RELATIVE DISPLACEMENT AND INDUCED MOTION: A DEVELOPMENTAL PERSPECTIVE
Early investigations into adult motion perception demonstrated that when there is only one object in a homogenous visual field adults' judgements of perceived motion are based upon subject-relative cues (displacements of an object with respect to the self). The motion reports of the 6 adult and 6 child subjects tested in Experiment 1 indicate that children as young as 3 years of age can use subject-relative cues to perceive motion and established child and adult thresholds at 1(DEGREES)31.37'/second and 12.23'/second respectively. With two or more objects in the visual field it becomes possible for adults to employ object-relative cues for motion judgements (reports based on displacements of an object with respect to another object).^ Motion reports based on object-relative cues do not allow the adult to determine which object in the visual field actually moved. In fact, which of two objects is perceived to move depends upon the attributes of the object: The larger object serves as a frame of reference and thus, regardless of which stimulus moves, is seen as the stationary object. This effect is more salient when the larger object surrounds the second stimulus. Experiment 2 examined object-relative motion reports of 36 children and 36 adults. The inducing effectiveness of three distinct frame types was tested: a solid square, a two-dot frame and a six-dot frame. In all conditions stimulus speeds were below the individuals' subject-relative thresholds, 1(DEGREES)11.22'/second and 5.9'/second for children and adults respectively.^ The results of Experiment 2 indicated that children as well as adults can take advantage of object-relative cues when stimulus movement is below the subject-relative threshold. They can accurately report the direction of displacement between two objects. Subjects tend to attribute motion to the smaller of two objects and the inducing properties (i.e., the tendency for a large moving object to cause a perceived apparent motion in the smaller, stationary object) of a large frame are strongest when it is surrounding, rather than adjacent to, a smaller object. Finally, children and adults demonstrate qualitatively similar patterns of responding to frames of differing stimulus properties even though they require much greater speeds of motion to respond to object-relative cues. Thus, while three-year-olds have the ability to use both subject-relative and object-relative cues, they are not as proficient with either type as adults.^
CAMENZULI, CHERYL ANN, "RELATIVE DISPLACEMENT AND INDUCED MOTION: A DEVELOPMENTAL PERSPECTIVE" (1983). ETD Collection for Fordham University. AAI8323516.