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

Adjustment errors (the difference between actual visual target positions and the position indicated by the participant) are plotted in Figure 10 as a function of the amount the eye moved in-between viewing the target (straight ahead) and setting the pointer light to match its remembered position. Eye movement estimates are approximate since we did not measure eye movement but only asked participants to fixate the position. Figure 11 plots adjustment errors against target position when participants looked at the initial target and then moved their eyes to the centre before setting the pointer light to indicate its previous position. No consistent errors were seen in any of the tested conditions: Eye position was taken accurately into account and there were no significant effects of eye position on the accuracy of the visual location adjustments (Experiment 2a: F(1, 7) = .45, nonsignificant; Experiment 2b: F(1, 9) = 1.82, nonsignificant).

Experiments 2c and 2d: The effect of head position on visual localization. Experiments 2c and 2d measured the effect of different eccentricities of head position on the perceived location of remembered visual targets. Experiments 2c and 2d were divided as in Experiments 2a and 2b, with the targets delivered while the eyes and head were straight ahead in Experiment 2c and with the eyes and head aligned with the target in Experiment 2d. For Experiment 2c, they moved their eyes and head to eccentric positions before moving a laser to indicate the remembered location whereas in Experiment 2d, they returned to straight ahead. In Experiment 2c, the correct strategy was to ignore head position completely throughout the experiments since participants were always asked to position the lights at the same place relative to the head. Thus a light that had been presented 15[degrees] left should be positioned after a 15[degrees] leftward head movement at 30[degrees] left on the screen, keeping its original 15[degrees] eccentricity relative to the head.

Far from being able to ignore their head position, Figure 12 shows that participants made localization errors as a function of head eccentricity when they remembered the target location relative to their heads (Experiment 2c).

There was a significant effect of head position on the accuracy of where participants positioned the indicator light, F(2, 14) = 4.91, p

Localizing the visual targets in Experiment 2d required participants to know about their head eccentricity since they viewed the target with their head pointing straight at it (confirmed by the laser pointer mounted on participants' heads). They then returned their head and eyes to the straight-ahead position before indicating where the target had been. Thus a light that had been presented 15[degrees] left and associated with a 15[degrees] leftward head movement should be positioned at 15[degrees] left (relative to both head and space) after the head and eyes have been returned to straight ahead. In a control condition, visual targets were presented eccentrically and participants aligned the laser to their remembered location with no intervening head movement (Figure 13; filled circles). Figure 13 (open circles) shows the error in participants' ability to do this task as a function of head eccentricity (and thus target eccentricity). There was a significant effect of head position on the accuracy of the light adjustments, F(3, 27) = 8.77, p