Efficient activation of letter-level representation in binocular rivalry with familiar letters
33.436, Sunday, May 12, 8:30 am - 12:30 pm, Orchid Ballroom
Eiji Kimura1, Ken Goryo2; 1Department of Psychology, Faculty of Letters, Chiba University, 2Faculty of Human Development and Education, Kyoto Women's University
Binocular rivalry between brief stimuli (onset rivalry) can be modulated by presenting a preceding stimulus. Analyzing the properties of the dominance modulation can provide insights into how different types of stimulus are represented in the visual system. This study investigated dominance modulation using familiar letters (Japanese Kana and Kanji letters) and found that letter-specific negative modulation was predominant. That is, monocularly presenting one of the rivalrous letters prior to dichoptic presentation phenomenally suppressed the same letter regardless of the eye of presentation and thus another letter became dominant in the subsequent onset rivalry. This letter-specific suppressive effect was observed when the duration of the rivalrous test stimulus was either short (30 ms) or long (200 ms). These results are different from those obtained with grating stimuli and color disks. The previous study using these simple stimuli (Abe, Kimura & Goryo, 2011, Journal of Vision, 11(13):6, 1-18) showed that strong eye-based suppressive effects were observed when the test duration was short (10 ms), whereas orientation- or color-based suppressive effects became stronger when the test duration was long (200 ms). Further investigation with letters showed that the letter-specific suppression was unaffected by reducing the size of the preceding letter. However, when a masking pattern was binocularly presented during the ISI between the preceding and rivalrous letters and thus letter-form processing of the preceding letter was interfered, the eye-based suppression was observed. These results suggest that letter-level representation, rather than the one associated with low-level local features, can be efficiently and binocularly activated and used to resolve binocular competition between letters. Further investigation with Kana letters showed that this letter-level information is not represented in an orientation-selective fashion; the upright preceding letter phenomenally suppressed the same upright test letter more strongly than the inverted one, and vice versa.