John van der Kamp

Visual search, anticipation and expertise in soccer goalkeepers.

We used a novel methodological approach to examine skill-based differences in anticipation and visual search behaviour during the penalty kick in soccer. Expert and novice goalkeepers were required to move a joystick in response to penalty kicks presented on film. The proportion of penalties saved was assessed, as well as the frequency and time of initiation of joystick corrections. Visual search behaviour was examined using an eye movement registration system. Expert goalkeepers were generally more accurate in predicting the direction of the penalty kick, waited longer before initiating a response and made fewer corrective movements with the joystick. The expert goalkeepers used a more efficient search strategy involving fewer fixations of longer duration to less disparate areas of the display. The novices spent longer fixating on the trunk, arms and hips, whereas the experts found the kicking leg, non-kicking leg and ball areas to be more informative, particularly as the moment of foot-ball contact approached. No differences in visual search behaviour were observed between successful and unsuccessful penalties. The results have implications for improving anticipation skill at penalty kicks.

Action goals influence action-specific perception

We examined the processes that mediate the emergence of action-specific influences on perception that have recently been reported for baseball batting and golf putting (Witt, Linkenauger, Bakdash, & Proffitt, 2008; Witt & Proffitt, 2005). To this end, we used a Schokokusswurfmaschine: Children threw a ball at a target, which, if hit successfully, launched a ball that the children then had to catch. In two experiments, children performed either a throwing-and-catching task or a throwing-only task, in which no ball was launched. After each task, the size of the target or of the ball was estimated. Results indicate that action-specific influences on perceived size occur for objects that are related to the end goal of the action, but not for objects that are related to intermediate action goals. These results suggest that action-specific influences on perception are contingent upon the primary action goals to be achieved.

Visual information for action planning in left and right congenital hemiparesis

Converging evidence suggests that compromised motor abilities in hemiparetic cerebral palsy are not solely due to impairments in motor execution, but are also related to deficits in action planning. The present study had two aims. First, we compared grip planning in a sequential task between participants with left-sided (n=12) or right-sided (n=10) congenital hemiparesis. Second, we studied the use of visual information for grip planning by having participants grasp a rod embedded in a rod-and-frame illusion. The results showed that especially participants with right hemiparesis revealed planning problems as most of them did not switch between different grip types at all or they switched in an inconsistent manner. In contrast, the majority of participants with left hemiparesis showed consistent planning of the first part of the task. Second, the results indicated that visual information provided by the illusion had an effect on grip planning in participants that used a consistent planning strategy, suggesting that the use of visual information in action planning was not affected in these participants. The results are discussed in relation to hemispheric differences in motor planning and visuo-motor integration in congenital hemiparesis.

Another look at the Müller-Lyer illusion: Different gaze patterns in vision for action and perception

Following Goodale and Milners [Goodale, M. A., & Milner, A. D. (1992). Separate visual pathways for perception and action. Trends in Neurosciences, 15(1), 20-25] proposal to distinguish the dorsal and ventral systems on basis of the functional demands they serve (i.e., action and perception), a vast literature has emerged that scrutinized if the dorsal and ventral systems indeed process information into egocentric and allocentric codes in accordance with their respective functions. However, a corollary of Goodale and Milners original proposal, that these functional demands also impose different constraints on information detection, has been largely overlooked. In the present study, we measured gaze patterns to investigate how information detection for action and perception differs. In two conditions, participants (N=9) grasped or made a manual estimate of the length of a shaft embedded in a Müller-Lyer configuration. The illusion significantly affected the manual estimates, but not the hand aperture during grasping. In line with these behavioral findings, significant differences in gaze patterns were revealed between the two tasks. Participants spent more time looking at areas that contain egocentric information (i.e., centre of the shaft) when grasping as compared to making a manual length estimate. In addition, participants, made more gaze shifts (i.e., especially between the two areas surrounding the shaft endpoints and including the arrowheads) when making the manual length estimate, enabling the pick up of allocentric information. This difference was more pronounced during task execution as compared to task preparation (i.e., before movement onset). These results support the contention that the functional distinction between the dorsal and ventral systems is not limited to the processing of information, but also encompasses the detection of information.

The Relation between Infants' Perception of Catchableness and the Control of Catching.

