Dual-target interference for the 'automatic pilot' in the dorsal stream

Performance-related stress mediates the online control and integration of sequential movements

The effects of stress on directing attention within performance have been broadly explained by self-focus and distraction perspectives, where stress causes attention to be drawn internally or toward the sources of worry, respectively. Recent studies that have adopted manual aiming under different levels of stress have illuminated our understanding of the stress-performance framework. The present study seeks to elaborate on this current trend by introducing a sequential task, where the integration of individual movement segments enhances the demands on preparation and control, and thus closely examines the explanatory power of the self-focus and distraction perspectives. This study involved executing aiming movements solely to one-target (1T), or continuing by extending (2TE) and reversing (2TR) the limb to a second target. Participants were instructed to simply execute rapid and accurate movements (low-stress), and additionally provided a socio-comparative stressor (high-stress). While there was no one- (1 T vs. 2TE) or two-target (1T vs. 2TR) advantage, there was a shorter movement time in the first segment of the one-target task that appeared to dissipate when under high-stress. In addition, the high-stress conditions caused shorter reaction and pause times, while the proportion of the sequence time decreased within the pause, but increased within the second segment. Consequently, the overall sequence time failed to differ between low- and high-stress. These findings indicate that the online control of movement is accommodated under high-stress. We suggest these procedures unfold following a primary focus to uphold the performance outcome. Thus, these findings appear to be consistent with the distraction perspective.

Attenuation of size illusion effect in dual-task conditions

We over-estimate or under-estimate the size of an object depending its background structure (e.g., the Ebbinghaus illusion). Since deciding and preparing to execute a movement is based on perception, motor performance deteriorates due to the faulty perception of information. Therefore, such cognitive process can be a source of a failure in motor performance, although we feel in control of our performance through conscious cognitive activities. If a movement execution process can avoid distraction by the illusion-deceived conscious process, the effect of the visual illusion on visuomotor performance can be eliminated or attenuated. This study investigated this hypothesis by examining two task performances developed for a target figure inducing the Ebbinghaus size illusion: showing visually perceived size of an object by index finger-thumb aperture (size-matching), and reaching out for the object and pretending to grasp it (pantomimed grasping). In these task performances, the size of the index finger-thumb aperture becomes larger or smaller than the actual size, in accordance with the illusion effect. This study examined whether the size illusion effect can be weakened or eliminated by the dual-task condition where actors' attention to judge the object's size and to produce the aperture size is interrupted. 16 participants performed the size-matching and pantomimed grasping tasks while simultaneously executing a choice reaction task (dual task) or without doing so (single task). Using an optical motion capture system, the size-illusion effect was analyzed in terms of the aperture size, which indicates the visually perceived object size. The illusion effect was attenuated in the dual task condition, compared to it in the single task condition. This suggests that the dual task condition modulated attention focus on the aperture movement and therefore the aperture movement was achieved with less distraction caused by illusory information.

Visual Selection of the Future Reach Path in Obstacle Avoidance

In two EEG experiments, we studied the role of visual attention during the preparation of manual movements around an obstacle. Participants performed rapid hand movements to a goal position avoiding a central obstacle either on the left or right side, depending on the pitch of the acoustical go signal. We used a dot probe paradigm to analyze the deployment of spatial attention in the visual field during the motor preparation. Briefly after the go signal but still before the hand movement actually started, a visual transient was flashed either on the planned pathway of the hand (congruent trials) or on the opposite, movement-irrelevant side (incongruent trials). The P1/N1 components that were evoked by the onset of the dot probe were enhanced in congruent trials where the visual transient was presented on the planned path of the hand. The results indicate that, during movement preparation, attention is allocated selectively to the planned trajectory the hand is going to take around the obstacle.

Attention in action and perception: Unitary or separate mechanisms of selectivity?

What is the relation between the two visual stream hypothesis and selective visual attention? In this chapter, we first consider this question at a theoretical level before presenting an example of work from our lab that examines the question: Under what conditions does the emotional content of a visual object influence visually guided action? Previous research has demonstrated that fear can influence perception, both consciously and unconsciously, but it is unclear when fear influences visually guided action. The study tested participants with varying degrees of spiderphobia on two visually guided pointing tasks, while manipulating the emotional valence of the target (positive and negative) and the cognitive load of the participant (single vs dual task). Participants rapidly moved their finger from a home position to a suddenly appearing target image on a touch screen. The images were emotionally negative (e.g., spiders and scorpions) or positive (e.g., flowers and food). In order to test the effect of emotional valence on the online control of the reach, the target either remained static or jumped to a new location. In both the single and dual tasks, a stream of digits were presented on the screen near the finger's starting location, but only in the dual task were participants asked to identify a letter somewhere in the stream. In the single task, increased fear of spiders reduced the speed and accuracy of the movement. In the dual task, increased fear impaired letter identification, but pointing actions were now equally efficient for low- and high-fear participants. These results imply that the finger's autopilot is influenced by emotional content only when attention can be fully devoted to the identification of the emotion-evoking images. As such, the results support the view that the mechanisms of selection are not the same in the two visual streams.

Age effects on voluntary and automatic adjustments in anti-pointing tasks

We examined the effects of age on automatic and voluntary motor adjustments in pointing tasks. To this end, young (20-25 years) and middle-aged adults (48-62 years) were instructed to point at a target that could unexpectedly change its location (to the left or right) or its color (to green or red) during the movement. In the location change conditions, participants were asked to either adjust their pointing movement toward the new location (i.e., normal pointing) or in the opposite direction (i.e., anti-pointing). In the color change conditions, participants were instructed to adjust their movement to the left or right depending on the change in color. The results showed that in a large proportion of the anti-pointing trials, participants made two adjustments: an early initial automatic adjustment in the direction of the target shift followed by a late voluntary adjustment toward the opposite direction. It was found that the late voluntary adjustments were delayed for the middle-aged participants relative to the young participants. There were no age differences for the fast automatic adjustment in normal pointing, but the early adjustment in anti-pointing tended to be later in the middle-aged adults. Finally, the difference in the onset of early and late adjustments in anti-pointing adjustments was greater among the middle-aged adults. Hence, this study is the first to show that aging slows down voluntary goal-directed movement control processes to greater extent than the automatic stimulus-driven processes.

