Are Different Actions Mediated by Distinct Systems of Knowledge in Infancy?

This chapter considers why studies of infant looking and reaching often suggest different patterns of cognitive and perceptual development. In some cases, convergent results have emerged from studies of infant looking and reaching, but differences are common. The most typical results suggest less adult-like perception and cognition in studies of reaching than in studies of looking. Several reaching studies, however, do not fit this pattern, suggesting that reaching actions may be mediated by distinct systems of knowledge and information processing. Comparisons of research on other behaviors, such as crawling and walking, also suggest that infant knowledge systems vary across actions. Research on how adult size perception differs between verbal and reaching response behaviors is considered and used as a template to interpret the developmental results. Like adults, when infants prepare to engage in particular actions, they seem to shift their sensitivity to particular sources of information and to process that information in action-relevant ways. These tendencies suggest that distinct knowledge systems mediate different actions in infancy.

Thoughts in space: the impact of environmental surround on cognitive processing.

The embodied cognition perspective has provided a formalization of the idea that the motor state is a characteristic of being that permeates all of human processing. We review this perspective and experimental evidence supporting its claim. It is further considered that the motor behaving human moves within various spaces, each affording different actions. To this end, it is proposed that the environmental surround is a critical variable in the embodied cognition perspective. Thoughts, inasmuch as they may be grounded in simulation of motor-behavioural responses, require time but also space. We suggest that these time-space considerations occur within a proposed concept of the potentiated state.

How preparation to touch or grasp alters visual size perception.

Prior studies have suggested that visually guided actions are resistant to the effects of some pictorial size illusions, e.g., the maximum grip aperture component of a grasp for an element of the Ebbinghaus illusion display. We present evidence that when participants prepare to grasp, the reduction in illusion magnitude observed for action components is also present for conscious perceptual judgments. Our studies characterize how visual size perception changes when we choose to engage in different size-mediated behaviors. Even when the stimuli used were identical for two different tasks, we found that available information was processed differently. In the studies, participants always selected which of the two targets was larger. In some conditions, the context in which the targets were presented induced a visual illusion of size. We varied the sizes of target pairs to assess the magnitude of these visual illusions. In some tasks, participants indicated their size choice verbally. For other tasks, participants reached to grasp or touch the target that they perceived as larger. Illusion magnitudes were smaller when participants engaged in actions directed at a target or when participants imagined performing those actions. This shift in visual processing persisted for several minutes after participants switched back to a verbal, non-grasping, non-touch task. A motor interference task eliminated the reduction in illusion magnitude.

Using touch or imagined touch to compensate for loss of proprioception: a case study.

Proprioception is the sense of the position of one's own body. Here, we present a case study of an individual with proprioceptive loss in one limb consequent to stroke. The patient indicated that merely touching his impaired arm with his unimpaired arm temporarily restored his proprioception. We examined this claim and the effects of imagined touch by the unimpaired arm. Assessments were made using three-dimensional tracking of reaching trajectories towards targets in conditions of light and darkness. Both actual and imagined touching significantly reduced movement error and jerk, specifically for targets located in regions that both hands would be able to reach.

Timing of anticipatory muscle tensing control: responses before and after expected impact.

It is widely accepted that human motor control is anticipatory in nature. Previous studies have used electromyography (EMG) to examine muscle responses to falling objects and identified anticipatory muscle tensing (AMT) as a spike in activation that occurs prior to object impact. Some studies have suggested that humans use an internal model of gravity to mediate precisely timed AMT responses. The present study further examines predictive motor control through the analysis of AMT during an object catching task. For some trials, participants watched an object falling toward the hand; for other trials, their eyes were closed. For some trials, the object fell downward and impacted the hand; for other randomly selected trials, the object abruptly stopped 12 cm above the hand, enabling an assessment of the effect of impact anticipation independent of the reflexive tactile response associated with an actual impact. In Experiment 1, AMT did not shift for approximately 113 ms after the abrupt stop of the ball. In Experiment 2, we randomly varied the start height of the object and found well-timed AMT with a 129-ms lag time. A control system based on simple memory for fall time duration cannot explain these findings. We argue that an AMT control system with a lag time of approximately 121 ms could not perform with human levels of accuracy without accounting for the acceleration of downward moving objects.

Planning to reach for an object changes how the reacher perceives it.

Three experiments assessed the influence of the Ebbinghaus illusion on size judgments that preceded verbal, grasp, or touch responses. Prior studies have found reduced effects of the illusion for the grip-scaling component of grasping, and these findings are commonly interpreted as evidence that different visual systems are employed for perceptual judgment and visually guided action. In the current experiments, the magnitude of the illusion was reduced by comparable amounts for grasping and for judgments that preceded grasping (Experiment 1). A similar effect was obtained prior to reaching to touch the targets (Experiment 2). The effect on verbal responses was apparent even when participants were simply instructed that a target touch task would follow the verbal task. After participants had completed a grasping task, the reduction in the magnitude of the illusion remained for a subsequent verbal-response judgment task (Experiment 3). Overall, the studies demonstrate strong connections between action planning and perception.

Different Gestalt processing for different actions? Comparing object-directed reaching and looking time measures.

Six experiments compared the Gestalt processing that mediates infant reaching and looking behaviors. Experiment 1 demonstrated that the positioning and timing of 8- and 9-month-olds' reaching was influenced by remembered relative motion. Experiment 2 suggested that a visible gap, without this relative motion, was not sufficient to produce these effects. Experiment 3 found that 6- and 7-month-olds required both remembered relative motion and a continuously visible gap to affect reaching; when two separate objects were placed adjacent to one another, they were treated as though they were connected. Experiments 4 and 5, using a looking time measure, identified a dissociation between looking and reaching performance. In Experiment 6, 6- and 7-month-olds' reaching was influenced when display parts differed in shape and color. In these experiments, Gestalt processing for looking was more influenced by remembered information than was Gestalt processing for reaching. For reaching, a low weighting of separation cues was also apparent.

Effects of the Ebbinghaus illusion on different behaviors: one- and two-handed grasping; one- and two-handed manual estimation; metric and comparative judgment.

Many studies have suggested that visually-guided action is largely immune to the effects of several pictorial illusions that strongly influence perceptual judgments. The judgments in these experiments, however, have usually involved comparisons of multiple elements within a display, whereas the visually-guided actions have typically involved a pincer grip directed to only one display element. The three experiments presented here assess the influence of this confound on the perception versus action illusion dissociation. In general, the studies suggest (a) that the confound affects perceptual judgment but not grasping or manual estimation, and (b) that difficult visuomotor tasks are more affected by the Ebbinghaus illusion than easier tasks. In Experiment 1, participants reached for or made judgments about plastic disks placed in the center of the Ebbinghaus illusion display. Some participants reached for or made judgments about only the disk on the right, whereas others reached for or judged both disks simultaneously. A large effect of the illusion was found for grasping and comparative judgment, but not for manual estimation or metric judgment. In Experiment 2, the disks were elevated slightly to make gripping the targets easier, and the effects of the illusion on grasping were greatly reduced. For Experiment 3, participants performed the manual estimation task while the hands were placed in view, on the surface of the table, and the effects of the illusion were significantly increased. Taken together, the experiments indicate that task difficulty and hand visibility affect whether a task will be influenced by pictorial illusions or not. One- and two-handed grasping seem to be affected approximately equally.