As suggested by Melcher (
2008b), the spatiotopic TAE may rely on remapping processes that are known to be specific to task-relevant (attended) targets (Goldberg, Bisley, Powell, & Gottlieb,
2006; Gottlieb, Kusunoki, & Goldberg,
1998). To investigate whether we can find a spatiotopic TAE when attention is explicitly directed to a stimulus, we conducted the experiment depicted in
Figure A2C (top row). With two adapting stimuli at equal distance from fixation, a central cue indicated to the observer to which of the two stimuli should be attended. During the adaptation interval 4 or 5 Gaussian-enveloped contrast decrements (
σ = 100 ms, contrast decrement = 0.75) occurred in this stimulus, which the observer had to count. After adaptation, the observer made a saccade to either the screen location where the attended stimulus had been, or the opposite side, where an opposite-orientation adaptation stimulus had been presented. After this saccade, a test was presented either at the spatiotopically corresponding location of the attended or non-attended stimulus, or at a retinotopically corresponding location. An additional condition tested, as in the other experiments, the non-specific TAE. The fixation mark changed position to a location on the screen with the same distance to the initial fixation position, but above or below the center of the screen. The observer saccaded to that location and the test stimulus was presented there, as was the case in the spatiotopic conditions. Results are shown in the middle row of
Figure A2C. In the retinotopically corresponding locations, there are strong TAEs in both the attended and non-attended conditions. In the spatiotopically corresponding locations, there was no TAE, whether attention had been explicitly directed to the adapting stimulus or not: in both cases the TAE was not significantly different from that found using the non-specific test. In all these additional experiments, parameters were identical to those stated for the main Experiments 1 and 2 with the exception of two parameters that were changed to match exactly those in the experimental code furnished by Dr. Melcher. Size of the stimuli was changed to
σ = 0.8 degrees of visual angle and spatial frequency was changed to 2.16 cycles per degree. Adaptation duration was 4 s in all additional experiments. In all experiments, eye movements were recorded and analyzed. As in the first experiment, gaze position was recorded in all trials, and trials in which gaze position was outside a 2.5-degree radius around the intended fixation position at any single time point during the trial's adaptation or fixation phases, the trial was excluded from further analysis. Note that subjects showing a spatiotopic TAE in the experiment in
Figure A2A in the peripheral-adaptation, changed experimental paradigm fail to show the same pattern of results upon retesting (
Figures A2B and
A2C). This variability was typical for spatiotopic TAEs indicating that the results that did reach significance for some subjects in some sessions were due to chance variations. In contrast, retinotopic TAEs were all significant, all the time, showing that the tilt aftereffect is robustly retinotopic and shows no evidence of spatiotopy.