Spatial representation in body coordinates: Evidence from errors in remembering positions of visual and auditory targets after active eye, head, and body movements

Canadian Journal of Experimental Psychology, Mar 2003 by Kopinska, A, Harris, L R

Experiment 1c. The effect of head-on-body position on auditory localization: Head stable in space, body eccentric. When the head moved on the trunk in Experiment 1b, it changed position relative both to the body and to external space. Experiment 1c measured which aspect of the movement was significant by keeping the head movement relative to the body the same, while removing the head's displacement in space. In-between the presentation of the target and aligning a new sound with the remembered position, participants kept their heads still (restrained as described in the methods) and rotated only their bodies. Thus the relative position of body and head were the same as in Experiment 1b but head position in space was unchanged. The task was defined in a head reference frame: Participants were asked to adjust the sound to match the remembered sound with respect to their heads.

The effect of eccentric head position on the body while maintaining a constant head position in space is plotted in Figure 6.

There was a systematic error in the sound adjustments to the remembered target-sound position, F(4, 28) = 0.032, p

These data show that when the body was rotated to the right side (corresponding to a leftward displacement of the head relative to the body), there was a perceived shift of auditory target location (judged with respect to the head) to the right, requiring a nulling shift to the left. This perceptual shift is thus in the same direction, relative to the head, as for the head-on-trunk movements of Experiment 1b.

Experiment 1d. The effect of body position on auditory localization: Head fixed with respect to body, both eccentric. To see whether shifts of the body-in-space contributed to the perceived shifts of auditory target locations found in Experiments 1b and 1c, we measured the location of remembered auditory targets after the head and body both moved together relative to space. The head was stabilized with respect to the body as described in the Method. The task was defined in a head reference frame: Participants were asked to adjust the sound to match the remembered sound with respect to their heads.

The effect of rotating the body and head together in space are shown in Figure 7. For each of the five auditory targets presented, there was no consistent effect of body position on the interaural sound pressure level difference that was matched with the remembered target position, F(4, 28) = 0.59, nonsignificant. The interaction effect of body and target position was also not significant, F(16, 112) = 0.53, nonsignificant).

Experiment 2: Visual Localization

METHOD

Overview. Experiment 2 used the same principles as Experiment 1 but for visual targets. Participants were presented with a reflected laser beam light target (eyes centred, target in periphery) and were asked to remember its position. They were then asked to move their eyes (Experiment 2a), or head and eyes (Experiment 2c) before repositioning the light to its previously seen location relative to the head. To control for the effects of eccentric viewing, these experiments were repeated with the participant looking at the target during the initial presentation (eyes eccentric, target on fovea) and then returned their eyes (Experiment 2b) or eyes and head (Experiment 2d) to the centre before adjusting the pointing light.