Abstract
Both crowding and binocular rivalry impede the perception of target stimuli. In our pilot experiment, we first measured the decrement of Landolt C's orientation discrimination performance due to crowding at 8 difference locations. We then measured the amount of decrement from interocular suppression using the same task and in the same locations. We found positive correlation between the two measurements, suggesting that binocular rivalry and crowding are related to each other. In this study, we investigated the nature of this interaction between crowding and binocular rivalry. Specifically, we tested whether the depth of binocular rivalry suppression was increased by surrounding distractors. Participant's task was to decide whether a vertical grating (target) was tilted towards clockwise or anticlockwise. In the crowding-only condition, a vertical grating (target) with five different orientations was presented in a dominant eye and we measured proportion of clockwise responses at these five different orientations. After fitting a cumulative Gaussian function to these data, we measured orientation discrimination thresholds and they were served as baseline. When four vertical gratings were additionally presented around the target, orientation discrimination thresholds were increased. However, the additional presentation of four horizontal gratings did not make any difference. In the binocular rivalry condition, we also presented a horizontal grating to the corresponding location of the target in a non-dominant eye. When vertical distractors surrounded the target, the orientation discrimination thresholds were increased regardless of the positions of distractors (dominant or non-dominant eye). This increment of thresholds was more than increment due to crowding only. However, the orientation discrimination thresholds were not increased regardless of the positions of distractors when horizontal distractors surrounded the target. These results suggest that crowding deepens the depth of suppression due to binocular rivalry.
This work was supported by the Korea Science and Engineering Foundation(KOSEF) grant funded by the Korea government(MEST) (NO. R01-2008-000-10820-0).