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The catchableness of a fly ball depends on whether the catcher can get to the ball in time; accurate judgments of catchableness must reflect both spatial and temporal aspects. Two experiments examined the perception of catchableness under conditions of restricted information pickup. Experiment 1 compared perceptual judgments with actual catching and revealed that stationary observers are poor perceivers of catchableness, as would be expected by the lack of information about running capabilities. In Experiment 2, participants saw the 1st part of ball trajectories before their vision was occluded. In 1 condition, they started to run (as if to catch the ball) before occlusion; in another, they remained stationary. Moving judgments were better than stationary judgments. This supports the idea that perceiving affordances that depend on kinematic, rather than merely geometric, body characteristics may require the relevant action to be performed. One of the assumptions of ecological psychology is that the environment is perceived in animal-relevant terms, that is, in terms of what the animal can do with and in the environment. Perception is seen as an active pickup of meaningful information that specifies the behavioral possibilities of the environment, also called affordances. These affordances (Gibson, 1979/1986) are the possibilities for action offered by the environment and the events that occur in it, described with respect to and in terms of the perceiving and acting animal. Ecological psychology claims that it is important for animals to perceive these affordances, so that the control of behavior can be adjusted to the possibilities for action that are supported by the environment. Most of the affordances that have been derived and investigated have concerned geometric relations between observer and environment (Carello, Grosofsky, Reichel,

Novice observers differ from each other in the kinematic variables they use for the perception of kinetic properties, but they converge on more useful variables after practice with feedback. The colliding-balls paradigm was used to investigate how the convergence depends on the relations between the candidate variables and the to-be-perceived property, relative mass. Experiment 1 showed that observers do not change in the variables they use if the variables with which they start allow accurate performance. Experiment 2 showed that, at least for some observers, convergence can be facilitated by reducing the correlations between commonly used nonspecifying variables and relative mass but not by keeping those variables constant. Experiments 3a and 3b further demonstrated that observers learn not to rely on a particular nonspecifying variable if the correlation between that variable and relative mass is reduced.