Visually directed action

Abstract

When people throw or walk to targets in front of them without visual feedback, they often respond short. With feedback, responses rapidly become approximately accurate. To understand this, an experiment is performed with four stages. 1) The errors in blind walking and blind throwing are measured in a virtual environment in light and dark cue conditions. 2) Error feedback is introduced and the resulting learning measured. 3) Transfer to the other response is then measured. 4) Finally, responses to the perceived distances of the targets are measured. There is large initial under-responding. Feedback rapidly makes responses almost accurate. Throw training transfers completely to walking. Walk training produces a small effect on throwing. Under instructions to respond to perceived distances, under-responding recurs. The phenomena are well described by a model in which the relation between target distance and response distance is determined by a sequence of a perceptual, a cognitive, and a motor transform. Walk learning is primarily motor; throw learning is cognitive.

Figure 1.

Grayscale images of the virtual room. Top: Lighted room. The room appeared in color with the wall blocks in various shades of gray and tan. The carpet was red and yellow, and the ceiling was gray with black circles. Bottom: Dark Room. Everything was black except the target disk lying on the floor. The disk was luminous green.

Figure 2.

Mean responses of the four subjects in the walk-trained group in the 12 experimental conditions. Top: Stage 1 (initial responses)—throwing and walking in light and dark prior to training. Middle: Stage 2 (walk training)—walking responses averaged over sessions 2, 3, and 4 of walk training and Stage 3 (transfer)— throwing after walk training with no feedback. Bottom: Stage 4 (respond to perceived position)—walk and throw.

Figure 3.

Mean responses of the four subjects in the throw-trained group in the 12 experimental conditions. Top: Stage 1 (initial responses)—throwing and walking in light and dark prior to training. Middle: Stage 2 (throw training)—throwing responses averaged over sessions 2, 3, and 4 of throw training and Stage 3 (transfer)—walking after throw training with no feedback. Bottom: Stage 4 (respond to perceived position)—walk and throw.

Figure 4.

A schematic illustration of the model. D: target distance, D_p: perceived distance; D_pc, cognitive distance; D_pcw, walked distance; D_pct, thrown distance. The three distances are related by mathematical transforms that are referred to as perceptual (p), cognitive (c), and walk (w) or throw (t). Some of the transforms can be null transforms that have no effect.

Figure 5.

Responses of all four throw-trained subjects in the light throw task in stages 1, 2, and 4. For subjects 6 and 7, stage 4 responses are close to stage 1 responses, consistent with the cognitive transform being completely nulled in stage 4. For subjects 5 and 8, there was essentially no nulling. Stage 4 responses are like stage 2 responses. The stage 4 instruction had no effect on these subjects’ responses.

Figure 6.

Mean response over subjects as a function of session or replication in all the dark cue conditions of stages 3 and 4. Each line corresponds to one target distance. In stage 3 there were three sessions with two replications in each.