Latane, Williams, and Harkins (1979) showed that a coactor's presence causes reduced individual effort (social loafing). Previously, it had been shown that coactor presence has a facilitating effect when the task is simple. This paradox can be resolved within the framework of Cottrell's version of the drive theory of social facilitation (Williams, Harkis, and Latane, 1980). The present study tested this notion by using a button-pushing task, varying coactor presence (vs. absence) and actor identiliability, The data obtained from 78 undergraduate students indicated: (a) Coactor's mere presence enhanced the emission of simple response (facilitation effect)
(b) when the coactor's presence reduced actor identifiability, it cancelled out the facilitation effect (loafing effect)
and (c) drive level, as measured by response latency, did not covary with response rate. These results suggest that loafing and facilitation effects of coactor's presence cancel one another when coactor presence reduces actor identifiability. The interpretation of the phenomena in terms of Cottrell's version was not supported. © 1985, The Japanese Psychological Association. All rights reserved.