RANGE EFFECTS IN TRANSIENT AND MAINTAINED GENERALIZATION GRADIENTS

In three experiments pigeons were trained to discriminate visual flick er rate stimuli. The stimulus set was varied so that the effects of ov erall stimulus range and border separation between positive and negati ve stimuli could be assessed. Experiments 1 and 2 showed that transien t generalization gradients were lower in height and flatter with incre ases in either border separation or overall stimulus range. Border sep aration and overall range interacted in that the effect of range was g reatest with relatively greater border stimulus separation. Experiment 3 showed that increased overall stimulus range reduced the magnitude of positive dimensional contrast in maintained gradients. Flattening o f the maintained gradient with increases in stimulus range was similar to flattening of post-discrimination gradients found in Experiments 1 and 2. The results from all experiments indicate that increases in ov erall stimulus range do not decrease discriminability of unchanged sti mulus values. Instead, increases in stimulus range may increase the va riability of response or criterial factors in discrimination.