John J Rieser | PubMed Health

PubMed2006

Environmental context influences visually perceived distance.

What properties determine visually perceived space? We discovered that the perceived relative distances of familiar objects in natural settings depended in unexpected ways onthe surrounding visual field. Observers bisected egocentric distances in a lobby, in a hallway, and on an open lawn. Three key findings were the following: (1) Perceived midpoints were too far from the observer, which is the opposite of the common foreshortening effect. (2) This antiforeshortening constant error depended on the environmental setting--greatest in the lobby and hall but nonsignificant on the lawn. (3) Context also affected distance discrimination; variability was greater in the hall than in the lobby or on the lawn. A second experiment replicated these findings, using a method of constant stimuli. Evidently, both the accuracy and the precision of perceived distance depend on subtle properties of the surrounding environment.

Adult↗

PubMed2005

Learning to throw on a rotating carousel: recalibration based on limb dynamics and projectile kinematics.

Skilled actions exhibit adjustment in calibration to bring about their goals. The sought-after calibrations change as a function of the environmental situation that stages the actions. In these experiments participants sat on one side of a rotating carousel and threw beanbags underhanded at a target fixed on the opposite side. Logically, aimed throwing in this situation involves adjustment to fit changes in limb dynamics (originating from Coriolis forces) and changes in perceived projectile kinematics (originating from the tangential velocity of thrower and target). We studied whether such adjustment involved one or multiple components of recalibration. An initial experiment showed that exposure to rotation while throwing beanbags produced a robust recalibration in the direction of underhanded throws as manifest in throwing at stationary targets from a stationary position. Following some initial decay this recalibration persisted and approached an asymptote. Subsequent experiments suggested two independent components of recalibration. One is based on limb dynamics and accounts for the initial decay. The other is based on the perceived projectile kinematics and accounts for the stable change in throwing direction. These results raised the question of how multiple components of recalibration of an action are related. We propose that movement components are independent and calibrated separately at different levels in the organization of an action.

Adult↗