In a two-key autoshaping procedure with pigeons, sessions consisted of 60 trials in which the simultaneous presentation of a red key and a green key was followed by operation of the feeder. In some sessions the feeder light was red; in others it was green. On the first session of exposure to this procedure, pigeons' autoshaped pecks occurred first and predominantly on the key whose color matched the feeder color, and this preference was resistant to change when, for each pigeon, the other feeder color was used in a second session. With other pigeons, the first autoshaping session with a given feeder color was preceded by a session of feeder presentations alone (no keys) with the other feeder color. For these pigeons, key-color preferences were inconsistent. A formal model is used to assess the contributions of generalization and overshadowing to these data.
Three groups of boys referred to a hospital study unit for evaluation of hyperactive behavior were tested on a classification task involving selective attention while on either dextroamphetamine (D) or placebo (P). In two sessions, groups had D first, P second (DP), or PD, or PP. Amphetamine reduces a response times in general and reduces interference due to orthogonally varying irrelevant information. Practice while on placebo improves performance in a subsequent placebo session. Practice while on amphetamine does not, however, improve performance in the subsequent session on placebo. Assessment of the extent of the drug-state-related practice effect is necessary for evaluation of long-term benefits of dextroamphetamine therapy in these children.
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