Figure 5.

Position invariance of the aftereffect. A, Schematic illustrating the eccentric placement of adapt/test walkers (see Materials and Methods). B, Opposite percept ratio averaged across observers at 1° (left; n = 5) and 2.5° (right; n = 5) eccentricities. Three observers took part in both conditions. Ratio measures were calculated by dividing the duration of the opposite percept after adaptation by the mean duration of that percept when presented in tracking trials at the eccentric location (i.e., separate denominators for left-side and right-side test locations). The horizontal dashed lines indicate a postadapt/control ratio of 1 (i.e., no adaptation). Error bars represent ±1 SE computed across observer means. At 1°, no main effect was found for test location relative to adapt location (i.e., the aftereffect transferred across hemifield) (F_(1,4) = 3.02; p = 0.16). No other main effects or interactions were significant. Although aftereffects were equivalent for same/opposite hemifield presentation at 1° (and equivalent in magnitude to trials in which both stimuli appeared at fixation) (data not shown), on average aftereffects transferred less strongly across hemifield in the 2.5° eccentricity condition. The main effect for same/opposite hemifield, however, was not significant (F_(1,4) = 2.36; p = 0.2), although this lack of significance may have resulted from the presence of one outlier dataset. Analyses revealed a significant interaction between adaptor direction and same/opposite hemifield presentation (F_(1,4) = 11.8; p < 0.05) and a trend toward interaction between adapt side (left/right) and same/opposite hemifield presentation (F_(1,4) = 7.13; p = 0.056). See Results for discussion.