Lost in dissociation: The main paradigms in unconscious cognition

Contemporary studies in unconscious cognition are essentially founded on dissociation, i.e., on how it dissociates with respect to conscious mental processes and representations. This is claimed to be in so many and diverse ways that one is often lost in dissociation. In order to reduce this state of confusion we here carry out two major tasks: based on the central distinction between cognitive processes and representations, we identify and isolate the main dissociation paradigms; we then critically analyze their key tenets and reported findings.

Automatic correction of hand pointing in stereoscopic depth

In order to examine whether stereoscopic depth information could drive fast automatic correction of hand pointing, an experiment was designed in a 3D visual environment in which participants were asked to point to a target at different stereoscopic depths as quickly and accurately as possible within a limited time window (≤300 ms). The experiment consisted of two tasks: "depthGO" in which participants were asked to point to the new target position if the target jumped, and "depthSTOP" in which participants were instructed to abort their ongoing movements after the target jumped. The depth jump was designed to occur in 20% of the trials in both tasks. Results showed that fast automatic correction of hand movements could be driven by stereoscopic depth to occur in as early as 190 ms.

Hitting a target is fundamentally different from avoiding obstacles

To successfully move our hand to a target, it is important not only to consider the target of our movements but also to consider other objects in the environment that may act as obstacles. We previously found that the time needed to respond to a change in position was considerably longer for a displacement of an obstacle than for a displacement of the target (Aivar, Brenner, & Smeets, 2008. Experimental Brain Research 190, 251-264). In that study, the movement constraints imposed by the obstacles differed from those imposed by the target. To examine whether the latency is really different for targets and obstacles, irrespective of any constraints they impose, we modified the design of the previous experiment to make sure that the constraints were matched. In each trial, two aligned 'objects' of the same size were presented at different distances to the left of the initial position of the hand. Each of these objects could either be a target or a gap (opening between two obstacles). Participants were instructed to pass through both objects. All possible combinations of these two objects were tested: gap-target, target-gap, gap-gap, target-target. On some trials one of the objects changed position after movement onset. Participants systematically responded faster to the displacement of a target than to the displacement of a gap at the same location. We conclude that targets are prioritized over obstacles in movement control.

How automatic is the hand's automatic pilot? Evidence from dual-task studies

The ability to correct reaching movements for changes in target position has been described as the hand's 'automatic pilot'. These corrections are preconscious and occur by default in double-step reaching tasks, even if the goal is to react to the target jump in some other way, for instance by stopping the movement (STOP instruction). Nonetheless, corrections are strongly modulated by conscious intention: participants make more corrections when asked to follow the target (GO instruction) and can suppress them when explicitly asked not to follow the target (NOGO instruction). We studied the influence of a cognitively demanding (auditory 1-back) task upon correction behaviour under GO, STOP and NOGO instructions. Correction rates under the STOP instruction were unaffected by cognitive load, consistent with the assumption that they reflect the default behaviour of the automatic pilot. Correction rates under the GO instruction were also unaffected, suggesting that minimal cognitive resources are required to enhance online correction. By contrast, cognitive load impeded the ability to suppress online corrections under the NOGO instruction. These data reveal a constitutional bias in the automatic pilot system: intentional suppression of the default correction behaviour is cognitively demanding, but enhancement towards greater responsiveness is seemingly effortless.

Attentional limits and freedom in visually guided action

Human vision supports both the conscious perception of objects (e.g., identifying a tea cup) and the control of visually guided action on objects (e.g., reaching for a tea cup). The distinction between these two functions is supported by neuroanatomy, neuropsychology, animal lesion studies, psychophysics and kinematics in healthy humans, as well as in overarching theories of the visual brain. Yet research on visual attention, which concerns limitations in processing information concurrently from multiple objects, has so far not fully exploited this functional distinction. Attention research has focused primarily on the conscious aspects of vision, to the relative neglect of the unconscious control of limb actions and whether we can perceive some objects concurrently while acting on others. Here we review research from our lab leading to the conclusions that (1) the finger is guided visually by an automatic pilot that uses different information from that of conscious vision, (2) conscious object identification interferes with concurrent planning of pointing to a second object, though not with the online control needed to complete the pointing action, (3) concurrent perception and action sometimes lead to benefits in motor performance, and (4) the automatic pilot is itself capacity limited in processing information concurrently from multiple locations. These findings help clarify the conditions under which interference-free multitasking is possible and point to new challenges for research on the attentional limits of unconscious visual processing.

The hand's automatic pilot can update visual information while the eye is in motion

When participants reach for a target, their hand can adjust to a change in target position that occurs while their eyes are in motion (the hand's automatic pilot) even though they are not aware of the target's displacement (saccadic suppression of perceptual experience). However, previous studies of this effect have displayed the target without interruption, such that the new target position remains visible during the fixation that follows the saccade. Here we test whether a change in target position that begins and ends during the saccade can be used to update aiming movements. We also ask whether such information can be acquired from two targets at a time. The results showed that participants responded to single and double target jumps even when these targets were extinguished prior to saccade termination. The results imply that the hand's automatic pilot is updated with new visual information even when the eye is in motion.