Fractal coordination in adults' attention to hierarchical visual patterns.

A display that contains hierarchically nested levels of order requires the perceiver to selectively attend to one of the levels. We investigate the degree to which such selective attention is sustained by a soft-assembled emergent coordinative process, one that does not require designated executive control. In the case of emergent soft-assembly, performance from one trial to the next should show characteristic interdependence, visible in the fractal structure of reaction time. To test this hypothesis, we asked participants across three experiments to decide whether two displays matched in a certain way (e.g., in a local element). In order to gauge this coordinative process, task constraints were experimentally manipulated (e.g., familiarity, predictability, and task instruction). Obtained reaction-time data were subjected to a spectral analysis to measure the degree of interdependence among trials. As predicted, results show correlated structure across trials, significantly different from what would be predicted by an independent-process view of selective attention. Results also show that the obtained spectral scaling exponents track the degree of coupling in the task as a function of the degree of task constraints. Findings are discussed in terms of the relative organism-environment coupling to sustain an adaptive behavior.