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Abstract:
The perception of a bistable stimulus is influenced by prior presentations of that stimulus. Such effects can be long lasting: e.g. position-dependent learned biases can persist for days, and reversing them requires extensive retraining (Haijiang et al., 2006). The effectiveness of training may therefore be influenced by pre-exposure to the ambiguous stimulus. Here we investigate the role of pre-exposure for learning a position dependent perceptual bias. We used rotating Necker cubes as the bistable stimuli that could be presented either above or below fixation. On training trials, additional cues (binocular disparity and occlusion) disambiguated the rotation direction for the cube. On test trials the rotating cube was presented without disambiguation cues. Subjects reported whether the front face of the cube and a moving dot moved in the same or opposite directions. Subjects received feedback about the correctness of their response. Using 350 training trials, subjects were exposed to different rotation directions for the above and below fixation locations of the cube. Following a 5-minute break a post-test (80 test trials) was performed. Separate subjects either directly started with the training, or were pre-exposed to the ambiguous stimulus in a pre-test (80 test trials). Subjects starting the training immediately, on average perceived the cube to be rotating in the trained direction for both locations on 83 of the post-test trials, replicating previous results. However, for the pre-exposed subjects, consistency with the trained percept-location contingency was only 58 in the post-test. In control conditions we simulated the pre-test using disambiguated trials and initially presented subjects with the reversed contingency than that which they would subsequently be exposed to during training. Post-test consistency with the trained contingency was 78. This shows that the pre-exposure interference does not necessarily depend on the initial perceptual history, suggesting a fundamental difference between test and training trials.
