Time allocation in a concurrent schedule of social interaction and monetary reinforcement: effects of d-amphetamine

Two mutually exclusive options (socializing versus monetary reinforcement) were concurrently available to two normal volunteers during 60-min experimental sessions under controlled laboratory conditions. The amount of money available in the monetary option was adjusted for individual subjects during baseline conditions until subjects divided their time approximately evenly between a social option in which they could converse with another same-sex volunteer or a monetary option in which money was earned for sitting quietly in a private room. In both subjects studied, d-amphetamine (5-25 mg) increased the percent of time allocated to the social option and total seconds of speech. This effect occurred even though increases in the time allocated to the social option necessarily resulted in a forfeiture of monetary reinforcement. The present results provide the first empirical evidence, to our knowledge, that d-amphetamine can increase the relative reinforcing effects of social interaction.