Sources of flexibility in human cognition: Dual-task studies of space and language

Under many circumstances, children and adult rats reorient themselves throu gh a process which operates only on information about the shape of the envi ronment (e.g., Cheng, 1986; Hermer & Spelke, 1996). In contrast, human adul ts relocate themselves more flexibly, by conjoining geometric and nongeomet ric information to specify their position (Hermer & Spelke, 1994). The pres ent experiments used a dual-task method to investigate the processes that u nderlie the flexible conjunction of information. In Experiment 1, subjects reoriented themselves flexibly when they performed no secondary task, but t hey reoriented themselves like children and adult rats when they engaged in verbal shadowing of continuous speech. In Experiment 2, subjects who engag ed in nonverbal shadowing of a continuous rhythm reoriented like nonshadowi ng subjects, suggesting that the interference effect in Experiment 1 did no t stem from general limits on working memory or attention but from processe s more specific to language. In further experiments, verbally shadowing sub jects detected and remembered both nongeometric information (Experiment 3) and geometric information (Experiments 1, 2, and 4), but they failed to con join the two types of information to specify the positions of objects (Expe riment 4). Together, the experiments suggest that humans' flexible spatial memory depends on the ability to combine diverse information sources rapidl y into unitary representations and that this ability, in turn, depends on n atural language. (C) 1999 Academic Press.