Dual-task interference in action programming and action planning - Evidence from the end-state comfort effect.

In the present study, we examined the extent of interference between a cognitive task (auditory n-back task) and different aspects of motor performance. Specifically, we wanted to find out whether such interference is more pronounced for aspects of planning as compared to programming. Here, motor planning is represented by a phenomenon called the "end-state comfort effect", the fact that we tolerate uncomfortable initial postures in favour of a more comfortable final posture. We asked participants to grasp differently sized cylindrical objects and to place them on target platforms of varying height (grasp-and-place task), So, participants were required to (1) adjust their hand opening to the object width (action programming) and (2) to plan whether to grasp the object higher or lower in order to be able to place it comfortably onto the low or high target platform. We found that participants demonstrated the end-state comfort effect by anticipating the final posture und planning the movement accordingly with a higher object-grasp for low end-target position and lower object-grasp height for high end-target position, respectively. The auditory task was negatively affected by having to perform a visuomotor task in parallel, suggesting that the two tasks share cognitive and attentional resources. No significant impact from the auditory task on the motor tasks was found. Accordingly, it was not possible to determine which of the two motor aspects (programming or planning) contributed more towards the interference observed in the auditory task. To address this question, we carried out a second experiment. For this second experiment we focussed on the interference effects found in the auditory task and contrasted two versions of the grasp-and-place task. In the first version of the task, the height of the target-shelf varied from trial-to-trial but the width of the target object remained the same. We assumed that this version had high planning demands and low programming demands. In the second version the width of the target object varied and the target-shelf height remained constant. Presumably this increased programming demands but reduced planning demands. Significant interference with the auditory task was only found for the first version, supporting the hypothesis that motor planning requires more cognitive resources and thus creates higher multitasking costs.

Grasping and perception are both affected by irrelevant information and secondary tasks: new evidence from the Garner paradigm.

In their Perception-Action Model (PAM), Goodale and Milner (1992) proposed functionally independent and encapsulated processing of visual information for action and perception. In this context, they postulated that visual input for action is processed in an automatized and analytic manner, which renders visuomotor behaviour immune to perceptual interferences or multitasking costs due to sharing of cognitive resources. Here, we investigate the well-known Garner Interference effect under dual- and single-task conditions in its classic perceptual form as well as in grasping. Garner Interference arises when stimuli are classified along a relevant dimension (e.g., their length), while another irrelevant dimension (e.g., their width) has to be ignored. In the present study, participants were presented with differently sized rectangular objects and either grasped them or classified them as long or short via button presses. We found classical Garner Interference effects in perception as expressed in prolonged reaction times when variations occurred also in the irrelevant object dimension. While reaction times during grasping were not susceptible to Garner Interference, effects were observed in a number of measures that reflect grasping accuracy (i.e., poorer adjustment of grip aperture to object size, prolonged adjustment times, and increased variability of the maximum hand opening when irrelevant object dimensions were varied). In addition, multitasking costs occurred in both perception and action tasks. Thus, our findings challenge the assumption of automaticity in visuomotor behaviour as proposed by the PAM.

Grasping Discriminates between Object Sizes Less Not More Accurately than the Perceptual System.

Ganel, Freud, Chajut, and Algom (2012) demonstrated that maximum grip apertures (MGAs) differ significantly when grasping perceptually identical objects. From this finding they concluded that the visual size information used by the motor system is more accurate than the visual size information available to the perceptual system. A direct comparison between the accuracy in the perception and the action system is, however, problematic, given that accuracy in the perceptual task is measured using a dichotomous variable, while accuracy in the visuomotor task is determined using a continuous variable. We addressed this problem by dichotomizing the visuomotor measures. Using this approach, our results show that size discrimination in grasping is in fact inferior to perceptual discrimination therefore contradicting the original suggestion put forward by Ganel and colleagues.

The visual guidance of action is not insulated from cognitive interference: A multitasking study on obstacle-avoidance and bisection.

The Perception-Action Model (PAM) considers the visual system to be divided into two streams defined by their specific functions, a ventral stream for vision and a dorsal stream for action. In this study we investigated two behavioral paradigms which according to PAM represent the two contrasting functions of the ventral and dorsal stream, namely bisection and obstacle-avoidance, respectively. It is an assumption of PAM that while ventral stream processing is ultimately linked with processing in other cognitive systems, dorsal stream processing is insulated from cognition. Accordingly it can be expected that a secondary task will interfere with bisection but not with obstacle-avoidance. We tested this prediction using a rapid serial visual presentation task as our secondary task (RSVP). Contrary to expectations we found significant interference for both bisection and obstacle-avoidance. Our findings suggest that dorsal-stream processing is not insulated from cognitive processes.