Reinforcing effects of illumination change in different phases of the rat's diurnal cycle

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48 albino rats, maintained on an equalized 24-hr. light-drak cycle, pressed a “positive” bar, which altered illumination of the test box, more often than they pressed a “neutral” bar which had no effect. Both bars were pressed at a higher rate by Ss tested during the dark rather than light part of the diurnal cycle. Ss tested for light onset, in a dark box, did not differ in positive-bar preference from Ss tested for light offset, in a lighted box. However, during successive test sessions positive-bar preference decreased for the light-onset groups and increased for the light-offset groups. It is concluded that bar pressing was reinforced by illumination change, regardless of level of bar pressing activity or direction of illumination change. (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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