Cognitive Load Can Explain Differences in Active and Passive Touch

Abstract

Active touch is often described as yielding better-quality information than passive touch. However, some authors have argued that passive-guided movements generate superior percepts due to a reduction in demands on the haptic sensory system. We consider the possibility that passive-guided conditions, as used in most active-passive comparisons, are relatively free from cognitive decision-making, while active conditions involve cognitive loads that are quite high and uncharacteristic of normal sensory processes. Thus studies that purport to show differences in active and passive touch may instead be revealing differences in the amount of cognition involved in active and passive tasks. We hypothesized that passive-guided conditions reduce not the sensory load but the cognitive load that active explorers must bear. To test this hypothesis Blood Oxygen Level Dependent (BOLD) activity was measured using functional Magnetic Resonance Imaging (fMRI) during active and passive-guided fingertip exploration of 2D raised line drawings. Active movements resulted in greater activation (compared with passive movements) in areas implicated in higher order processes such as monitoring and controlling of goal-directed behavior, attention, execution of movements, and error detection. Passive movements, in contrast, produced greater BOLD activity in areas associated with touch perception, length discrimination, tactile object recognition, and efference copy. The activation of a greater number of higher-order processing areas during active relative to passive-guided exploration suggests that instances of passive-guided superiority may not be due to the haptic system's limited ability to cope with sensory inputs, but rather the restriction imposed by the use of a single finger such that active exploration may require cognitive strategies not demanded in the passive condition. Our findings suggest that previous attempts to compare active and passive touch have, in order to simplify tasks, inadvertently introduced cognitive load at the expense of normal sensory inputs.