The authors studied how infants come to perceive and act adaptively by presenting 35 three- to nine-month-olds with balls that approached at various speeds according to a staircase procedure. They determined whether infants attempted to reach for the ball and whether they were successful (i.e., contacted the ball). In addition, the time and distance of the ball at the onset of the catching movements were measured for the successful interceptions. The authors found that not only catching skill but also the perceptual judgments of the catchableness improved with age; infants started to take their catching ability into account when judging whether a ball was catchable. Moreover, the authors observed that infants who made imprecise perceptual judgments were more likely to use a distance control strategy, whereas infants who made accurate perceptual judgments were more likely to use the more adaptive time strategy to control the catching movements. They conclude that the present study supports the proposal that, even in prelocomotor infants, the development of perception is intricately linked to or constrained by development in the visual control of action.

A Judd illusion in far-aiming: evidence of a contribution to action by vision for perception

The present study addresses the role of vision for perception in determining the location of a target in far-aiming. Participants (Nxa0=xa012) slid a disk toward a distant target embedded in illusory Judd figures. Additionally, in a perception task, participants indicated when a moving pointer reached the midpoint of the Judd figures. The number of hits, the number of misses to the left and to the right of the target, the sliding error (in mm) and perceptual judgment error (in mm) served as dependent variables. Results showed an illusory bias in sliding, the magnitude of which was comparable to the bias in the perception of target location. The determination of target location in far-aiming is thus based on relative metrics. We argue that vision for perception sets the boundary constraints for action and that within these constraints vision for action autonomously controls movement execution, but alternative accounts are discussed as well.

Differential effects of a visual illusion on online visual guidance in a stable environment and online adjustments to perturbations

In the reported, experiment participants hit a ball to aim at the vertex of a Müller-Lyer configuration. This configuration either remained stable, changed its shaft length or the orientation of the tails during movement execution. A significant illusion bias was observed in all perturbation conditions, but not in the stationary condition. The illusion bias emerged for perturbations shortly after movement onset and for perturbations during execution, the latter of which allowed only a minimum of time for making adjustments (i.e., approx.170 ms). These findings indicate that allocentric information is exploited for online control when people make rapid adjustments in response to a sudden change in the environment and not when people guide their limb movements to interact with a stable environment.

Anticipatory reaching of seven- to eleven-month-old infants in occlusion situations

The present study examined 7- to 11-month-old infants anticipatory and reactive reaching for temporarily occluded objects. Infants were presented with laterally approaching objects that moved at different velocities (10, 20, and 40 cm/s) in different occlusion situations (no-, 20 cm-, and 40 cm-occlusion), resulting in occlusion durations ranging between 0 and 4s. Results show that except for object velocity and occlusion distance, occlusion duration was a critical constraint for infants reaching behaviors. We found that the older infants reached more often, but that an increase in occlusion duration resulted in a decline in reaching frequency that was similar across age groups. Anticipatory reaching declined with increasing occlusion duration, but the adverse effects for longer occlusion durations diminished with age. It is concluded that with increasing age infants are able to retain and use information to guide reaching movements over longer periods of non-visibility, providing support for the graded representation hypothesis (Jonsson & von Hofsten, 2003) and the two-visual systems model (Milner & Goodale, 1995).

On the relation between action selection and movement control in 5- to 9-month-old infants

Although 5-month-old infants select action modes that are adaptive to the size of the object (i.e., one- or two-handed reaching), it has largely remained unclear whether infants of this age control the ensuing movement to the size of the object (i.e., scaling of the aperture between hands). We examined 5-, 7-, and 9-month-olds’ reaching behaviors to gain more insight into the developmental changes occurring in the visual guidance of action mode selection and movement control, and the relationship between these processes. Infants were presented with a small set of objects (i.e., 2, 3, 7, and 8xa0cm) and a large set of objects (i.e., 6, 9, 12, and 15xa0cm). For the first set of objects, it was found that the infants more often performed two-handed reaches for the larger objects based on visual information alone (i.e., before making contact with the object), thus showing adaptive action mode selection relative to object size. Kinematical analyses of the two-handed reaches for the second set of objects revealed that inter-trial variance in aperture between the hands decreased with the approach toward the object, indicating that infants’ reaching is constrained by the object. Subsequent analysis showed that between hand aperture scaled to object size, indicating that visual control of the movement is adjusted to object size in infants as young as 5xa0months. Individual analyses indicated that the two processes were not dependent and followed distinct developmental trajectories. That is, adaptive selection of an action mode was not a prerequisite for appropriate aperture scaling, and vice versa. These findings are consistent with the idea of two separate and independent visual systems (Milner and Goodale in Neuropsychologia 46:774–785, 2008) during early infancy.