings were reduced to 25 ms, resulting in one drop per opening. Drops were delivered at 4 Hz, and each drop was accompanied by a beep sound. Each stimulus pair was presented for 10 s or until the animal responded by touching either stimulus. A new stimulus was presented 3 s after the end of the preceding trial. Monkeys were allowed to work alone to satiety for at least 3 hr per day, and they usually stopped working after 2 hr, or 300–600
trials. The monkeys’ average daily fluid intake was always more than 30 ml/kg. They had ad lib food. Reaction time histograms for each monkey individually or for the adults or juveniles as a population were fit by least-squares with a log Gaussian: Rolziracetam y=A∗e0.5∗2(ln(x/c)/σ),y=A∗e0.5∗(ln(x/c)/σ)2,where A is the amplitude of the Gaussian, c is the center, and σ is the width; we took c, the center of the log Gaussian as the reaction time for each distribution. To find out how long it took each monkey to learn novel symbols, we calculated the behavioral value of each novel symbol, as each symbol was introduced. To do this, we extracted from the entire data set all trials in which the novel symbol was one of the options and took bins of 10 trials (per monkey), and for each bin we calculated the fraction of larger (novel symbol) choices as a function of the value of the other choice. For each bin, we took the behavioral value of the novel symbol as the point of subjective equality as a function of the other choice values from the best fitting sigmoid (cumulative normal distribution) for those points.
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